Issues in Potable Reuse The Viability of Augmenting Drinking Water Supplies with Reclaimed Water (1998) / Chapter Skim
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4 Methods for Assessing Health Risks of Reclaimed Water
4 Methods for Assessing Health Risks of Reclaimed Water
Pages 118-163
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From page 118... ...
The chapter also discusses the complications of and alternative strategies for using epidemiological studies to evaluate health risks of potable water reuse. EVALUATING MICROBIAL CONTAMINANTS Efforts to monitor water quality for microbiological safety have historically relied on measurements of one or more groups of coliform bacteria as indicators of fecal contamination, treatment efficiency, and the integrity of the water distribution systems.
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promulgated the Surface Water Treatment Rule for drinking water in 1989 (U.S.
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The data will be used in future risk analyses to establish the necessary drinking water treatment performance criteria for the protection of public health. The results will be applicable to potable reclamation projects as well.
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Finally, PCR remains only qualitative in that the results are presented as positive or negative. The development of quantitative techniques using PCR would be very useful for assessments of the microbiological quality of drinking water.
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No standard procedure exists for Salmonella testing in reclaimed water. As described above, PCR is a rapid detection method that can be combined with more traditional cell culture techniques to assess viability of bacterial pathogens.
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The adsorbed viruses are eluted and concentrated to a smaller volume using an organic flocculation procedure. This final concentrate may be inoculated into cell cultures to detect cytopathic effects, or it may be tested by PCR or other types of tests.
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These include emerging viruses of concern such as Norwalk viruses. Indicator Techniques Several types of microorganisms have been suggested as alternatives to coliform bacteria as indicators of water quality, fecal pollution, and public health risks.
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examined the removal of coliphages and enteroviruses in drinking water treatment. The total removal and/or inactivation of enteroviruses by the complete drinking water process was estimated at 7 logy, based on coliphage removal.
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Microbial Risk Assessment Human health risk assessment is a scientific process that attempts to identify and quantify the health risks from exposure to environmental hazards. The use of risk assessment in drinking water began in 1974 with the congressional mandates of the Safe Drinking Water Act.
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Haas (1983) first developed dose-response models using data from human volunteers who ingested various levels of viruses, protozoan cysts or oocysts, or bacteria.
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The values for exposure in drinking water were estimated based on concentrations reported in surface waters and using treatment reductions of 99.9 percent for Giardia, 99.99 percent for rotavirus, and 99.9999 percent for Salmonella. With these assumptions, the risk of infection ranged from a low of 2.7 x 10-4 to a high of 4.9 x 10-3, depending on the microorganism.
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These models account for typical numbers of infected, ill, recovering, and immunocompromised subpopulations in computing the passage of an infectious disease through a community. Actual levels of exposure to microorganisms through drinking water have been difficult to estimate, because the data on reductions of many pathogens are limited and extrapolations are often needed to determine tap water concentrations.
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Giardia lamblia 1.33 0.11d Viral gastroenteritis 0.22 0.11d Child day care center (Pickering et al., 1981) Drinking water in Colorado (Morens et al., 1979)
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Safety Evaluations of Reclaimed Water Calculations of health risk from chemicals in drinking water are largely based on extrapolations of the results of toxicological experiments on animals and estimates of human exposure to the chemical. Based on such risk information, national standards have been established for a limited but growing number of chemical contaminants in drinking water.
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If all wastewaters had the same composition, one could extrapolate the apparent safe consumption of a drinking water augmented with treated wastewater from one community to another. However, the complexity and potential variability in the chemical composition of wastewaters from different localities make such extrapolation quite difficult.
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For special purposes, testing of lower life forms, such as bacteria in cell cultures, is used; this is known as in vitro testing. Food and drug industries have developed fairly standardized testing strate
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This test was subsequently applied to a wide variety of environmental problems, including drinking water and reclaimed water, in the hopes that it would provide a cost-effective method for evaluating carcinogenic hazards in the environment. The apparent success of the test spawned an interest in developing in vitro techniques to detect other toxicological end points.
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Generally the tests are run on at least two species to ensure that no large interspecies differences in responses are distorting the test results. Conventionally, risk assessments are made from these data, with ap
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The general practice has been to test such products to the point where there is clear evidence of some toxic effect, then compare the toxic doses to the levels normally used in food or drugs to ensure an appropriate margin of safety. The Role of Toxicological Testing in Water Reclamation Projects The 1982 National Research Council evaluation of health considerations for the potable use of reclaimed water found that it was a practical impossibility to identify and test the toxicity of all of the individual compounds present in reused water, and that it was ultimately necessary to test the toxicity of mixtures of chemicals instead.
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Notwithstanding these complications, and based on the general testing logic outlined in Table 4-6, the 1982 NRC panel recommended that a final comparison should be made between reused and conventional water based on the outcomes of a series of tiered tests designed to give information on the relative toxicities of the concentrates from the two water supplies (Table 4-7~. Phase I of this recommended protocol includes in vitro assessments of mutagenic and carcinogenic potential by means of microbial and mammalian cell mutation and in viva evaluations of acute and short-term subchronic toxicity, teratogenicity, and clastogenicity.
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. No single in vitro testing system addresses a substantial fraction of the many potential health effects that chemicals can have on animals or humans, and there seems little hope that any combination of in vitro tests will do so or be able to substitute for experiments on live animals in the foreseeable future.
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have shown no toxicological effects produced by reclaimed water, the extrapolation of these results to other reuse systems is greatly complicated by possible differences between municipal wastewaters from different systems, potential changes in wastewater composition over time, and the types of monitoring that would be needed to ensure continued toxicological safety of the reclaimed water. Further complicating these extrapolations are the many chemicals present at low dose levels in drinking water from either natural or wastewater-influenced sources, which may interact with one another in an additive, synergistic, or antagonistic manner to produce biological effects
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Immunocompromised individuals, such as those undergoing organ transplant treatments or cancer chemotherapy or those infected with HIV, may suffer further immunosuppressive effects by exposure to some chemicals in drinking water at even very low dose levels. Given the millions of people using public drinking water supplies, it is reasonable to expect that such scenarios currently exist, and they should be factored into risk assessment strategies for treatment of public water supplies from any origin.
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Determining whether an observed pattern of disease is associated with exposures to contaminants in drinking water requires a specifically designed epidemiologic study. The use of epidemiologic methods to study health risks associated with drinking water has been recently reviewed by Craun et al.
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Exposure and health outcome are characterized on an aggregate level. For example, initial studies of the potential health risks from chlorination by-products in drinking water
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With this design, cases and controls are queried directly about their residence history and water consumption habits, which provides greatly improved estimates of risk associated with exposure to water from different sources. Case-control studies allow the association between exposure and a single disease or health outcome to be evaluated while controlling for individual risk factors.
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However, taken together, these criteria allow critical evaluation of specific epidemiologic findings in a broader context. Exposure Assessment Estimating actual exposure to microbial pathogens or chemical contaminants in drinking water is a difficult task.
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in tap water or (2) estimating the presence, and possibly the amount, of the contaminant based on characteristics of the water source and treatment processes (such as a chlorinated surface water supply versus an untreated ground water supply)
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It has been hypothesized that polymorphisms in the GSTT1 gene may contribute to susceptibility to colon and rectal cancer. GSTT1 is involved in detoxification of a variety of halogenated organic compounds, including organic compounds present in chlorinated drinking water (bromoform, dibromochloromethane, dichlorobromomethane, and dichloromethane)
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The best method for measuring health outcomes in epidemiologic studies of health effects associated with water exposure depends on the study design and the health outcomes in question. Prospective studies of endemic waterborne infectious diseases have used personal health diaries to record episodes of gastrointestinal symptoms (Payment et al., 1991~.
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that can distort the relationship between water exposure and health outcome. Sources of Bias and Error When planning epidemiologic studies or reviewing the results of previous studies, one must examine whether the results could be affected by systematic errors in the sampling strategy or data collection procedures.
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In water studies, misclassification of exposure is a major concern. Information on an individual's exposure to a specific water supply may be based on information from death certificates or water utility bills.
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Microbiological Methods and Risk Assessment There is a lack of information nationwide on the levels of viral and protozoan pathogens in all waters and the efficacy of both conventional water treatment and wastewater treatment for water reclamation in reducing these levels. The Information Collection Rule, promulgated in 1996 by the EPA, is a first step toward providing some of the exposure data needed for more effective risk assessments, but additional steps are needed to improve methods for assessing risks posed by microbial pathogens in water reuse projects.
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Microbial risk assessment requires better estimates of exposure, which should be based on monitoring data, to identify the concentration of microbial pathogens in raw wastewater, wastewater treated with various processes, ambient water, and drinking water treated with various processes. State officials, water utilities, and water research scientists should document survival rates of relevant protozoa in natural environments.
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From page 156... ...
While this approach has been used to develop risk assessments and regulations for recognized chemical contaminants in drinking water, there has been little experience in applying the strategy to determine health risks posed by the poorly characterized mixtures of organic chemicals in reclaimed water. The current state of knowledge in toxicology is too limited to make meaningful risk assessments based on in vitro data alone.
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The strongest observational study design for establishing a cause-and-effect relationship between exposure to waterborne disease agents and disease occurrences is a cohort study, which compares the disease rates over time among individuals who are exposed to reclaimed water to disease rates among individuals who use a different water source. REFERENCES Asano, T., L
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1985. Clostridium perfringens, a reliable indicator of stream water quality.
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1991a. Giardia and Cryptosporidium in filtered drinking water supplies.
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1989. Drinking Water and Health: Selected Issues in Risk Assessment, Vol.
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1993. Clostridium perfringens and somatic coliphages as indicators of the efficiency of drinking water treatment for viruses and protozoan cysts.
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ted.) Drinking Water Microbiology.
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1989c. National primary drinking water regulation; filtration and disinfection; turbidity; Giardia lamlia; viruses, Legionella and heterotophic bacteria.
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