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Keeping Pace with Science and Engineering. 1993. Pp. 141-164. Washington, DC: National Academy Press. Trihalomethanes and Other By-Products Formed by Chlorination of Drinking Water Philip C. Singer Chlorine has been used to disinfect drinking water in the United States and in most of the world since 1908. Its widespread use has been credited with the control of a number of waterborne diseases, most notably typhoid fever and cholera. However, with the discovery in 1974 of trihalomethanes (THMs) in chlorinated drinking water and, subsequently, other halogenated disinfection by-products with potential adverse health impacts, the practice of chlorination has been seriously questioned. Trihalomethanes in finished drinking water have been regulated in the United States since 1979 and the U.S. Environmental Protection Agency (EPA) is considering adopting more stringent regulations for THMs; it may also establish maximum contaminant levels or treatment techniques for several other disinfection by-products (DBPs). This paper reviews the scientific findings associated with the formation of THMs and other disinfection by-products and discusses how these find- ings have affected strategies for controlling these by-products in drinking water, and the corresponding improvement in the protection of public health. There are a number of confounding issues associated with the management and regulatory strategies for controlling THMs and the other disinfection by-products; these confounding factors are included in the discussion. CHRONOLOGY OF SCIENTIFIC FINDINGS Figure 1 presents a chronology of the more noteworthy scientific find- ings involving the formation of THMs and other disinfection by-products 141

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142 Science and Engineering - THMs discovered in chlorinated drinking water - First of many epidemiological studies linking cancer and the consumption of chlorinated drinking water ~ 1 970 - EPA conducts National Organics ~ 1975 Reconnaissance Survey - National Cancer Institute identifies chloroform - ~ I as a carcinogen I, in= . - Natural organic material (humic substances)- ~ identified as principal precursors of THMs ~ 1 c 80 1 EPA conducts National Organics Monitoring Survey Di - and trichloroacetic acids identified from chlorination of natural organic material and in chlorinated drinking water. Other disinfection by- products identified, as well. Evidence that THMs comprise only a fraction of the total organic halides. - l Di - and trichloroactic acids identified as animal carcinogens Metropolitan Water District of Southern California conducts nationwide survey of disinfection by-products in drinking water BrO3 discovered as a significant by-product I of ozonation of Br-containing waters I' LeChevatiier discovers that Glardia ! occurrence may be greater than initially believed PHILIP C. SINGER Policy and Regulation - ~- Congress legislates Safe Drinking Water Act - EPA issues advance notice of proposed rulemaking for organic chemicals in water - ~- EPA proposes maximum contaminant level for total THMs - ~-THMs regulated Utilities serving more than 75,000 people must comply with THM rule - Utilities serving from 10,000 to 75,000 must comply with THM rule - EPA proposes treatment techniques to comply with maximum contaminant level for total THMs _ _ _ 1 985 - - Congress legislates SDWA amendments - EPA proposes Surface Water Treatment Rule - EPA proposes Total Coliform Rule ,___ ~ - AWWARF survey determines impact of THM ,===- _ ~ regulation onwaterutilities - EPA finalizes Surface Water Treatment Rule ' ,- 19 go - EPA finalizes Total Coliform Rule l ~ - EPA initiates approach to balance microbial risks and risks associated with disinfection by-products _ _ _ _ _ L EPA originally expected to establish maximum contaminant levels for additional disinfection by-products and more stringent maximum contaminant levels for THMs; proposed rule delayed until 1993 EPA considers ~enhanced" Surface Water Treatment Rule - EPA requests negotiated rulemaking (RegNeg) for disinfection by-products FIGURE 1 Timeline of significant scientific and regulatory events for trihalo- methanes and other chlorination by-products. .

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THMs AND OTHER DISINFECTION BY-PRODUCTS 143 generated during the treatment of drinking water. Trihalomethanes were first identified in finished drinking water in 1974, both in the Netherlands in Rotterdam (Rook, 1974) and in the United States in New Orleans, Louisi- ana (Bellar et al., 1974~. Their presence was linked to the practice of chlorinating water. In 1975 the U.S. Environmental Protection Agency con- ducted the National Organics Reconnaissance Survey of 80 cities in the United States and found that the four THMs chloroform (CHC13), bromo- dichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl), and bromoform (CHBr3) occurred widely in chlorinated drinking water and resulted from the practice of chlorination (Symons et al., 1975~. Figure 2 shows that in the 80-city survey, total trihalomethane concentrations in the finished drink- ing water correlated with the nonpurgeable organic carbon concentrations in the raw water. From March 1976 to January 1977 the EPA conducted the National Organics Monitoring Survey, which verified the findings of the earlier survey, and demonstrated that THMs continued to form to a signifi- cant extent in the finished water distribution system (Brass et al., 1977~. 4.0 _ 3 o - ~n a) a) 2.0 ct . _ .0 _ co 0 1.0 . . ~ . ...W ..S~. o 0 5 10 15 20 Nonpurgeable Organic Carbon (mg/L) FIGURE 2 Relationship between trihalomethane formation in finished water and nonpurgeable organic carbon in source water. SOURCE: Symons et al. (1981~. -

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44 PHILIP C. SINGER A number of studies conducted in the late 1970s and early 1980s indi- cated that many other halogenated by-products also formed in drinking wa- ter as a result of chlorination, in addition to the TlIMs. These studies were conducted by chlorinating raw drinking water and humic material, the prin- cipal organic component of most natural waters, and by making measure- ments in finished drinking water. The most frequently identified disinfec- tion by-products, in addition to the THMs, were di- and trichloroacetic acid, di- and trichloroacetonitrile, chlorinated ketones, chloral hydrate, and chlo- ropicrin (e.g., Christman et al., 1983; Coleman et al., 1984; Miller and Uden, 1983; Oliver, 1983; Quimby et al., 1980; Reckhow and Singer, 1984: Rook, 1977; Trehy and Bieber, 1981~. Numerous other halogenated disin- fection by-products have been identified, but with less frequency and at trace levels (e.g., Stevens et al., 1989~. The formation of halogenated disin- fection by-products from the reaction between chlorine and natural organic material (NOM) is given by the following general equation: C1' + NOM ~ CHC1~ + Other THMs + Other DBPs - Despite the fact that researchers have identified hundreds of haloge- nated disinfection by-products in chlorinated water, the total concentration of those compounds that have been quantified amounts to only about 50 percent of the total organic halide (TOX) content (e.g., Christman et al., 1983; Reckhow and Singer, 1984; Singer and Chang, 1989~. By separately measuring the total organic halide concentration in chlorinated water using an adsorption/pyrolysis/coulometric detection procedure (Standard Methods, 1985), researchers have demonstrated that the sum of the measured THMs, haloacetic acids (HAAs), haloacetonitriles, etc., when converted to chlo- rine-equivalent concentrations, accounts for only about 50 percent of the measured total organic halide concentration, also in chlorine-equivalent units. This means that approximately half of the halogenated disinfection by-prod- ucts consist of unidentified halogenated compounds. In 1988-89 the Metropolitan Water District of Southern California and James M. Montgomery Consulting Engineers, in a project jointly sponsored by the EPA, the California Department of Health Services, and the Associa- tion of Metropolitan Water Agencies, conducted the most comprehensive survey of disinfection by-products in finished drinking water to date (Krasner et al., 1989; McGuire et al., 19891. The investigators analyzed finished drinking water in 35 utilities nationwide, 10 of which were in California, for a variety of disinfection by-products for which analytical techniques were available (see Table 1~. The study was directed at detecting disinfec- tion by-products, seasonal patterns in their formation, the effects of raw water quality on the levels and distribution of the by-products analyzed, and effects of treatment modifications on by-product formation.

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THMs AND OTHER DISINFECTION BY-PRODUCTS TABLE 1 Targeted Compounds in Nationwide Disinfection By-Product Survey Trihalomethanes Chloroform Bromodichloromethane Dibromochloromethane Bromoform Haloacetic acids Chloroacetic acid Dichloroacetic acid Trichloroacetic acid Bromoacetic acid Dibromoacetic acid Haloacetonitriles Dichloroacetonitrile Trichloroacetonitrile B romochloro ace ton itril e Dibromoacetonitrile Haloketones 1, 1 -dichloropropanone 1,1, 1 -trichloropropanone Miscellaneous chloro-organics Chloropicrin Chloral hydrate Cyanogen chloride 2,4,6-trichlorophenol Aldehydes Formaldehyde Acetaldehyde SOURCE: McGuire et al. (1989). 145 The results of this survey indicated that THMs were the by-products present in the highest concentrations in finished drinking water, with the haloacetic acids present at approximately 50 percent of the total THM con- centration. The mean and median total THM concentrations were 39 and 36 micrograms/liter (,ug/L), respectively, while the median total haloacetic acid concentration was 17 ,ug/L. fRecent research by J.M. Montgomery Consult- ing Engineers (1992) and Singer et al. (1992) suggests a higher ratio of haloacetic acids to trihalomethanes.] A number of water samples had sig- nificant concentrations of by-products containing bromine because the source waters had high concentrations of bromide ion.

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146 PHILIP C. SINGER As a result of all of these findings, epidemiologists and toxicologists have conducted numerous studies in an attempt to evaluate the impact of chlorination on public health and, particularly, the health effects of the specific halogenated disinfection by-products that have been identified. A large number of epidemiological studies have been conducted in the United States since 1974. These studies have repeatedly shown a weak association between the chlorination of drinking water and an increased incidence of cancer, but a causal relationship between exposure to chlorinated drinking water and cancer has not be established (Craun, 1991~. Most of the histori- cal studies have demonstrated weak relationships between bladder, colon, and rectal cancers and the consumption of chlorinated drinking water, but more recent studies have also shown evidence of relationships between pan- creatic cancer (IJsselmuiden et al., 1992) and birth defects (Bove et al., 1992a,b) with the consumption of chlorinated drinking water. Although there is no single study that can be cited as a seminal study linking chlori- nation and cancer, it is the sheer weight of evidence provided by the large number of studies showing a positive relationship, albeit a weak one, that underscores the concern, from a cancer risk perspective, about the safety of drinking chlorinated water (Morris et al., 1992~. These epidemiological studies have been extensively reviewed by Bull and Kopfler (1991), Craun (1988, 1991), and the National Research Council (NRC, 1980, 1987~. From a toxicological viewpoint, chloroform has been shown to induce liver tumors in mice and kidney tumors in rats (Jorgenson et al., 1985; National Cancer Institute, 1976~. Bromodichloromethane has been shown to induce renal tumors in mice and rats, liver tumors in mice, and intestinal tumors in rats (National Toxicology Program, 1986~. Bromoform produced intestinal tumors in male and female rats (National Toxicology Program, 1989~. Dichloroacetic acid and trichloroacetic acid induced the formation of hepatic tumors in mice (Bull et al., 1990; Herren-Freund et al., 1987~. Accordingly, based on these animal studies, it can be concluded that a number of halogenated by-products formed during the chlorination of drink- ing water are probable human carcinogens. The National Research Council (1987) and Bull and Kopfler (1991) recently reviewed and profiled the health effects of a number of disinfectants and disinfection by-products. Accord- ing to Bull and Kopfler (1991), the only halogenated by-products that ap- pear to approach concentrations of regulatory concern in chlorinated drink- ing water are the four THMs, di- and trichloroacetic acid, chloropicrin, and trichlorophenol, although the EPA has generated a different list of candidate compounds for regulation, as illustrated in Table 2 (Regli et al., 1992~. Another class of halogenated by-products, the halogenated furanones, exemplified by MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2~5H)-furanone], have been found in chlorinated drinking water (Kronberg et al., 1988) at concentrations on the order of 50 nanograms/liter (0.050 ,ug/L). Despite _~

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THMs AND OTHER DISINFECTION BY-PRODUCTS TABLE 2 Candidate Disinfection By-Products for Regulation 147 Possible Maximum Health Effects and Contaminant Level Compound Cancer Status Goal Trihalomethanes Chloroform Cancer, B2 0 Bromodichloromethane Cancer, B2 0 Dibromochloromethane Liver, C 60 ,ug/L Bromoform Cancer, B2 0 Haloacetic Acids Trichloroacetic Acid Liver, C 100 ,ug/L Dichloroacetic Acid Cancer, B2 0 Other Chloral Hydrate Liver, C 5 ,ug/L Bromate Cancer, B2 0 Chlorine Blood, D 4 mg/L Chloramines Blood, D 4 mg/L Chlorine Dioxide Blood, Neurological, D 0.8 mg/L Chlorite Blood, D 0.3 mg/L CODE: B2 = Probable human carcinogen; C = Possible human carcinogen; D = Inadequate or no evidence of human or animal carcinogenicity SOURCE: Regli et al. (1992). their low concentrations, they have been shown to be responsible for up to 50 percent of the mutagenicity of chlorinated drinking water. The signifi- cance of this class of compounds to public health has been questioned, however, because of the likelihood that they are detoxified in mammalian systems following ingestion. The link between mutagenicity and human carcinogenicity is a subject of scientific debate. In fact, interpretations of the health effects studies overall have been extensively criticized by scientists, engineers, and water utility managers. In 1991 the International Agency for Research on Cancer concluded that there was inadequate evidence for the carcinogenicity of chlorinated drink- ing water in humans or laboratory animals and that chlorinated drinking water was not classifiable as to its carcinogenicity (World Health Organiza- tion, 1991~. The issues involve the weakness of the reported epidemiologi- cal relationships between cancer and consumption of chlorinated drinking water, the high dosages of test compounds administered to laboratory ani- mals to induce tumors, and the validity of the models used to extrapolate from these high dosage effects to the low concentrations at which these compounds are found in drinking water. These are issues common to many -

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148 PHILIP C. SINGER environmental contaminants. There is little question that estimation of the public health risk involved in consuming chlorinated drinking water and in establishing maximum contaminant levels for disinfection by-products is fraught with uncertainty. CHRONOLOGY OF REGULATORY ACTIONS The chronology of regulatory actions taken in response to the scientific discoveries concerning the formation of trihalomethanes in chlorinated drinking water and the associated health concerns is also shown in Figure 1. Follow- ing passage of the Safe Drinking Water Act by Congress in 1974 and the findings of the National Organics Reconnaissance Survey, the Environmen- tal Protection Agency published its advance notice of proposed rulemaking on July 14, 1976 to address control options for organic chemical contami- nants in drinking water (EPA, 1976~. Two approaches were considered: establishing maximum contaminant levels for specific organic chemicals or for surrogates (indicators) of these organic chemicals, and establishing des- ignated treatment techniques to control specific organic contaminants or their surrogates. On February 9, 1978, the EPA published a proposed rule to amend the National Interim Primary Drinking Water Regulations to include a maxi- mum contaminant level and associated monitoring and reporting require- ments for total trihalomethanes (EPA, 1978~. At the same time, the EPA proposed a requirement for the use of granular activated carbon or equiva- lent technology for application to drinking water that was presumed to be vulnerable to contamination by synthetic organic chemicals of industrial . . Orlgln. Following a period of public comment, on November 29, 1979, the EPA adopted its final rule for the control of THMs in drinking water (EPA, 19791. The rule amended the National Interim Primary Drinking Water Regulations by establishing a maximum contaminant level for total THMs of 0.10 milligrams/liter (mg/L) (100 ,ug/L). For community water systems serving 75,000 or more persons, the effective date of compliance with the maximum contaminant level was November 29, 1981, and for community water systems serving 10,000 to 75,000 persons, the effective date of com- pliance with the maximum contaminant level was November 29, 1983. Com- pliance for systems serving fewer than 10,000 customers was left to the discretion of the individual states. The THM rule also established monitor- ing and reporting requirements that revolved around the collection and analysis of samples from representative locations in the water distribution system on a quarterly basis. The rule stipulated that the running annual average of the arithmetic sum of the concentrations of all four TlIM species had to be less than or equal to 0.10 mg/L. - .

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THMs AND OTHER DISINFECTION BY-PRODUCTS 149 The earlier proposed requirement for the use of granular activated car- bon for vulnerable water supplies was not included in the final THM rule, but was subsequently adopted as part of EPA's regulations controlling syn- thetic organic chemicals in drinking water. tThe Safe Drinking Water Act Amendments of 1986 declared granular activated carbon treatment to be the best available technology (BAT) for the control of synthetic organic chemi- cals.] The EPA's selection of an interim maximum contaminant level of 0.10 mg/L was based on balancing public health considerations against the tech- nological and economic feasibility of limiting total THM concentrations to such levels in public water systems in the United States. In addition, the limited data base available at that time, from the standpoint of both occur- rence and health effects, prevented the EPA from establishing individual maximum contaminant levels for each of the four THM species. Finally, the EPA did not extend the maximum contaminant level to community water systems serving fewer than 10,000 persons because of concerns about the technical and economic feasibility of such systems being able to comply with the rule without jeopardizing their disinfection practices and putting their customers at an increased risk of waterborne diseases. It was assumed that many water utilities would ultimately be able to achieve total THM concentrations as low as 0.010 to 0.025 mg/L (10-25 ,ug/ L), and EPA suggested these values as future goals to be considered in the Revised National Primary Drinking Water Regulations. On February 28, 1983, in accordance with the stipulations of the Safe Drinking Water Act, the EPA identified the best technology and treatment techniques that community water systems could use to achieve compliance with the maximum contaminant level for total THMs (EPA, 1983~. These techniques were believed to be "generally available, taking costs into con- sideration." The specific techniques identified were the use of chloramines or chlorine dioxide as alternative or supplemental disinfectants and oxi- dants, improved clarification for THM precursor removal, moving the point of chlorination to reduce THM formation, and the use of powdered activated carbon to remove THMs or THM precursors. Additional techniques not determined to be "generally available" included the use of ozone as an alternative or supplemental disinfectant or oxidant, aeration for THM re- moval, off-line water storage, consideration of alternative sources of raw water, and implementation of clarification if not currently practiced. Following promulgation of the THM rule and the setting of a maximum contaminant level for total THMs in finished drinking water, the water treat- ment industry responded by adopting practices to limit THM formation. The principal treatment modifications involved moving the point of chlori- nation downstream in the water treatment plant, optimizing the coagulation process to enhance the removal of THM precursors, and using chloramines

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150 PHILIP C. SINGER to supplement or replace the use of free chlorine. Young and Singer (1979) had shown that moving the point of chlorine application from the raw water to a location after clarification could reduce THM formation by approxi- mately 40 percent. A number of other researchers (e.g., Babcock and Singer, 1979; Johnson end Randtke, 1983; Kavanaugh, 1978; Semmens end Field, 1980) had demonstrated that up to 75 percent of the THM precursors could be removed by coagulation, sedimentation, and filtration if the coagulant dose and pH were optimized. Other researchers (e.g., Brodtmann et al., 1980; Duke et al., 1980; Lange and Kawczynski 1978; Norman et al., 1980) had shown that the addition of ammonia to water containing chlorine essen- tially stopped the subsequent formation of THMs. This made the use of chloramines a very simple, inexpensive, and therefore attractive approach for limiting THM formation. However, because chloramines are a much weaker disinfectant than free chlorine, concern about compromising the microbiological quality of drinking water became an important issue. McGuire and Meadow (1988) surveyed 727 water utilities for the American Water Works Association Research Foundation (AWWARF) to determine the extent to which utilities were in compliance with the maximum contami- nant level for total THMs, and the cost of achieving such compliance. The results showed that enactment of the THM regulation resulted in a 40-50 percent average reduction in total THM concentrations for the larger utili- ties surveyed. The median total THM concentration among all the respon- dents was 38 ~g/L, a value not much different than the results of EPA's National Organics Reconnaissance Survey (Symons et al., 1975) or the Na- tional Organics Monitoring Survey (Brass et al., 1977~. The principal dif- ferences were that the utilities with high THM levels were able to reduce their THM concentrations substantially, as shown in Figure 3. Of those systems that implemented THM control measures, the majority did one or more of the following things: (1) modified their pointers) of chlorine applica- tion, (2) changed their chlorine dosages, and (3) adopted the use of chloramines to ensure compliance with the maximum contaminant level for total THMs. A large number of utilities changed from free chlorine to chloramines as their primary disinfectant. Table 3 summarizes the treatment modifications made by the utilities included in the survey. Although compliance with the 0.10 mg/L (100 ,ug/L) maximum contaminant level was found to be not particularly costly, it was concluded that reducing the maximum contami- nant level significantly below 50 ~g/L would cause a large number of utili- ties to exceed the maximum contaminant level and would require extensive capital expenditures to bring these utilities into compliance with such a more stringent value. In summary, the scientific findings on THMs and other halogenated disinfection by-products in chlorinated drinking water led to health effects studies that showed that chloroform and other disinfection by-products were

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THMs AND OTHER DISINFECTION BY-PRODUCTS 1 ,000 500 u, 100 a) o . _ 50 10 5 O 151 NOMS all ~ .fK~iNiORS phases avert 1/ l 10 30 50 70 90 95 99 99.9 99.99 1 AWWARF utility survey Percentage Less Than or Equal to Given Concentration FIGURE 3 Frequency distribution of survey data from American Water Works Association Research Foundation (AWWARF) Utility Survey compared with the National Organics Reconnaissance Survey (NORS) and the National Organics Mon- itoring Survey (NOMS). SOURCE: McGuire and Meadow (1988~. Reprinted from the Journal of the American Water Works Association by permission. Copyright @) 1988, American Water Works Association. carcinogenic in laboratory animals and that people drinking chlorinated wa- ter might be at somewhat greater risk in developing bladder, colon, and rectal cancer than those consuming unchlorinated drinking water. Addi- tional scientific findings involving the formation and behavior of THMs and the other disinfection by-products led to the development of water treatment strategies to limit the formation of halogenated disinfection by-products. The enactment of the THM regulation resulted in treatment modifications that subsequently reduced the extent of THM formation and, most likely, of many of the other disinfection by-products as well, thereby lowering the public health risk associated with THMs and the consumption of chlori- nated drinking water. Implementation of some of these modifications, how- ever, may have compromised the microbiological quality of drinking water (see later discussion). ;'

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54 PHILIP C. SINGER At the heart of the Surface Water Treatment Rule is the CT concept, which specifies that a sufficient concentration (C) of disinfectant must per- sist in the water for a satisfactory contact time (T) in order to ensure an adequate degree of inactivation. CT values were developed from experi- mental results for a variety of disinfectants, specifically free chlorine, chloramines, chlorine dioxide, and ozone, for a variety of solution condi- tions (e.g., pH and temperature), and for various degrees of inactivation of Giardia and viruses. CT credit of 2- to 2.5-log removal (99 to 99.7 percent) for Giardia and 1- to 2-log removal (90 to 99 percent) for viruses were allocated to surface water treatment systems practicing filtration, with the remaining degrees of inactivation of the two groups of organisms to be achieved by chemical disinfection. Another key aspect of the Surface Water Treatment Rule that affected the disinfection by-product issue was the requirement that a disinfectant residual of at least 0.2 mg/L must be maintained at all times in the water entering the distribution system, and measurable disinfectant residuals must be achieved in more than 95 percent of the distribution system samples analyzed. The Total Coliform Rule was also initially proposed in 1987 (EPA, 1987b) and finalized in 1989 (EPA, 1989b). This rule also mandated greater attention to disinfection practices, particularly with regard to maintaining the biological quality of treated water in the distribution system. A significant impact of the disinfection requirements of both the Sur- face Water Treatment Rule and the Total Coliform Rule was that many of the water utilities, such as those surveyed by McGuire and Meadow (1988), which had previously modified their disinfection practices to comply with the 1979 THM regulation might not be in compliance with the CT or re- sidual disinfectant requirements of the Surface Water Treatment Rule and the various stipulations of the Total Coliform Rule. This was especially true for those utilities that adopted chloramination for primary disinfection. Accordingly, the population served by these utilities was potentially being exposed to a greater microbial risk as a result of modified disinfection practices. Furthermore, even without the Surface Water Treatment Rule and Total Coliform Rule, most of the utilities surveyed by McGuire and Meadow indicated they would have difficulty complying with a maximum contami- nant level for total THMs significantly below 50 ,ug/L. Clearly, given the stringent provisions of the two new rules, reduction of the maximum con- taminant level to less than 50 ,ug/L would be expected to have an even greater economic impact than that projected by the McGuire and Meadow survey. Hence, in developing national regulations for the control of disinfec- tants and disinfection by-products, the EPA must ensure that the maximum contaminant levels established for the disinfectants and disinfection by ~.

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THMs AND OTHER DISINFECTION BY-PRODUCTS 155 products are consistent with the requirements of the Surface Water Treat- ment Rule, the impending Groundwater Disinfection Rule (EPA, 1992a), and the Total Coliform Rule in that they do not cause changes in water treatment practices that result in significant increases in risk from waterborne pathogens or from other disinfection by-products that do not get regulated at that time. Furthermore, as stated above, the new regulations would have to apply to all public water systems using disinfection, not just to those serving more than 10,000 persons. In developing the maximum contaminant levels for disinfection by- products, EPA's approach has been to consider various THM concentrations as maximum contaminant levels, evaluate different treatment options that could meet these maximum contaminant levels, determine the costs associ- ated with these options, and establish an appropriate maximum contaminant level for the THMs with corresponding treatment technologies to achieve compliance. The focus has continued to be directed at THMs because of the greater availability of data on occurrence, toxicological effects, and treat- ment control methodologies, although increasing amounts of data are being generated for the haloacetic acids in response to their perceived significance from an occurrence and health effects point of view. Because chloroform, bromodichloromethane, bromoform, and dichloro- acetic acid are tentatively classified as probable human carcinogens based on the latest toxicological information (Regli et al., 1992), the Safe Drink- ing Water Act essentially requires the EPA to set the maximum contaminant level goals for these compounds at zero. The Safe Drinking Water Act also requires the EPA to set the actual maximum contaminant levels as close to the maximum contaminant level goal as is technologically and economically feasible to achieve. For carcinogenic compounds that have a maximum contaminant level goal of zero, the EPA attempts to establish maximum contaminant levels at concentrations which ensure that the average indi- vidual lifetime risk of acquiring cancer through exposure to these com- pounds in drinking water is no more than one in ten thousand to one in a million (equivalent to a 10-4 to 10-6 risk). For those chlorinated disinfection by-products tentatively classified as probable human carcinogens, Table 4 lists the drinking water concentrations corresponding to 10-4, 1O-5, and 10-6 increased lifetime cancer risks (Regli et al., 1992), along with the reported range of occurrence. Given the mea- sured concentrations of these disinfection by-products in drinking water, it is clear that utilities would have great difficulty complying with maximum contaminant levels for the THMs at anything more stringent than a 10-5 risk level, and a maximum contaminant level for dichloroacetic acid (DCAA) at anything more stringent than a 10-4 risk level. While it might be possible to achieve maximum contaminant levels corresponding to these risk levels by reducing the dose of chlorine for drinking water treatment, the Surface

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156 PHILIP C. SINGER TABLE 4 Drinking Water Concentrations Associated with Various Levels of Increased Lifetime Cancer Risk Disinfection Concentration (,ug/L) Range of By-Product 10-4 10-5 10-6 Occurrence (pg/L) . Bromodichloromethane 100 10 1 0-100 Bromoform 400 40 4 0-50 Chloroform 600 60 6 0-340 Dichloroacetic acid 10 1 0.1 0-80 SOURCE: Regli et al. (1992). Water Treatment Rule prevents this from happening by requiring strict ad- herence to CT values and disinfectant residuals that would ensure compli- ance with the specified levels of pathogen inactivation and the correspond- ing reduction in microbial risk. Alternatively, other disinfectants could be used in place of free chlorine to meet the requirements of the Surface Water Treatment Rule, but these alternatives are not without their own health risks. For example, the use of chlorine dioxide results in the presence of chlorite (ClO2-) and chlorate (ClO3-) in the treated water (Rav-Acha et al., 1984; Werdehoff and Singer, 1987~. Chlorite is formed as a by-product from the reaction of chlorine dioxide, and both chlorite and chlorate are frequently found as contaminants in chlorine dioxide feed streams (Griese et al., 19911. Chlorite has been found to be toxic in animals (Court et al., 1982), and a maximum contami- nant level goal of 0.3 mg/L has been suggested (Regli et al., 1992~. In the case of ozone, the principal by-products appear to be aldehydes such as formaldehyde, acetaldehyde, glyoxal, and methyl glyoxal (Glaze et al., 1991~. There is not enough information at this time to ascertain the health risks of exposure to these chemicals in drinking water. However, in water containing bromide, ozonation can lead to the formation of undesir- able levels of bromate (BrO3~) and brominated organic by-products such as bromoform, dibromoacetic acid, etc. (Amy and Siddiqui, 1991; Krasner et al., 1993~. Bromate is also tentatively classified as a probable human car- cinogen, with a 5 ,ug/L concentration in drinking water corresponding to a 10-4 individual lifetime cancer risk, and 0.5 ,ug/L (below most analytical detection limits) for a 10-5 risk (Regli et al., 1992~. Therefore, while ozone is a more potent disinfectant than free chlorine, its widespread applicability may be limited by the bromide content of the source water and the corre- sponding formation of bromate. In addition, because ozone is relatively unstable in water, a secondary disinfectant is required in order to maintain a disinfectant residual in the distribution system.

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THMs AND OTHER DISINFECTION BY-PROD UCTS 157 The use of chloramines in place of free chlorine to minimize disinfec- tion by-product formation is limited because of their poor virucidal and cysticidal properties, that is, the high CT requirements make chloramines impractical for primary disinfection in most cases. Chloramines still re- main an attractive option for secondary disinfection, that is, for maintaining a persistent disinfectant residual in the distribution system. Also, the application of alternative primary disinfectants may enhance the formation of some by-products during secondary disinfection. For ex- ample, ozonation leads to high concentrations of chloral hydrate when the secondary disinfectant is free chlorine (Logsdon et al., 1992; McKnight and Reckhow, 1992~. Some additional confounding factors involve the emergence of crypto- sporidiosis as a major waterborne disease; several outbreaks have occurred within the past five years (Rose, 1988~. Although they were not considered in the development of the Surface Water Treatment Rule, Cryptosporidium cysts have been found to be appreciably more resistant to conventional disinfectants than Giardia, and higher CT values may be required to inacti- vate this organism. Such CT criteria are still in the developmental stage. In addition, LeChevallier et al. (1991) have recently reported that concentra- tions of Giardia and Cryptosporidium cysts in raw drinking water may be orders of magnitude higher than originally expected. Although the infectiv- ity of the cysts was not verified, these findings suggest that the specifica- tions for 3-log and 4-log inactivation or removal of Giardia and viruses, respectively, in the Surface Water Treatment Rule may not be restrictive enough to reduce the risk of exposure to these waterborne diseases to levels that EPA deems acceptable. Accordingly, the EPA is considering adopting an "enhanced" Surface Water Treatment Rule. If this were done, increased contact times with chlorine or higher doses of chlorine would be required to provide enhanced disinfection. The result would almost certainly be an increase in the formation of halogenated by-products. These considerations draw attention to the conundrum facing water utilities and regulators, that is, while a great deal of attention has been directed at formation of disinfection by-products and reducing the chemical risks asso- ciated with these by-products, insufficient attention has been focused on the microbial risks associated with modified disinfection practices and the pres- ence of disease-causing and disinfection-resistant organisms in raw water supplies. From the standpoint of reducing microbial risk from these infec- tious agents, greater reliance on chlorine and other chemical disinfectants might be desirable despite the increased formation of disinfection by-prod- ucts and their attendant chemical risks. All of the above confounding factors are considered, to some degree, in EPA's Disinfection By-Product Risk Assessment Model (Regli et al., 1992~. The EPA first proposed this model in November 1990 as an innovative

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158 PHILIP C. SINGER approach to balance the risk between exposure to microbial hazards and exposure to disinfectants and disinfection by-products. The approach in- volves (1) identification of candidate best available technologies for con- trolling both disinfection by-products and pathogens; (2) determination of the degree to which these technologies are consistent with the criteria of the Surface Water Treatment Rule and the Total Coliform Rule, and with the potential criteria of an enhanced Surface Water Treatment Rule; (3) evalua- tion of the predicted performance of these candidate best available tech- nologies in a variety of source water qualities (e.g., total organic carbon, bromide concentrations); (4) consideration of candidate maximum contami- nant levels for THMs and haloacetic acids based upon predicted levels that can be achieved by the candidate best available technologies for a reason- able number of water systems; (5) consideration of potential net changes in risk from exposure to both disinfection by-products and pathogens; and (6) the costs to implement such changes. EPA is still developing their risk assessment model for disinfection by- products. Initial predictions indicated that there would be a dramatic in- crease in the incidence of waterborne disease if more stringent maximum contaminant levels for THMs and other disinfection by-products were es- tablished, but there is a vast amount of uncertainty associated with the model, deriving primarily from inadequate scientific (primarily toxicologi- cal and microbiological), technological, and cost information. While the risk assessment modeling approach is a laudable one, it represents a rather ambitious undertaking, given the lack of supporting documentation that is needed for incorporation into the model. In fact, it is the lack of such information in the face of the confounding factors enumerated above that, in large part, has led the EPA to recommend that the disinfection by-product regulations be developed through the pro- cess of negotiated rulemaking (RegNeg). This process is an alternative to traditional rulemaking, in which representatives of all interested parties, including the EPA, meet and collectively develop the proposed rule by con- sensus. The process is managed by a third party that convenes the meetings and oversees the deliberations. On September 15, 1992, the EPA issued a notice of intent to proceed with a negotiated rulemaking (EPA, 1992b). The RegNeg process for disinfection by-products is under way and is scheduled to be completed by mid-1993. DISCUSSION AND CONCLUSIONS There can be no questioning the fact that the regulation of disinfection by-products is a difficult issue. In some ways, the regulatory process for THMs worked effectively, at least in the early stages. Scientific evidence supported the need to control THMs. THMs were found in chlorinated _

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THMs AND OTHER DISINFECTION BY-PRODUCTS 159 water and were produced as a result of the chlorination process. They induced cancers in laboratory animals. Epidemiological studies suggested that people drinking chlorinated water appeared to be subjected to a some- what increased incidence of cancers of the urinary and digestive tracts. Accordingly, THMs were regulated. The result of the regulation was a lowering of THM levels in drinking water at a relatively modest cost. Sci- entific findings led to a regulatory decision that produced a favorable out- come at little cost to society, although there is some question whether the effectiveness of disinfection was adversely affected. All of the above was accomplished over a period of about 10 years. It has been the attempt to fine-tune and expand the original objective, and subsequent recognition that control of the chemical risks associated with disinfection by-products may increase risks associated with disease- causing microorganisms, that has led to the difficulties described in this paper. New analytical techniques have allowed many more contaminants in drinking water to be identified. Some of these contaminants are present in the raw water, and a number are produced by chemicals added to purify the water. Some, like the THMs and haloacetic acids, are present in concentra- tions as high as 50-100 ,ug/L. Most are present at what would be called trace concentrations, that is, less than 10 ,ug/L. Despite the survey by McGuire et al. (1989), there is no comprehensive data base profiling the nationwide occurrence of disinfection by-products in chlorinated drinking water. Among the disinfection by-products, halogenated by-products have been the easiest to identify and quantify analytically, although only about 50 percent of the mass of these halogenated by-products (on a halogen-equiva- lent basis) has been accounted for. Little information is available on the nature of the remaining 50 percent, or the health effects associated with this material. Identification of by-products resulting from the chlorination of water continues to be an active area of analytical research. In addition, the focus of analytical activity on by-products of chlorina- tion does not mean that alternative oxidants and disinfectants do not gener- ate by-products too. Analytical techniques have not advanced to the point where the polar compounds that are invariably produced by these alterna- tive chemical additives such as ozone and chlorine dioxide can be reliably measured. Identification of some of these other by-products is just begin- ning to occur, but it is likely to be a long time before a mass balance on the organic carbon content of finished drinking water can be attempted. Assessment of the health effects of these trace contaminants is probably the major source of scientific uncertainty. Epidemiologically, it cannot yet be concluded that there is a significant cancer risk in drinking chlorinated water. Confident quantification of this risk requires additional study. Toxi

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160 PHILIP C. SINGER cologically, it can be concluded that some of these disinfection by-products cause cancer in laboratory animals when administered in large doses, but questions arise when attempts are made to extrapolate these results to the low exposures associated with drinking water. The scientific basis for mak- ing such low dose extrapolations is still debatable, yet the need is great if reliable risk estimates are to be made. Technologically, it is widely accepted that the formation of THMs and other chlorinated by-products can be lowered by decreasing the use of free chlorine. However, requirements for reliable disinfection of drinking water to control waterborne pathogens are deservedly more stringent than ever before, and likely to become even more stringent. There is a fear among many that lower maximum contaminant levels for THMs and other disinfec- tion by-products may compromise one of the fundamental objectives of water treatment, that is, disinfection. If disinfectants other than free chlo- rine were to be used, there are uncertainties with regard to the public health impact of some of these alternatives, particularly in bromide-containing waters. From a regulatory standpoint, it would not be desirable to establish regulations that would essentially limit the use of free chlorine and force utilities to use alternative disinfectants whose public health risk is more uncertain at this time because of analytical deficiencies. Alternative control options involve the use of technologies that would remove disinfection by-product precursors (natural organic matter) from the water before a disinfectant is added. Technologies for achieving this objec- tive consist of enhanced coagulation, granular activated carbon adsorption, and membrane filtration. The first of these is not effective in all waters, for reasons that are not yet known. Research on this subject is continuing. Using granular activated carbon adsorption to control disinfection by-prod- ucts has been demonstrated to be a relatively expensive process for most waters, and adoption of maximum contaminant levels for disinfection by- products that are based on the use of granular activated carbon as the best available technology is likely to have a major economic impact on society. Opponents of such a requirement cite the high cost of this technology for a questionable societal benefit. Membrane filtration is a relatively new de- velopment in water treatment technology. A number of technical issues must be addressed before this technology can be implemented on a large scale. These include control of membrane fouling, ultimate disposal of the concentrated waste from the process, and efficiency of product recovery. In addition, like granular activated carbon, membrane filtration has a relatively high price tag. EPA's proposal to use a Disinfection By-Product Risk Assessment Model to aid them in the rulemaking process is a logical approach in view of the complexities involved in the disinfection/disinfection by-products issue. Unfortunately, the scientific data base needed to support such an approach - .

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THMs AND OTHER DISINFECTION BY-PRODUCTS 161 at this time is weak. Either more research is needed to provide the missing pieces, and there are a significant number of missing pieces as discussed in this paper, or a compromise position will have to be adopted, as was the case in 1979. The negotiated rulemaking process that is under way is likely to lead to such a compromise position for the short term. The long-term regulation of disinfection by-products must await additional scientific findings. REFERENCES Amy, G.L., and M. S. Siddiqui. 1991. Ozone-bromide interactions in water treatment. Pp. 807-824 in Proceedings of the American Water Works Association Annual Conference. Denver, Colo.: American Water Works Association. Babcock, D. B., and P. C. Singer. 1979. Chlorination and coagulation of humic and fulvic acids. Journal of the American Water Works Association 71(3):149. Bellar, T. A., J. J. Lichtenberg, and R. C. Kroner. 1974. The occurrence of organohalides in chlorinated drinking water. Journal of the American Water Works Association 66:703. Bove, F. J., M. C. Fulcomer, J. B. Klotz, and others. 1992a. Report on Phase IV-A: public drinking water contamination and birthweight, fetal deaths, and birth defects; a cross- sectional study. Trenton, N.J.: New Jersey Department of Health. Bove, F. J., M. C. Fulcomer, J. B. Klotz, and others. 1992b. Report on Phase IVB: Public drinking water contamination and birthweight, and selected birth defects; a case-control study. Trenton, N.J.: New Jersey Department of Health. Brass, H. J., M. A. Feige, T. Halloran, J. W. Mello, D. Munch, and R. F. Thomas. 1977. The national organic monitoring survey: Samplings and analyses for purgeable organic com- pounds. Pp. 393-416 in Drinking Water Quality Enhancement Through Source Protec- tion, R. B. Pojasek, ed. Ann Arbor, Mich.: Ann Arbor Science Publishers. Brodtmann, N. V., W. E. Koffskey, and J. DeMarco. 1980. Studies on the use of combined chlorine (monochloramine) as a primary disinfectant of drinking water. Pp. 777-788 in Water Chlorination: Environmental Impact and Health Effects, Vol III, R. L. Jolley et al., eds. Ann Arbor, Mich.: Ann Arbor Science Publishers. Bull, R. J., and F. C. Kopfler. 1991. Health effects of disinfectants and disinfection by- products. Denver, Colo.: American Water Works Association Research Foundation. Bull, R. J., I. M. Sanchez, M. A. Nelson, J. L. Larson, and A. D. Lansing. 1990. Liver tumor induction in B6C3F1 mice by dichloroacetate and trichloroacetate. Toxicology 63:341- 359. Christman, R. F., D. L. Norwood, D. S. Millington, J. Donald Johnson, and A. A. Stevens. 1983. Identity and yields of major halogenated products of aquatic fulvic acid chlorina- tion. Environmental Science and Technology 17(10):625-628. Coleman, W. E., J. W. Munch, W. H. Kaylor, R. P. Streicher, H. P. Ringhand, and J. R. Meier. 1984. Gas chromatography/mass spectroscopy analysis of mutagenic extracts of aqueous chlorinated humic acid: A comparison of the by-products of drinking water contaminants. Environmental Science and Technology 18(9):674. Couri, D., M. S. Abdel-Rahman, and R. J. Bull. 1982. Toxicological effects of chlorine dioxide, chlorite, and chlorate. Environmental Health Perspectives 46:13. Craun, G. F. 1988. Surface water supplies and health. Journal of the American Water Works Association 80(2):40. Craun, G. F. 1991. Epidemiological studies of organic micropollutants in drinking water. In The Handbook of Environmental Chemistry, O. Hutzinger, ed. Berlin: Springer Verlag. Duke, D. T., J. W. Siria, B. D. Burton, and D. W. Amundsen. 1980. Control of trihalomethanes in drinking water. Journal of the American Water Works Association 72(8):470.

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62 PHILIP C. SINGER Glaze, W. H., H. S. Weinberg, S. W. Krasner, and M. J. Sclimenti. 1991. Trends in aldehyde formation and removal through plants using ozonation and biological active filters. Pp. 913-943 in Proceedings of the American Water Works Association Annual Conference. Denver, Colo.: American Water Works Association. Griese, M. H., K. Hauser, M. Berkemeier, and G. Gordon. 1991. Using reducing agents to eliminate chlorine dioxide and chlorite ion residuals in drinking water. Journal of the American Water Works Association 83(5):56. Herren-Freund, S. L., M. A. Pereira, M. D. Khoury, and G. Olson. 1987. The carcinogenicity of trichloroethylene and its metabolites, trichloroacetic acid and dichloroacetic acid, in mouse liver. Toxicology and Applied Pharmacology 90:183. IJsselmuiden, C. B., C. Gaydos, B. Feighner, W. L. Novakoski, D. Serwadda, L. H. Caris, D. Viahov, and F. W. Comstock. 1992. Cancer of the pancreas and drinking water: A population-based case-control study in Washington County, Maryland. American Journal of Epidemiology 136(7):836. Johnson, D. E., and S. J. Randtke. 1983. Removing non-volatile organic chlorine and its precursors by coagulation and softening. Journal of the American Water Works Associa- tion 75(5):249. Jorgenson, T. A., E. F. Meierhenry, C. J. Rushbrook, R. D. Bull, and M. Robinson. 1985. Carcinogenicity of chloroform in drinking water to male Osborne-Mendel rats and female B6C3F1 mice. Fundamentals of Applied Toxicology 5:760-769. Kavanaugh, M. C. 1978. Modified coagulation for improved removal of trihalomethane precursors. Journal of the American Water Works Association 70(11):613. Krasner, S. W., M. J. McGuire, J. J. Jacangelo, N. L. Patania, K. M. Reagan, and E. M. Aieta. 1989. The occurrence of disinfection by-products in U.S. drinking water. Journal of the American Water Works Association 81 (8) :41. Krasner, S. W., W. H. Glaze, H. S. Weinberg, P. A. Daniel, and I. N. Najm. 1993. Formation and control of bromate during ozonation of waters containing bromide. Journal of the American Water Works Association 85(1):73. Kronberg, L., B. Holmbom, M. Reunanen, and L. Tikkanen. 1988. Identification and quantifi- cation of the Ames mutagenic compound 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)- furanone and of its geometric isomer (E)-2-chloro-3-(dichloromethyl)-4-oxybutenoic acid in chlorine-treated humic water and drinking water extracts. Environmental Science and Technology 22(9):1097. Lange, A. L., and E. Kawczynski. 1978. Controlling organics: The Contra Costa County Water District experience. Journal of the American Water Works Association 70(11):63. LeChevallier, M. W., D. N. Norton, and R. G. Lee. 1991. Occurrence of Giardia and Cryptosporidium in surface water supplies. Applied Environmental Microbiology 57:2610. Logsdon, G. S., S. Foellmi, B. Long, R. Dawson, M. Ferguson, and D. Neden. 1992. Filtra- tion pilot plant studies for Greater Vancouver's water supply. In Proceedings of the American Water Works Association Annual Conference. Denver, Colo.: American Water Works Association. McGuire, M. J. 1989. Preparing for the disinfection by-products rule: A water industry status report. Journal of the American Water Works Association 81(8):35. McGuire, M. J., and R. G. Meadow. 1988. AWWARF trihalomethane survey. Journal of the American Water Works Association 80(1):61. McGuire, M. J., S. W. Krasner, K. M. Reagan, et al. 1989. Disinfection by-products in United States drinking waters. Washington, D.C.: U.S. Environmental Protection Agency. McKnight, A., and D. A. Reckhow. 1992. Reactions of ozonation by-products with chlorine and chloramines. In Proceedings of the American Water Works Association Annual Conference. Denver, Colo.: American Water Works Association. Miller, J. W., and P. C. Uden. 1983. Characterization of non-volatile aqueous chlorination products of humic substances. Environmental Science and Technology 17(3):150. ~.

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THMs AND OTHER DISINFECTION BY-PRODUCTS 163 Montgomery, J. M., Consulting Engineers Inc. 1992. Effect of coagulation and ozonation on the formation of disinfection by-products. Denver, Colo.: American Water Works Asso . . clarion. Morris, R. D., A. M. Audet, I. F. Angelillo, T. C. Chalmers, and F. Mosteller. 1992. Chlorina- tion, chlorination by-products, and cancer: A meta-analysis. American Journal of Public Health 82(7):955. National Cancer Institute. 1976. Report on the carcinogenesis bioassay of chloroform. NTIS PB-264-018. Bethesda, Md.: National Cancer Institute. National Research Council. 1980. Drinking Water and Health, Vol. 3. Report of the Safe Drinking Water Committee. Washington, D.C.: National Academy Press. National Research Council. 1987. Drinking Water and Health: Disinfectants and Disinfectant By-Products, Vol. 7. Washington, D.C.: National Academy Press. National Toxicology Program. 1986. Toxicology and carcinogenesis studies of bromodichloromethane in F344/N rats and B6C3F1 mice. Technical Report Series No. 321, NIH Publication No. 88-2537, CAS No. 75-27-4. Washington, D.C.: U.S. Department of Health and Human Services. National Toxicology Program. 1989. Toxicology and carcinogenesis studies of tribromomethane (bromoform) in F344/N rats and B6C3F1 mice. Technical Report Series No. 350, NIH Publication No. 89-2805, CAS No. 75-25-2. Washington, D.C.: U.S. Department of Health and Human Services. Norman, T. S., L. L. Harms, and R. W. Looyenga. 1980. The use of chloramines to prevent trihalomethane formation. Journal of the American Water Works Association 72(3):176. Oliver, B. G. 1983. Dihaloacetonitriles in drinking water: Algae and fulvic acid as precursors. Environmental Science and Technology 17(2):80. Quimby, B. D., M. F. Delaney, P. C. Uden, and R. M. Barnes. 1980. Determination of the aqueous chlorination products of humic substances by gas chromatography with micro- wave emission detection. Analytical Chemistry 52:259. Rav-Acha, C., A. Serri, E. Choshen, and B. Limoni. 1984. Disinfection of drinking water rich in bromide with chlorine and chlorine dioxide, while minimizing the formation of unde- sirable by-products. Water Science and Technology 17:611. Reckhow, D. A., and P. C. Singer. 1984. The removal of organic halide precursors by preozonation and alum coagulation. Journal of the American Water Works Association 76(4):151. Regli, S., J. E. Cromwell, X. Zhang, A. B. Gelderloos' W. D. Grubbs, F. Letkiewicz, and B. A. Macler. 1992. Framework for decision making: An EPA perspective. EPA 811-R-92- 005, August. Washington, D.C.: U.S. Environmental Protection Agency. Rook, J. J. 1974. Formation of haloforms during chlorination of natural waters. Water Treatment and Examination 23:234. Rook, J. J. 1977. Chlorination reactions of fulvic acids in natural waters. Environmental Science and Technology 11 (5):478. Rose, J. B. 1988. Occurrence and significance of Cryptosporidium in water. Journal of the American Water Works Association 80(2):53. Semmens, M., and T. Field. 1980. Coagulation: Experiences in organics removal. Journal of the American Water Works Association 72(8):476. Singer, P. C., and S. D. Chang. 1989. Correlations between trihalomethanes and total organic halides formed during drinking water treatment. Journal of the American Water Works Association 81(8):61. Singer, P. C., A. Obolensky, and A. D. Greiner. 1992. Relationships among disinfection by- products in chlorinated drinking waters. In Proceedings of the Water Quality Technology Conference. Denver, Colo.: American Water Works Association. Standard Methods for the Examination of Water and Wastewater. 1985. Sixteenth edition. American Public Health Association, Washington, D.C. .

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64 PHILIP C. SINGER Stevens, A. A., L. A. Moore, C. J. Slocum, B. L. Smith, D. R. Seeger, and J. C. Ireland. 1989. Chlorinated humic acid mixtures: Criteria for detection of disinfection by-products in drinking water. Chapter 39 in Aquatic Humic Substances: Influence on Fate and Trans- port of Pollutants, I. H. Suffett and P. MacCarthy, eds. Advances in Chemistry Series 219. Washington, D.C.: American Chemical Society. Symons, J. M., T. A. Bellar, J. K. Carswell, J. DeMarco, K. L. Kropp, G. G. Robeck, D. R. Seeger, C. J. Slocum, B. L. Smith, and A. A. Stevens. 1975. National organics recon- naissance survey for halogenated organics in drinking water. Journal of the American Water Works Association 67:634. Symons, J. M., A. A. Stevens, R. M. Clark, E. E. Geldreich, O. T. Love, Jr., and J. DeMarco. 1981. Treatment Techniques for Controlling Trihalomethanes in Drinking Water. EPA- 600/2-81-156, September. Cincinnati, Ohio: U.S. Enviromental Protection Agency. Trehy, M. L., and T. I. Bieber. 1981. Detection, identification and quantitative analysis of dihaloacetonitriles in chlorinated drinking water. Pp. 941-975 in Advances in the Identi- fication and Analysis of Organic Pollutants in Water, Vol. 2., L. H. Keith, ed. Ann Arbor, Mich.: Ann Arbor Science Publishers. U.S. Environmental Protection Agency. 1976. Organic chemical contaminants: control op- tions in drinking water. Federal Register 41(136):28991, July 14, 1976. U.S. Environmental Protection Agency. 1978. Control of organic contaminants in drinking water. Federal Register 43(28):5756, February 9, 1978. U.S. Environmental Protection Agency. 1979. National interim primary drinking water regu- lations; control of trihalomethanes in drinking water. Federal Register 44(231):68624, November 29, 1979. U.S. Environmental Protection Agency. 1983. National interim primary drinking water regu- lations; trihalomethanes. Federal Register 48(40):8406, February 28, 1983. U.S. Environmental Protection Agency. 1987a. National primary drinking water regulations; filtration and disinfection; turbidity, Giardia lamblia, viruses, Legionella, and heterotrophic bacteria. Federal Register 52(212):42173, November 3, 1987. U.S. Environmental Protection Agency. 1987b. Drinking water; national primary drinking water regulations; total coliforms. Federal Register 52(212):42224, November 3, 1987. U.S. Environmental Protection Agency. 1989a. National primary drinking water regulations; filtration and disinfection; turbidity, Giardia lamblia, viruses, Legionella, and heterotrophic bacteria. Federal Register 54(124):27486, June 29, 1989. U.S. Environmental Protection Agency. 1989b. Drinking water; national primary drinking wafer regulations; total coliforms. Federal Register 54(212):27544, June 29, 1989. U.S. Environmental Protection Agency. 1992a. Draft groundwater disinfection rule. Federal Register 57(148): 33960, July 31, 1992. U.S. Environmental Protection Agency. 1992b. Intent to form an advisory committee to negotiate the disinfection byproducts rule and announcement of public meeting. Federal Register 67 (179) :42533, September 15, 1992. Werdehoff, K. S., and P. C. Singer. 1987. Chlorine dioxide effects on THMFP, TOXFP, and the formation of inorganic by-products. Journal of the American Water Works Associa- tion 79(9):107. World Health Organization. 1991. Chlorinated drinking-water; chlorination by-products; some other halogenated compounds; cobalt and cobalt compounds. In IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 52. International Agency for Research in Cancer, Lyon. Young, J. S., and P. C. Singer. 1979. Chloroform in public water supplies: a case study. Journal of the American Water Works Association 71(2):87. -