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--> 5 Selecting Contaminants on the CCL for Future Action: Recommended Decision Process The EPA faces a challenging task in determining which contaminants on the Drinking Water Contaminant Candidate List (CCL) warrant regulation. As explained in Chapter 2, existing algorithms for ranking environmental contaminants are of limited use for this purpose, because many of them were designed for priority setting, not necessarily for regulatory action, and because of data gaps and the need for policy judgments. This chapter presents a decision-making framework for selecting contaminants from a CCL for future action. It also discusses criteria for evaluating four categories of data—exposure, health effects, treatment, and analytical methods—that are needed for making this selection. Decision-Making Framework While a ranking algorithm may be appropriate for helping to determine contaminants to be listed on the CCL, this approach is not suitable for determining the appropriate disposition of contaminants on the CCL. Rather, the process requires considerable expert judgment to address uncertainties from the inevitable gaps in information about exposure potential and/or health effects; to evaluate, from a public health perspective, the many different effects that contaminants can cause; and to interpret available data in terms of statutory requirements. Therefore, such decisions necessarily involve subjective judgments, and the law designates EPA to make them. For each contaminant on the CCL, there are three possible outcomes of EPA's decision process:
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--> Consider for immediate regulatory action, as required by the Safe Drinking Water Act (SDWA) Amendments of 1996, if information is sufficient to judge that a contaminant ''may adversely affect public health" and is known or is substantially likely to occur in public water systems with a frequency and at levels that pose a threat to public health. Drop from the CCL if information is sufficient to determine that the contaminant does not pose a risk to public health in drinking water. Conduct additional research on health effects and/or exposure if information is insufficient to determine whether the contaminant should be regulated. These three outcomes are not mutually exclusive. For example, based on available evidence, EPA might choose to initiate regulatory action and issue a health advisory, while simultaneously pursuing research to fill information gaps that might result in subsequent further modifications of the regulatory level. The committee believes that public health will be served best by leaving EPA as much discretion as possible, within the limits of law. Figure 5-1 shows in simplified outline a general decision process that the committee recommends for EPA use in deciding which of the above three outcomes (or combinations of outcomes) is appropriate for each contaminant on the CCL. The left side of the figure shows the suggested timing to progress through each step of the process. The framework applies to both chemical and microbiological contaminants; differences in either their characteristics or the information available about them do not justify separate decision processes. The time line on Figure 5-1 is provided to help EPA allocate time and resources in order to meet the 1996 Safe Drinking Water Act (SDWA) Amendments' requirement to publish regulatory determinations for least five contaminants from the CCL by August 2001. The committee recognizes that almost one year of the originally allotted time (three and one-half years following publication of the first CCL) have already passed. Thus, while conveying the urgency with which EPA must act to reach the mandated regulatory decisions, the suggested time line should be of more direct use following the publication of future CCLs. As indicated on the figure, the steps in the decision process are as follows: 1. Gather and analyze available health effects, exposure, and treatment and analytical methods data for each contaminant. This step should be initiated immediately. It is a standard task with which EPA staff are well familiar. While data on the ability of drinking water treatment technologies to remove the contaminant and analytical methods to measure the contaminant should be gathered at this stage to avoid delays in future regulatory action, these data should not be part of the decision about whether to regulate a contaminant. Any contaminant that poses a health risk in drinking water, as defined in the SDWA Amendments of 1996, should be considered for regulation. The second half of this
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--> Figure 5-1 Phased process for setting priorities among contaminants on the CCL.
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--> chapter describes factors to consider when gathering and assessing data on contaminant health effects, exposure, and treatment and analytical methods. 2. Conduct a preliminary risk assessment for each contaminant based on the available data. The preliminary risk assessment integrates the hazard and exposure analyses to assess the public health implications of the contaminant. It should include consideration of possible effects of the contaminant on sensitive subpopulations, such as pregnant women, infants, the elderly, and those with compromised immune systems. It should be carried out even if there are data gaps and discrepancies in order to provide a basis for an initial decision on the disposition of the contaminant and, where there are such gaps, to guide research efforts. EPA's usual approaches to risk assessment are appropriate, and the committee does not see the need to create new procedures for this step. Although a critical step in the process, the preliminary risk assessment should not be overly detailed, time consuming, or resource intensive. It should resemble risk assessments conducted by EPA under the Toxic Substances Control Act to evaluate data on new chemicals, rather than the massive multi-year risk assessments (e.g., for dioxins) that EPA often performs. 3. Issue a decision document for each contaminant describing the outcome of the preliminary risk assessment (i.e., whether the contaminant will be considered for regulation, dropped from the CCL, or retained on the CCL pending further research). This document should be issued within 12 months of compilation of the CCL. The document should describe information available to EPA at the time of the preliminary risk assessment, the weight EPA staff put on the available information and why, the reasons for EPA's decision, an action plan for implementing the decision (for example, indicating what research to conduct and how), and contacts for more information. It should be written in a language and format accessible by all interested parties. 4. Issue a health advisory for each contaminant not dropped from the CCL after the preliminary risk assessment. The health advisory should be completed within three months of the decision (within 15 months of the CCL's completion). The purpose of such an advisory should be the same as for any drinking water advisory: to alert interested parties to the possibility of a threat to public health worthy of attention and to describe the nature of the available evidence, without committing EPA to any particular future action on the contaminant. Health advisories are currently used for drinking water contaminants when the occurrence of the contaminant is not deemed widespread enough to justify imposing monitoring requirements on all utilities and to advise, even in the presence of a promulgated regulation, those to whom the regulation would not apply yet who might be vulnerable to contaminated drinking water (for example, private well owners). The committee recommends that the purpose of health advisories be expanded beyond these current uses to promulgate information about all contaminants remaining on the CCL after the preliminary risk assessment.
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--> 5. Begin compiling a regulatory package or conducting research for each contaminant remaining on the CCL after the preliminary risk assessment. This step should begin in tandem with issuance of the health advisory and should not wait until the advisory is completed. For contaminants not slated for regulation, research results should be fed back into another preliminary risk assessment, and a new decision document should be issued based on the results of this second risk assessment. The committee's recommendation for a swift (12-month) initial decision on whether a contaminant should be put on a regulatory list is not intended to interfere with the agency's need to add and remove contaminants from such a list at any time within the five-year life of the CCL. This rapid initial action is intended to ensure that, to the extent that available information supports such an action, EPA begins as early as possible to develop a regulatory package that could support a decision to promulgate a regulation. Further, initial decisions should be made within 12 months to be sure that any information gaps (such as treatment availability and costs) standing in the way of issuing a regulation can be filled as quickly as possible. In using this decision framework, EPA should keep in mind the importance of involving all interested parties (including regulated utilities, state and local regulators, public interest representatives, and consumers). The decision document for each contaminant should be disseminated for review by these parties, although consultation with these parties should not delay initiation of actions on the decisions that EPA has reached. Given the valid scientific disagreements noted in Chapter 1 and the way information and values are inevitably entwined, EPA would be wise to seek the insights of parties with a wide range of perspectives on contaminant priority setting during the entire decision process, not just in the period of formal regulatory procedures. Soliciting comments on the decision document will offer EPA independent perspectives and is an effective way to ensure that criteria developed after consideration of all the relevant issues have not been overlooked. In the long run, this will likely lead to a less contentious regulatory development process, if interested parties believe their views have been considered. The EPA should also keep in mind that public health should be the guiding principle for making its decisions and that the decision to eliminate contaminants from the CCL should not be made lightly. However, there are cases when information initially used to include a contaminant on a CCL was faulty, and EPA should not be required to retain that contaminant on the list. Just as a decision to exclude a contaminant on the previous CCL from a new CCL would be explained and justified in the Federal Register announcing the draft CCL, a decision document would explain why EPA has decided to drop a contaminant from a CCL at other times. Conversely, if new information suggests that the contaminant is worthy of being included on the CCL after it has been eliminated
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--> from the CCL, it should be returned to the CCL. Moreover, if important new information suggests that an unregulated contaminant not listed on the CCL is being found in many water systems and may pose health risks, EPA should consider adding it to the CCL immediately, or consider invoking its immediate regulatory authority under the "urgent threats to public health" provisions of the SDWA (1412[b][D]). Uncertainty in the Decision Process Under ideal circumstances, EPA would have a decision process that exactly selects only those contaminants whose regulation will reduce disease, disability, or death and dismisses those contaminants that have little or no effect on human health. Unfortunately, the true state of nature ("the truth") remains either unknown or shrouded in uncertainty for the majority of contaminants on the CCL. It is likely, therefore, that there will be some error in the decision process, allowing some contaminants that should be regulated to pass through while placing other, harmless contaminants on a regulatory track. In making judgments about which contaminants to regulate, the committee recommends that EPA err on the side of public health protection. The CCL lists contaminants that are likely to pose greater risks to the public, compared to a list of randomly selected chemicals and microorganisms. For lists enriched in substances that pose risks, even a highly accurate decision process can result in many substances that need to be regulated remaining unregulated. Appendix A explains in mathematical terms why this is so. As shown in the appendix, a highly accurate decision process, when applied to such an enriched list, can still result in nearly a third of substances that need to be regulated going unregulated, while at the same time slating for regulation just three percent of substances that do not need to be regulated. Thus, for such a list, when the decision about whether or not to consider a contaminant for regulation is a close call, EPA should decide in favor of regulation. Implementing the Decision Framework: Examples Boxes 5-1, 5-2, 5-3, and 5-4 provide examples of how the initial data analysis step of the proposed decision framework might be implemented (or might have been implemented had the decision framework been available in the past) for four contaminants: trichloroethylene, a currently regulated contaminant; Cryptosporidium, which is monitored under the Information Collection Rule, but is not on the CCL; and aldicarbs and Rhodamine WT, which were both on an early draft of the CCL but were dropped before the final CCL was issued. In presenting these examples, the committee does not seek to substitute its own judgment for EPA's. Rather, as these cases illustrate, implementing the decision framework requires a careful survey of available health effects and
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--> BOX 5-1 Trichloroethylene: Decision Process for a Regulated Contaminant Trichloroethylene (TCE), a widely used organic solvent, is currently regulated in drinking water at a level of 5 micrograms per liter. The current regulation, however, was not developed as a direct result of an EPA contaminant selection and decision-making process but because Congress, in the 1986 Safe Drinking Water Act amendments, required that EPA develop a regulation for TCE and 82 other contaminants that had been slated for future regulation. At the time, Congress reacted to the belief that EPA had been too slow in developing drinking water standards following passage of the 1974 Safe Drinking Water Act and, in particular, that EPA had neglected to consider sufficiently the importance of regulating organic compounds such as TCE. If EPA had applied the decision framework recommended in this report in 1977, the decision would likely have been (1) issue a health advisory, (2) conduct additional research on exposure and health effects, and (3) consider possible regulation, based upon the partial data that were available. Exposure data: The primary exposure data on TCE available in 1977 were from the National Organics Monitoring Survey (NOMS), conducted in 1976-1977 (Westrick, 1990). NOMS involved the sampling of finished water (prior to distribution) from 113 water systems. The final phase of the survey found TCE above the reporting limit of 0.2-0.3 micrograms per liter in 2 of 17 ground water supplies and 17 of 88 surface water supplies, with a maximum reported concentration of 15 micrograms per liter. It is important to note that, at that time, this reported occurrence of TCE was not deemed significant. In addition, this survey was limited in that it covered mostly large water systems determined to be vulnerable to contamination. To obtain a more representative estimate of TCE occurrence EPA may have wanted to conduct additional surveys using random samples of water systems of various sizes. In fact, EPA conducted such a survey, the Community Water Supply Survey, in 1979 and found no TCE in 106 surface water systems and TCE at levels above 0.5 micrograms per liter in 14 of 330 ground water systems, with a maximum reported concentration of 210 micrograms per liter (Westrick, 1990). Thus, in 1977, additional research on exposure to TCE in drinking water likely would have been required before deciding whether to regulate TCE. Health effects data: Health effects data on TCE were also limited in 1977. Researchers knew that TCE was metabolized to trichloroacetic acid, trichlorethanol, and small amounts of chloroform and monochloroacetate in animals (NRC, 1977), but neither the kinetics of the pathways nor any possible species differences between various strains of mice, between mice and rats, and between rats and either mice or humans was known except in the most rudimentary way. A chronic bioassay had shown liver cancer in mice but not in rats. Epidemiological data were available essentially only for high-dose occupational accident type exposures (i.e., case studies), not for the low doses found in drinking water. There was even some discussion that TCE was found as a disinfection byproduct (NRC, 1977). Conclusions: In 1977, the existing health effects data likely would have been insufficient to drop TCE from the CCL. Therefore, TCE would warrant additional research and a health advisory. EPA would have had to decide whether or not the partial data available were sufficient to regulate the contaminant at precautionary levels.
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--> BOX 5-2 Cryptosporidium: Decision Process for an Unregulated Contaminant Cryptosporidium, an enteric protozoan, while monitored under the Information Collection Rule, is not one of the microbial contaminants listed on the current CCL. Using the framework in this report, the preliminary risk assessment of this contaminant will likely lead EPA to a decision that it should move forward with regulatory action, although additional data (for example, on removal of this organism in different treatment processes and development of reliable monitoring methods) are likely needed to complete the regulation. Exposure data: While other enteric protozoa have long been known to be transmitted by contaminated water, the potential for waterborne transmission of Cryptosporidium to humans was not recognized until the 1980s. The first documented waterborne outbreak, transmitted by well water in a small Texas community, occurred in 1984 (D'Antonio et al., 1985); a second documented outbreak occurred in Georgia in 1987 (Hayes et al., 1989). Several more outbreaks have been reported since then, with the largest occurring in Milwaukee in 1993 and affecting 400,000 individuals (MacKenzie et al., 1994; Smith and Rose, 1998). An increasing amount of research on the occurrence of Cryptosporidium has occurred since the first reported outbreaks. Surveys on the occurrence of oocysts were published by 1988 (Rose, 1988). Thus, the occurrence of Cryptosporidium in drinking water is known to be widespread enough to warrant concern. Health effects data: Early work on Cryptosporidium focused on its effects on animals. First described in 1907 in the intestinal tract of mice (Tyzzer, 1907), Cryptosporidium was later reported to cause diarrheal disease in young mammals, particularly calves (Barker and Carbonell, 1974; Anderson and Bulgin, 1981). Mammalian isolates were shown to cause infection in other mammals, and thus this protozoan was known to cross species barriers. The first identified case in humans occurred in 1976 (Meisel et al., 1976), but cryptosporidiosis was not thought to be a cause of severe disease until the AIDS epidemic struck; the disease leads to mortality in 50 percent of cases in the immunocompromised population (MMWR, 1982). By the early 1980s, Cryptosporidium was known to cause illness (five to seven days of diarrhea) in populations with normal immune functions (Tzipori, 1983). Conclusions: This organism has caused major public health concerns and is not limited to isolated water supplies. Therefore, EPA's preliminary risk assessment will likely lead EPA to decide to initiate regulatory action. exposure data on the contaminant followed by policy judgments about the significance of the risk as indicated by the available data and additional research to close essential data gaps. Treatment and analytical data are not described in these examples because they are not part of the initial decision about whether a contaminant should be moved forward to the list of contaminants to consider for regulation, although assessment of these data needs to begin in tandem with exposure and health effects assessments in order to avoid delaying regulatory action and to help set research priorities.
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--> BOX 5-3 Aldicarbs: Decision Process for an Unregulated Contaminant Aldicarb, a highly toxic insecticide used on such crops as potatoes, peanuts, sugar bees, soybeans, sugarcane, and cotton, is not currently regulated. The exposure and health effects data summarized below are as they existed in 1984, when aldicarb was first considered for regulation. Using historical data, one possible conclusion that EPA might have reached in 1984 if the framework had been available then is that aldicarb should be considered for a health advisory and that EPA would need to decide whether the population potentially exposed to aldicarb is sufficiently large to warrant establishing a national drinking water standard. Exposure data (as of 1989): Aldicarb and its degradates (including aldicarb sulfoxide and aldicarb sulfone) have been found in ground water at levels that would be anticipated to be of health concern. Aldicarbs appear most frequently in agricultural areas with sandy soil, and public water supply wells in those areas are at risk of being contaminated. Water from wells near treated fields in eight states contained aldicarb at concentrations ranging from 10 to 200 micrograms per liter (EPA, 1984); these concentrations exceed health criteria suggested by the National Research Council in its 1977 report Drinking Water and Health (NRC, 1977). Higher levels (up to 500 micrograms per liter) have been found in New York. (EPA, 1984). Health effects data (as of 1984): Aldicarb is known to be toxic in animals and humans by the same mechanism. Mammals readily absorb aldicarb from their gastrointestinal tract. On an acute basis, aldicarb is one of the most potent, both orally and dermally, of the widely used insecticides (rat oral LD50: 0.8 mg/kg for males and 0.65 mg/kg for females; mouse oral LD50: 0.3 to 0.5 mg/kg). Aldicarb is also a potent toxin in humans, as was shown by a study in groups of four adult men (NRC, 1977). At the highest dose (0.1 mg/kg), those tested experienced mild cholinergic symptoms. Cholinesterase depression occurred at lower doses (0.05 mg/kg and 0.025 mg/kg), although the findings were not statistically significant. The subchronic and chronic effects of ingesting aldicarb were studied in a 93-day rat study; two two-year rat studies; a two-year dog study; a three-generation rat study; a rat teratology study; and a mouse carcinogenicity study. These studies did not identify a more sensitive endpoint than cholinesterase inhibition. The no-observed-adverse-effect level for cholinesterase inhibition is 0.1 mg/kg/day. Based on these data, a suggested no-adverse-effect level for drinking water is 7 micrograms/liter (NRC, 1977). Conclusions: Historical health effects data as of 1984 were sufficient to indicate that aldicarb posed a risk at concentrations found in drinking water. Therefore, according to the decision framework, EPA would have had to decide whether or not to regulate aldicarb based on its policy judgment as to whether exposure occurs with a frequency and at levels that pose a public health threat.
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--> BOX 5-4 Rhodamine WT: Dropping a Contaminant from the CCL A few chemicals will "come and go" from the CCL because consensus emerges quickly that they do not present a serious threat to drinking water quality. The decision framework proposed in this report is designed to accommodate such cases by allowing a contaminant to be dropped from the CCL after release of a decision document showing that the contaminant does not pose a significant risk in drinking water. Reasonable handling of contaminants that are judged to be of very low priority is illustrated by the case of Rhodamine WT. In the announcement of the first draft CCL (EPA, 1997), EPA included this fluorescent dye because the dye's use as a tracer in ground water flow studies apparently had resulted in detectable concentrations above the National Sanitation Foundation's (NSF's) standard of 0.1 mg/L. However, commenters on the draft list pointed out that the 0.1 mg/L standard was for drinking water and that the data that raised EPA's concern came from "ground water not associated with drinking water production," for which the NSF standard is 100 mg/L. In light of this clarification and because (1) there are no data indicating adverse health effects of Rhodamine WT and (2) the dye is used for very specific and limited purposes, EPA chose not to list Rhodamine WT on the final CCL. Conclusions: If these data had come to light after Rhodamine WT was included on a CCL, a decision document explaining EPA's reasoning would have allowed the contaminant to be dropped from the CCL. As noted by EPA, sufficient data are necessary to conduct analyses on extent of exposure and risk to populations via drinking water in order to determine appropriate regulatory action (EPA, 1998). If sufficient data are not available, additional data must be obtained before any meaningful assessment can be made for a specific contaminant. At the time of the final CCL's publication, the "regulatory determination priorities" category of the CCL included those contaminants for which EPA had sufficient data to conduct exposure and risk analyses. Therefore, the five or more contaminants considered for regulation by August 2001, as required by the SDWA amendments, would likely be selected from this category. However, EPA cautioned that the future regulatory action categories of the final CCL were based on current information, and some movement between categories could be expected as additional data are obtained and evaluated. General Guidelines for Evaluating Contaminant-Related Data Because of the variability in the types and quality of data available on different contaminants, defining precise criteria for placing contaminants in the three
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--> decision categories (regulate, drop from CCL, or research) is not possible, as the examples presented in Boxes 5-1, 5-2, 5-3, and 5-4 illustrate. Nevertheless, establishing general guidelines is possible. Below, the committee recommends such guidelines for evaluating data on contaminant exposure, health effects, and treatment and analytical methods. Assessing Exposure Data Exposure data should be gathered from sources that will predict the dose of drinking water contaminants for individuals, whether it be through ingestion, inhalation or dermal absorption. Table 5-1 represents a hierarchy of data types for the assessment of exposure. Ideally, the best estimate of an individual's exposure to drinking water contaminants would be determined from samples collected at the person's tap. Such samples reflect all of the changes that might occur in the distribution system, treatment plant, and source waters that precede it. By integrating the results of a tap-sampling program, it is possible to obtain a picture of population exposure to the contaminant of interest. Rarely is a census of tap water quality available, however. Tap sampling information is more difficult to obtain because of potential problems with access and costs. It is also prohibitively expensive to determine the tap water quality of every customer. While some utilities use consumers' taps as sample points, utilities are converting to dedicated sampling stations located on distribution system mains to obtain representative samples of the water under their control. The second most useful sampling locations to estimate contaminant exposure are in a drinking water distribution system. Distribution sampling locations must be carefully selected to represent the characteristics of the contaminants being monitored. For example, concentrations of trihalomethanes and a variety of other disinfection byproducts change during transport through distribution systems as a result of continued exposure to chlorine. Thus, the trihalomethane regulation requires that these compounds be sampled at three average and one TABLE 5-1 Hierarchy of Data Needed for Exposure Assessment Concentration at the tap Concentration in the distribution system Concentration in finished water of the water treatment plant Concentration in raw (source) water Concentration in watersheds and aquifers Concentration in historical contaminant release data Concentrations in production data Concentrations in biota and human tissue
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--> Assessing Analytical Methods Data To ensure that data on the occurrence of drinking water contaminants are adequate for exposure assessment, sampling and measurement methods must be reliable and well documented. Analytical methods for currently regulated contaminants in drinking water are well documented and should be adequate for most commonly recognized contaminants that comprise much of the CCL. The greatest analytical challenges lie in the identification of new contaminants and the quantification of emerging contaminants that are intrinsically difficult to measure. Along with written summaries of health effects, exposure, and treatment techniques data, EPA will need to summarize available analytical methods for contaminants on the CCL, focusing especially on newly recognized contaminants. Chemical Contaminants From an analytical perspective, it is useful to classify contaminants in drinking water as volatile, semivolatile, and nonvolatile. Volatile organic chemicals (VOCs) have relatively high vapor pressures (0.1 to 380 torr) (Mukund et al., 1995). Therefore, most VOCs are easily purged from the aqueous phase to the gas phase and are separated by gas chromatography. However, if not purged from finished water, remaining VOCs can lead to a large source of exposures by inhalation of indoor air, especially through showering. Variations on this approach have proven to be very robust and are routinely used for the analysis of VOCs in drinking water. In fact, six of the thirteen methods commonly used for determination of organic contaminants in drinking water (see Table 5-2) are for VOCs, and these methods were cited in the Federal Register of July 8, 1987, under the National Primary Drinking Water Regulations (EPA, 1987). In contrast with VOCs, semivolatile organic compounds (SVOCs) have moderate vapor pressures (10-7 to 0.1 torr) and are not as amenable to routine analysis. Seven standard methods for non-VOC compounds were cited in proposed drinking water regulations in the Federal Register of May 22, 1989, and are also summarized in Table 5-2 (EPA, 1989). However, it will be necessary to develop and standardize new methods for SVOCs and nonvolatile organic compounds in order to obtain the occurrence data necessary to monitor and regulate some of the new and emerging contaminants that may appear on future CCLs. Analytical methods for detecting a wide range of chemical contaminants in drinking water are regularly published in the open research literature; and are not listed in Table 5-2. These methods are not generally validated by EPA, but they represent an important source of information on analytical methods for new and emerging chemical contaminants.
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--> TABLE 5-2 EPA Methods for Determining Organic Compounds in Drinking Water Number Method Name 502.1 Volatile Halogenated Organic Compounds in Water by Purge and Trap Gas Chromatography 502.2 Volatile Organic Compounds in Water By Purge and Trap Capillary Column Gas Chromatography with Photoionization and Electrolytic Conductivity Detectors in Series 503.1 Volatile Aromatic and Unsaturated Organic Compounds in Water by Purge and Trap Gas Chromatography 504 1,2-Dibromoethane (EDB) and 1,2-Dibromo-3-Chloropropane (DBCP) in Water by Microextraction and Gas Chromatography 505 Analysis of Organohalide Pesticides and Commercial Polychlorinated Biphenyl Products in Water by Micro-Extraction and Gas Chromatography 507 Determination of Nitrogen-and Phosphorus-Containing Pesticides in Water by Gas Chromatography with a Nitrogen-Phosphorus Detector 508 Determination of Chlorinated Pesticides in Water by Gas Chromatography with an Electron Capture Detector 508A Screening for Polychlorinated Biphenyls by Perchlorination and Gas Chromatography 515.1 Determination of Chlorinated Acids in Water by Gas Chromatography with an Electron Capture Detector 524.1 Measurement of Purgeable Organic Compounds in Water by Packed Column Gas Chromatography/Mass Spectrometry 524.2 Measurement of Purgeable Organic Compounds in Water by Capillary Column Gas Chromatography/Mass Spectrometry 525.1 Determination of Organic Compounds in Drinking Water by Liquid-Solid Extraction and Capillary Column Gas Chromatography/Mass Spectrometry 531.1 Measurement of N-Methylcarbamoyloximes and N-Methylcarbamates in Water by Direct Aqueous Injection HPLC with Post Column Derivatization Source: EPA, 1988 Microbiological Contaminants Methods are available for detecting the presence of almost any microorganism of concern, although difficulties can arise in collecting samples, determining frequency and sample sites, and interpreting the relationship between positive samples and public health (Hurst et al., 1997). Bacteria While cultivation techniques are well developed for enteric bacterial indicators, such as coliform and fecal coliform bacteria, little attention has been paid to the development of methods for analyzing enteric bacterial pathogens in water.
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--> This is, in part, because of the historical success of using these indicators in preventing the occurrence of most enteric bacterial waterborne disease outbreaks. In general, if pathogens are present in great enough concentrations, they can be assayed directly. However, as discussed in Chapter 1 (see Figure 1-1), the causative pathogens of more than half of reported waterborne disease outbreaks are then identified. Three basic methods are used for detection and enumeration of bacteria in environmental samples (Toranzos and McFeters, 1997): (1) most probable number (MPN), (2) membrane filter (MF), and (3) presence-absence (PA). The MPN method measures the growth of organisms taken from a sample (or a serially diluted sample) on (usually) selective media through production of turbidity, acid, or gas. When the positive tubes have been identified and recorded, it is possible to estimate the number of organisms in the original sample by using an MPN table that gives the number of organisms per certain volume. MPN methods are very labor intensive and require large amounts of media and glassware, and, in the case of pathogens, may require several days to complete. In the MF test, a given volume of liquid is passed through a filter with a pore size less than the diameter of the bacteria, and then the filter is placed on the growth media. The bacteria then grow on the surface of the membrane as individual colonies. This method is more accurate, less time consuming, and more rapid than the MPN method. Lastly, PA tests, while not quantitative per se, can answer the simple question of whether the target organism is present in a sample. Since some standards require the absence of an indicator or pathogen in a certain volume (e.g., 0 coliforms per 100 ml of drinking water), the PA method can be used as a pass/fail screening test. For the most part, culturable analytical methods have been used for bacteria, however, in some cases, only a small percentage of the total viable organisms present may be detected using these methods of bacterial detection (Colwell et al., 1996). Microscopic techniques, such as the use of antibodies, genetic probes, image analysis, and flow cytometry, have become highly sophisticated, specific, and rapid for the detection of bacteria (Lawrence et al., 1998). Staining with specific genetic probes can address not only total bacterial numbers but the genetic composition and taxonomic status of populations. Thus, the state of the microorganism, as well as its identification, can now be ascertained. Applications for digital microscopy include quantification, viability, metabolic condition, as well as the structure of the microenvironment. However, more emphasis needs to be placed on sample concentration and the use of more specific techniques for bacteria such as Helicobacter, which cannot be cultured. Viruses Methods for virus detection in water depend on their concentration in volumes ranging from 10 to 2,000 liters. This is accomplished by the adsorption of
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--> the viruses to positively charged filters, which adsorb the negatively charged viruses from water (Sobsey and Glass, 1980). Adsorbed viruses are eluted from the filters with a protein solution and further concentrated to a final volume by precipitation of the proteins before assay. These concentrates are assayed in animal cell cultures of human or primate origin. The presence of the virus is indicated by production of cytopathogenic effects (CPE) (the destruction of the individual cells) or formation of plaques or clear zones produced by the destruction of cells under an agar overlay. The isolated viruses are identified by serological neutralization tests. Currently, viral cultivation methods have largely been optimized for the detection of enteroviruses, and little information is available on other types of viruses that may be present at equal or greater concentrations in drinking water. The filters used to concentrate viruses from water do not concentrate all types of viruses with equal efficiency because of differences in charge on the different types of viruses (Gerba, 1984). Several studies have reported greater concentrations of adenoviruses than enteroviruses (e.g., Grohman et al., 1993) in sewage and sewage-polluted waters. An additional problem is that many viruses (e.g., hepatitis A) may grow in cell culture without the production of CPE. Further, it can take several days to many weeks before the virus produces CPE. A final problem is that sometimes substances are concentrated from the water that are toxic to the cell culture. Additional research is needed to overcome these problems and to develop better techniques for assessing all types of waterborne viruses, not just enteric viruses. Protozoa Protozoan parasites are sufficiently large that they can be observed under a normal light microscope, allowing for detection and quantification, and microscopy remains the traditional method for detecting protozoa. Standard methods have been developed for collection, recovery, and detection of enteric protozoa. Typically, protozoan parasites are collected from large volumes of water by size exclusion through spun filters with a nominal pore size of one micron. These filters also collect suspended matter in the water and this makes visualization of the parasite cysts or oocyst difficult to observe (Rose et al., 1989; LeChevallier and Trok, 1990). To separate parasites from debris, the filters are cut apart and washed with an eluting solution of detergent. The eluate containing the cysts/oocysts and debris is further concentrated by centrifugation, where centrifugation separates the cysts/oocysts from much of the debris. The semi-purified sample is collected from the gradient and labeled with monoclonal antibodies specific to the cyst or oocyst cell wall using a specific immunofluorescent assay (IFA) procedure. The sample can be examined by epifluorescent microscopy for fluorescence, shape, and size, and by phase contrast or Nomarski
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--> differential interference contrast microscopy for internal features (LeChevallier et al., 1991a,b). The efficiency of recovery for cysts/oocysts for this process has been investigated in detail, with overall recovery rates varying from 28 percent to 86 percent for Giardia and from 5 percent to 68 percent for Cryptosporidium (LeChevallier et al., 1995; Nieminski et al., 1995). However, current methods for recovering and detecting parasites always underestimate the true concentration in environmental samples. While the use of IFA greatly aids the detection of cysts/oocysts, background fluorescence and nonspecific binding of the antibody may decrease their accurate identification. Another limitation is that no single antibody has been found to bind specifically only to species that cause infection in humans; thus, protozoa infecting only lower animals may also be detected. An added problem is that the viability of the cysts/oocysts cannot be assessed by IFA. LeChevallier et al. (1991a) reported that 10 percent to 30 percent of the organisms found in water samples were empty, without internal features, suggesting they were not viable. It is not clear whether this is an artifact of sample processing. New analytical methods are currently under development for improving both the recovery and detection of protozoa as well as interpretation of the results (Jakubowski et al., 1996). Methods using cell culture infectivity have been successfully applied to address the important question of Cryptosporidium viability (Slifko et al., 1997a,b). Immunomagnetic separation (IMS) techniques use antibodies tagged to iron beads and a magnetic system to pull the target oocysts and cysts from the suspension. These techniques have been applied in microscopic detection and polymerase chain reaction approaches (Johnson et al., 1995; Deng et al., 1997). Several IMS kits are now available for Cryptosporidium (e.g. Dynal in Lake Success, NY; Crypto-ScanTM in Portland, ME). The use of in-situ hybridization to identify Cryptosporidium (Lindquist, 1997) has widespread application for identification and detection efforts, because both microscopy and the specificity of the probe can be used. This also allows for such instrumentation as flow cytometry and digital microscopy to be used, which can greatly reduce the analytical time. To improve understanding of the relationship between potential exposure to waterborne oocysts and cysts and public health outcomes, the greatest research need may be in addressing the viability methods. In addition, when, where, and how often to sample for protozoa should be addressed, with corresponding development of guidance. Molecular Techniques Advances in molecular biology have allowed for the development of more rapid, sensitive, and lower-cost approaches to the detection of pathogens in the environment. These methods are designed to detect and analyze the genetic material of the organisms. Since each organism has a unique genetic code, this
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--> can be used not only to identify specific species but also to ''fingerprint" the strain and clone it. Once a new pathogen has been isolated and its nucleic acid analyzed, methods can be rapidly developed for its detection. These methods also offer the potential to detect microorganisms without the need for cultivation. The polymerase chain reaction (PCR) has offered the most promise for the rapid detection of pathogens in the environment and has been used for bacteria, protozoa, and viruses (Johnson et al., 1995; Toranzos, 1997). This method involves the specific amplification of the DNA in the genome of the microorganism with the aid of primers. Primers are fragments of DNA that are complementary to the DNA strain to be amplified (sequences specific to the region of the genome to be amplified). Within a few hours, millions of genome copies are produced. The principle of the method involves the repetitive enzymatic synthesis of DNA. Amplification only takes place if the specific nucleic acid of the target organism is present. PCR has a number of advantages, including (1) specificity of the assay, (2) ability to detect non-cultivable microorganisms, (3) rapidity of the assay (24 hours), (4) ability to conduct multiple assays, and (5) use of automated instrumentation. PCR also has a number of limitations for use directly in environmental samples. First, the maximum volume that currently can be assayed is 0.1 ml. Extracts or concentrates from environmental samples for enteric viruses and protozoa range from 2 ml to 30 ml or more. Thus, further sample concentration is needed (Johnson et al., 1995). Second, environmental samples and concentrates usually contain substances that interfere with detection by masking the target DNA or inhibiting the enzyme reaction. This results in often laborious and time-consuming processing of samples (Abbaszadegan et al., 1993; Schwab et al., 1995; Toranzos, 1997), though it is possible to detect as little as one to two organisms when interfering substances are removed. Lastly, PCR will also detect dead or inactivated microorganisms (Reynolds et al., 1991; Kaucner and Stinear, 1998). Therefore without cultivation procedures it is not possible to assess viability. While PCR could not be used to assess the performance of disinfection processes, it is still useful for assessing occurrence where viability may not be an immediate need. This is the only method available for the detection of some currently uncultivable waterborne pathogens, such as the Norwalk virus. Summary: Conclusions and Recommendations In summary, the committee recommends that EPA use a phased process (see Figure 5-1) for determining which contaminants on the CCL are appropriate candidates for regulatory action and which will require research. The recommended process would proceed as follows: Within approximately one year of completion of the CCL, EPA should conduct a three-part assessment of each contaminant on the CCL. For each
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--> contaminant, the three parts consist of (1) a review of existing health effects data, (2) a review of existing exposure data, and (3) a review of existing data on treatment options and analytical methods. The first part of the assessment should consider data on the contaminant's effects on sensitive populations, such as pregnant women, infants, the elderly, and those with compromised immune systems. While general guidelines for reviewing existing data are possible and are presented in this chapter, an important component of the reviews will be policy judgments by EPA about the significance of the data. After completion of the three-part assessment, EPA should conduct a preliminary risk assessment based on available data identified in the three-part assessment. The risk assessment, which integrates hazard and exposure analyses to estimate the public health implications of the contaminant, should be carried out, even if there are data gaps, to provide a basis for an initial decision about the disposition of the contaminant and to guide research efforts, where needed. The preliminary risk assessment, while a critical step in the process, should not be overly detailed or resource intensive. After completing the preliminary risk assessment for each contaminant, EPA should prepare a separate decision document, that indicates whether the contaminant will be dropped from the CCL because it does not pose a risk, will be slated for additional research (on health effects, exposure, or risk reduction), or will be considered for regulation. The decision document should explain the reasoning for EPA's determination and should be publicly disseminated for comment. Decision documents for contaminants dropped from the CCL should specify the health and exposure data that EPA used to conclude that the contaminant poses little or no risk. When the three-part assessment or preliminary risk assessment identifies important information gaps, EPA should develop a research and monitoring plan to fill such gaps in time to serve as the basis for a revised assessment and decision document before the end of the three-and-a-half-year cycle required by Congress for evaluating contaminants on the CCL. In filling information gaps, EPA should solicit the voluntary participation of industry and others and should use its other authorities (such as those under the Toxic Substances Control Act) to help fill data gaps. Health advisories should be issued for all contaminants remaining on the CCL after completion of an initial set of decision documents. A health advisory is an informal technical guidance document that defines a nonregulatory (i.e., nonenforceable) concentration of a drinking water contaminant at which no adverse health effects are anticipated to occur over specific exposure durations. To provide the public with the best available information about the contaminant, EPA should develop a health advisory for any contaminant for which credible evidence of a risk in drinking water exists, even if existing data are insufficient to develop a full regulation. Contaminants subject to a health advisory may need
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--> additional research and monitoring even after completion of a revised assessment and decision document. Decisions to drop a contaminant from the CCL, to issue a health advisory, or to proceed toward regulation should be based on health risk considerations only. However, EPA should fill data gaps in treatment technologies and analytical methods to avoid delaying regulatory action for contaminants for which current information on treatment and detection is inadequate. In implementing this phased process, EPA should keep in mind that it should act immediately on all contaminants that meet the statutory tests of (1) adversely affecting public health, (2) being known or substantially likely to occur in public water systems with a frequency and at levels that pose a threat to public health, and (3) presenting a meaningful opportunity for health risk reduction. Development of regulations for contaminants that meet these three requirements (which are specified in the SDWA amendments) should not be delayed by implementation of the phased approach. The ability to act quickly and short-circuit the phased evaluation process is especially critical for protecting the public from newly discovered high-risk contaminants. EPA will need to remain flexible in order to be prepared to address such immediate risks. References Abbaszadegan, M., M. S. Huber, C. P. Gerba, and I. L. Pepper. 1993. Detection of enteroviruses in groundwater with the polymerase chain reaction. Applied Environmental Microbiology 59:1318-1324. Anderson, B. C. and M. S. Bulgin. 1981. Enteritis caused by cryptosporidiosis in calves. Veterinary Medicine of Small Animal Clinics 76:865-868. Barker, I. K., and P. L. Carbonell. 1974. Cryptosporidium agni sp.n. from lambs and Cryptosporidium bovis sp.n. from a calf with observations on the oocyst. Z. Parasitenkd. 44:289. Bove, F. J., M. C. Fulcomer, J. B. Klotz, et al. 1995. Public drinking water contamination and birth outcomes. American Journal of Epidemiology 141:850-862. Colwell, R. R., P. Brayton, A. Huq, B. Tall, P. Harrington, and M. Levine. 1996. Viable but nonculturable vibrio cholera 1 revert to a cultivable state in the human intestine. World Journal of Microbiology and Biotechnology 12:28-31. D'Antonio, R. G., R. E. Winn, J. P. Taylor, T. L. Gustafson, W. L. Current, M. M. Rhodes, G. W. Gary, and R. A. Zajac. 1985. A waterborne outbreak of cryptosporidiosis in normal hosts. Annals of Internal Medicine 103:886-888. Deng, M. Q., D. O. Cliver, and T. W. Mariam. 1997. Immunomagnetic capture PCR to detect viable Cryptosporidum parvum oocysts from environmental samples. Applied and Environmental Microbiology 63(8):3134-3138. EDSTAC (Endocrine Disruptor Screening and Testing Advisory Committee). 1998. Final Report: Volume I. August 1998. EPA (U.S. Environmental Protection Agency). 1979. National Interim Primary Drinking Water Regulations; Control of Trihalomethanes in Drinking Water; Final Rule. Federal Register 44(231):68624-68707. EPA. 1984. Aldicarb; Special Review of Pesticide Products Containing Aldicarb. Federal Register 49(134):28320-28323.
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Representative terms from entire chapter: