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Review article, effects of water pollution on human health and disease heterogeneity: a review.

• 1 Research Center for Economy of Upper Reaches of the Yangtse River/School of Economics, Chongqing Technology and Business University, Chongqing, China
• 2 School of Economics and Management, Huzhou University, Huzhou, China

Background: More than 80% of sewage generated by human activities is discharged into rivers and oceans without any treatment, which results in environmental pollution and more than 50 diseases. 80% of diseases and 50% of child deaths worldwide are related to poor water quality.

Methods: This paper selected 85 relevant papers finally based on the keywords of water pollution, water quality, health, cancer, and so on.

Results: The impact of water pollution on human health is significant, although there may be regional, age, gender, and other differences in degree. The most common disease caused by water pollution is diarrhea, which is mainly transmitted by enteroviruses in the aquatic environment.

Discussion: Governments should strengthen water intervention management and carry out intervention measures to improve water quality and reduce water pollution’s impact on human health.

Introduction

Water is an essential resource for human survival. According to the 2021 World Water Development Report released by UNESCO, the global use of freshwater has increased six-fold in the past 100 years and has been growing by about 1% per year since the 1980s. With the increase of water consumption, water quality is facing severe challenges. Industrialization, agricultural production, and urban life have resulted in the degradation and pollution of the environment, adversely affecting the water bodies (rivers and oceans) necessary for life, ultimately affecting human health and sustainable social development ( Xu et al., 2022a ). Globally, an estimated 80% of industrial and municipal wastewater is discharged into the environment without any prior treatment, with adverse effects on human health and ecosystems. This proportion is higher in the least developed countries, where sanitation and wastewater treatment facilities are severely lacking.

Sources of Water Pollution

Water pollution are mainly concentrated in industrialization, agricultural activities, natural factors, and insufficient water supply and sewage treatment facilities. First, industry is the main cause of water pollution, these industries include distillery industry, tannery industry, pulp and paper industry, textile industry, food industry, iron and steel industry, nuclear industry and so on. Various toxic chemicals, organic and inorganic substances, toxic solvents and volatile organic chemicals may be released in industrial production. If these wastes are released into aquatic ecosystems without adequate treatment, they will cause water pollution ( Chowdhary et al., 2020 ). Arsenic, cadmium, and chromium are vital pollutants discharged in wastewater, and the industrial sector is a significant contributor to harmful pollutants ( Chen et al., 2019 ). With the acceleration of urbanization, wastewater from industrial production has gradually increased. ( Wu et al., 2020 ). In addition, water pollution caused by industrialization is also greatly affected by foreign direct investment. Industrial water pollution in less developed countries is positively correlated with foreign direct investment ( Jorgenson, 2009 ). Second, water pollution is closely related to agriculture. Pesticides, nitrogen fertilizers and organic farm wastes from agriculture are significant causes of water pollution (RCEP, 1979). Agricultural activities will contaminate the water with nitrates, phosphorus, pesticides, soil sediments, salts and pathogens ( Parris, 2011 ). Furthermore, agriculture has severely damaged all freshwater systems in their pristine state ( Moss, 2008 ). Untreated or partially treated wastewater is widely used for irrigation in water-scarce regions of developing countries, including China and India, and the presence of pollutants in sewage poses risks to the environment and health. Taking China as an example, the imbalance in the quantity and quality of surface water resources has led to the long-term use of wastewater irrigation in some areas in developing countries to meet the water demand of agricultural production, resulting in serious agricultural land and food pollution, pesticide residues and heavy metal pollution threatening food safety and Human Health ( Lu et al., 2015 ). Pesticides have an adverse impact on health through drinking water. Comparing pesticide use with health life Expectancy Longitudinal Survey data, it was found that a 10% increase in pesticide use resulted in a 1% increase in the medical disability index over 65 years of age ( Lai, 2017 ). The case of the Musi River in India shows a higher incidence of morbidity in wastewater-irrigated villages than normal-water households. Third, water pollution is related to natural factors. Taking Child Loess Plateau as an example, the concentration of trace elements in water quality is higher than the average world level, and trace elements come from natural weathering and manufacture causes. Poor river water quality is associated with high sodium and salinity hazards ( Xiao et al., 2019 ). The most typical water pollution in the middle part of the loess Plateau is hexavalent chromium pollution, which is caused by the natural environment and human activities. Loess and mudstone are the main sources, and groundwater with high concentrations of hexavalent chromium is also an important factor in surface water pollution (He et al., 2020). Finally, water supply and sewage treatment facilities are also important factors affecting drinking water quality, especially in developing countries. In parallel with China rapid economic growth, industrialization and urbanization, underinvestment in basic water supply and treatment facilities has led to water pollution, increased incidence of infectious and parasitic diseases, and increased exposure to industrial chemicals, heavy metals and algal toxins ( Wu et al., 1999 ). An econometric model predicts the impact of water purification equipment on water quality and therefore human health. When the proportion of household water treated with water purification equipment is reduced from 100% to 90%, the expected health benefits are reduced by up to 96%.. When the risk of pretreatment water quality is high, the decline is even more significant ( Brown and Clasen, 2012 ).

To sum up, water pollution results from both human and natural factors. Various human activities will directly affect water quality, including urbanization, population growth, industrial production, climate change, and other factors ( Halder and Islam, 2015 ) and religious activities ( Dwivedi et al., 2018 ). Improper disposal of solid waste, sand, and gravel is also one reason for decreasing water quality ( Ustaoğlua et al., 2020 ).

Impact of Water Pollution on Human Health

Unsafe water has severe implications for human health. According to UNESCO 2021 World Water Development Report , about 829,000 people die each year from diarrhea caused by unsafe drinking water, sanitation, and hand hygiene, including nearly 300,000 children under the age of five, representing 5.3 percent of all deaths in this age group. Data from Palestine suggest that people who drink municipal water directly are more likely to suffer from diseases such as diarrhea than those who use desalinated and household-filtered drinking water ( Yassin et al., 2006 ). In a comparative study of tap water, purified water, and bottled water, tap water was an essential source of gastrointestinal disease ( Payment et al., 1997 ). Lack of water and sanitation services also increases the incidence of diseases such as cholera, trachoma, schistosomiasis, and helminthiasis. Data from studies in developing countries show a clear relationship between cholera and contaminated water, and household water treatment and storage can reduce cholera ( Gundry et al., 2004 ). In addition to disease, unsafe drinking water, and poor environmental hygiene can lead to gastrointestinal illness, inhibiting nutrient absorption and malnutrition. These effects are especially pronounced for children.

Purpose of This Paper

More than two million people worldwide die each year from diarrhoeal diseases, with poor sanitation and unsafe drinking water being the leading cause of nearly 90% of deaths and affecting children the most (United Nations, 2016). More than 50 kinds of diseases are caused by poor drinking water quality, and 80% of diseases and 50% of child deaths are related to poor drinking water quality in the world. However, water pollution causes diarrhea, skin diseases, malnutrition, and even cancer and other diseases related to water pollution. Therefore, it is necessary to study the impact of water pollution on human health, especially disease heterogeneity, and clarify the importance of clean drinking water, which has important theoretical and practical significance for realizing sustainable development goals. Unfortunately, although many kinds of literature focus on water pollution and a particular disease, there is still a lack of research results that systematically analyze the impact of water pollution on human health and the heterogeneity of diseases. Based on the above background and discussion, this paper focuses on the effect of water pollution on human health and its disease heterogeneity.

Materials and Methods

Search process.

This article uses keywords such as “water,” “water pollution,” “water quality,” “health,” “diarrhea,” “skin disease,” “cancer” and “children” to search Web of Science and Google Scholar include SCI and SSCI indexed papers, research reports, and works from 1990 to 2021.

Inclusion-Exclusion Criteria and Data Extraction Process

The existing literature shows that water pollution and human health are important research topics in health economics, and scholars have conducted in-depth research. As of 30 December 2021, 104 related literatures were searched, including research papers, reviews and conference papers. Then, according to the content relevancy, 19 papers were eliminated, and 85 papers remained. The purpose of this review is to summarize the impact of water pollution on human health and its disease heterogeneity and to explore how to improve human health by improving water pollution control measures.

Information extracted from all included papers included: author, publication date, sample country, study methodology, study purpose, and key findings. All analysis results will be analyzed according to the process in Figure 1 .

FIGURE 1 . Data extraction process (PRISMA).

The relevant information of the paper is exported to the Excel database through Endnote, and the duplicates are deleted. The results were initially extracted by one researcher and then cross-checked by another researcher to ensure that all data had been filtered and reviewed. If two researchers have different opinions, the two researchers will review together until a final agreement is reached.

Quality Assessment of the Literature

The JBI Critical Appraisal Checklist was used to evaluate the quality of each paper. The JBI (Joanna Briggs Institute) key assessment tool was developed by the JBI Scientific Committee after extensive peer review and is designed for system review. All features of the study that meet the following eight criteria are included in the final summary:1) clear purpose; 2) Complete information of sample variables; 3) Data basis; 4) the validity of data sorting; 5) ethical norms; (6); 7) Effective results; 8) Apply appropriate quantitative methods and state the results clearly. Method quality is evaluated by the Yes/No questions listed in the JBI Key Assessment List. Each analysis paper received 6 out of 8.

The quality of drinking water is an essential factor affecting human health. Poor drinking water quality has led to the occurrence of water-borne diseases. According to the World Health Organization (WHO) survey, 80% of the world’s diseases and 50% of the world’s child deaths are related to poor drinking water quality, and there are more than 50 diseases caused by poor drinking water quality. The quality of drinking water in developing countries is worrying. The negative health effects of water pollution remain the leading cause of morbidity and mortality in developing countries. Different from the existing literature review, this paper mainly studies the impact of water pollution on human health according to the heterogeneity of diseases. We focuses on diarrhea, skin diseases, cancer, child health, etc., and sorts out the main effects of water pollution on human health ( Table 1 ).

TABLE 1 . Major studies on the relationship between water pollution and health.

Water Pollution and Diarrhea

Diarrhea is a common symptom of gastrointestinal diseases and the most common disease caused by water pollution. Diarrhea is a leading cause of illness and death in young children in low-income countries. Diarrhoeal diseases account for 21% of annual deaths among children under 5 years of age in developing countries ( Waddington et al., 2009 ). Many infectious agents associated with diarrhea are directly related to contaminated water ( Ahmed and Ismail, 2018 ). Parasitic worms present in non-purifying drinking water when is consumed by human beings causes diseases ( Ansari and Akhmatov., 2020 ) . It was found that treated water from water treatment facilities was associated with a lower risk of diarrhea than untreated water for all ages ( Clasen et al., 2015 ). For example, in the southern region of Brazil, a study found that factors significantly associated with an increased risk of mortality from diarrhoea included lack of plumbed water, lack of flush toilets, poor housing conditions, and overcrowded households. Households without access to piped water had a 4.8 times higher risk of infant death from diarrhea than households with access to piped water ( Victora et al., 1988 )

Enteroviruses exist in the aquatic environment. More than 100 pathogenic viruses are excreted in human and animal excreta and spread in the environment through groundwater, estuarine water, seawater, rivers, sewage treatment plants, insufficiently treated water, drinking water, and private wells ( Fong and Lipp., 2005 ). A study in Pakistan showed that coliform contamination was found in some water sources. Improper disposal of sewage and solid waste, excessive use of pesticides and fertilizers, and deteriorating pipeline networks are the main causes of drinking water pollution. The main source of water-borne diseases such as gastroenteritis, dysentery, diarrhea, and viral hepatitis in this area is the water pollution of coliform bacteria ( Khan et al., 2013 ). Therefore, the most important role of water and sanitation health interventions is to hinder the transmission of diarrheal pathogens from the environment to humans ( Waddington et al., 2009 ).

Meta-analyses are the most commonly used method for water quality and diarrhea studies. It was found that improving water supply and sanitation reduced the overall incidence of diarrhea by 26%. Among Malaysian infants, having clean water and sanitation was associated with an 82% reduction in infant mortality, especially among infants who were not breastfed ( Esrey et al., 1991 ). All water quality and sanitation interventions significantly reduced the risk of diarrhoeal disease, and water quality interventions were found to be more effective than previously thought. Multiple interventions (including water, sanitation, and sanitation measures) were not more effective than single-focus interventions ( Fewtrell and Colford., 2005 ). Water quality interventions reduced the risk of diarrhoea in children and reduced the risk of E. coli contamination of stored water ( Arnold and Colford., 2007 ). Interventions to improve water quality are generally effective in preventing diarrhoea in children of all ages and under 5. However, some trials showed significant heterogeneity, which may be due to the research methods and their conditions ( Clasen et al., 2007 ).

Water Pollution and Skin Diseases

Contrary to common sense that swimming is good for health, studies as early as the 1950s found that the overall disease incidence in the swimming group was significantly higher than that in the non-swimming group. The survey shows that the incidence of the disease in people under the age of 10 is about 100% higher than that of people over 10 years old. Skin diseases account for a certain proportion ( Stevenson, 1953 ). A prospective epidemiological study of beach water pollution was conducted in Hong Kong in the summer of 1986–1987. The study found that swimmers on Hong Kong’s coastal beaches were more likely than non-swimmers to complain of systemic ailments such as skin and eyes. And swimming in more polluted beach waters has a much higher risk of contracting skin diseases and other diseases. Swimming-related disease symptom rates correlated with beach cleanliness ( Cheung et al., 1990 ).

A study of arsenic-affected villages in the southern Sindh province of Pakistan emphasized that skin diseases were caused by excessive water quality. By studying the relationship between excessive arsenic in drinking water caused by water pollution and skin diseases (mainly melanosis and keratosis), it was found that compared with people who consumed urban low-arsenic drinking water, the hair of people who consumed high-arsenic drinking water arsenic concentration increased significantly. The level of arsenic in drinking water directly affects the health of local residents, and skin disease is the most common clinical complication of arsenic poisoning. There is a correlation between arsenic concentrations in biological samples (hair and blood) from patients with skin diseases and intake of arsenic-contaminated drinking water ( Kazi et al., 2009 ). Another Bangladesh study showed that many people suffer from scabies due to river pollution ( Hanif et al., 2020 ). Not only that, but water pollution from industry can also cause skin cancer ( Arif et al., 2020 ).

Studies using meta-analysis have shown that exposure to polluted Marine recreational waters can have adverse consequences, including frequent skin discomfort (such as rash or itching). Skin diseases in swimmers may be caused by a variety of pathogenic microorganisms ( Yau et al., 2009 ). People (swimmers and non-swimmers) exposed to waters above threshold levels of bacteria had a higher relative risk of developing skin disease, and levels of bacteria in seawater were highly correlated with skin symptoms.

Studies have also suggested that swimmers are 3.5 times more likely to report skin diseases than non-swimmers. This difference may be a “risk perception bias” at work on swimmers, who are generally aware that such exposure may lead to health effects and are more likely to detect and report skin disorders. It is also possible that swimmers exaggerated their symptoms, reporting conditions that others would not classify as true skin disorders ( Fleisher and Kay. 2006 ).

Water Pollution and Cancer

According to WHO statistics, the number of cancer patients diagnosed in 2020 reached 19.3 million, while the number of deaths from cancer increased to 10 million. Currently, one-fifth of all global fevers will develop cancer during their lifetime. The types and amounts of carcinogens present in drinking water will vary depending on where they enter: contamination of the water source, water treatment processes, or when the water is delivered to users ( Morris, 1995 ).

From the perspective of water sources, arsenic, nitrate, chromium, etc. are highly associated with cancer. Ingestion of arsenic from drinking water can cause skin cancer and kidney and bladder cancer ( Marmot et al., 2007 ). The risk of cancer in the population from arsenic in the United States water supply may be comparable to the risk from tobacco smoke and radon in the home environment. However, individual susceptibility to the carcinogenic effects of arsenic varies ( Smith et al., 1992 ). A high association of arsenic in drinking water with lung cancer was demonstrated in a northern Chilean controlled study involving patients diagnosed with lung cancer and a frequency-matched hospital between 1994 and 1996. Studies have also shown a synergistic effect of smoking and arsenic intake in drinking water in causing lung cancer ( Ferreccio et al., 2000 ). Exposure to high arsenic levels in drinking water was also associated with the development of liver cancer, but this effect was not significant at exposure levels below 0.64 mg/L ( Lin et al., 2013 ).

Nitrates are a broader contaminant that is more closely associated with human cancers, especially colorectal cancer. A study in East Azerbaijan confirmed a significant association between colorectal cancer and nitrate in men, but not in women (Maleki et al., 2021). The carcinogenic risk of nitrates is concentration-dependent. The risk increases significantly when drinking water levels exceed 3.87 mg/L, well below the current drinking water standard of 50 mg/L. Drinking water with nitrate concentrations lower than current drinking water standards also increases the risk of colorectal cancer ( Schullehner et al., 2018 ).

Drinking water with high chromium content will bring high carcinogenicity caused by hexavalent chromium to residents. Drinking water intake of hexavalent chromium experiments showed that hexavalent chromium has the potential to cause human respiratory cancer. ( Zhitkovich, 2011 ). A case from Changhua County, Taiwan also showed that high levels of chromium pollution were associated with gastric cancer incidence ( Tseng et al., 2018 ).

There is a correlation between trihalomethane (THM) levels in drinking water and cancer mortality. Bladder and brain cancers in both men and women and non-Hodgkin’s lymphoma and kidney cancer in men were positively correlated with THM levels, and bladder cancer mortality had the strongest and most consistent association with THM exposure index ( Cantor et al., 1978 ).

From the perspective of water treatment process, carcinogens may be introduced during chlorine treatment, and drinking water is associated with all cancers, urinary cancers and gastrointestinal cancers ( Page et al., 1976 ). Chlorinated byproducts from the use of chlorine in water treatment are associated with an increased risk of bladder and rectal cancer, with perhaps 5,000 cases of bladder and 8,000 cases of rectal cancer occurring each year in the United States (Morris, 1995).

The impact of drinking water pollutants on cancer is complex. Epidemiological studies have shown that drinking water contaminants, such as chlorinated by-products, nitrates, arsenic, and radionuclides, are associated with cancer in humans ( Cantor, 1997 ). Pb, U, F- and no3- are the main groundwater pollutants and one of the potential causes of cancer ( Kaur et al., 2021 ). In addition, many other water pollutants are also considered carcinogenic, including herbicides and pesticides, and fertilizers that contain and release nitrates ( Marmot et al., 2007 ). A case from Hebei, China showed that the contamination of nitrogen compounds in well water was closely related to the use of nitrogen fertilizers in agriculture, and the levels of three nitrogen compounds in well water were significantly positively correlated with esophageal cancer mortality ( Zhang et al., 2003 ).

In addition, due to the time-lag effect, the impact of watershed water pollution on cancer is spatially heterogeneous. The mortality rate of esophageal cancer caused by water pollution is significantly higher downstream than in other regions due to the impact of historical water pollution ( Xu et al., 2019 ). A study based on changes in water quality in the watershed showed that a grade 6 deterioration in water quality resulted in a 9.3% increase in deaths from digestive cancer. ( Ebenstein, 2012 ).

Water Pollution and Child Health

Diarrhea is a common disease in children. Diarrhoeal diseases (including cholera) kill 1.8 million people each year, 90 per cent of them children under the age of five, mostly in developing countries. 88% of diarrhoeal diseases are caused by inadequate water supply, sanitation and hygiene (Team, 2004). A large proportion of these are caused by exposure to microbially infected water and food, and diarrhea in infants and young children can lead to malnutrition and reduced immune resistance, thereby increasing the likelihood of prolonged and recurrent diarrhea ( Marino, 2007 ). Pollution exposure experienced by children during critical periods of development is associated with height loss in adulthood ( Zaveri et al., 2020 ). Diseases directly related to water and sanitation, combined with malnutrition, also lead to other causes of death, such as measles and pneumonia. Child malnutrition and stunting due to inadequate water and sanitation will continue to affect more than one-third of children in the world ( Bartlett, 2003 ). A study from rural India showed that children living in households with tap water had significantly lower disease prevalence and duration ( Jalan and Ravallion, 2003 ).

In conclusion, water pollution is a significant cause of childhood diseases. Air, water, and soil pollution together killed 940,000 children worldwide in 2016, two-thirds of whom were under the age of 5, and the vast majority occurred in low- and middle-income countries ( Landrigan et al., 2018 ). The intensity of industrial organic water pollution is positively correlated with infant mortality and child mortality in less developed countries, and industrial water pollution is an important cause of infant and child mortality in less developed countries ( Jorgenson, 2009 ). In addition, arsenic in drinking water is a potential carcinogenic risk in children (García-Rico et al., 2018). Nitrate contamination in drinking water may cause goiter in children ( Vladeva et al.., 2000 ).

Discussions

This paper reviews the environmental science, health, and medical literature, with a particular focus on epidemiological studies linking water quality, water pollution, and human disease, as well as studies on water-related disease morbidity and mortality. At the same time, special attention is paid to publications from the United Nations and the World Health Organization on water and sanitation health research. The purpose of this paper is to clarify the relationship between water pollution and human health, including: The relationship between water pollution and diarrhea, the mechanism of action, and the research situation of meta-analysis; The relationship between water pollution and skin diseases, pathogenic factors, and meta-analysis research; The relationship between water pollution and cancer, carcinogenic factors, and types of cancer; The relationship between water pollution and Child health, and the major childhood diseases caused.

A study of more than 100 literatures found that although factors such as country, region, age, and gender may have different influences, in general, water pollution has a huge impact on human health. Water pollution is the cause of many human diseases, mainly diarrhoea, skin diseases, cancer and various childhood diseases. The impact of water pollution on different diseases is mainly reflected in the following aspects. Firstly, diarrhea is the most easily caused disease by water pollution, mainly transmitted by enterovirus existing in the aquatic environment. The transmission environment of enterovirus depends on includes groundwater, river, seawater, sewage, drinking water, etc. Therefore, it is necessary to prevent the transmission of enterovirus from the environment to people through drinking water intervention. Secondly, exposure to or use of heavily polluted water is associated with a risk of skin diseases. Excessive bacteria in seawater and heavy metals in drinking water are the main pathogenic factors of skin diseases. Thirdly, water pollution can pose health risks to humans through any of the three links: the source of water, the treatment of water, and the delivery of water. Arsenic, nitrate, chromium, and trihalomethane are major carcinogens in water sources. Carcinogens may be introduced during chlorine treatment from water treatment. The effects of drinking water pollution on cancer are complex, including chlorinated by-products, heavy metals, radionuclides, herbicides and pesticides left in water, etc., Finally, water pollution is an important cause of children’s diseases. Contact with microbiologically infected water can cause diarrhoeal disease in children. Malnutrition and weakened immunity from diarrhoeal diseases can lead to other diseases.

This study systematically analyzed the impact of water pollution on human health and the heterogeneity of diseases from the perspective of different diseases, focusing on a detailed review of the relationship, mechanism and influencing factors of water pollution and diseases. From the point of view of limitations, this paper mainly focuses on the research of environmental science and environmental management, and the research on pathology is less involved. Based on this, future research can strengthen research at medical and pathological levels.

In response to the above research conclusions, countries, especially developing countries, need to adopt corresponding water management policies to reduce the harm caused by water pollution to human health. Firstly, there is a focus on water quality at the point of use, with interventions to improve water quality, including chlorination and safe storage ( Gundry et al., 2004 ), and provision of treated and clean water ( Khan et al., 2013 ). Secondly, in order to reduce the impact of water pollution on skin diseases, countries should conduct epidemiological studies on their own in order to formulate health-friendly bathing water quality standards suitable for their specific conditions ( Cheung et al., 1990 ). Thirdly, in order to reduce the cancer caused by water pollution, the whole-process supervision of water quality should be strengthened, that is, the purity of water sources, the scientific nature of water treatment and the effectiveness of drinking water monitoring. Fourthly, each society should prevent and control source pollution from production, consumption, and transportation ( Landrigan et al., 2018 ). Fifthly, health education is widely carried out. Introduce environmental education, educate residents on sanitary water through newspapers, magazines, television, Internet and other media, and enhance public health awareness. Train farmers to avoid overuse of agricultural chemicals that contaminate drinking water.

Author Contributions

Conceptualization, XX|; methodology, LL; data curation, HY; writing and editing, LL; project administration, XX|.

This article is a phased achievement of The National Social Science Fund of China: Research on the blocking mechanism of the critical poor households returning to poverty due to illness, No: 20BJY057.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: water pollution, human health, disease heterogeneity, water intervention, health cost

Citation: Lin L, Yang H and Xu X (2022) Effects of Water Pollution on Human Health and Disease Heterogeneity: A Review. Front. Environ. Sci. 10:880246. doi: 10.3389/fenvs.2022.880246

Received: 21 February 2022; Accepted: 09 June 2022; Published: 30 June 2022.

Reviewed by:

Copyright © 2022 Lin, Yang and Xu. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Xiaocang Xu, [email protected]

This article is part of the Research Topic

Bioaerosol Emission Characteristics and the Epidemiological, Occupational, and Public Health Risk Assessment of Waste and Wastewater Management

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A Comprehensive Review for Groundwater Contamination and Remediation: Occurrence, Migration and Adsorption Modelling

Osamah al-hashimi.

1 Babylon Water Directorate, Babylon 51001, Iraq

2 School of Civil Engineering and Built Environment, Liverpool John Moores University, Liverpool L3 3AF, UK; [email protected] (K.H.); [email protected] (E.L.); [email protected] (T.M.Č.)

Khalid Hashim

3 Department of Environmental Engineering, College of Engineering, University of Babylon, Babylon 51001, Iraq

Edward Loffill

Tina marolt Čebašek, ismini nakouti.

4 Built Environment and Sustainable Technology Research Institute, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK; [email protected]

Ayad A. H. Faisal

5 Department of Environmental Engineering, College of Engineering, University of Baghdad, Baghdad 10001, Iraq; moc.oohay@lasiafazmahladebadaya

Nadhir Al-Ansari

6 Department of Civil, Environmental and Natural Resources Engineering, Lulea University of Technology, 97187 Lulea, Sweden; [email protected]

Associated Data

The data presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

The provision of safe water for people is a human right; historically, a major number of people depend on groundwater as a source of water for their needs, such as agricultural, industrial or human activities. Water resources have recently been affected by organic and/or inorganic contaminants as a result of population growth and increased anthropogenic activity, soil leaching and pollution. Water resource remediation has become a serious environmental concern, since it has a direct impact on many aspects of people’s lives. For decades, the pump-and-treat method has been considered the predominant treatment process for the remediation of contaminated groundwater with organic and inorganic contaminants. On the other side, this technique missed sustainability and the new concept of using renewable energy. Permeable reactive barriers (PRBs) have been implemented as an alternative to conventional pump-and-treat systems for remediating polluted groundwater because of their effectiveness and ease of implementation. In this paper, a review of the importance of groundwater, contamination and biological, physical as well as chemical remediation techniques have been discussed. In this review, the principles of the permeable reactive barrier’s use as a remediation technique have been introduced along with commonly used reactive materials and the recent applications of the permeable reactive barrier in the remediation of different contaminants, such as heavy metals, chlorinated solvents and pesticides. This paper also discusses the characteristics of reactive media and contaminants’ uptake mechanisms. Finally, remediation isotherms, the breakthrough curves and kinetic sorption models are also being presented. It has been found that groundwater could be contaminated by different pollutants and must be remediated to fit human, agricultural and industrial needs. The PRB technique is an efficient treatment process that is an inexpensive alternative for the pump-and-treat procedure and represents a promising technique to treat groundwater pollution.

1. Introduction

Earth is known as the blue planet or the water planet because of the reality that most of its surface is covered by water, and it is the only planet in the solar system that has this huge quantity of water [ 1 , 2 ]. For various authorities and agencies dealing with water problems, the conservation of surface and groundwater purity without pollution is indeed an aim. In addition, groundwater is the main potable water supply used in many nations; this is also water for agriculture and industry [ 3 , 4 ]. The effect of global warming, climate change, the rise in weather temperature and evaporation increment, population growth, excessive use of fresh water in agriculture and industrial activities have all led to increasing reliance on groundwater [ 5 , 6 ]. Groundwater became fundamental for social and economic development. It is the sole source for drinking to about 2.5 billion people around the world [ 7 ]. There are many reasons to develop groundwater, but among the most important are [ 8 ]:

• (1) Groundwater usually lies in underground natural reservoirs. This promotes groundwater as a convenient source of water. Additionally, groundwater can be found in different quantities depending on aquifer capacity. Many times, aquifers detaining water larger than many human-made reservoirs; for example, the Ogalalla aquifer located in the United States produced up to 500 Km 3 of water for four decades, which is larger than Nasser lake in Egypt. The huge quantities of groundwater give an ability to pump water during the drought period, while surface water (in some places) is unable to be pumped in these quantities or at such high quality during such period.
• (2) In many cases, groundwater quality is better than surface water. This is due to the ability of aquifers to provide natural protection for groundwater from contamination.
• (3) Groundwater is a cheap, reliable source of water. It can be pumped out using small capital and can be drilled close to the location needed for water. Additionally, groundwater can be easily organized, managed and developed. For example, individuals can easily construct and operate their groundwater well on their land.

Pumping and treatment is a common technique used for groundwater treatment; however, the lack of groundwater quality restoration in the long term has been demonstrated in this method. An innovative approach to groundwater remediation is, therefore, necessary. The permeable reactive barrier (PRB) is proven as a promising technology for groundwater treatment by an interaction between the reactive material and the contaminant when the dissolved compounds migrate. In the permeable reactive barrier (PRB), water moves in a natural gradient, and no further energy is used to achieve the treatment [ 9 ]. The PRB is classified as in situ treatment, and the contaminant is transformed in the contaminated site into less toxic or immovable forms. The key benefits of the PRB innovation are minimal maintenance costs and long durability. However, the aim of this work is that future researchers will find a clear, in-depth and detailed explanation of groundwater contaminants, movement and detailed theoretical explanation for the fate of contaminants in the environment.

2. Groundwater Contamination

Groundwater is the global population’s main source of fresh water and is used for domestic, food production and industrial purposes. About a third of the world’s population depends on groundwater as the main water source for their drinking purposes [ 10 ]. According to the United Nations Environmental Agency (UNEP), there are 32 cities around the world with a population greater than 10 million known as “megacities”; about 16 of these cities majorly rely upon groundwater [ 8 ]. In China, there are 657 cities, and approximately 400 cities are using water from the ground as the main source for their water supplies [ 11 ]. It is without doubt that subsurface water/groundwater is an essential resource of water to humanity; furthermore, it is vital for the ecological system on earth. Keeping this water resource sustainable, accessible, effective and efficient is a major concern for scientists working in a related field. However, urbanization, farming, industry and climate change all pose significant threats to the quality of groundwater. Toxic metal, hydrocarbons, contaminants such as organic trace pollutants, pharmaceutical pollutants, pesticides and other contaminants are endangering human health, natural ecosystems and long-term socioeconomic development [ 12 , 13 ]. Chemical contamination has been a major subject in groundwater investigations in recent decades. While groundwater contamination poses a significant threat to human populations, it also provides a chance for researchers to learn more about how our underground aquifers have evolved, as well as for decision makers to understand how we might maintain the quality and quantity of these resources [ 14 ]. According to the Canadian government, the contamination of groundwater can be defined as the addition of undesired substances by human activities [ 15 ]. Chemicals, brines, microbes, viral infections, medications, fertilizers and petroleum can all contribute to groundwater contamination. However, groundwater contamination is differs from surface water contamination in that it is unseen, and recovery of the resource is difficult and expensive at the current technological level [ 16 ].

Due to human and natural activities, chemicals and pollutants may be found in groundwater. Metals such as arsenic, cadmium and iron could be dissolved in groundwater and may be found in high concentrations. Human activities such as industrial discharges, waste disposal and agriculture activities are the main cause of groundwater contamination. Furthermore, it could happen due to urban activities such as the excessive use of fertilizers, pesticides and chemicals in which pollutants migrate to groundwater and reach the water table. In any case, using groundwater for drinking, irrigation or industrial purposes requires different tests to ensure that it is suitable for these purposes.

The presence of inorganic contaminants in groundwater is a big concern especially when groundwater is used for drinking or agricultural purposes. If these contaminants are presented in the groundwater with levels higher than the permissible recommended concentration, they cause health problems throughout the food chain [ 17 ]. Table 1 presents different inorganic pollutants in groundwater, sources and health effects.

Inorganic pollutants presented in groundwater.

In addition, discharging organic pollutants into the environment and water resources represents a pressing concern for people’s health. The existence of organic contaminants in groundwater represents a crucial environmental problem, as it may affect the water supply reservoirs and people’s health [ 18 ]. Additionally, it can affect the ecological system [ 19 ]. Usually, groundwater contaminants come from two sources: (1) landfills, solid waste disposal lands, sewer leakage and storage tanks leakage and (2) agriculture and farmyard drainage [ 20 ]. Table 2 shows the most common organic pollutants usually found in the groundwater, the sources and the health effect.

Organic contaminants, source to groundwater and their effects.

In the environment, groundwater in shallow or deep aquifers is never found completely sterile [ 21 ]. Coliform organisms and bacteria are the main cause of the microbiological pollution of groundwater. When present, these pollutants need immediate attention to protect lives from outbreaks of pathogenic disease [ 22 ]. Microbiological contaminants naturally occur in the environment by the intestines of humans, warm-blooded animals and plants. These microorganisms could cause dysentery, typhoid fever and different diseases [ 21 ].

3. Groundwater Treatment Technologies

In recent decades, scientists developed sophisticated and highly successful techniques for the remediation of water from many contaminants. These techniques generally focused on the treatment of surface water resources such as a river, lakes and water reservoirs. However, in recent years, scientists and environmental researchers have become more aware of treating underground water, and groundwater has become an essential source of water in most places; it represents about 30% of the freshwater reserve in the world [ 29 , 32 , 37 , 38 ]. Groundwater is usually treated by drilling water wells, pumping the polluted water to ground facilities to perform different approaches of treatment such as air stripping and treatment tower and granular activated carbon (GAC). Pressurized air bubbles are also used to treat contaminated groundwater. The selection of the effective treatment/remediation procedure depends on the characteristics of contaminants and pollutants, in addition to the reactive media available [ 39 ].

3.1. Pump and Treat Method

One of the popular procedures to remediate contaminated groundwater is by dissolved chemicals, solvents, metals and fuel oil [ 40 ]. In this procedure, contaminated groundwater is piped to ground lagoons or directly to treatment units, which treat the groundwater using various methods such as activated carbon or air stripping. Finally, the treated water is to be discharged either to the nearest sewer system or re-pumped to the subsurface [ 37 ]. This technique can treat large volumes of contaminated groundwater but has many disadvantages, such as the high cost, spreading of contaminants into the ecosystem, as well as its long operation time; in addition, it may cause a reversal to the hydraulic gradient [ 41 , 42 , 43 ] as cited in [ 40 ].

3.2. Air Sparging Procedure and Soil Vapor Extraction

The procedure of air sparging and soil vapor extraction (SVE) is considered one of the most common techniques used in remediating groundwater contaminated by volatile organic contaminants (VOCs). It is considered efficient, fast and relatively economical [ 44 ]. This method involves the injection of pressurized air at the lowest point of the contaminated groundwater; this will clean up the groundwater by changing the state of volatile hydrocarbons to a vapor state. While pumping air under the saturated zone, pollutants are stripped out of the aquifer and oxygen is provided for the biodegradation of contaminants [ 45 ]. The extracted air is to be treated by vacuum extraction systems to remove any toxic contaminants [ 46 ]. The limitations for this method are the high cost when working in hard surface area and when many deep wells are required for the treatment. In addition, soil heterogeneity may lead to uneven treatment of the contaminated groundwater.

3.3. The Permeable Reactive Barriers (PRBs)

It is an innovative remediation technique [ 47 ]. Practically, it is in situ technology to remediate groundwater using reactive media designed to intercept a contaminated plume. Typically, reactive media is designed to degrade volatile organics, immobilizing metals. PRB media is placed with porous materials such as sand; this will enhance the hydraulic conductivity, so the plume of contaminants will pass through the PRB under a natural gradient descent [ 37 , 48 ].

In the treatment wall, contaminants are removed by adsorbing, transforming, degrading and precipitating the targeted pollutants during water flow through barrier trenches. PRBs are defined as an in situ remediation zone in which contaminants are passively captured, removed or broken down while it allows uncontaminated water to pass through. The primary removal method is either physical (sorption, precipitation), chemical (ion exchange) or biological [ 49 , 50 , 51 , 52 ].

There are many geometries for placing the permeable reactive barriers (PRBs): (1) A continuous wall that contains reactive media. This is the most common placement in which the reactive media is placed perpendicular to the contaminated plume of groundwater flow; (2) funnel and gate in which contaminant plume is directed to a treatment filtering gate by two-sided impermeable walls at sites in which the soil is very heterogeneous, placing the PRB in the most permeable portion of the soil. Furthermore, when the contaminant’s distribution is non-uniform, the pollutant’s concentration can be better homogenized when entering the PRB gate; (3) radial filtration/caisson configuration in which the filter is placed in a cylindrical shape of reactive media surrounded by coarse material with a core of course materials. Additionally, there must be a radial centripetal flow by applying a hydraulic gradient. The third type of PRB has a long lifespan and a better treatment efficiency by extending the contact time between the pollutant and the reactive barrier [ 47 , 53 , 54 ].

Different reactive materials can be used to remediate contaminants, for example, zero-valent iron (ZVI; Fe0), which is a mild reductant and can treat heavy metals. ZVI can de-halogenate may halogenate hydrocarbon derivatives [ 55 ]. Bio-sparging materials and slow oxygen releasing compounds have the ability to treat groundwater containing petroleum hydrocarbon plums such as nitrobenzene and aniline by utilizing the biodegradation of these pollutants in PRBs [ 56 ]. Vegetative materials could be used in PRBs such as mulch to remediate chlorinated solvents and perchlorates [ 57 ].

Contaminants can also be precipitated on chemical reactive materials in the PRBs, for example, fly ash, ferrous slats, lime, phosphates and zeolites, iron/sand, iron/gravel, iron/sponge, granular activated carbon, organic carbon, copper wool and steel wool [ 37 , 54 ].

3.3.1. Characteristics of the Reactive Medias

Choosing a good reactive media depends on the following characteristics [ 58 ]:

• 1. Reactivity: The ability of reactive media to react/remediate contaminants and the equilibrium constant. All these factors are necessary to determine the required time for the remediation, which is important to calculate the volume and size of the in situ reactive barriers.
• 2. Stability: It is required that any good reactive material is to be active for a long period to remediate groundwater. Additionally, it is also necessary that the reactive media stay under the surface as a secondary precipitate. Once the PRB is installed, it is very expensive to be excavated and replaced with a new PRB.
• 3. Cost and availability: it is very important that the reactive media be available and inexpensive.
• 4. Hydraulic conductivity: the PRB must have a permeability equal to or greater than the surrounding soil to ease the groundwater flow within the PRB and achieve the remediation.
• 5. Environmental compatibility: Reactive media need to be similar/match the surrounding subsurface soil by mean of grain size for the goal that there will be no change in the hydraulic conductivity of the soil. Additionally, it needs no unwanted by-products to be produced during the remediation.

3.3.2. Uptake Mechanism of Contaminants

In the remediation of groundwater from contaminants, four physical, chemical and biological uptake mechanisms are considered as uptake mechanisms [ 58 , 59 , 60 ], which are: (1) adsorption and ion exchange, (2) abiotic redaction, (3) biotic reduction and (4) chemical precipitation. Remediation of contaminants in groundwater can be achieved by two or more of these mechanisms [ 61 ].

• (1) Adsorption and Ion Exchange

The process in which species in an aqueous environment are attached to a solid surface is referred to as adsorption. Usually, adsorption interaction is considered a rapid and reversible phenomenon. Adsorbents such as zero-valent iron (ZVI), zeolite and amorphous ferric oxyhydroxide (AFO) are the most common adsorbents used in the adsorption of contaminants; most of the adsorbents have a large surface area per gram and could be used in a PRB. ZVI has the most adsorption rate, and it is the most popular reactive media used in PRBs. Adhesion of pollutant’s ions, atoms or molecules while it is in a liquid, gas or dissolved solid state is referred to as adsorption. It utilizes chemical forces to create a thin film of the adsorbate on the adsorbent’s surface. The adsorbent is any kind of material that can adsorb substances through its surface area characteristics. In the adsorption theory, the surface area of the adsorbent is predominant. The solid phase that provides a working adsorption area is the adsorbent, while the substances and species adsorbed on the adsorbent are referred to as the adsorbate. Adsorption efficiency depends on adsorbate concentration, liquid-phase temperature and pH [ 62 ].

Ion exchange is a process of remediation of inorganic chemicals and dissolved metals from liquids and groundwater. The ion exchange process is that the ion (a single atom or group of atoms) is either positively charged after its loss of electrons or negatively charged after gaining an electron. When liquids loaded by pollutants pass through the ion exchange resin, contaminated substances will be exchanged by the effect of metallic ions attraction by the resins. These resins can be re-generated after being exhausted, or it may be a single-use resin [ 63 , 64 ]. Ion exchange phenomena is a reversible reaction process in which a pollutant’s ion is replaced with an identical ion on the immobilizing barrier. Most ion exchangers are natural such as zeolite, but also, there are very good synthesized ion exchanger resins that can be used in specific needs, especially for the treatment of inorganic contaminants [ 58 , 60 ]. The ion exchange method is applicable to remediate heavy metals [ 65 ] and dissolved metals (chromium) from polluted liquids. Additionally, this method could be used to treat non-metallic pollutants such as nitrate and ammonia [ 63 ]. The limitation to the use of this method is that the oxidation of the soil will cause damage to the resin and will decrease remediation efficiency [ 66 , 67 ]. Another concern is that the contaminant has not been destroyed if treated by the ion exchange method; it is only transferred to another medium that needs to be disposed of. This method is not good if the groundwater contains oil or grease, as these pollutants may clog the exchange resin [ 67 ].

• (2) Abiotic Reduction

The chemical reactions that lead to the decomposition of contaminants in groundwater are referred to as abiotic remediation. In this technique, the harmful compounds are to be reduced either by immobilization in the treatment wall of the reactive barriers, or it is permitted to pass through the barrier in a harmless form. Zero-valent iron (ZVI) is the most popular reactive material used in the abiotic remediation of groundwater; after the reaction of ZVI with the contaminants, low solubility minerals will be precipitated, for example, the remediation of U and Cr from groundwater, which is removed by the precipitation of these contaminants by the abiotic process. Equation (1) shows the ability of ZVI to reduce U(VI) to U(IV) in groundwater with high carbonate and moderate pH via producing UO 2 (Uraninite), which is a solid, less crystalline product of uranium.

For the chromium (Cr), ZVI reducing Cr(VI) to Cr(IV) [ 58 , 60 ] as shown in Equation (2):

Cr(VI) could be reduced to Cr(III) by ferrous iron via introducing dissolved dithionite ions ( S 2 O 4 2 − ) to an aquifer, which can reduce the solid phase of ferric iron. Dithionite oxidizes to sulphite ( S O 3 2 − ) and F e 3 + is lowered to F e 2 + . Cr(III) is to be stalemated by precipitate in the solid form of Cr(III) and Fe(III) hydroxide along with the reduction in some halogenated organic compounds by the effect of F e 2 + as shown in Equations (3) and (4).

• (3) Biotic Redaction/Oxidation

When physical or chemical remediation of groundwater shows little or no degradation of contaminants, then degrading pollutants with a biological oxidation process may be helpful. Many pollutants such as chlorinated solvents tend to be easily reduced if oxidized; here, microorganisms will perform a reduction process by exploiting contaminants as their main source for energy and the required materials to synthesize their cells [ 49 ]. The bioremediation technique is a very effective remediation process based upon the degradation of contaminants by microorganisms; remediation efficiency in this process depends on the working environment, such as the temperature, pH, electron acceptors and the concentration of nutrients [ 68 ]. In biodegradation, it is necessary that germs use electron acceptors to accept any electrons liberated from pollutants; electrons transfer, releasing energy that is essential for microbes’ lives. In the presence of oxygen, under aerobic conditions (which is preferable), energy producing from this process is higher than that released without the presence of oxygen. Additionally, the oxidation rate of contaminants is higher. In the groundwater, the presence of oxygen is usually little; in this case, the anaerobic microbes electron acceptors is utilized. However, it is effective to remediate groundwater contaminated by monoaromatic hydrocarbons by using oxygen-releasing compounds in the PRBs [ 49 , 56 , 69 ].

The basic concept of biotic reduction, biotic oxidation, is to supply an electron donor along with nutrient materials to be used by microorganisms to break down the contaminants. Leaf mulch, wheat straw and sawdust can be used as electron donors, and municipal waste can be used as a nutrient material. Dissolved sulphate in the wastewater is a good electron acceptor, which can oxidate organic materials and can consume acidity coupling with metal reduction as shown in the below Equations (5) and (6):

• (4) Chemical Precipitation

This process consists of contaminants removal as hydroxides (Equation (7)) and carbonates (Equation (8)) via mineral precipitation resulting from increased pH. Firstly, contaminants are reduced to a less soluble species, and finally, they are retained as minerals in the barrier. Limestone (CaCo 3 ) and apatite [Ca 5 (PO 4 ) 3 (OH)] are commonly used in chemical precipitation

A summary of the available and common reactive media is presented in Table 3 ; the geochemical process, nature of contaminants, reactivity and availability are significant factors in the selection of the best convenient reactive media in remediating groundwater.

Reactive media for the remediation of groundwater contaminated by metals and radionuclides (Bronstein, 2005).

4. Modelling of Sorption Process

“Sorption” refers to the physical or chemical process in which a substance becomes in contact with another, which consists of two processes:

• (1) “Adsorption” is a surface process; substances transfer from their aqueous phase (liquid or gas) to the solid phase surface that provides a surface for adsorption known as “adsorbent”; the species transformed from the aqueous phase to the surface of the solid phase is called “adsorbate” [ 62 ]. The existence of nitro groups on the adsorbate stimulating adsorption, hydroxyl, azo groups increases the adsorption rate, while the presence of sulfonic acid groups decreases adsorption [ 70 ].
• (2) “Absorption” is defined as the whole transfer of substances from one phase to another without forces being applied to the molecules. The relationship governing the transfer of substances in aqueous porous media and the mobility of substances from liquid or gas states to the solid state is referred to as “isotherm” [ 71 ]. Adsorption isotherms is curvy relationships connecting the equilibrium concentration of a solute on the surface of an adsorbent ( q e ) to the concentration of solute in its aqueous state ( C e ); both phases should be in contact with each other [ 70 , 72 ].

4.1. Sorption Isotherm Models

Several isotherm models are used to describe sorption parameters and the adsorption of pollutants as follows:

4.1.1. Freundlich Model

In 1909, Freundlich gave an imperial relationship that describes the capability of a unit mass of solid to adsorb gas in the presence of pressure. The Freundlich adsorption isotherm is a curve correlation between a solute concentration on a solid’s interface and the solute concentration in the adjacent aqueous environment [ 73 ]. The Freundlich isotherm model describes absorption in the terms of adsorbate concentration as follows:

where K f   m g g   is the coefficient of the Freundlich isotherm, n < 1, which describes the empirical coefficient expresses the amount of sorption [ 72 , 74 , 75 ]. ( K f )   a n d   (n) can be calculated by solving equation xx logarithmically and plotting ln q e verses ln C e where K f = 10 y − i n t e r c e p t and the slop of ( 1 n ) as shown below:

According to the Freundlich isotherm, the sorbet contaminants is directly proportional to their concentration at a small amount and decreases when contaminants accumulate at the surface of the reactive media [ 76 ].

4.1.2. Langmuir Model

The theoretical Langmuir isotherm model has been derived to describe the physical besides the chemical adsorption, as well as quantifying and describing the sorption on sites located on the adsorbent. Langmuir assumes the following [ 70 , 71 , 76 ]:

• Each adsorbate molecule is to be adsorbed on a well-defined binding site on the adsorbent, and adsorption reaches saturation when all these sites are occupied.
• Each active binding site on the adsorbent interacts with one adsorbate molecule only.
• No interaction existed between adsorbed molecules. All sites are homogeneous (energetically equivalents).
• The surface is uniform, and monolayer adsorption occurs.

Accordingly, the equation of the Langmuir isotherm model is:

where C e (mg/L) represents the concentration of solute in the bulk solution at the equilibrium state. q m (mg/g) represents the maximum adsorption capacity. b is a constant that represents sorption free energy. q e (mg/g) represents the amount of the adsorbed solute by a unit weight of adsorbent within the equilibrium conditions. The Langmuir equation’s constant can be determined with the linearization of Equation (12) as follows:

This equation describes that C e q e is plotted as a function of C e , the parameters of q m and b   are determined from the slope ( 1 q m ) with y-intercept ( 1 q m b ) linear regression to Equation (12) [ 76 ].

4.1.3. Temkin Model

The Temkin isotherm assumes that heats of adsorption would more often decrease than increase with the increase in solid surface coverage. It takes into account the adsorbing species–adsorbent interaction. Temkin isotherm has the following formula:

where R represents gas universal constants (8.314 J/mol K). T is the absolute temperature (K). a T e and b T e are constants.

4.1.4. Brunauer–Emmett–Teller (BET) Model

The BET was developed based on the Langmuir model in an attempt to minimize the Langmuir isotherm restrictions. This isotherm assumes that more molecules can be adsorbed on the monolayer, and it is possible within this isotherm that bi-layer (multi-layer) adsorption will occur. This isotherm could be proclaimed as:

where q m is the maximum adoption capacity, b represents a dimensionless constant, and C s is the concentration in the case of saturated sites and homogenous surfaces.

4.2. Kinetic Models

Adsorption kinetic models are important to describe the solution uptake rate and adsorption required time [ 74 , 75 , 77 ]; these models providing a description for the sorption process onto the sorbents. The sorption mechanism occurs in three steps; the first one is the diffusion of adsorbate through the aqueous phase surrounding the adsorbent; secondly, the diffusion of adsorbate in the pore of the particle (intrapore diffusion); finally, the adsorption occurrence due to physical or chemical interaction between the adsorbate and adsorbent [ 75 , 78 , 79 ]. However, three kinetic models are used to describe the sorption mechanism and the predominated stage as follows:

4.2.1. Pseudo-First-Order Model

A model that is quantified according to Equation (15) below:

where q e is the contaminant’s amount sorbet in equilibrium conditions (mg/g), q t represents a contaminant’s quantity sorbet during any given time (t) (mg/g), k 1 is a constant rate of pseudo-first-order adsorption (min −1 ).

The pseudo-first-order equation has been integrated at boundary conditions of t = 0 to t = t and q t = 0 to q t = q e , then transferred to a linear form as shown in Equations (16) and (17) [ 80 ].

For this kinetic model, log q e − q t must be plotted against time interval; if the intercept of q e theoretical differs than q e experimental , then the reaction does not follow the model of the pseudo first order.

4.2.2. Pseudo-Second-Order Model

The kinetic model of pseudo-second-order adsorption is applicable for small initial concentrations to calculate the initial sorption rate [ 74 ]. The pseudo-second-order equation for the sorption rate has the following form:

where q t is the magnitude of adsorbate, which is adsorbed by an adsorbent (mg g −1 ) at a given time (min), q e represents the amount of adsorbate adsorbed (mg g −1 ) in equilibrium conditions. k 2 is a constant of the second-order sorption rate (mg (mg min) −1 ) [ 80 ].

4.2.3. Intra-Particle Diffusion Model

In 1962, Weber and Morris proposed the kinetic model of intra-particle diffusion, and it has been used for the analysis of adsorption kinetics of lead ions by adsorbent (CHAP) [ 76 , 80 , 81 ]. Based on this model, the uptake graph of ( q t ) versus the squared root of time ( t 0.5 ) must be linear in the overall adsorption process; in addition, if the line intersects with the origin, then the intra-particle diffusion is the predominant adsorption process. The k d represents the intra-particle diffusion initial rate (mg (mg min) −1 ), which could be calculated through the following formula:

where q t represents the amount of sorbate on the solid phase (surface of sorbent) at any time t (mg g −1 ), and t represents time (min).

5. Contaminant Transport Equation and Breakthrough Curves

Soil is a dynamic system in which toxic contaminants are used as a sink or a pathway. When contamination occurs on the surface soil, some of these contaminants will percolate under the water table and form a plume of contaminants. This plume will be developed over time ( t ), and contaminants will be driven downstream, as shown in Figure 1 . It is very important to understand how these contaminants will dissolve in the flow and how they will be carried out downstream; it is very important to discover the concentration of these contaminants as a function of time. The predominant mechanism for the attenuation and retardation of contaminants is sorption. Sorption phenomena will happen when the solid phase of the environment attenuate these contaminants, which will lead to contaminants being removed from the water, and the concentration of pollutants will be reduced downstream. The transport mechanism of pollutants in a saturated environment is the advection that carries contaminants without mixing. The hydrodynamic dispersion is driven by molecular diffusion and mechanical dispersion. If the hydraulic dispersion goes to zero, then the transport will be conservative, and there will be no retardation or any attenuation to the contaminants; on the contrary, if there is retardation to the contaminates, then the concentration of contaminants will be reduced at the downstream by the effect of sorption.

Contaminants concentration development in groundwater (“t1, t2–t6” are time intervals).

5.1. Modeling of Contaminants Transport

5.1.1. advection.

In the advection, contaminants transport downstream along with the flow with advective velocity. It is the physical transport of contaminants across the space:

where V x a is the linear advective velocity.

Darcy velocity is given by the meaning of Darcy law, which is:

where ( K ) is the hydraulic conductivity, ( K r ) is the relative conductivity, ( θ ) is the volumetric moisture content, and ( ∂ h ∂ x ) is the head gradient in the x-direction.

where (F x ) is the advective flux ( K g t . m 2 ), ( V x a ) is the advective liner velocity ( m s e c ), ( n ) is the effective porosity, and ( c ) is the concentration of contaminants ( k g m 3 )

Substitute   F x , F y   and F z   in the conservative equation:

In the saturated medium, ( n ) = 1.

5.1.2. Hydrodynamic Dispersion

Molecular diffusion.

In a stagnant fluid, diffusion is the process of molecules random movement. It is basically driven by the concentration gradient and occurs by the Brownian motion. Therefore, diffusion usually increases with the increment of entropy.

In general, diffusion follows Fick’s first law:

where ( F ) is the mass of solute per unit area per unit time ( M L 2 T ), ( D d ) is the diffusion coefficient ( L 2 T ) ≈ 10 − 9 ( m 2 s e c ), and ( ∂ c ∂ x ) is the concentration gradient ( M L 3 L ).

According to the mass conservation of dissolved contaminants:

The time-dependent concentration equation is:

n = 1 in a saturated medium.

Substituting Fick’s first law in Equation (28)

For a one dimensional flow:

The diffusion coefficient ( D d ) here is the free diffusion coefficient (i.e., in water); if the flow medium is porous, then the effective diffusion coefficient ( D * ) is used due to the effect of the tortuous flow path:

w is related to the tortuosity (T): T = l e l ≥ 1 as shown in the below Figure 2 ; laboratory studies showed that 0.01 > w   ≤ 0.5

Determination of tortuosity in a porous medium.

Mechanical Dispersion

There is a number of mechanisms that lead to the assurance of the mechanical mixing of contaminants in the aquifer as follows:

• (a) Mechanical dispersion due to pore size

When dissolved contaminants pass through a porous medium, pore size will affect the hydraulic conductivity of this media; when particles are fine, porosity will be below, and the advective velocity will be slow, as shown in Figure 3 .

Mechanical dispersion due to pore size.

• (b) Mechanical dispersion due to path length

If a pore is medium, the mechanical mixing may happen due to the effect of the length of the pathway, which will be passed by the dissolved contaminants. Each molecule of contaminants will pass through a different pathway that is unequal with the pathway of other particles, as illustrated in the below Figure 4 .

Mechanical dispersion due to path length.

• (c) Tylor dispersion

Taylor mechanical dispersion occurs when dissolved contaminants pass around the aquifer’s solid particles. Solids pass faster in a middle way between two particles than another pass near a solid particle, as shown in Figure 5 . This is because the linear velocity in the centre of pores is greater than that near the edge of solid particles.

Tylor mechanical dispersion.

All the above mechanisms lead to mechanical mixing for solute contaminants in both the longitudinal direction (with the main flow direction) and the transverse direction (out of the main flow direction).

The coefficient of mechanical dispersion ( D ) is related to aquifers’ dispersivity (α), which reflects the extent to which the aquifer is dispersive and the advective velocity of flow.

where ( D L ) and ( D T ) are the mechanical dispersion coefficient in the longitudinal and transverse directions (m 2 /sec), respectively. ( α L   ) and ( α T ) are the longitudinal and transverse dispersivity (m), respectively. ( V L a ) and ( V T a ) are the longitudinal and transverse advective velocity (m/sec).

In the low permeability medium, the permeability is near to zero; in this case, there will be no effect on the mechanical dispersion, and only the diffusion will be predominant.

5.1.3. Advection–Diffusion Equation

The theory of contaminants transport model in porous media is subjected to a partial differential equation governing space and time. The theory incorporates four different processes, all merged in one equation; one process is advection, which means that a substance follows the direction of water (driven by water flow) and itself moves with convection. The second process is dispersion, which is caused by the heterogeneity of pollutants, and a package of contaminants will move faster than the others. Then, there is a chemical reaction, which described by a kinetic equation. Finally, there is the adsorption to the soil, which means that the contaminant may spend some of its time tied to the solid phase and sometimes in the mobile water. The equation that describes all of this is the advection–dispersion equation, as follows:

In the above equation, the change in mass per unit volume ( m ) of the contaminants due to the reactions within the aquifer is referred to as ( r ).

where ( F x ) is the total flux in the ( X ) direction. ( V x n C ) is the addictive flux, and (– ( n D x ∂ C ∂ x )) is the dispersive flux.

Substituting ( F x ) in Equation (37) for (x, y and z) directions:

In the 1D flow, with a constant dispersion coefficient and constants porosity in space and time (=1 in a saturated medium), the equation of advection–dispersion can be written as:

The term ( r ) is considered an important factor in the attenuation of contaminants in a porous media, which is related to the sorption, the predominant process of contaminants attenuation in a permeable reactive barrier during contaminants’ mass transfer. Generally, ( r ) depends on the bulk density ( ρ b ) of the medium and the amount of contaminants sorbed ( q ) with time, thus:

By substituting the value of ( r ) (Equation (41)) in Equation (40), the advection–dispersion will be as follows:

The sorption process is represented in the above equation by the term ρ b n ∂ q ∂ t , ( q ) represents contaminants concentration that sorbed on the solid phase of the reactive media, which can be described by the Langmuir or Freundlich isotherm models as a function of concentration. Equation (42) can be rewritten as follows:

where ( R ) is the retardation factor, which reflects the effect of retardation of contaminants during its transport to the downstream.

The “breakthrough curve” describes the relationship between the concentration of contaminant vs. time, which is an important tool for design and optimizes the sorption in a field-scale PRB by relating the data obtained from laboratory columns to the field scale breakthrough curves. In a continuous constant influent of contaminants, the breakthrough curve will be shaped as (S); the best point on this curve is referred to as the breakthrough point, which has an outlet concentration of contaminants that matches the desired concentration in water. A summary of empirical and theoretical models used to predict the breakthrough curves are described below:

• Bohart–Adams model

The purpose of performing column experiments is to calculate the relationship between the concentration and time, the breakthrough curve in addition to calculate the maximum adsorbent capacity of adsorption. Results will be used to design a full-scale adsorption column. The Bohart–Adams model is one of the models that has been formulated to fulfil this purpose; it has been based on the rate of surface reaction theory [ 82 ]. This model has been built on the following assumptions [ 48 ]:

• 1. This model can describe the concentration at low levels ( C « C 0 ) ( C = 0.15   C 0 ).
• 2. When t → ∞ ; q 0 → N 0   with saturation concentration.
• 3. The external mass transfer is limiting adsorption speed.
• 4. The Bohart–Adams model has the following formula: C C 0 = 1 1 + exp K N 0 Z U − K C 0 t (44) where C 0   and C represents the instantaneous (initial) concentration of the pollutant in solution (mg/L). K is the kinetic constant (L/g/min). N 0 represents the congestion concentration (mg/L). Z represents column bed depth (cm). t represents the time of service (min), and U is the velocity of the flow (cm/min).
• Thomas model.

The Thomas model is widely used to calculate adsorbent maximum adsorption capacity. It uses data obtained from continuous column experiments. The Thomas adsorption column is given below:

where C 0   and C are the concentrations of influent (mg/L). K T is the constant rate (mL/mg/min), q represents the higher adsorption capacity (mg/g), M represents an adsorbent quantity in the column (g), t is the time of adsorption (min), and Q is the feed flow rate (mL/min). The Thomas model is based on the following assumption:

• 1. No dispersion is driven.
• 2. The Langmuir isotherm coincide with the equilibrium state.
• 3. Adsorption kinetics ( K ) should follow the rate of pseudo-second-order law.
• Yoon–Nelson model

In this model, the decreasing probability of each adsorbate is proportional to its breakthrough adsorption on the adsorbent. The following formula is a representation of this model:

where K Y N represents the Yoon–Nelson rate constant. The Yoon–Nelson model is limited by its rough form.

• Clark Model

Clark’s breakthrough curves were based on the mass transfer principle in conjunction with the Freundlich isotherm. Clark has developed his breakthrough curves as follows:

where n represents the exponent of the Freundlich isotherm,   A and r represents the parameters of the kinetic equation.

Wang et al. (2003) invented a new model based on the mass transfer model. It has been used as a solution of Co and Zn ions in a fixed bed under the following assumptions:

• 1. The adsorption mechanism is isothermal.
• 2. The mass transfer equation is as the following: − d y d t = K w x y (48) where K w represents the kinetic constant, the fraction of adsorbed metal ions is represented by y . (with x + y = 1 ) ,     x represents the fraction of metal ions moving through the fixed bed.
• 1. There is symmetry in the breakthrough curve.
• 2. The axial dispersion in the column is negligible.

By integrating the above equation and presuming that y = y w at t = t w . w = 0.5 , the entire breakthrough equation can be expressed as:

where ( x ) can be expressed as:

Finally, the Wand model, similar to the Yoon–Nelson model, cannot provide enough detail on the adsorption mechanism.

6. Review of Previous Research on the Use of PRBS

The first permeable reactive barrier was constructed at a Canadian air force base in (1991) [ 83 ]; since that date, many studies have been conducted to examine the PRB’s efficiency. There were 624 publications that discussed the permeable reactive barrier from 1999 to 2009 [ 84 , 85 ]. Previous research has been conducted to study the ability of different reactants to remediate different pollutants in the permeable reactive barrier. The following is a list of the most important scientific studies.

The remediation of groundwater contaminated by chlorinated ethenes such as vinyl chloride (VC), dichloroethene (DCE) and trichloroethene (TCE) was studied using in situ biodegradation with a special functional microorganism known as Burkholderia cepacia ENV435 [ 86 ]. The researchers chose these microorganisms for many important characteristics, such as their good adhesion ability to aquifers’ solids; in addition, these microorganisms can establish an organized existence without the need to induce co-substrates. Furthermore, these organisms can grow in a high density in fermenters (−100 g/L), and finally, they can accumulate high internal energy, which this microorganism can use to resist the effect of chlorinated solvents and survive. Results showed the concentrations of VC, DCE and TCE decreased by 78% after two days of organism injection.

The output of a pilot-scale PRB for the remediation of chlorinated volatile organic compound-contaminated groundwater (VOCs) has been investigated. This study used a granular zero-valent iron reactive barrier, which was mounted in a funnel with a gate mechanism. Results showed that consistent VOC degradation was observed over the research period. It is observed that the degradation mechanism is due to pH increment, which leads bicarbonate ( H C O 3 − ) to convert to carbonate ( C O 3 2 − ), the carbonate combines cations ( C a 2 + ,   F e 2 + ,   M g 2 + ,   etc . ) in solution, which form mineral precipitates. It is observed that mineral precipitates formed in the reactive media represented as an unconquerable limitation to the treatment process [ 87 ].

A zero-valent iron PRB’s effectiveness in eliminating chlorinated aliphatic hydrocarbons (CAHs) has been investigated. The contact of reactive media (ZVI) with the CAHs in an aqueous environment caused a rise in the pH; this resulted in the precipitation of carbonate minerals and a loss of 0.35% of the porosity in the reactive fraction of the PRB [ 88 ].

The rapid evolution of the PRB’s application from a full in situ implementation on a laboratory level to treat groundwater polluted by various types of inorganic and metals was assessed [ 89 ]. This study concluded that different reactive media can be used in the preamble reactive barrier to remove inorganic compounds, such as the use of zero-valent iron PRB to remove TC, U and Cr from groundwater. Furthermore, solid-state organic carbon may be used to extract dissolved solids associated with acid-mine drainage. According to this research, there are different mechanisms for the treatment of inorganic anions; for example, the rate of Cr(VI), TC (VII), U(VI) and NO 3 could be successfully decreased by the mean of reduction using zero-valent iron (Fe 0 ). According to a monitoring program for a Cr(VI)-contaminated area, the concentration of Cr(VI) has decreased from 8 mg L −1 to > 0.01 mg L −1 , owing to a decrease in Eh and an increase in pH.

At a former uranium production site in Monticello, Utah [ 90 ] investigated the design and efficiency of a PRB in extracting arsenic, uranium, selenium, vanadium, molybdenum and nitrate. In this study, field and laboratory column tests have been performed. The reactive media in PRB was the zero-valent iron. After one year from PRB installation, the performance of ZVI–PRB is described by the reduction in concentrations of elements up-gradient and down-gradient of the barrier. The inlet concentrations of arsenic, manganese, molybdenum, nitrate, selenium, uranium and vanadium were 10.3, 308, 62.8, 60.72, 18.2, 396 and 395 µg/L, respectively. These concentrations have reduced to be >0.2, 117, 17.5, >65.1, 0.1, >0.24 and 1.2 µg/L, respectively. The removal mechanism for these radionuclides is by reducing uranium to lower molecules along with precipitation. Additionally, adsorption is another chemical process that leads to a reduction in these elements.

The use of a reactive biological barrier to remove nitrate pollutants has been investigated. The autotrophic sulphur-oxidizing bacteria has been used as an electron donor, and sulphur granules have been used as a biological agent. Sulphur-oxidizing bacteria colonized the sulphur particles and removed nitrate, according to the findings. The best operation conditions have been investigated, and it was found that an environment near the neutral pH achieved 90% removal of nitrates [ 91 ].

The efficacy of a ZVI barrier mounted in the field in eliminating chromium solid-phase association has been studied, and the removal efficiency after 8 years of operation has been investigated. Results showed that ZVI has the ability to reduce the concentration of Cr from an average <1500 µg/L to about >1 µg/L. The reduction in Cr(VI) to Cr(III) along with the oxidation of Fe(0) to Fe(II) and Fe(III), resulting in Fe(III)-Cr(III) precipitating as oxyhydroxides and hydroxides, has been discovered to be the most common Cr removal mechanism. It was also discovered that the reacted iron produced a coating of goethite (α-FeOOH) with Cr, resulting in precipitation [ 92 ].

Experiments have been performed to discover the efficiency of seven selected organic substrates in removing inorganic nitrogen in the form of NO 3 − , NO 2 − and/or NH 4 + in a denitrification PRB in batch scale experiments. Softwood, hardwood, coniferous, mulch, willow, compost and leaves were all reactive materials. The softwood was found to be suitable for use as a reactive medium in PRB due to its very good ability to denitrify nitrogen. Reduction in nitrate was due to the effect of denitrification (which represents 90% of the nitrate removal of which the dissimilatory nitrate reduction to ammonia (DNRA) represents 10% of the removal process [ 93 ].

The efficacy of activated carbon PRB for removing cadmium from contaminated groundwater has been investigated. The original cadmium concentration was 0.020 mg/L, but after it passed through a PRB of activated carbon, the polluted plume was adsorbed, and the cadmium concentration was nearly zero for the first three months. After that, the barrier became saturated, but the effluent cadmium concentration remained below the quality limit of 0.005 mg/L for more than seven months [ 94 ].

The use of polyvinylpyrrolidone (PVP-K30)-modified nanoscale ZVI in removing tetracycline from liquid has been investigated. Tests revealed that PVP-nZVI consists of Fe(0) in the core and ferric oxides on the shell. PVP-nZVI will adsorb tetracycline and its degradation products, according to the findings. It is also observed that the adsorption of tetracycline has been reduced with time due to the formation of H 2 PO 4 − , which has a strong tendency to react with the mineral surface [ 95 ].

Tetracycline adsorption using graphene oxide (GO) as a reactive media has been investigated. Results showed that tetracycline formed a π–π interaction and cation–π bonds with the surface of GO, with the Langmuir and Temkin models providing the best fit isotherms for adsorption and the Langmuir model calculating a maximum adsorption capacity of 313 mg g −1 . The kinetics of the adsorption model are also equipped with a pseudo-second-order model with a better sorption constant ( k ), 0.065 g mg −1 h −1 than other adsorbents, according to the results [ 96 ].

The design, construction and testing of a permeable barrier at the Casey station in Antarctica to remediate and avoid the spread of an old diesel fuel spill have been discovered. Five segments of a bio-reactive barrier were allocated and installed in the funnel and gate configuration, each segment divided into three zones; the first one is a slow-release fertilizer zone to enhance the biodegradation, the second zone is responsible for hydrocarbon and nutrient capture and degradation, while the third zone is responsible for cation capture and access to nutrients produced by the first zone. The first zone’s reactive media was a nutrient source, followed by hydrocarbon sorption materials (granular activated carbon plus zeolite); to extract cations nutrient released and accessed from the first region, sodium activated clinoptilolite zeolite is used. Oxygen delivery to the system was applied to enhance the microbial reactions. The function of each zone is the first zone to provide nutrients such as phosphorate to the microorganism. Due to its high surface area and microporous surface (500–1500) m 2 /kg, granulated activated carbon can adsorb hydrocarbon pollutants in the second zone. In the third zone, the Australian sodium zeolite is placed to capture any accessed ammonium cation from the solution due to its high ability to exchange ions with ammonium. Tests and results showed that the ion exchange of zeolite best-controlled nutrient concentration, while the sodium zeolite captured any migrated ammonia from the groundwater. Additionally, results showed that the fuel is degraded in the PRB faster than in the hydrocarbon spill area field. In the cold world, activated carbon–PRB is a strong technology for removing hydrocarbons.

In batch and fixed-bed column experiments, the adsorption of tetracycline (TC) and chloramphenicol (CAP) was investigated by [ 97 ] using bamboo charcoal (BC) as a reactive medium. The predominant mechanism of TC and CAP adsorption on BC is π – π   electron-donor–acceptor (EDA), cation–π bond in combination with H-bond interaction, while the hydrophobic and electrostatic interaction has a minor effect on the adsorption. Results showed that BC has a strong adsorption capacity to TC and CAP; with increasing influent concentration and flow rate, adsorption efficiency improves. Surface diffusion was the most common mass transfer mechanism for antibiotic adsorption [ 98 , 99 ].

An overview of the use of PRBs in the remediation of a broad range of pollutants, demonstrating that it is a viable alternative to the pump-and-treat process, has been discussed by [ 85 ]. The most popular PRB reactive media, according to this study, is zero-valent iron (ZVI). Efficient PRB architecture requires accurate site characterization, groundwater flow and flow conditions requirements and ground flow modelling.

The potential efficiency of a microscale zero-valent iron PRB in removing tetracycline (TC) and oxytetracycline (OTC) with the formation of transformation products during the remediation have been discovered. To investigate the effect of solution pH, a series of batch experiments were carried out, including iron dose and environment temperature. Results showed that pH has a key factor controlling the efficiency of removal; increasing iron dose and working temperature also increased the removal efficiency. Pseudo-second-order model and Langmuir isotherm were found to be most fitted to adsorption kinetics and removal isotherms [ 100 ].

The effectiveness of removing copper ions Cu(II) and zinc ions Zn (II) heavy metals from groundwater using cement kiln dust and a sand PRB was investigated by [ 48 ]. In this research, the re-use of a very fine by-product powder resulted from the cement industry known as cement kiln dust (CKD) has been investigated to remove appointed heavy metals instead of throwing this CKD into the environment. The optimum weight ratio of CKD/sand, which provides the best remediation, has been investigated in column tests from 99 days of operation time. The remediation mechanisms were the adsorption/desorption, precipitation/dissolution and adsorption/desorption of the pollutants. Contaminant transport in porous media, as well as breakthrough curves, are also explored. Breakthrough curves refer to the relationship between the concentration of the contaminants at any time in any position in the domain. Results showed that the best CKD/sand ratio was (10:90 and 20:80) because other ratios showed a loss in the hydraulic conductivity and loss in groundwater flow due to the accumulation of contaminants mass in the voids between the sand causing clogging and flow loss.

The mechanism of remediating pharmaceutical pollutants (tetracycline) from groundwater using zero-valent iron coupled with microorganisms as reactive media has been investigated by [ 55 ]. In this research, three PRB columns have been studied, beginning with columns filled by zero-valent iron, the second with zero-valent iron and microorganisms and, finally, the third one with microorganisms. Results revealed that zero-valent iron has the best effect on removing tetracycline. Removal efficiency reaches 50% while it was 40% with zero-valent iron and microorganisms’ PRB and 10% by the effect of microorganisms’ PRB. The mechanism of this reaction is that the zero-valent iron (Fe 0 ) has been adsorbed and reduced tetracycline, Fe 0 converted to Fe +2 and Fe +3 , and the tetracycline has been degraded.

The use of a bio-PRB coupled with a good aeration system to remediate groundwater polluted with nitrobenzene and aniline have been studied. To degrade the NB and AN, suspension-free cells of the degrading consortium and the immobilized consortium were used in this study. Results showed that both AN and NB were completely degraded within 3 days in the immobilized consortium, while it needs 3–5 days to degrade using the free cells. It was also discovered that in the presence of oxygen, the removal efficiency of NB and AN was increased [ 56 ].

In a permeable reactive barrier, [ 101 ] investigated the effect of MnO 2 and its mechanism of tetracycline elimination. The zero-valent iron serves as the reactive media in this PRB. In this research, three PRB columns were studied, the first one with ZVI, the second had ZVI-MnO 2 , while the third consisted of MnO 2 only. Results show that the ZVI in the presence of MnO 2 is the most effective material in removing TC. Its removal efficiency reached 85%, while the ZVI removed about 65% and the MnO 2 removed 50% of TC. This research revealed that MnO 2 accelerated the transformation of Fe 2+ to Fe 3+ , then the Fe 3+ degraded tetracycline. The functional group that played the predominant role in this reaction is the hydroxyl radical produced in this process.

A series of laboratory and field studies in the Ukrainian city of Zhovty Vody has been performed to assess the reliability of a reactive barrier made up of zero-valent iron and organic carbon mixtures to remediate uranium-contaminated groundwater. In these studies conducted by [ 102 ], three reactive media were examined. The first was zero-valent iron, which was used to study the sorption, reduction and precipitation of redox oxyanions; the second was the phosphorate materials, which has been used to transfer the dissolved materials to other phases; the third was bioremediation materials and organic carbon substrates. The study revealed that the treatment mechanism of the uranium is sorption by the ZV, and it also observed that the microbes have the ability to sorb the uranium U(VI) to the bacterial cell walls. Due to the effect of enzymatic production, dissolved oxygen reduced first, then due to the effect of denitrification, UO 2 CO 3 reduced to uranite and sulphate reduced to sulphide; finally, amorphous uranium oxide will be formed on the microorganism surfaces. In this research, new placement of the reactive media has been used in which rows of cylinders with iron reactive media have been placed instead of the regular funnel and gate placement; this placement reduced the in situ installation cost.

The effectivity of PRB made from sodium alginate/graphene oxide hydrogel beds (GSA) for the remediation of ciprofloxacin (CPX) antibiotic contaminating the groundwater has been investigated. In this research, the key factors affecting the performance have been studied, and longevity and the cost of PRB have been discussed, and a proper design for the PRB has been proposed. Results show that the adsorption capacity of CPX on the GSA was 100 mg for each gram of GSA at pH 7.0; the leading mechanism in the adsorption process was the pore filling, H-bonding, ion exchange, electrostatic interaction and hydrophobic interaction. The results indicate that the GSA’s ability to remove CPX from groundwater when used in a PRB is concrete evidence that GSA is a good option for removing CPX from groundwater [ 103 ].

The removal of tetracycline from aqueous solutions using binary nickel/nano zero-valent iron (NiFe) reactive media in column reactors has been studied. Results show that if a mixture of 20 mg/L of TC plus 120 mg/L of NiFe in a 90 min time of interaction, TC will be removed by 99.43%. In this research, sand particles loaded with reactive media (NiFe) have been used. Electrostatic interaction has been used to load the reactive media on sand particles. A Tc removal mechanism was investigated using UV-Visible spectroscopy, TOC, FTIR and SEM analysis [ 104 ].

The use of the PRB system in preventing the migration of radiocesium into groundwater using natural zeolite and sepiolite has been investigated. These reactive media are natural, low-cost materials. Two-dimensional bench-scale prototypes at the steady flow conditions have been used in the experiment. Information on the transport behaviour of radiocesium and changes in hydraulic conductivity were investigated in this study. It has been determined that the remediation phase would reduce hydraulic conductivity over time. As a result, by combining sand with reactive media, the PRB has been modified to achieve steady-state operating conditions of flow [ 105 ].

The effectivity of the use of PRB of cement kiln dust as a reactive media in an acidic environment (pH 3) to remediate groundwater contaminated with dissolved benzene has been studied by [ 9 ]. Experiments were performed for 60 days with batch and column tests. Results showed that benzine removing efficiency reached more than 90%, and the best CKD/sand ratio was 5/95, 10/90 and 15/85, which achieved the best hydraulic conductivity. Results also show that barrier longevity reached (half a year) when CKD was about 15%. FTIR test results showed that adsorption happened due to the formation of H bonding and cation.

The removal of meropenem antibiotic with a cement kiln dust (CKD) PRB through batch and continuous column experiments have been studied by [ 106 ]. Results showed that pH 7.0 had a 60 mg adsorption potential for every 1 g of CKD, according to the findings. Initial concentration, flow rate and influence have all had an impact on CKD efficiency. Meropenem adsorption occurred due to the O-containing functional group’s effect on the surface of CKD, which leads to an H-bonding and π – π   a n d   n – π EDA interaction (donor–acceptor) between the CKD and the meropenem, which all lead to the adsorption.

The sustained treatment of a bio-wall and its effectivity in remediating groundwater contaminated by chlorinated volatile organic compounds (TCE) after 10 years of bio-wall installation has been studied by [ 107 ]. The reactive medium used in this barrier was mulch, utilizing the benefit of its high cellulose content (<79%). This research investigates a reactive barrier of mulch (1615 m long × 10.7 m depth × 0.6 m thickness). This bio-barrier consisted of 42% mulch, 11% cotton, 32% sand and 15% rock to increase the permeability. It is estimated that groundwater retention time within the barrier is 2–50 days, while groundwater speed was (0.002–0.3 m/day). Contaminants were trichloroethene (TCE), tetrachloroethene (PCE), dichloroethene (DCE) and vinyl chloride (VC). After 10 years of the bio-wall installation, results showed that mulch bio-wall effectively degrades TCE from groundwater to daughter products, TCE concentrations remained below the USEPA maximum levels, while it was over these levels in the up-gradient side of the bio-wall. The microbial population, geochemical environment of the barrier was still active. Investigating the concentration patterns, microbial community and the geochemical environment of the bio-wall demonstrates that the bio-wall is an effective reductive to the volatile organic contaminants.

The effectiveness of a horizontal PRB with a reactive media of zero-valent iron to prevent the scattering of chlorinated solvent vapour in the unsaturated region was investigated by [ 108 ]. In this research, the potential feasibility of using PRBs placed in a horizontal direction was investigated. The reactive medium in this study was the zero-valent iron (ZVI) powder mixed with sand, and the TCE was tested as a model for the (VOCs). Tests were performed in batch reactors. Results showed after 3 weeks of treatment and based on the type of ZVI powder, the concentration of TCE vapour was reduced in a range of 35–99%. The ZVI’s best output is determined by the particular surface area.

The use of sewage sludge and cement kiln dust to produce hydroxyapatite nanoparticles has been investigated. The removal of tetracycline using the new formed hydroxyapatite were examined and the best operation conditions were 2 h contact time, dosage 0.4 g/50 mL, agitation speed 200 rpm with a mixture molar ratio Ca/P = 1.662, the removal efficiency reached 90% with a TC maximum adsorption capacity of 43.534 mg for each gram of hydroxyapatite filter cake. Results show that adding 10% sand (to enhance the hydraulic conductivity of the PRB) to the hydroxyapatite reduced the adsorption capacity to be 41.510 mg/g. XRD, FTIR and SEM analytical tests proved that the predominant mechanism for the remediation of TC is due to the adaptation on the hydroxyapatite surface. During the process, two functional groups, (-OPO3H-) and (CaOH2+), were formed, both of which are positively charged with the ammonium functional group and negatively charged with the phenolic diketone moiety of TC species. The removal of TC was also aided by the effect of hydrogen bonding and surface complexes formed between TC and Ca [ 109 ].

7. Conclusions and Perspective

In recent decades, there has been an increment in the dependence on groundwater as a major source of freshwater for daily human needs, but in many places, groundwater is being polluted by organic and inorganic contaminants. It is very important to remediate groundwater before use to prevent the spread of contaminants to the neighbour environment. Many techniques and reactive materials have been used in the remediation of contaminated groundwater; one of the most popular technologies is PRBs, which is considered an affordable technology. It allows the treatment of multiple pollutants if a multi-barrier is being used. In PRB technology, there is no adverse contamination that may happen, as contaminants will not be brought out to the surface. On the other hand, this technology may have some limitations, such as the difficulty of detailed site characterization required prior to the design of PRB, and only contaminants passing the PRB could be treated in addition to the limited field data for the longevity of the PRB, so the prospective tendency is to use new by-product materials to improve PRB performance. In this way, the environment will be saved by the disposal of these unwanted by-products and will be considered a (green) refreshment to the environment.

Groundwater contamination is now a global issue; solving this problem involves close coordination between scientists at universities and government agencies, as well as the industry and decision makers at all levels. The way ahead for solving this problem must include addressing the levels of groundwater contamination in different countries by using developed measures, techniques and policies. In addition, the variation of the influence of groundwater contamination in different countries must be well studied, including the effect on climatic regions and geological features. To study groundwater contamination in the future, groundwater scientists will need to adopt and apply new technologies such as artificial intelligence, “big data” analysis, drone surveys and molecular and stable isotope analysis technologies. Finally, governments, especially those with developing economies, need to invest more in groundwater and encourage researchers, training and research in this important, valuable field.

Author Contributions

O.A.-H. and K.H. organized the conceptualization of the idea and the methodology employed in this paper. Following that, E.L., T.M.Č., I.N., A.A.H.F. and N.A.-A. worked on the critical evaluation of the existing techniques. All authors have read and agreed to the published version of the manuscript.

This research received no external funding.

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Water Pollution: A Review

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Water is a very important element for living organisms, and it is helpful in the circulation and transmission of nutrients in the biosphere. Due to industrialization, urbanization, and rapid increase in human population, the demand for water has increased sharply, and the quality has declined drastically. Although water has the ability to purify itself, when the concentration of pollutants generated from man-made sources becomes so high that it exceeds the self-purifying ability of water, then the water becomes polluted. Degradation of the physical, chemical, and biological characteristics of water by natural and man-made processes in such a way that it is unsuitable for humans and other biological communities. This is called water pollution.

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Water Pollution Research Paper Topics

This comprehensive guide to water pollution research paper topics is designed to provide students studying environmental science with a wealth of options for their research papers. The guide offers a broad array of topics, divided into ten categories, each containing ten unique research topics. Additionally, the guide provides expert advice on how to choose a topic from the multitude of water pollution research paper topics and how to write a compelling research paper on water pollution. The guide also introduces iResearchNet’s writing services, which offer students the opportunity to order a custom water pollution research paper on any topic. The services boast a range of features designed to ensure the delivery of high-quality, custom-written papers.

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Effects of Water Pollution

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Water Pollution Solutions

• Water treatment technologies.
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Water Pollution Policies

• The Clean Water Act.
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Water Pollution Case Studies

• The Flint water crisis.
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Water Pollution and Public Health

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Water Pollution and Climate Change

• The impact of rising temperatures on water pollution.
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Water Pollution and Social Issues

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Water Pollution and Technology

• The role of technology in water pollution detection.
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Water Pollution and Sustainability

• The role of sustainable development in water pollution control.
• Water pollution and the Sustainable Development Goals.
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• The role of sustainable agriculture in water pollution control.
• Sustainable cities and water pollution.
• Sustainability and water security.
• The role of sustainability in water policy.

In conclusion, this comprehensive list of water pollution research paper topics offers a wide range of options for students interested in studying this critical environmental issue. Whether you’re interested in the causes, effects, solutions, or social implications of water pollution, there’s a topic here for you. Remember, the best research papers start with a topic you’re passionate about, so choose a topic that resonates with you and start exploring.

Water Pollution Research Guide

Water pollution is a critical environmental issue that poses significant challenges to ecosystems, human health, and sustainable development. As students of environmental science, it is vital to understand the complexities of water pollution and its implications for our planet. One of the essential tasks assigned to students in this field is to write research papers on water pollution, which not only enhance their knowledge but also contribute to the collective efforts in finding solutions. In this comprehensive guide, we will explore a wide range of water pollution research paper topics, provide expert advice on choosing suitable topics, and offer valuable insights on how to write an impactful research paper.

Water pollution encompasses various sources and factors, including industrial waste, agricultural runoff, sewage discharge, and chemical contaminants. By delving into research papers on water pollution, students can gain a deeper understanding of the causes, effects, and potential mitigation strategies for this environmental concern. Moreover, these research papers serve as platforms for students to contribute to the existing body of knowledge and propose innovative solutions to combat water pollution effectively.

Throughout this guide, we will present a diverse range of water pollution research paper topics that cover different aspects of the issue. These topics will be organized into comprehensive categories to facilitate your exploration and ensure you find a subject that aligns with your interests and academic goals. By addressing topics such as the impact of industrial pollutants on aquatic ecosystems, the role of agriculture in water contamination, and the effectiveness of wastewater treatment methods, you can explore the multifaceted dimensions of water pollution and contribute to the ongoing efforts to address this global challenge.

In addition to the extensive list of water pollution research paper topics, we will provide expert advice on how to choose the most suitable topic for your study. Selecting the right research topic is crucial as it determines the scope, relevance, and impact of your research. Our expert tips will guide you through the process, helping you identify areas of interest, narrow down your focus, and ensure that your chosen topic aligns with your academic goals and research objectives.

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Choosing a compelling and impactful research topic is crucial when writing a water pollution research paper. It sets the foundation for your study and determines the scope and relevance of your research. With numerous dimensions to explore within the realm of water pollution, selecting the right topic can be a challenging task. To help you navigate this process effectively, we have compiled expert advice and practical tips to guide you in choosing the most suitable water pollution research paper topic. Consider the following ten tips:

• Identify your interests and passion : Begin by reflecting on your personal interests and areas of passion within the field of water pollution. Do you have a particular interest in industrial pollutants, agricultural runoff, or plastic waste in water bodies? Identifying your interests will help you stay motivated throughout the research process.
• Conduct preliminary research : Before finalizing a topic, conduct preliminary research to familiarize yourself with the current state of knowledge in the field. Read scholarly articles, research papers, and reports related to water pollution to gain insights into existing gaps, emerging trends, and potential research areas.
• Narrow down your focus : Once you have an understanding of the broad field of water pollution, narrow down your focus to a specific aspect or subtopic that aligns with your interests and research goals. For example, you could explore the impact of microplastics on marine ecosystems or the effectiveness of water pollution regulations in urban areas.
• Consider the research context : Take into account the geographical context and research opportunities available to you. Is there a specific region or local water body where you can conduct fieldwork or gather data? Considering the research context can add depth and relevance to your study.
• Evaluate the research significance : Assess the significance and potential impact of your chosen topic. Does it address an important research gap, contribute to existing knowledge, or offer practical implications for water pollution management and conservation efforts? Aim for a topic that has both academic and real-world relevance.
• Consult with your professor or advisor : Seek guidance from your professor or research advisor, as they can provide valuable insights and suggestions based on their expertise. They can help you refine your research questions, identify suitable methodologies, and offer suggestions for relevant literature.
• Consider interdisciplinary perspectives : Water pollution is a complex issue that requires interdisciplinary approaches. Consider incorporating perspectives from other disciplines such as ecology, chemistry, public health, or policy analysis. This interdisciplinary approach can add depth and richness to your research.
• Explore emerging trends and technologies : Stay updated with the latest research advancements, emerging trends, and innovative technologies in the field of water pollution. Investigate how new methodologies, monitoring techniques, or data analysis tools can be applied to your research topic to enhance its impact and contribute to the field.
• Balance feasibility and interest : While it is essential to choose a topic that interests you, also consider its feasibility within the scope of your research project. Assess the availability of data, resources, and the time required to conduct research on your chosen topic.
• Seek ethical considerations : Consider the ethical implications of your research topic, especially if it involves human subjects, sensitive ecosystems, or policy-related issues. Ensure that your research design adheres to ethical guidelines and safeguards the welfare of those involved.

By following these expert tips, you can select a compelling and meaningful water pollution research paper topic that aligns with your interests, contributes to the field, and inspires you throughout your research journey. Remember that the chosen topic will shape your research direction and influence the significance of your findings.

How to Write a Water Pollution Research Paper

Writing a water pollution research paper requires careful planning, systematic organization of ideas, and adherence to academic standards. In this section, we will provide you with ten practical tips to guide you through the process of writing an effective and compelling research paper on water pollution.

• Understand the research question : Start by clearly understanding the research question or objective of your study. Identify the specific aspect of water pollution you aim to investigate and formulate a concise and focused research question that will guide your entire paper.
• Conduct a comprehensive literature review : Before diving into writing, conduct a thorough literature review to familiarize yourself with existing research on the topic. Identify key theories, concepts, and findings that will serve as the foundation for your own study. Analyze the gaps and controversies in the literature that your research can address.
• Develop a solid research methodology : Outline the research methodology that will best address your research question. Determine whether your study will involve quantitative analysis, qualitative research, or a combination of both. Clearly define your variables, sampling methods, data collection techniques, and analytical tools.
• Gather relevant and reliable data : Collect data from credible sources to support your research findings. This may involve fieldwork, laboratory analysis, surveys, interviews, or secondary data collection. Ensure that your data is accurate, relevant, and representative of the research problem.
• Analyze and interpret the data : Once you have collected the necessary data, conduct a rigorous analysis using appropriate statistical or qualitative techniques. Interpret the results in light of your research question and objectives. Use clear and concise language to present your findings, tables, charts, or graphs to enhance understanding.
• Structure your paper effectively : Organize your research paper in a logical and coherent manner. Begin with an introduction that provides background information, states the research question, and outlines the structure of the paper. Follow with a literature review, methodology section, results and discussion, and a conclusion that summarizes your findings and implications.
• Provide a critical analysis : While presenting your research findings, critically analyze the data and discuss its strengths, limitations, and implications. Highlight the significance of your findings in relation to existing knowledge and theories. Identify any areas for further research or potential policy implications.
• Use clear and concise language : Communicate your ideas effectively by using clear and concise language throughout the paper. Avoid jargon or complex terminology unless necessary, and ensure that your arguments and explanations are easily understood by your target audience.
• Cite and reference sources accurately : Give credit to the authors of the works you have referenced by using proper citation and referencing formats, such as APA, MLA, or Chicago style. This ensures that your paper is academically sound and avoids any plagiarism concerns.
• Revise and edit your paper : Before finalizing your research paper, thoroughly revise and edit it for clarity, coherence, grammar, and punctuation. Ensure that your arguments flow logically, the structure is coherent, and the writing is polished. Seek feedback from peers or professors to improve the quality of your paper.

By following these ten tips, you can write a comprehensive and well-structured water pollution research paper that contributes to the field and effectively communicates your findings. Remember to maintain a critical mindset, engage with relevant literature, and present your research in a clear and concise manner.

Custom Research Paper Writing Services

When it comes to writing a high-quality and impactful research paper on water pollution, iResearchNet offers a range of writing services that cater to the specific needs of students studying environmental science. Our team of expert writers, who hold advanced degrees in the field, are committed to delivering custom research papers that meet the highest academic standards. Here are thirteen features that make our writing services the ideal choice for your water pollution research paper:

• Expert degree-holding writers : Our team consists of writers with advanced degrees in environmental science and related fields. They possess in-depth knowledge and expertise in water pollution, ensuring that your research paper is written by a subject matter expert.
• Custom written works : We understand the importance of originality and customization. Your research paper will be crafted from scratch, tailored to your specific requirements and research objectives. We never resell or reuse papers, ensuring that your work is unique and plagiarism-free.
• In-depth research : Our writers are skilled researchers who are adept at conducting comprehensive literature reviews and gathering relevant data on water pollution. They will incorporate the latest research and data into your paper, providing a solid foundation for your study.
• Custom formatting : Whether you require APA, MLA, Chicago/Turabian, Harvard, or any other formatting style, our writers are well-versed in various citation and formatting guidelines. They will ensure that your paper adheres to the specific formatting requirements of your institution.
• Top quality : We are committed to delivering research papers of the highest quality. Our writers pay attention to detail, use credible sources, and employ rigorous analysis to provide you with a well-researched and well-written paper.
• Customized solutions : We understand that every research paper is unique, with its own set of requirements and objectives. Our writers will work closely with you to understand your specific needs and tailor their approach to meet them effectively.
• Flexible pricing : We offer competitive and transparent pricing options to accommodate various budgets. Our pricing is based on factors such as the complexity of the research paper, the deadline, and the academic level. You can choose the package that best suits your needs.
• Short deadlines : We understand that time constraints can be a challenge. With our short deadline options, you can receive a high-quality research paper even if you have limited time available. Our writers are skilled at working efficiently and meeting tight deadlines.
• Timely delivery : We prioritize timely delivery of your research paper. Our writers are committed to meeting the agreed-upon deadlines, ensuring that you have sufficient time to review the paper and make any necessary revisions.
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• Easy order tracking : You can easily track the progress of your order through our user-friendly platform. Stay updated on the status of your research paper and communicate with your assigned writer directly.
• Money-back guarantee : We are confident in the quality of our work. If, for any reason, you are not satisfied with the final research paper, we offer a money-back guarantee to ensure your peace of mind.

By choosing iResearchNet for your custom water pollution research paper, you can benefit from the expertise of our writers, the quality of our work, and the convenience of our services. Our goal is to provide you with a research paper that meets your requirements, contributes to the field, and helps you achieve academic success.

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102 Water Pollution Essay Topic Ideas & Examples

Water pollution essays are an excellent way to demonstrate your awareness of the topic and your position on the solutions to the issue. To help you ease the writing process, we prepared some tips, essay topics, and research questions about water pollution.

🌎 Air and Water pollution: Essay Writing Tips

🏆 best water pollution essay topics & examples, 📌 remarkable air and water pollution research topics, 👍 good research topics about water pollution, ❓ research questions about water pollution.

Water’s ready availability in many locations makes it an easy choice for a variety of purposes, from cleaning to manufacturing to nuclear reactor cooling. However, many companies will then dump water, now mixed with waste, back into rivers or lakes without adequate cleaning, leading to significant environmental pollution.

However, there are other types of harm, such as noise pollution, which are less obvious but also dangerous to sea life. It is critical that you understand what you should and should not do during your writing process.

The stance that big manufacturing industries are the sole culprits of the damage done to the world’s rivers and oceans is a popular one. However, do not neglect the effects of other water pollution essay topics such as microorganisms.

Microbes can spread dangerous illnesses, making them a danger for both water inhabitants and the people who then use that water. Furthermore, they can eat up oxygen if left unchecked, starving fish and other water organisms and eventually making them die out.

Such situations usually result from agricultural practices, which can lead to powerful nutrients entering the water and enabling algae and other microorganisms to grow excessively. An overly lively environment can be as harmful as one where everything is threatened.

With that said, industrial manufacturers deserve much of the attention and blame they receive from various communities. Construction of dedicated waste-cleaning facilities is usually possible, but companies avoid doing so because the process will increase their costs.

You should advocate for green practices, but be mindful of the potential impact of a significant price increase on the global economy. Also, be sure to mention more exotic pollution variations in your types of water pollution essay.

Provide examples of noise pollution or suspended matter pollution to expand on the topic of the complexity of the harm humanity causes to the ecosphere.

You should show your understanding that there are many causes, and we should work on addressing all of them, a notion you should repeat in your water pollution essay conclusions.

However, you should try to avoid being sidetracked too much and focus on the titles of pollution and its immediate causes.

If you stretch far enough, you may connect the matter to topics such as the status of a woman in Islam. However, doing so contributes little to nothing to your point and deviates from the topic of ecology into social and religious studies.

Leave the search for connections to dedicated researchers and concentrate on discussing the major causes that are known nowadays. By doing this, you will be able to create an excellent and powerful work that will demonstrate your understanding of the topic.

Here are some tips for your writing:

• Be sure to discuss the different types of pollution that is caused by the same source separately. Surface and groundwater pollution are different in their effects and deserve separate discussions.
• Focus on the issues and not on solutions, as an essay does not provide enough space to discuss the latter in detail.
• Be sure to discuss the effects of pollution on people and other land inhabitants as well as on water creatures.

Check IvyPanda to get more water pollution essay titles, paper ideas, and other useful samples!

• Water Pollution: Causes, Effects and Possible Solutions This is why clean water is required in all the places to make sure the people and all the living creatures in the planet live a good and healthy life.
• Air and Water Pollution in the Modern World The high number of vehicles in the city has greatly promoted air pollution in the area. Poor sewerage system, high pollution from industries and automobiles are among the major causes of air and water pollutions […]
• Water Pollution: Causes, Effects, and Prevention Farmers should be encouraged to embrace this kind of farming which ensures that the manure used is biodegradable and do not end up accumulating in the water bodies once they are washed off by floods.
• Water Pollution in the Philippines: Metropolitan Manila Area In this brief economic analysis of water pollution in Metro Manila, it is proposed to look at the industrial use of waters and the household use to understand the impact that the population growth and […]
• Coca-Cola India and Water Pollution Issues The first difficulty that the representatives of the Coca-Cola Company happened to face due to their campaign in the territory of India was caused by the concerns of the local government.
• Water Pollution and Management in the UAE The groundwater in UAE meets the needs of 51% of users in terms of quantity mainly for irrigation. Surface water is the source of groundwater and plays a major role in groundwater renewal.
• Water Pollution in a Community: Mitigation Plan Though for the fact that planet earth is abundant with water and almost two-thirds of the planet is made up of water still it is viewed that in future years, a shortage of water may […]
• Cashion Water Quality: Spatial Distribution of Water Pollution Incidents This essay discusses the quality of water as per the report of 2021 obtained from the municipality, the quality issue and the source of pollution, and how the pollution impacts human health and the environment […]
• Mud Lick Creek Project – Fresh Water Pollution This potential source of pollutants poses significant risks to the quality of water at the creek in terms altering the temperature, pH, dissolved oxygen, and the turbidity of the water.
• Water Pollution as a Crime Against the Environment In particular, water pollution is a widespread crime against the environment, even though it is a severe felony that can result in harm to many people and vast territories.
• Importance of Mercury Water Pollution Problem Solutions The severity of the mercury contamination consequences depends on the age of the person exposed to the contamination, the way of contamination, the health condition, and many other factors.
• Newark Water Crisis: Water Pollution Problem The main problem was rooted in the fact that lead levels in the drinking water were highly elevated, which is dangerous and detrimental to the population’s health.
• Water Pollution: OIL Spills Aspects The effects of the oil spill on a species of ducks called the Harlequin ducks were formulated and the author attempted to trace out the immediate and residual effects of the oil on the birds.
• Food Distribution and Water Pollution Therefore, food distribution is one of the central reasons for water pollution. According to Greenpeace, one of the ways to improve the ecology of the planet is by creating healthy food markets.
• Water Pollution and Associated Health Risks The results of plenty of studies indicate the existence of the relation between the contamination of water by hazardous chemicals and the development of respiratory and cardiovascular diseases, cancer, asthma, allergies, as well as reproductive […]
• Lake Erie Water Pollution There are worries among the members of the community that the lake could be facing another episode of high toxicity, and they have called for the authorities to investigate the main causes of the pollution […]
• Storm Water Pollution Prevention Plan All players need to be trained in significant areas of business so as they can handle them with care and beware of the potential they have in causing damage.
• Water Pollution in the US: Causes and Control Although water pollution can hardly be ceased entirely, the current rates of water pollution can be reduced by resorting to the sustainable principle of water use in both the industrial area and the realm of […]
• Water Pollution and Its Challenges Water pollution refers to a situation where impurities find way into water bodies such as rivers, lakes, and ground water. This is a form of pollution where impurities enter water bodies through distinct sources such […]
• Water Pollution Sources, Effects and Control Unfortunately, not all the users of water are responsible to ensure that proper disposal or treatment of the used water is done before the water is returned to the water bodies.
• Water in Crisis: Public Health Concerns in Africa In the 21st century, the world faces a crisis of contaminated water, which is the result of industrialization and is a major problem in developing countries.
• Air and Water Pollution Thus, it is classified as a primary pollutant because it is the most common pollutants in the environment. In the environment, the impact of carbon monoxide is felt overtime, since it leads to respiratory problems.
• Causes of Water Pollution and the Present Environmental Solution Prolonged pollution of water has even caused some plants to grow in the water, which pose danger to the living entities that have their inhabitants in the water.
• Water Pollution & Diseases (Undeveloped Nations) Restriction on movement and access to the affected area affects trade and the loss of human life and deteriorated health is a major blow on the economy and on the quality of human life.
• Water and Water Pollution in Point of Economics’ View This research tries to explain the importance of water especially in an economist’s perspective by explaining the uses of water in various fields, pollution of water and the agents of pollution.
• Environmental Justice Issues Affecting African Americans: Water Pollution Water pollution in the 1960s occurred due to poor sewage systems in the urban and rural areas. Unlike in the 1960s, there are reduced cases of water pollution today.
• Water Pollution and Wind Energy Chemical pollution of water is one of the leading causes of death of aquatic life. It is thus evident that chemical pollution of water not only has negative effects on health, but it also substantially […]
• Air and Water Pollution in Los Angeles One of the major problems facing major cities and towns in the world is pollution; wastes from firms and households are the major causes of pollution.
• Water Pollution Causes and Climate Impacts The biggest percentage of sewage waste consists of water, treating the wastes for recycling would help in maintaining a constant supply of water.
• Water Pollution Origins and Ways of Resolving The evidence provided by environmental agencies indicates that industrial agriculture is one of the factors that significantly contribute to the deterioration of water quality.
• Water Pollution in the Jamaican Society
• Water Pollution and Abstraction and Economic Instruments
• Water Pollution and Individual Effects of Water Pollution
• Understanding What Causes Water Pollution
• An Analysis of Water Pollution as a Global Plague That Affects the People, Animals and Plants
• Water Pollution Through Urban and Rural Land Use and Freshwater Allocation in New Zealand
• Water Pollution: Globalization, One of the Causes and Part of the Solution
• Voluntary Incentives for Reducing Agricultural Nonpoint Source Water Pollution
• The Impact of Water Pollution on Public Health in Flint, Michigan
• Understanding Water Pollution and Its Causes
• The Promises and Pitfalls of Devolution: Water Pollution Policies in the American States
• We Must Fight Against Water Pollution
• Transaction Costs and Agricultural Nonpoint-Source Water Pollution Control Policies
• Water Pollution and Drinking Water Quality
• Water Pollution: An Insight into the Greatest Environmental Risk
• US Water Pollution Regulation over the Past Half Century: Burning Waters to Crystal Springs
• Environmental Impact and Health Risks of Water Pollution to a Child
• Water Pollution Environment Effects Chemicals
• The Negative Effects of Water Pollution on Fish Numbers in America
• The Problem of Oil Spills and Water Pollution in Alaska
• Water Pollution in the United State: The Causes and Effects
• California Water Pollution Act Clean Laws
• The Need to Immediately Stop Water Pollution in the United States
• Water Pollution, Causes, Effects and Prevention
• The Water Pollution Prevention in Oceanic Areas
• Water Pollution and the Biggest Environmental Issues Today
• Fresh Water Pollution Assignment
• Water pollution in Southeast Asia and China
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• The Impacts of Water Pollution on Economic Development in Sudan
• The Importance of Recycling to Prevent Water Pollution
• Water Pollution and Its Effects on The Environment
• The Sources, Environmental Impact, and Control of Water Pollution
• Water Quality and Contamination of Water Pollution
• Water Pollution and the World’s Worst Forms of Pollution
• The Problem of Water Pollution and the Solutions
• Comparing Contrast Legislative Approach Controlling Water Pollution Industrial
• An Analysis of the Water Pollution and it’s Effects on the Environment
• Water Pollution and The Natural Environment
• The Importance of Clean Drinking Water Pollution
• Water Pollution and Arsenic Pollution
• The Issue of Water Pollution in the Drinking Water in Brisbane
• What Are the Causes and Effects of Water Pollution?
• What Is the Effect of Water Pollution on Humanity?
• How Can Leaders Tackle with Water Pollution in China?
• What Is the Drinking Water Pollution Control Act?
• What Was the Social Water Pollution?
• How Non-Point Is Water Pollution Controlled in Agriculture?
• What Is Canada’s Water Pollution Dilemma?
• Water Pollution: Why Is There Trash in the Ocean?
• What Are the Problems Associated with Water Pollution?
• What Is the Connection Between Air and Water Pollution?
• How Water Pollution Effects Marine Life?
• What Are the Leading Factors of Water Pollution Around the World?
• Why Is Water Pollution an Important Issue Environmental Sciences?
• What Are the Factors That Causes Water Pollution and Its Effects on the World Today?
• What Are There Inorganic Chemicals Cause Water Pollution?
• How Does Drinking Water Pollution Impact the World Environmental Sciences?
• Is There a Connection Between Drinking Water Quality and Water Pollution?
• How to Deal with the Big Problem of Deforestation and Water Pollution in Brazil and the Colombian Amazon?
• Why Is China’s Water Pollution Challenge?
• What Is the Ground Water Pollution Assignment?
• How to Deal the Big Problem of Water Pollution in the World?
• How to Reduce Air and Water Pollution?
• What Is the Harmonizing Model with Transfer Tax on Water Pollution Across Regional Boundaries in China’s Lake Basin?
• Are the Causes and Effects of Water Pollution Determined in Lake Huron?
• Can Water Pollution Policy Be Efficient?
• What Are the Kinds of Water Pollution Environmental Sciences?
• What Causes Water Pollution and Its Effects?
• What Effect Does Water Pollution Have on KZN Citizens?
• How Is Water Pollution Managed in Viet Nam’s Craft Villages?
• What Should You Know About Water Pollution?
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The global clean water crisis looms large

Water scarcity will intensify with climate and socioeconomic change, disproportionately impacting populations located in the Global South. So concludes a new Utrecht University article published in Nature Climate Change on 23 May 2024, which used a state-of-the-art global water quantity and quality model to estimate clean water scarcity until the end of the century.

Humans require clean water for drinking and sanitation purposes, but also for the production of food, energy and manufactured goods. As communities and policymakers grapple with water scarcity issues on the ground, researchers at Utrecht University aim to shed light on the escalating global clean water crisis.

Current and future water scarcity

Using simulations from a state-of-the-art water quantity and quality model, the authors assess present-day and future global water scarcity. "Climate change and socioeconomic developments have multi-faceted impacts on the availability and quality of, and demands for, water resources in the future," says lead author Dr. Edward Jones. "Changes in these three aspects are crucial for evaluating future water scarcity."

The study estimates that 55% of the global population currently lives in areas that experience a lack of clean water in at least one month per year. "By the end of the century, this may be as high as 66%," remarks Jones.

Strong regional differences in future water scarcity

While global water scarcity is projected to intensify in the future, both the changes and impacts will not occur equally across all world regions. Future increases in water scarcity in Western Europe and North America, for example, are concentrated in just a few months of the year -- predominantly driven by water quantity aspects. Conversely, water scarcity increases in developing countries are typically more widespread in space and persist for a larger portion of the year.

Jones remarks, "Increases in future exposure are largest in the Global South. These are typically driven by a combination of rapid population and economic growth, climate change and deteriorating water quality."

Quality: the invisible part of water scarcity

Water quality -- despite being crucial for safe water use -- remains an under-represented component of water scarcity assessments. "Previous assessments still predominantly focus on water quantity aspects only," explains Jones. "Yet, the safe use of water also depends on the quality."

Therefore, a key aim of this study was also to normalise the inclusion of water quality in water scarcity assessments -- and in the design of management strategies for alleviating water scarcity.

Jones concludes, "The lack of clean water presents a systemic risk to both humans and ecosystems, which is becoming increasingly difficult to ignore. Our work highlights that, alongside substantially reducing our water demands, we must place an equally strong focus on eliminating water pollution in order to turn the tide on the global water crisis."

• Environmental Issues
• Drought Research
• Resource Shortage
• Environmental Policies
• World Development
• Land Management
• Water scarcity
• Global warming controversy
• Climate engineering
• Global climate model
• Climate change mitigation
• Scientific opinion on climate change
• Temperature record of the past 1000 years

Story Source:

Materials provided by Utrecht University . Note: Content may be edited for style and length.

Journal Reference :

• Edward R. Jones, Marc F. P. Bierkens, Michelle T. H. van Vliet. Current and future global water scarcity intensifies when accounting for surface water quality . Nature Climate Change , 2024; DOI: 10.1038/s41558-024-02007-0

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A drying Salton Sea: Research finds higher particulate pollution after water diverted to San Diego

by UC Davis

When desert winds stir up dust from the Salton Sea's exposed lakebed, nearby communities suffer from increased air pollution. The deterioration coincides with reduced flows into California's largest lake, finds a new research paper in the American Journal of Agricultural Economics .

Disadvantaged communities have been affected more than others in the areas near the Salton Sea, which has been shrinking for years, said the paper's co-leading author, Eric Edwards. He is an assistant professor of agricultural economics at University of California, Davis, who did the research while at North Carolina State University.

"We have a dusty area, and any time there is wind, it's going to pick up dust and move it around," Edwards said. "We think this new dust is increasing the amount of pollution faced by disadvantaged communities in the region surrounding the lake."

An overflowing river

The Salton Sea formed in 1905 after the Colorado River overflowed its banks and the floodwaters settled into what was known as the Salton Sink. It was primarily fed by water runoff from agricultural operations for almost a century. As the southern part of California struggled to meet growing water demand, the Imperial Irrigation District agreed to send water to San Diego for urban use.

Imperial, which supplies water to vast desert farms as well as seven towns and two special districts, is the largest user of Colorado River water. The agreement with San Diego required agricultural water users to increase efficiency and reduce their water consumption , which reduced water running into the Salton Sea, Edwards said.

The reductions increased the lake's salt content, which is higher than in the Pacific Ocean. This also harmed wildlife habitats and created localized air pollution . The area is the subject of many environmental restoration projects.

Studying implications

Edwards and others used a particle transport model to study the effects of changing water diversions on particulate pollution.

They found that the paths of fine particulate matter—which can cause asthma, heart and respiratory issues when inhaled—were associated with higher air pollution readings after Imperial began reducing runoff water to the Salton Sea around 2011 in order to transfer it to San Diego, a practice that continues today.

Researchers modeled lakebed exposure by dividing the lake's shoreline into 1-square-kilometer grids and collected air pollution data daily for over 20 years, from 1998 to 2018. They added data about the exposed lakebed, or playa, and used a sophisticated physics model called HYSPLIT to factor in wind levels and particle size to track the movement of dust over time. State health screening information available by ZIP code added more to the story by pinpointing disadvantaged areas, asthma rates and other vulnerabilities.

Lake levels were higher in 1998 before the transfers, so the change was not evident until later years, when the lakebed became more exposed.

"We show that during that post-2011, there is an increase in particles going through disadvantaged communities relative to non-disadvantaged communities, which are farther away from the sea," Edwards said.

In the paper, the pollution paths are depicted on a map of the state. The Salton Sea is marked with a black dot, and red lines radiate from there to distances of 100 miles or more.

"From every exposed grid cell you have these paths predicting where the particles are going based on physics," Edwards said. "That's the path of emissions."

Prior research suggests that dust particles from newly exposed playa are more susceptible to wind erosion.

"There's lots of evidence that playa is particularly emissive in terms of dust," Edwards said. "If it's dry, those particles get picked up readily by the wind and create dust—and at rates higher than areas that have been exposed to the wind over long periods of time."

Informing decisionmakers

Edwards said policymakers and regulators should consider the health and environmental impacts of water diversions in their decision making.

"The drying up of the Salton Sea has serious health consequences that have generally fallen on more disadvantaged populations, who may not be well equipped to advocate for policies that improve their health," he said. "Policymakers need to think about how to facilitate the movement of water via market transactions, which are essential, while also accounting for potential negative effects on the environment."

Ryan Abman from San Diego State University and Dana Hernandez-Cortes from Arizona State University contributed equally with Edwards to the research and journal article.

Provided by UC Davis

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Mercury poisoning near Grassy Narrows First Nation worsened by ongoing industrial pollution, study suggests

New research shows sulfate, organic matter are exacerbating methylmercury levels.

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A new study from the University of Western Ontario suggests mercury contamination in northwestern Ontario's English-Wabigoon River has been made worse by ongoing industrial pollution.

Contamination of the river system dates back to the 1960s and 70s , when the pulp and paper mill dumped an estimated nine tonnes of mercury into the water.

The mercury has impacted generations of people living in Grassy Narrows First Nation, also known as Asubpeeschoseewagong Netum Anishinabek, a community about 150 kilometres from Dryden near the Ontario-Manitoba border, and Wabaseemoong Independent Nation.

However, the new study, published Thursday, has found that discharge of wastewater from the Dryden Paper Mill, combined with existing mercury, has created high levels of methylmercury – an even more toxic compound.

"Other forms of mercury don't accumulate as strongly as methylmercury, but because it accumulates, it builds up to high levels in organisms, presenting that greater risk," said Brian Branfireun, a biology professor at the University of Western Ontario. "It's actually more serious than I even imagined."

The experiment was conducted by masters student Eric Grimm under Branfireun's supervision.

Dianne Loewen, communications and engagement co-ordinator for Dryden Fibre Canada, the owner of the Dryden Paper Mill, said in an email to CBC News on Wednesday that she could not comment on the study.

"Dryden Fibre Canada only recently acquired the mill from Domtar. We are not in a position to comment as we have not seen, nor have we been briefed on, Dr. Branfireun's report."

Dryden Fibre Canada took over the mill from Domtar in August 2023.

Poison through the food chain

While the wastewater coming from the mill today does not contain mercury, it does contain high levels of sulfate and organic matter, which "feed the bacteria that produce methylmercury from inorganic mercury in the environment," the study says.

These toxins build up in the river's fish, which are then passed on to the people that consume them.

"The accumulation of methylmercury in the human body causes neuromuscular problems and can also lead to death," Branfireun said.

Grassy Narrows Chief Rudy Turtle reacts to new mercury research

Just under 1,000 people live in Grassy Narrows First Nation, and fish are a staple part of the community's diet.

"Most of the families continue to fish, they continue to eat the fish. It's something they've done for hundreds of years – you can't really stop them," said Grassy Narrows Chief Rudy Turtle in an interview with CBC News.

It is estimated that 90 per cent of Grassy Narrows' population has symptoms of mercury poisoning, which causes problems including tremors, insomnia, memory loss, neuromuscular effects, headaches and cognitive and motor dysfunction.

• Grassy Narrows chief calls out feds amid 'ridiculous' delays to mercury treatment centre construction
• As First Nations chiefs in northern Ontario call for health-care action, youth demand more involvement

For years, Turtle has called for the paper mill to be closed and for the river to be cleaned up. The community has also been anxiously awaiting the construction of a Mercury Care Home, for which the federal government signed a funding agreement in 2020.

"We continue to be poisoned," said Turtle, who himself has shared his experiences with mercury poisoning.

Mercury Care Home construction slated for summer

Anispiragas Piragasanathar, a spokesperson for Indigenous Services Canada (ISC), provided CBC News an emailed statement about the Mercury Care Home.

Piragasanathar said the federal government has committed:

• $77M to build the Mercury Care Home.
• $68.9M for operations, maintenance and specialized service delivery.

"ISC continues to support Grassy Narrows leadership as they take steps toward realizing their vision for health-care delivery in their community through the Mercury Care Home," Piragasanathar said.

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"Together, we have developed key construction milestones to ensure that the Mercury Care Home is built in a timely manner." 

Construction is planned to begin by July 1 and take about two to three years to complete.

Turtle said he is pleased with the additional funds the government has committed to the project this year, and that a ceremony will be held in the community once the shovels hit the ground.

No simple solutions

It is possible to remove the methylmercury from the water – but it won't be easy, Branfireun said.

"We are talking about potentially hundreds of kilometres of rivers and lakes and wetlands in a very complicated landscape that is not developed," he said.

While cleaning up the river will take substantial time and resources, removing the sulfate and organic matter is a more manageable solution for the short-term, Branfireun said.

"It wouldn't completely solve the mercury problem in fish in this river, but it would dramatically improve it while these other remediation strategies are being implemented over the next few decades."

Michael Rennie is an associate professor at Lakehead University's biology department, as well as a research fellow at the International Institute for Sustainable Development (IISD) Experimental Lakes Area.

While he was not involved in the methylmercury study, he said he is not surprised by the results. 

We are talking about potentially hundreds of kilometres of rivers and lakes and wetlands in a very complicated landscape that is not developed. - Brian Branfireun, University of Western Ontario

"It shows a pretty clear role for the impact that the mill has on the system now just from the effluent that's going into it from the current operations," Rennie said in an interview with CBC News.

There are ways to reduce the impact of mill operations on the river, Rennie said, such as settling ponds or new environmental policies, but the level of contamination throughout the system means there are no simple solutions.

"I don't think this is saying, 'Oh my God, we have to close the mill.'

"What I think it's saying is there are likely industrial processes that can be put in to help reduce sulfate concentrations that are coming out of that effluent to help reduce organic matter, that will at least not make the problem continue to be worse," he said.

Branfireun is expected to share the study's findings on Thursday morning at the Earth Sciences Centre in Toronto.

Study shows ongoing pollution at Grassy Narrows First Nation

About the author.

Sarah Law is a CBC News reporter based in Thunder Bay, Ont., and has also worked for newspapers and online publications elsewhere in the province. Have a story tip? You can reach her at [email protected]

With files from Brett Forester and Philip Lee-Shanok

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College of Agricultural and Environmental Sciences

A Drying Salton Sea Pollutes Neighboring Communities

Research finds higher particulate pollution after water diverted to san diego.

• by Emily C. Dooley
• May 29, 2024

When desert winds stir up dust from the Salton Sea’s exposed lakebed, nearby communities suffer from increased air pollution. The deterioration coincides with reduced flows into California’s largest lake, a new research paper in the American Journal of Agricultural Economics finds. 

Disadvantaged communities have been affected more than others in the areas near the Salton Sea, which has been shrinking for years, said the paper’s co-leading author Eric Edwards. He is an assistant professor of agricultural economics at University of California, Davis, who did the research while at North Carolina State University. 

“We have a dusty area, and any time there is wind, it’s going to pick up dust and move it around,” Edwards said. “We think this new dust is increasing the amount of pollution faced by disadvantaged communities in the region surrounding the lake.”

An overflowing river

The Salton Sea formed in 1905 after the Colorado River overflowed its banks and the floodwaters settled into what was known as the Salton Sink. It was primarily fed by water runoff from agricultural operations for almost a century. As the southern part of California struggled to meet growing water demand, the Imperial Irrigation District agreed to send water to San Diego for urban use. 

Imperial, which supplies water to vast desert farms as well as seven towns and two special districts, is the largest user of Colorado River water. The agreement with San Diego required agricultural water users to increase efficiency and reduce their water consumption, which reduced water running into the Salton Sea, Edwards said. 

The reductions increased the lake’s salt content, which is higher than in the Pacific Ocean . This also harmed wildlife habitats and created localized air pollution. The area is the subject of many environmental restoration projects. 

Studying implications

Edwards and others used a particle transport model to study the effects of changing water diversions on particulate pollution.

They found that the paths of fine particulate matter – which can cause asthma, heart and respiratory issues when inhaled – were associated with higher air pollution readings after Imperial began reducing runoff water to the Salton Sea around 2011 in order to transfer it to San Diego, a practice that continues today. 

Researchers modeled lakebed exposure by dividing the lake’s shoreline into 1-square-kilometer grids and collected air pollution data daily for over 20 years, from 1998 to 2018. They added data about the exposed lakebed, or playa, and used a sophisticated physics model called HYSPLIT to factor in wind levels and particle size to track the movement of dust over time. State health screening information available by ZIP Code added more to the story by pinpointing disadvantaged areas, asthma rates and other vulnerabilities. 

Lake levels were higher in 1998 before the transfers, so the change was not evident until later years, when the lakebed became more exposed. 

“We show that during that post-2011, there is an increase in particles going through disadvantaged communities relative to non-disadvantaged communities, which are farther away from the sea,” Edwards said.

In the paper, the pollution paths are depicted on a map of the state. The Salton Sea is marked with a black dot, and red lines radiate from there to distances of 100 miles or more. 

“From every exposed grid cell you have these paths predicting where the particles are going based on physics,” Edwards said. “That’s the path of emissions.” 

Prior research suggests that dust particles from newly exposed playa are more susceptible to wind erosion. 

“There’s lots of evidence that playa is particularly emissive in terms of dust,” Edwards said. “If it’s dry, those particles get picked up readily by the wind and create dust—and at rates higher than areas that have been exposed to the wind over long periods of time.” 

Informing decision makers

Edwards said policymakers and regulators should consider the health and environmental impacts of water diversions in their decision making.

“The drying up of the Salton Sea has serious health consequences that have generally fallen on more disadvantaged populations, who may not be well equipped to advocate for policies that improve their health,” he said. “Policymakers need to think about how to facilitate the movement of water via market transactions, which are essential, while also accounting for potential negative effects on the environment.”

Ryan Abman from San Diego State University and Dana Hernandez-Cortes from Arizona State University contributed equally with Edwards to the research and journal article. 

The U.S. Department of Agriculture’s National Institute of Food and Agriculture supported this research. 

Media Resources

• Eric Edwards, Department of Agricultural and Resource Economics,  [email protected]
• Emily C. Dooley, College of Agricultural and Environmental Sciences, 530-650-6807,  [email protected]  
• Kat Kerlin, UC Davis News and Media Relations, 530-750-9195, [email protected]
• Susanne Clara Bard, San Diego State University Strategic Communications and Public Affairs, 202-441-8976,  [email protected]  

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