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The following references are some examples of the numerous studies that are listed at the US National Library of Medicine - Health Information. Select 'Disinfection Byproducts', 'Disinfection By-Products', or "Water Disinfection" to learn more about the available information pertaining to disinfected water.
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J Toxicol Environ Health, 2002 Jan 11, 65(1):1-142
"Sources, Pathways, and Relative Risks of Contaminants in Surface Water and Groundwater: A perspective Prepared for the Walkerton Inquiry." Ritter L, Solomon K, Sibley P, Hall K, Keen P, Mattu
G, Linton B. Canadian Network of Toxicology Centres, and Department
of Environmental Biology, University of Guelph, Ontario, Canada.
On a global scale, pathogenic contamination of drinking water poses the most significant health risk to humans, and there have been countless numbers of disease outbreaks and poisonings throughout history resulting from exposure to untreated or poorly treated drinking water. However, significant risks to human health may also result from exposure to nonpathogenic, toxic contaminants that are often globally ubiquitous in waters from which drinking water is derived. With this latter point in mind, the objective of this commission paper is to discuss the primary sources of toxic contaminants in surface waters and groundwater, the pathways through which they move in aquatic environments, factors that affect their concentration and structure along the many transport flow paths, and the relative risks that these contaminants pose to human and environmental health. In assessing the relative risk of toxic contaminants in drinking water to humans, we have organized our discussion to follow the classical risk assessment paradigm, with emphasis placed on risk characterization. In doing so, we have focused predominantly on toxic contaminants that have had a demonstrated or potential effect on human health via exposure through drinking water. In the risk assessment process, understanding the sources and pathways for contaminants in the environment is a crucial step in addressing (and reducing) uncertainty associated with estimating the likelihood of exposure to contaminants in drinking water. More importantly, understanding the sources and pathways of contaminants
strengthens our ability to quantify effects through accurate measurement and testing, or to predict the likelihood of effects based on empirical models. Understanding the sources, fate, and concentrations of
chemicals in water, in conjunction with assessment of effects, not only forms the basis of risk characterization, but also provides critical
information required to render decisions regarding regulatory initiatives, remediation, monitoring, and management. Our discussion is divided into two primary themes. First we discuss the major sources of contaminants from anthropogenic activities to aquatic surface and groundwater and the pathways along which these contaminants move to become incorporated into drinking water supplies. Second, we assess the health significance of the contaminants reported and identify uncertainties associated with exposures and potential effects. Loading of contaminants to surface waters, groundwater, sediments, and drinking water occurs via two primary routes:
(1) point-source pollution and
(2) non-point-source pollution.
Point-source pollution originates from discrete sources whose inputs into aquatic systems can often be defined in a spatially explicit manner. Examples of point-source pollution include industrial effluents (pulp and paper mills, steel plants, food processing plants), municipal sewage treatment plants and combined sewage-storm-water overflows, resource extraction (mining), and land disposal sites (landfill sites, industrial impoundments). Non-point-source pollution, in contrast, originates from poorly defined, diffuse sources that typically occur over broad geographical scales. Examples of non-point-source pollution include agricultural runoff (pesticides, pathogens, and fertilizers), storm-water and urban runoff, and atmospheric deposition (wet and dry deposition of persistent organic pollutants such as polychlorinated biphenyls [PCBs] and mercury). Within each source, we identify the most important contaminants that have either been demonstrated to pose significant risks to human health and/or aquatic ecosystem integrity, or which are suspected of posing such risks. Examples include nutrients, metals, pesticides, persistent organic pollutants (POPs), chlorination by-products, and pharmaceuticals. Due to the significant number of toxic contaminants in the environment, we have necessarily restricted our discussion to those chemicals that pose risks to human health via exposure through drinking water. A comprehensive and judicious consideration of the full range of contaminants that occur in surface waters, sediments, and drinking water would be a large undertaking and clearly beyond the scope of this article. However, where available, we
have provided references to relevant literature to assist the reader in undertaking a detailed investigation of their own. The information collected on specific chemicals within major contaminant classes was used to determine their relative risk using the hazard quotient (HQ) approach. Hazard quotients are the most widely used method of assessing risk in which
the exposure concentration of a stressor, either measured or estimated, is compared to an effect concentration (e.g., no-observed-effect concentration or NOEC). A key goal of this assessment was to develop a perspective on the relative risks associated with toxic contaminants that occur in drinking water. Data used in this assessment were collected from literature
sources and from the Drinking Water Surveillance Program (DWSP) of Ontario. For many common contaminants, there was insufficient environmental exposure (concentration) information in Ontario drinking water and groundwater. Hence, our assessment was limited to specific compounds within major contaminant classes including metals, disinfection by-products, pesticides, and nitrates. For each contaminant, the HQ was estimated by expressing the maximum concentration recorded in drinking water as a
function of the water quality guideline for that compound. There are limitations to using the hazard quotient approach of risk characterization. For example, HQs frequently make use of worst-case data and are thus designed to be protective of almost all possible situations that may occur. However, reduction of the probability of a type II error (false negative)
through the use of very conservative application factors and assumptions can lead to the implementation of expensive measures of mitigation for stressors that may pose little threat to humans or the environment. It is important to realize that our goal was not to conduct a comprehensive, in-depth assessment of risk for each chemical; more comprehensive assessments of managing risks associated with drinking water are addressed in a separate issue paper by Krewski et al. (2001a). Rather, our goal was to provide the reader with an indication of the relative risk of major
contaminant classes as a basis for understanding the risks associated with the myriad forms of toxic pollutants in aquatic systems and drinking water. For most compounds, the estimated HQs were < 1. This indicates that there is little risk associated with exposure from drinking water to the compounds tested. There were some exceptions. For example, nitrates were found to commonly yield HQ values well above 1 in many rural areas. Further, lead, total trihalomethanes, and trichloroacetic acid yielded HQs
> 1 in some treated distribution waters (water distributed to households). These latter compounds were further assessed using a probabilistic approach; these assessments indicated that the maximum allowable concentrations (MAC) or interim MACs for the respective compounds were exceeded <5% of the time. In other words, the probability of finding these
compounds in drinking water at levels that pose risk to humans through ingestion of drinking water is low. Our review has been carried out in accordance with the conventional principles of risk assessment.
Application of the risk assessment paradigm requires rigorous data on both exposure and toxicity in order to adequately characterize potential risks of contaminants to human health and ecological integrity. Weakness rendered by poor data, or lack of data, in either the exposure or effects stages of the risk assessment process significantly reduces the confidence that can be placed in the overall risk assessment. Overall, while our review suggested selected instances of potential risks to human health from exposure to contaminants in drinking water, we also noted a distinct paucity of information on exposure levels for many contaminants in this matrix. We suggest that this represents a significant limitation to conducting sound risk assessments and introduces considerable uncertainty with respect to the management of water quality. In this context, future research must place greater emphasis on targeted monitoring and assessment of specific contaminants (e.g., pharmaceuticals) in drinking water for which there is currently little information. This could be conducted using a tiered risk approach, beginning with, for example, a hazard quotient assessment. Potentially problematic compounds identified in these preliminary assessments would then be subjected to more comprehensive risk assessments using probabilistic methods, if sufficient data exist to do so. On this latter point, adequate assessment of potential risks for many contaminants in drinking water is currently limited by a paucity of toxicological information. Generating this important information is a critical research need and would reduce the uncertainty associated with conducting risk assessments.
Occup Environ Med. 2004 Jan, 61(1):65-72
"Assessing Spatial Fluctuations, Temporal Variability, and Measurement Error in Estimated Levels of Disinfection By-products in Tap Water: Implications for Exposure Assessment." Symanski E, Savitz DA, Singer PC. Environmental Sciences, University of Texas School of Public Health, Houston, Texas 77030, USA. esymanski@sph.uth.tmc.edu
AIMS: To assess spatial fluctuations, temporal variability, and errors due to sampling and analysis in levels of disinfection by-products in routine monitoring tap water samples and in water samples collected in households within the same distribution system for an exposure assessment study. METHODS: Mixed effects models were applied to quantify seasonal effects and the degree to which trihalomethane (THM) levels vary among households or locations relative to variation over time within seasons for any given location. In a separate analysis, the proportion of total variation due to
measurement error arising from sampling and analysis was also quantified.
RESULTS: THM levels were higher in the summer relative to other seasons. Differences in the relative magnitude of the intra- and inter-household components of variation were observed between the two sets of THM measurements, with a greater proportion of the variation due to differences within seasons for the routine monitoring data and a greater proportion of
the variation due to differences across locations for the exposure assessment study data. Such differences likely arose due to differences in the strategies used to select sites for sampling and in the time periods over which the data were collected. With the exception of bromodichloromethane, measurement errors due to sampling and analysis contributed a small proportion of the total variation in THM levels.
CONCLUSIONS: The utility of routine monitoring data in assigning exposure in epidemiological studies is limited because such data may not represent the magnitude of spatial variability in levels of disinfection by-products across the distribution system. Measurement error contributes a relatively small proportion to the total variation in THM levels, which suggests that gathering a greater number of samples over time with fewer replicates
collected at each sampling location is more efficient and would likely yield improved estimates of household exposure.
Chemosphere 2004 Feb, 54(7):1017-23.
"Removal of NOM from Drinking Water: Fenton's and Photo-Fenton's Processes." Murray CA, Parsons SA. School of Water Sciences, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, UK.
The control of disinfection by-products during water treatment is primarily undertaken by reducing the levels of precursor species prior to chlorination. As many waters contain natural organic matter at levels of up to 15 mgl(-1) there is a need for a range of control methods to support conventional coagulation. Two such processes are the Fenton and photo-Fenton's processes and in this paper they are assessed for their potential to remove NOM from organic rich waters. The performance of both processes is shown to be depentent on pH, Fe: H2O2 ratio as well as Fe2+ dose. Under optimum conditions both processes achieved greater than 90% removal of DOC and UV254 absorbance. This removal lead to the trihalomethane formation potential of the water being reduced from 140 to below 10 microgl(-1), well below UK and US standards.
Appl Environ Microbiol. 2003 Jul, 69(7):4227-35.
"Single-cell Protein Profiling of Wastewater Enterobacterial Communities Predicts Disinfection Efficiency. Ponniah G, Chen H, Michielutti R, Salonen N, Blum P. School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588-0666, USA.
The efficiency of enterobacterial disinfection is dependent largely on enterobacterial community physiology. However, the relationship between enterobacterial community physiology and wastewater processing is unclear. The purpose of this study was to investigate this relationship. The influence of wastewater treatment processes on enterobacterial community physiology was examined at the single-cell level by using culture-independent methods. Intracellular concentrations of two conserved proteins, the growth-related protein Fis and the stationary-phase protein Dps, were analyzed by epifluoresence microscopy of uncultivated cells by using enterobacterial group-specific polyclonal fluorochrome-coupled antibodies. Enterobacterial single-cell community protein profiles were distinct for different types of biological treatment. The differences were not apparent when bulk methods of protein analysis were used. Trickling filter wastewater yielded Fis-enriched communities compared to the communities in submerged aeration basin wastewater. Community differences in Fis and Dps contents were used to predict disinfection efficiency. Disinfection of community samples by heat exposure combined with cultivation in selective media confirmed that enterobacterial communities exhibited significant differences in sensitivity to disinfection. These
findings provide strategies that can be used to increase treatment plant performance, reduce the enterobacterial content in municipal wastewater, and minimize the release of disinfection by-products into receiving water.
Environ Manage 2003 Apr, 31(4):476-88.
"Drawing the Battle Lines: Tracing the "Science War" in
the Construction of the Chloroform and Human Health
Risks Debate. Driedger SM, Eyles J. Department of Geography, University of Ottawa, 60 University Private, Ontario, Canada, K1S 6N5.
driedger@uottawa.ca
The United States Environmental Protection Agency (US EPA) and the Chlorine Chemistry Council, the Chemical Manufacturers Association, and others have been embroiled in a legal challenge concerning the US EPA's "reversal" regarding the scientific assessment of chloroform's carcinogenicity. This issue arose during the US EPA's November 1998 promulgation of a Maximum
Contaminant Level Goal for chloroform in the Stage 1 Final Rules for Disinfectants and Disinfection Byproducts in drinking water. In this paper we adopt a claimsmaking approach: to trace the development and outcome of the chloroform court challenge in the USA, to examine the construction of scientific knowledge claims concerning chloroform risk assessments, and to
investigate how different interpretations of scientific uncertainties regarding the evidence are contested when such uncertainties are brought into a regulatory and judicial arena. This "science war" (Chlorine Chemistry Council and others v. US EPA and others) took place in the US Court of Appeals for the District of Columbia Circuit. The scientific
"authority" in the construction of scientific claims in this dispute is based on the International Life Sciences Institute expert panel report on chloroform. Examining these science wars is important because they signal critical shifts in science policy agendas. The regulatory outcome of the chloroform science war in the United States can have profound implications for the construction and acceptance of scientific claims regarding drinking water in other jurisdictions (e.g., Canada). In this challenge, we argue that the actors involved in the dispute constructed "boundaries" around accepted and credible scientific claims.
Can J Microbiol. 2002 Jul, 48(7):567-87.
"A Review of Drinking-Water-Associated Endotoxin, including Potential Routes of Human Exposure." Anderson WB, Slawson RM, Mayfield CI. Department of Civil Engineering, University of Waterloo, ON, Canada. wbanderson@uwaterloo.ca
In the past decade efforts have been made to reduce the formation of harmful disinfection byproducts during the treatment and distribution of drinking water. This has been accomplished in part by the introduction of processes that involve the deliberate encouragement of indigenous biofilm growth in filters. In a controlled environment, such as a filter, these biofilms remove compounds that would otherwise be available as disinfection byproduct precursors or support uncontrolled biological activity in distribution systems. In the absence of exposure to chlorinated water, most biofilm bacteria are gram negative and have an outer layer that contains endotoxin. To date, outbreaks of waterborne endotoxin-related illness attributable to contamination of water used in hemodialysis procedures have been only infrequently documented, and occurrences linked to ingestion or through dermal abrasions could not be located. However, a less obvious conduit, that of inhalation, has been described in association with aerosolized water droplets. This review summarizes documented drinking-water-associated incidents of endotoxin exposure attributable to hemodialysis and inhalation. Typical endotoxin levels in water and conditions under which substantial quantities can enter drinking water
distribution systems are identified. It would appear that endotoxin originating in tap water can be inhaled but at present there is insufficient information available to quantify potential health risks.
Occup. Environ. Med. 2001 July, 58(7): 447-52.
"Use of Routinely Collected Data on Trihalomethane in
Drinking Water for Epidemiological Purposes." Keegan T, Whitaker H, Nieuwenhuijsen MJ, Toledano MB, Elliott P, Fawell J, Wilkinson M, Best N.
The TH Huxley School of the Environment, Earth Sciences and Engineering, Imperial College of Science Technology and Medicine, RSM Prince Consort Road, London SW7 2BP, UK.
OBJECTIVES: To explore the use of routinely collected trihalomethane (THM) measurements for epidemiological studies. Recently there has been interest in the relation between byproducts of disinfection of public drinking water and certain adverse reproductive outcomes, including stillbirth, congenital malformations, and low birth weight.
METHOD: Five years of THM readings (1992--6), collected for compliance with statutory limits, were analysed. One water company in the north west of
England, divided into 288 water zones, provided 15,984 observations for statistical analysis. On average each zone was sampled 11.1 times a year. Five year, annual, monthly, and seasonal variation in THMs were examined as well as the variability within and between zones.
RESULTS: Between 1992 and 1996 the total THM (TTHM) annual zone means were less than half the statutory concentration, at approximately 46 microg/l.
Differences in annual water zone means were within 7%. Over the study period, the maximum water zone mean fell from 142.2 to 88.1 microg/l. Mean annual concentrations for individual THMs (microg/l) were 36.6, 8.0, and 2.8 for chloroform, bromodichloromethane (BDCM), and dibromochloromethane
(DBCM) respectively. Bromoform data were not analysed, because a high proportion of the data were below the detection limit. The correlation between chloroform and TTHM was 0.98, between BDCM and TTHM 0.62, and
between DBCM and TTHM -0.09. Between zone variation was larger than within zone variation for chloroform and BDCM, but not for DBCM. There was only little seasonal variation (<3%). Monthly variation was found although there were no consistent trends within years.
CONCLUSION: In an area where the TTHM concentrations were less than half the statutory limit (48 microg/l) chloroform formed a high proportion of TTHM. The results of the correlation analysis suggest that TTHM concentrations provided a good indication of chloroform concentrations, a reasonable indication of BDCM concentrations, but no indication of DBCM. Zone means were similar over the years, but the maximum concentrations reduced considerably, which suggests that successful improvements in treatment have been made to reduce high TTHM concentrations in the area. For chloroform and BDCM, the main THMs, the component between water zones was greater than variation within water zones and explained most of the overall exposure variation. Variation between months and seasons was low and showed no clear trends within years. The results indicate that routinely collected data can be used to obtain exposure estimates for epidemiological studies at a small area level.
Anal Chem. 2002 May 1, 74(9):260A-267A.
"Analyzing Drinking Water for Disinfection Byproducts." Urbansky ET, Magnuson ML. U.S. Environmental Protection Agency Office of Research and Development, National Risk Management Research Laboratory, Water Supply and Water Resources Division, Cincinnati, OH 45268, USA. urbansky.edward@epa.gov
[No summary available]
Environ Sci Technol.2002 May 1, 36(9):198A-205A.
"Disinfection Byproducts: The Next Generation." Richardson SD, Simmons JE, Rice G. U.S. EPA, National Exposure Research Laboratory,
Athens, GA, USA.
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