Fecal pollution of water
Fecal pollution of water from a health point of view is the contamination of water with disease-causing organisms (pathogens) that may inhabit the gastrointestinal tract of mammals, but with particular attention to human fecal sources as the most relevant source of human illnesses globally. Ingestion of water contaminated with feces is responsible for a variety of diseases important to humans via what is known as the fecal-oral route of transmission. Food, air, soil, and all types of surfaces can also be important in the transmission of fecal pathogens, and thereby implicated in disease outbreaks. Most fecal microorganisms, however, are not pathogenic. Indeed, some are considered beneficial to the host as they can outcompete pathogens for space and nutrients, complement the biochemical potential of the host’s gastrointestinal tract, and help in the development of the host immune system. Nonetheless, animal feces can also carry a number of important frank and opportunistic pathogens, capable of inflicting debilitating illnesses and, in some cases, death.
In 1998, it was estimated that 2.2 million deaths were associated with diarrhea each year, a good percentage of them due to fecal pollution of water, with the vast majority of victims being children in poor countries. This should not be a surprise as it has been estimated that more than 1 billion people worldwide lack access to safe drinking water, and more than 2 billion lack sanitation. Sadly, very little progress has been made in the last 20 years to ameliorate these problems, particularly due to the rapidly increasing global population. On the contrary, problems associated with fecal pollution of water are likely to worsen in coming decades, as more people are moving to coastal areas, most people now live in urban centers, many of which have out of control growth rates, and demands for animal meat products are increasing due to current trends in dietary regimes. Considering that per capita water availability and quantity are diminishing worldwide, it is reasonable to assume that fecal pollution of water is one of the most important and difficult challenges for future generations.
It was not until the 19th century that water was unquestionably implicated in a number of illnesses and outbreaks. In fact, for centuries water treatment was performed primarily to increase the palatability of water. In most cases water treatment consisted of filtration through cloth which improved both palatability and overall appearance of drinking water. It was not until John Snow was able to attribute a cholera outbreak in London to fecally polluted drinking water in the mid 1850s that the scientific community accepted that sewage was an important source of disease. These studies marked the beginning of modern epidemiology. Other important contemporary developments included the experiments disproving the Theory of Spontaneous Generation by Louis Pasteur, the proposal of the Germ Theory by Robert Koch, and the further improvement of vaccination procedures (Table 1). The development of the microscope and bacterial culturing techniques were also critical in helping to establish the link between microbial water quality and fecal pathogens. Bacterial indicators of fecal pollution were soon proposed and used with some regularity by the turn of the 20th century. Some of the first waterborne pathogens described in the scientific literature like Vibrio cholerae (agent for cholera) and Salmonella typhi (agent for typhoid fever), are still major sources of ill health in developing regions of the world.
The 19th century also witnessed the significance of water treatment technologies to public health. For example, water filtration was demonstrated to be a relatively effective method to improve drinking water quality by Koch in the 1890s, when he showed the difference that filtration made in the number of cholera cases between cities using the same drinking water sources. Shortly after, Sims Woodhead used a "bleach solution" to sanitize drinking water distribution mains at Maidstone, Kent (England) following a typhoid outbreak. The introduction of chlorine as part of disinfection of drinking water was perhaps one of the most important advances to improved public health ever. For example, the number of typhoid cases in the U.S. went from approximately 30 cases per 100,000 people prior to the introduction of chlorination in 1908 to about 400 for the entire U.S. population by the late 1990s (Figure 1). Ozone disinfection, which was introduced in Europe in the early 1900s, is now becoming a more popular alternative to chlorine treatment due to its ability to kill chlorine-resistant pathogens, decompose anthropogenic chemicals, and because it does not generate carcinogenic chlorinated disinfection by-products, although bromate is a by-product of concern and necessary control.
|Table 1. Milestones in water microbiology and waterborne diseases|
Circa 400 B.C.: Hippocrates develops the Humoral theory and recommends boiling and straining water.
1668: Francesco Redi's experiments with maggots challenge the theory of spontaneous generation.
1677: Anton Van Leeuwenhoek reports the discovery of microorganisms using a microscope.
1768: Lazzaro Spallanzani designs biogenesis experiments.
1774: Carl Wilhelm Scheele discovers chlorine in Sweden
1849: William Budd publishes a book entitled Malignant cholera, its mode of propagation and its prevention
1850s: John Snow links the London cholera outbreak to a contaminated well on Broad Street.
1859: Louis Pasteur designs experiments disproving the theory of spontaneous generation.
1877 - 1882: Louis Pasteur develops the Germ theory of disease.
1882: Filtration of London drinking water begins.
1890: Robert Koch refines the postulates to identify the causative microbial agent of a particular disease
1890s: Chlorine is proven an effective disinfectant of drinking water.
1890s: Robert Koch suggests that the low incidence of cholera in Altona was due to the filtration of water supply.
1896: The Louisville Water Company used coagulation and rapid-sand filtration to remove bacteria from water.
1899: The Refuse Act was established to control pollution discharges into navigable waters.
1902: Belgium implements the first continuous use of chlorine to make drinking water biologically "safe".
1905: Chlorine was added to London’s water supply.
1908: First public water supply in Jersey City (NJ) begins a chlorination disinfection program.
1908: Chick-Watson Law of microbial disinfection.
1912: U.S. Congress passes the Public Health Service Act.1914: First standards under the Public Health Service Act are established.
1948: U.S. Water Pollution Control Act
1955: Hepatitis epidemic in New Delhi, India due to inadequate water treatment (one million people infected).
1962: U.S. Public Health Service Drinking Water Standards Revision is accepted as minimum standards for all public water suppliers.
1965: Reported cases of polio in the U.S. decreased from 20,000 in 1955 to 100 due to immunization.
1972: U.S. Clean Water Act, provisions for restoring and maintaining all bodies of surface water
1974: The Safe Drinking Water Act is passed
1993: Milwakee Cryptosporidium outbreak (over 400,000 cases estimated)
2000: Beaches Environmental Assessment and Coastal Health (BEACH) Act
Adopted from Santo Domingo and Hansel, 2008
Regulations were introduced in the 20th century first to protect drinking water, then more recently, water used in recreational activities. Organizations like the World Health Organization and the European Union, and countries like the U.S. and Australia, have played key roles in developing effective microbial water quality regulations. In spite of this, fecal pollution continues to be a serious problem as evidenced by the number of waterborne outbreaks worldwide, particularly in developing countries. Even though most cases are unreported as the disease can run its course in less than 48 hours, estimates of the number of annual cases associated with fecal pollution run into the hundreds of millions worldwide. Moreover, the public health impact of fecal pollution of water has been reported to be greater than diseases like malaria when estimated as disability adjusted life years (DALYs), which measures the potential years of “healthy” life lost due to poor health and premature death.
Microbial water quality is traditionally monitored using culture-based techniques that selectively promote the growth of bacterial indicators of fecal pollution. In recent years the WHO have strongly promoted the use of the fecal bacterium Escherichia coli (E. coli) as the principle fecal indicator for waters. Previously, a larger group of bacteria related to E. coli but not all specific to feces (known as the total coliforms) had been promoted, but with the advent of more rapid and selective methods it is more reliable to directly measure E. coli, rather than either total or so-called fecal coliforms. The most commonly used indicators for surface waters are the fecal coliforms and E. coli, although another bacterial group, the entercocci are often used to better assess health risks associated with marine recreational waters. Alternate indicators for surface waters have been suggested, including Clostridium perfringens, Bifidobacterium spp., Bacteroides fragilis, coliphages, and enteric viruses.
Fecal coliforms (a subset of the total coliforms) are classified as Gram-negative rod-shaped bacteria while enterococci are Gram-positive coccoid bacteria. This classification scheme is based on a staining technique developed by a Danish bacteriologist (J.M.C. Gram) which takes advantage of the differences in cell wall thickness between the two major groups of bacteria. Both fecal coliforms/E. coli and entercocci are present in relatively high numbers in the mammalian intestinal tract, which is considered their primary habitat. However, some recent findings have questioned the use of the current indicators used for regulatory activities. For example, some fecal bacterial indicators (i.e., E. coli and enterococci) have been isolated in secondary habitats. Furthermore, the persistence and growth of fecal bacterial indicators have been implied in several studies. These results suggest that there are scenarios in which the presence of indicators does not necessarily correlate with fecal contamination events.
For several reasons, fecal bacterial indicators are used, often inappropriately, as surrogates of waterborne and foodborne pathogens to assess human health risks instead of direct monitoring of pathogens. Currently used indicators are easy to grow and are often present in higher numbers than pathogens. In contrast, the detection and enumeration of most pathogens require time-consuming concentration methods to increase the chances of detection, and quantification is often imprecise. Molecular fingerprinting or gene sequencing is often required to further discriminate between true pathogens and non-pathogenic strains. More importantly, pathogens from the three main microbial groups (viruses, bacteria and parasitic protozoa) often require different isolation and identification protocols, and consequently the diversity of pathogens present in a fecally impacted water body cannot be captured using one technique. Additionally, many pathogens can not be cultivated in the laboratory and therefore molecular identifications pick up infectious and non-infectious (dead) types. Hence, the health implications of pathogen detections can be ambiguous, such as for noroviruses and Cryptosporidium oocysts by the polymerase chain reaction (PCR) and antibody staining respectively.
Ideally, a good fecal microbial indicator should comply with many of several criteria. For example, indicator levels in environmental waters should bear some relation to the degree or extent of pollution, that is, the indicator must be present in waters whenever the pathogens of concern are present, particularly when their presence signals imminent danger, while absent or at very low levels in clean waters. To ease detection, indicators should occur in higher numbers than the pathogens and grow readily on relatively simple media. Indicators must be more resistant to disinfectants and to the aqueous environment than the pathogens; they must yield characteristic and simple reactions enabling an unambiguous identification; they should preferably be randomly distributed in the sample to be tested, their growth in artificial media must be largely independent of any other organism present, and should not be able to proliferate to any greater extent than pathogens in aquatic environment. There is however, no such ideal fecal indicator, which has lead many to the conclusion that a range of indicators are probably required to address the range and differing behaviors of microbial pathogens.
Epidemiological studies have been used to establish the correlation between fecal bacterial indicator densities and the risks associated with swimming in polluted recreational waters. It should be noted that most epi-studies have been conducted in waters presumed to be primarily impacted with human fecal sources (e.g., wastewater treatment plants), and as a result the risks associated with non-human sources are not well understood. Additionally, since most epidemiological studies have been conducted in temperate regions, the risks associated with the suggested standards are not known for tropical countries.
In the United States, regulations for recreational waters are based on the geometric mean of five samples within a 30-day period using the following formula:
where X is the fecal bacterial indicator densities calculated for a particular sample, n is the number of samples taken for a given period of time, and G is the calculated geometric mean. There are also regulations based on not exceeding bacterial indicator levels in any given grab sample (Table 2; USEPA, 1986).
As part of the new risk-management approach to recreational and drinking water regulations, quantitative microbial risk assessment (QMRA) models have been used to predict risks and identify system locations for appropriate pathogen management in a proactive, rather than end-point reactive manner (Figure 2, Medema et al., 2006). These models are based on levels of expected/measured pathogen and indicator numbers in fecal sources, data regarding the removal, fate and transport of the target pathogens in the environment in question, as well as human dose-response models to estimate ill effects. Such models can have increasing amounts of local information and detail to reduce uncertainties when risks are perceived to be unacceptable (Figure 3). One of the basic problems with QMRA models dealing with fecal pollution is the intrinsic variability of pathogens/indicators associated with different fecal sources, particularly non-human sources, the lack of dose-response data associated with different sources of pollution, and the diversity of pathogens potentially associated with any given pollution event. Like epidemiological studies, QMRA relies on the accuracy of the enumeration methods used to estimate the levels of the microbial target in question.
Diseases associated with fecally-polluted water and associated pathogens
Exposure to fecally contaminated water does not always translate into infection. However, the higher the fecal bacterial levels in water, the higher the chances of pathogens to be present in significant numbers too. Poor hygienic conditions also accelerate the fecal-oral route of pathogen transmission. Pathogen levels in water and predisposition of the person exposed play important roles in disease. Impact of exposure to fecal pathogens tends to be a greater problem for immuno-compromised and immuno-suppressed people, like infants, the aging, and those experiencing debilitating illnesses (e.g., pneumonia and AIDS).
Among the diseases associated with poor microbial water quality, those causing dehydrating diarrhea are of critical importance as they could lead to death within 48 hours after the initial symptoms. These extreme cases are more predominant in countries where overcrowding and poor sanitary conditions are the norm. Examples of fecal waterborne diseases are gastroenteritis, typhoid and paratyphoid fevers, salmonellosis, cholera, meningitis, hepatitis, encephalitis, amoebic meningoencephalitis, cryptosporidiosis, giardiasis, dysentery, and amoebic dysentery (Table 3). Water fecal pollution is also responsible for a number of skin, eye, and ear infections.
Human feces carry the primary agents of disease; however, animal excreta are also implicated in many human illnesses associated with water fecal pollution. Zoonotic diseases are those that are passed to humans via animals or animal products. Direct contact with the animals is not a prerequisite of zoonosis as fecally contaminated waters can be an intermediate medium. Feces from cattle, swine, poultry, wildlife, and pets are known to be important vectors of waterborne pathogens like Escherichia coli O157:H7, Campylobacter jejuni, Campylobacter coli, Arcobacter spp., Giardia duodenalis, and Cryptosporidium parvum. Reptiles can also be vectors of zoonotic agents, such as Salmonella Mississippi. Additionally, animal urine is a potential vector of Leptospira, a disease endemic to the tropics.
As a group, fecal pathogens are a very diverse group of organisms, as many bacteria, protozoa, and viruses can cause disease. Most of the waterborne pathogens are also important foodborne pathogens, although some are more often associated with foodborne outbreaks (e.g., Campylobacter and Salmonella). Pathogenic fungi have not been implicated in waterborne outbreaks, although yeast and molds present in human feces are often isolated from environmental waters. Among the fecal bacteria, the most commonly reported waterborne pathogens are E. coli O157:H7, Shigella spp., Campylobacter jejuni, Salmonella enterica non-Typhoid, Plesiomonas shigelloides, and Yersinia spp., to mention a few. Some of the fecal bacterial pathogens are primarily associated with recreational waters, while others are primarily a problem in drinking waters. It should be noted that most fecal microorganisms are non-pathogenic in nature. In fact, in most cases, only a small number of strains within the corresponding bacterial species are considered pathogenic. There are also naturally-occurring aquatic Vibrio, Aeromonas, and Mycobacterium spp. that are important non-fecal waterborne pathogens. Legionella spp. can also be transmitted by water, but its public health significance is commonly related to their environmental growth associated with amoeba within microbial slimes (biofilms) and aerosol transmission from warm waters.
Giardia and Cryptosporidium spp. are the most commonly reported protozoan pathogens in developed regions, the latter responsible for the 1993 Milwaukee (WI, USA) outbreak, one of the most important waterborne outbreaks of the last century. Other important parasitic protozoa are Enterocytozoon bieneusi, Encephalitozoon intestinalis, Entamoeba histolytica, Cyclospora cayetanensis, and Toxoplasma gondii. While these species are pathogenic to humans, animals are important vectors for the dissemination of these parasitic protozoa. The free-living protozoa also contain pathogenic members, such as Acanthamoeba and Naegleria spp., but they are not considered of strict fecal origin as they occur naturally in soil as well as in aquatic habitats, particularly warm waters.
Viruses are increasingly becoming important fecal waterborne pathogens as improved detection methods are establishing a strong link between them and reported outbreaks of unknown etiology (i.e., causes or origin of disease). Some of the most important fecal viral pathogens are noroviruses, enteroviruses, adenoviruses, rotaviruses, and hepatitis A and E viruses. Overall, viruses are more resistant to environmental conditions than bacterial indicators, which in part explain the frequent lack of correlation between currently used indicators and the occurrence of enteric viruses.
|Table 3. Examples of waterborne pathogens|
|Name of micro-organisms||Major diseases||Major reservoirs and primary sources|
|Salmonella typhi||Typhoid fever||Human feces|
|Salmonella paratyphi||Paratyphoid fever||Human feces|
|Other Salmonella||Salmonellosis||Human and animal feces|
|Shigella spp.||Bacillary dysentery||Human feces|
|Vibrio cholera||Cholera||Human feces and freshwater zooplankton|
|Enteropathogenic E. coli||Gastroenteritis||Human feces|
|Yersinia enterocolitica||Gastroenteritis||Human and animal feces|
|Campylobacter jejuni||Gastroenteritis||Human and animal feces|
|Legionella pneumophila and related bacteria||Acute respiratory illness (legionellosis)||Thermally enriched water|
|Leptospira spp.||Leptospirosis||Animal and human urine|
|Various mycobacteria||Pulmonary illness||Soil and water|
|Opportunistic bacteria||Variable||Natural waters|
|Polio viruses||Poliomyelities||Human feces|
|Coxsackie viruses A||Aseptic meningitis||Human feces|
|Coxsackie viruses B||Aseptic meningitis||Human feces|
|Echo viruses||Aseptic meningitis||Human feces|
|Other enteroviruses||Encephalities||Human feces|
|Adenoviruses||Upper respiratory and gastrointestinal illness||Human feces|
|Hepatitis A virus||Infectious hepatitis||Human feces|
|Hepatitis E virus||Infectious hepatitis; miscarriage and death||Human feces|
|Norovirus||Gastroenteritis||Human feces to fomites and water|
|Acanthamocba castellani||Amoebic meningoencephalitis||Human feces|
|Balantidium coli||Balantidosis (dysentery)||Human and animal feces|
|Cryptosporidium homonis, C. parvum||Cryptosporidiosis (gastroenteritis)||Water, human and other mammal feces|
|Entamoeba histolytica||Amoebic dysentery||Human and animal feces|
|Giardia lamblia||Giardiasis (gastroenteritis)||Water and animal feces|
|Naegleria fowleri||Primary amoebic meningoencephalitis||Warm water|
|Ascaris lumbricoides||ascariosis||Animal and human feces|
|Adapted from Ashbolt, 2004|
Human vs. animal fecal pollution and source tracking
One basic assumption in microbial water quality risk assessment models is that risk associated with human fecal matter is much greater than from non-human sources, as well as being more manageable. This is a reasonable assumption considering that some pathogens (i.e., human enteric viruses) show a high degree of host-specificity. That is not to say that animal fecal pollution does not carry significant risk. In fact, a considerable number of reported outbreaks, particularly in developed countries, are associated with protozoan and bacterial zoonotic pathogens (i.e., of animal origin). From a regulatory standpoint, there are two main types of fecal pollution sources, namely point sources and non-point sources. Examples of point sources are publicly owned treatment works (POTWs), discharges from industrial facilities, and stormwater discharges associated with industrial activity, construction and urban runoff. In the U.S., fecal loadings of point sources are controlled via the National Pollutant Discharge Elimination System (NPDES) permit program which regulates agricultural, municipal, and industrial discharges into waters. Non-point sources include effluents from leaky septic systems, domesticated animals (i.e., livestock), pets (e.g., cats and dogs) and wildlife. Furthermore, livestock and wildlife often have direct access and excrete into waterways and recreational waters. Rainfall and snowmelt can also transport fecal microorganisms from non-point sources into water bodies.
The 2000 National Water Quality Inventory reported that of the impaired surface waters in the U.S., 13% were due to the presence of fecal indicator bacteria. A major contribution to these impaired waters is thought to be from non-point sources like animal farming operations and wildlife. Hence it is critical to better understand the correlation between different fecal sources and health risks. This information is also relevant to professionals responsible for managing fecal pollution. While traditional monitoring assesses the presence of fecal bacteria and the potential for pathogen presence, these methods do not discriminate between the different types of fecal sources.
Microbial source tracking (MST) methods attempt to identify the source of contamination, allowing for improved risk analysis and better risk management. MST is based on the hypothesis that conditions in the gut, including temperature, pH and diet, as well as host-microbial interactions will select for specific microbial populations which can be identified using a variety of techniques. Early on, most MST methods required the development of fingerprint databases of traditional bacterial indicators. These methods are collectively known as library dependent methods. More recently, library independent methods that do not require microbial cultivation and the development of large culture-based databases of microbial fingerprints have been favored by the source tracking community. Methods like host-specific PCR allow for faster and more economic means of fecal source detection. However, the field application of MST methods has been a significant challenge, particularly for estimating source-specific fecal loadings, as specificity, distribution, abundance, and environmental survival of targeted host-specific populations could vary significantly in different hosts and under different environmental conditions. While these are challenging issues the simultaneous monitoring of fecal indicators, pathogens, and source identifiers is not an unreachable goal considering the rapid advances in biotechnology (e.g., microarrays, sequencing) and computational sciences (i.e., bioinformatics).
Other impacts of fecal pollution
Fecal pollution of waters has a significant impact on other areas besides the water industry. For example, many foodborne outbreaks can be directly or indirectly attributed to the contact of foods with polluted water during a number of food production/processing steps. Of all foodstuffs, molluscan shellfish are identified with the most foodborne outbreaks and cases of illness. Water used for shellfishing is strictly regulated, but many unreported cases are presumed to occur every year. Fruit and vegetables are also frequently impacted by fecally–polluted irrigation water, of particularly concern for uncooked crops and fruits. Water-related foodborne outbreaks have resulted in shortages of food supply and in extreme circumstances could also potentially create international problems resulting from the tension between trading countries. Deliberate contamination of food supplies via fecally-polluted waters is also of concern as a potential source of bioterrorism agents.
Since disinfection treatment demands (i.e., total chlorine and energy) increase with increased levels of fecal pollution, an overall increase in pollution translates into higher treatment costs that are passed to the consumer and stakeholders alike. Failure to meet drinking water consumer expectations has resulted in an increase in the consumption of bottled water, which is approximately one thousand-fold more expensive than tap water. Fecal pollution also has a considerable economic impact on areas that depend on tourism. For example, beach closures can be devastating to a local economy. The same thing can be said for areas that depend on fishing and shellfisheries.
The high level of nutrients and pathogens that fecal pollution introduces to aquatic environments can have a negative impact on the receiving biota and overall ecosystem health. For instance, increases in nutrient loadings can increase the level of algal and toxin-producing cyanobacteria (blue-green algae) primary productivity. This phenomenon, known as eutrophication, significantly reduces available (dissolved) oxygen in the water as the algae rots, ultimately causing the death of aquatic biota. Eutrophication is responsible for a considerable reduction of commercial and recreational fishing in some coastal areas. Eutrophication also causes an increase in dissolved organic matter which could then increase the persistence/survival of human and marine animal pathogens. Chemicals (i.e., fertilizers) associated with agricultural practices have been suggested as partly responsible for eutrophication; however, intensive livestock operations are an important contributor as well. From a human health perspective, human enteroviruses have been detected in coral mucus samples providing evidence that human sewage is also reaching such delicate coastal ecosystems. Additionally, fecal pollution increases the exposure of marine mammals to relevant terrestrial pathogens, as in the exposure of sea otters to Toxoplasma gondii and Sarcocystis neurona, whose primary sources include cats and wildlife feces, respectively.
Humans have long recognized that water is vital to all life forms. Undeniably, ancient civilizations flourished or disappeared depending on their access to clean water. Today, people in developed countries consider water as an unlimited resource because most citizens in such countries have relatively easy access to inexpensive potable water. However, the lack of water is being felt even in the U.S., as the scarcity of water in some states, especially in the southeast, is becoming the subject of regional political conflicts. In reality, there is a huge public misperception regarding water availability and its management. Potable water is not abundant even though water occupies more than two-thirds of the Earth. Liquid freshwater, which is used as the primary supply of drinking water, constitutes a very small fraction of the water on the planet. Due to issues like climate change, poorly managed water usage, agricultural irrigation practices, and population growth, the sustainability of water resources has now become an important issue globally. The expected increase in the total production of human and animals feces (due to population growth and meat consumption), is bound to have a detrimental effect on microbial water quality in both coastal and inland waters of developed countries. In developing countries the future is grimmer, because of lack of economical resources and appropriate sanitary conditions. Better management practices, remediation strategies, and overall awareness of the global issues associated with fecal pollution are needed in order to improve the chances of sustainable water resources for future generations in all countries.
- Ashbolt, N.J., W.O.K. Grabow, and M. Snozzi. 2001 Indicators of microbial water quality. In Water Quality: Guidelines, Standards and Health. Risk assessment and management for water-related infectious disease. L. Fewtrell and J. Bartram (eds). pp. 289-315. IWA Publishing, London.
- Ashbolt, N.J. 2004. Microbial contamination of drinking water and disease outcomes in developing regions. Toxicology 198:229-238.
- Bonde, G. J. 1977. Bacterial indicators of water pollution. Adv. Aquatic Microbiol. 1:273-364.
- Medema, G., J.-C. Loret, T.A. Stenström, and N. Ashbolt. 2006. Quantitative Microbial Risk Assessment in the Water Safety Plan. Final Report on the EU MicroRisk Project. Brussels: European Commission.
- Prüss, A. 1998 Review of Epidemiological studies on health effects from exposure to recreational water. Int. J. Epidemiol. 27:1–9.
- Simpson, J.M., J.W. Santo Domingo, and D.J. Reasoner. 2002. Microbial source tracking: state of the science. Environ. Sci. Technol. 36:5279-5288.
- Sadowsky, M.J., D.R. Call, and J.W. Santo Domingo. 2007. The Future of Microbial Source Tracking. In M. J. Sadowsky and J. W. Santo Domingo (ed.), Fundamentals of Microbial Source Tracking. ASM Press, Washington. DC.
- Santo Domingo, J.W., D.G. Bambic, T.A. Edge, and S. Wuertz. 2007. Quo vadis source tracking? Towards a strategic framework for environmental monitoring of fecal pollution. Water Res. 41:3539-3552.
- Santo Domingo, J.W. and J. Hansel. 2008. Waterborne Diseases and Microbial Quality Monitoring for Recreational Water Bodies Using Regulatory Methods. In Oceans and Human Health: Risks and Remedies from the Sea. P.J. Walsh, S.L. Smith, L.E. Fleming, H. Solo-Gabriele, W.H. Gerwick (eds.), Elsevier Science Publishers, New York.
- USEPA (U.S. Environmental Protection Agency), 1986. Ambient Water Quality Criteria for Bacteria. U.S. Environmental Protection Agency, Office of Water, EPA440/5-84-002.
- USEPA, 2002. The 2000 National Water Quality Inventory. EPA-841-R-02-001, U.S. EPA Office of Water, Washington, D.C.
- WHO (World Health Organization). 2000. Global Water Supply and Sanitation Assessment. World Health Organization. Geneva.
- WHO. 2003. Guidelines for Safe Recreational Water Environments. Vol. 1: Coastal and Fresh Waters. World Health Organization. Geneva
- WHO. 2004. Guidelines for Drinking-water Quality Third Edition. Volume 1. World Health Organization. Geneva
- WHO and UNICEF. 2004. Meeting the Millennium Development Goals (MDG) Drinking Water and Sanitation target – A mid-term Assessment of Progress. WHO/UNICEF. Geneva
Other suggested readings
- LeChevallier, M.W. and M. Buckley. 2007. Clean Water: What is Acceptable Microbial Risk?, American Society for Microbiology, Washington D.C. (PDF)
- USEPA. 2005. Microbial Source Tracking Guide Document. J.W. Santo Domingo (ed), Office of Research and Development, Washington, DC. EPA-600/R-05/064. 131 pp. (PDF)
- UNEP. 2006. Challenges to international waters: regional assessments in a global perspective. Global International Waters Assessment. United Nations Environment Programme, Nairobi, Kenya
- WHO 2003b. Emerging Issues in Water and Infectious Disease. World Health Organization, Geneva.