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OUTLOOK The chlorination question Highlights of the recent conference in California Water chlorination is both a bane and a benefit to man. Recognition of some of the health problems caused by chlorine in drinking water led to the first water chlorination conference in Oak Ridge, Tenn., in 1975. Since then, a conference has been held every two years. The last one took place in Pacific Grove, Calif., at the end of October and was attended by about 200 persons. Seventy papers were presented and 38 poster presentations were given. Why does there continue to be so much research in the area of water chlorination? One reason is that probably no other public health issue affects a larger proportion of the U.S. population. Another is that chlorine is used to disinfect not only potable water supplies, but the wastewater from sewage treatment plants. It is also added to the water circulating inside the cooling towers of electric power plants. In this way, lakes, streams, and oceans annually receive a great deal of chlorine, which undoubtedly affects aquatic ecosystems. Chlorine is also employed in food processing to control the growth of bacteria and other pathogens. Recognition that water chlorination causes health risks and harm to aquatic life has not led to its demise. Consulting engineer George White said that chlorine use is 20-40% greater than reported in 1975 and growing steadily, especially in the area of disinfection. The many applications of water chlorination and the fact that it presents complex and demanding scientific problems have made it a subject for much research. A great deal has been learned in the past six years. Toxicological information relevant to drinking water disinfection was virtually nonexistent prior to 1976. However, according to James Fava of Ecological Analysts (Sparks, Md.) and William Davis (U.S. EPA), the basic
questions regarding chlorination have not changed even though the experimental evidence about the chemistry of chlorination and its effects on man and aquatic life has expanded greatly. We are still asking, for instance, if chlorination is the best treatment method for drinking water. Would another disinfectant be safer for human health? Do we really need to disinfect wastewater from sewage treatment plants? Other disinfectants Alternative disinfectants that have been considered are chlorine dioxide, ozone, chloramines, UV irradiation, iodination, or some combination of these processes. The first three have been given the most attention. However, as Richard Bull (U.S. EPA, Cincinnati) pointed out, all forms of disinfection commonly used alter the composition of trace organic chemicals because the efficacy of disinfectants "depends on their ability to alter organic chemicals by either chemical or physical means." This does not mean that another disinfectant may never be found safer than chlorine. At present, not enough research has been done to assess the relative hazards of the various alternatives to chlorine. An advantage of chlorine dioxide (CIO2) is that it forms very few chlorinated products. But this is probably outweighed by many serious draw-
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backs. C 1 0 2 produces chlorite (C10 2 ~), which presents an acute toxicological hazard. Bull stated at the conference that C10 2 ~ has been shown to oxidize hemoglobin to the nonfunctional pigment methemoglobin; at lower levels it produces hemolytic anemia. It may also depress sperm production. In addition, C 1 0 2 itself may possess activity as an antithyroid agent, though the mechanism for this is not yet understood. Chloramines also have associated hazards. A major concern is their mutagenic properties. Bull said that chloramine has been found to produce methemoglobinemia when present in water used for dialysis of patients with chronic kidney failure. However, when animals are exposed to chloramine orally, this effect has not been observed. Ozone is an effective disinfectant and is used quite commonly in Europe. But it is expensive and must be used in combination with some other chemical because ozone leaves no residual to continue disinfection after water is distributed into the system. Consequently, a small amount of chlorine is usually added to the water after ozonation. Health effects of chlorination What has been learned about the adverse health effects of chlorine and the products it forms? Surprisingly, Environ. Sci. Technol., Vol. 16, No. 1, 1982
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Bean: One or two key chemical reactions may explain a great deal
Fava: The basic questions regarding chlorination have not changed
Jolley: Bromochloramines are important haloamines in chlorinated seawater
the toxicological effects of chlorine itself (technically a mixture of HOC1 and OCl~ depending on pH) have received almost no study—a major gap in the presently available research. There is only one long-term investigation of chlorine toxicity, an experiment by Druckery that indicates no harmful effects from drinking water containing 100 mg/Lof chlorine provided to rats over seven generations. Chlorinated water supplies do seem to present a hazard. At the conference Earle Nestmann (Canada Health and Welfare) reported on a study of the mutagenicity of 30 chlorinated water supplies in Canada. Out of four samples taken from every water treatment plant, he found at least one sample from each to be mutagenic. He also reported that compared with other organics, trihalomethanes (THMs), the regulated byproducts of chlorination in the U.S., did not seem to be well correlated with mutagenicity. The health effects of THMs have been studied in some detail. Chloroform has been found to cause cancer in both mice and rats. The carcinogenicity of the other THMs has not been established definitely, but is being examined in the national toxicology carcinogenesis bioassay program. Michael Pereira (U.S. EPA, Cincinnati) discussed his research concerning the mechanism by which TH Ms induce cancer. The object of his study was to determine whether they are initiators or promoters of cancer. If initiators, they would presumably act by a genetic mechanism; that is, they would act through interaction with genetic material of the target cell and the effects would be irreversible. If promoters, the THMs would act through an epigenetic mechanism, and the effect would be reversible, i.e., the damage would stop once the promoter was removed unless it had already caused an actual tumor. Clarifying this is important: if a carcinogen is an initiator, it is believed
to have no threshold level below which it has zero effect; if it is a promoter, it is thought to have a threshold level. Therefore, such a study can aid in formulating models that help to define a level at which to regulate THMs. Pereira's results are preliminary but indicate that THMs are promoters of cancer. They appear to have "the weakest, if any, tumor-initiating activity." Besides THMs, chlorination also produces other byproducts. Their identification has been a relatively slow process. And all of them—there are a great many—have still not been identified. The formation of chlorinated phenols has been known for many years. They show up in the chlorination of wastewaters. 2,4,6-Trichorophenol has been demonstrated to be a carcinogen in both mice and rats, and Jerry Exon of the University of Idaho has found some evidence for the fetotoxic effect of 2-chlorophenol at high doses in rats. Haloacetonitriles are also products of chlorination and a dichloroacetonitrile has been shown to be mutagenic in the Ames test. Preliminary data also indicate that this chemical is a tumor initiator. The formation of organic jV-chloramines has been postulated and a model compound ,/V-chloropiperidene has been shown to be formed in aqueous solution. It has direct mutagenic activity. The treatment of wastewater is important because advanced treatment is being studied as a potential source for replenishment of groundwater supplies. Martin Reinhard of Stanford University found wastewater samples only weakly mutagenic before disinfection but strongly mutagenic after treatment with chlorine. He noted that bromination occurred during chlorination and suspected a connection between bromination and increased mutagenicity. In a poster session, general chairman of the conference Robert Jolley
(Oak Ridge National Laboratory) reported on his study of the mutagenicity and chemical characterization of the nonvolatile organics in disinfected wastewater effluents. Chlorine was used as a disinfectant on some samples and ozone was used on others. In both cases, disinfection most often led to an increase in the number of mutagenic materials. However, sometimes the reverse was true, i.e., the mutagenicity of a few samples was decreased by disinfection. This inconclusive evidence calls for a better understanding that new research might provide. In food processing, chlorine is applied directly to some foods, such as fish and chicken, and indirectly to others because it is employed to sanitize equipment. George Braude of the Food and Drug Administration presented a paper about the lack of data concerning the effects of chlorination on foods. He said: "Very little information is available regarding the identity, exposure level, and potential toxicity of chlorinated or oxidized reaction products resulting from the use of chlorine-containing sanitizers in food processing."
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Environ. Sci. Technol., Vol. 16, No. 1, 1982
Population studies What epidemiological evidence do we have that chlorinated drinking water is causing increased cancer rates? Kenny Crump, Science Research Systems (Ruston, La.), stated that "although a causal relationship between chlorinated drinking water and cancer has not been established, the evidence is to a considerable extent suggestive of such a relationship for rectal cancer and, to a lesser extent, bladder and colon cancer." He listed five case-control studies, conducted by different investigators using data from widely separated geographic areas of the U.S., which found in each case elevations in cancer rates for one or more types of cancer. He said that although no single study is definitive, these independent findings "reduce the possi-
bility that the increases are due to ei ther chance or confounding factors." Some drawbacks of these studies are that the measures of water quality were very crude and data to control for confounding factors was limited to those provided by death certificates. Theresa Young described a matched-pair case-control study car ried on in Iowa in which "only colon cancer mortality was found to be sig nificantly greater among those exposed to chlorinated water." She indicated that an important weakness was the lack of individual water exposure histories. She also found that when T H M levels were compared to cancer rates, no dose-related risk gradient was found, but that "when other variables indicative of organic contamination were considered, an interesting risk gradient emerged." According to this study, other contaminants present in chlorinated water may be more carci nogenic than T H M s . Future epidemiological studies may provide more definitive evidence. A large case-control study of bladder cancer, sponsored by the National Cancer Institute, is nearing completion in which interview data should provide much more extensive control for con founding factors. In an epidemiology overview, Kenneth Cantor, National Cancer Institute, said that many brominated analogs of chlorinated compounds may have higher carcino genicity and may play an important role as cancer agents. Cost-benefit analysis With such uncertainties about the actual contribution of water chlorination to adverse health effects, it would seem impossible to do a cost-benefit analysis of the different methods of water treatment. One conference participant felt that such analysis could lead to investment in alternative methods that would eventually prove less advantageous. In contrast, another participant, Talbot Page of the California Institute of Technology, said: " W e believe a cost-benefit approach offers a useful perspective to the problem of chemi cals in drinking water." He claimed that cost-benefit analysis allows one to organize research around areas where filling the gaps will have the most ef fect on decision making. He pointed out that a "decision to postpone action, awaiting better in formation, is just as much a decision as one to undertake action," and said that his analysis shows there would be a net benefit associated with installing granular activated carbon filters in some cities. If these filters are used
before chlorination, they remov he precursor substances that give rise to chlorination byproducts. Analytical measurements Previously, there was no quick method of measuring total residual halogens (HOBr, HOC1, NH 2 C1, and Ν Η Br 2 ) down to parts per billion lev els, and operators of power plants said that a standard of 50 ppb residual halogen would be unrealistic because we couldn't measure it. At the con ference, James Carpenter, now with the Nuclear Regulatory Commission, reported a simple fluorometric method that quickly measures total halogens with an accuracy of ± 0.1 ppb and distinguishes the different species by adjusting the pH. Harvey Sellner of the E P C O Company (Danbury, Conn.) described an amperometric technique of continuously monitoring total residual chlorine at levels in the region below 1 ppb. The chemistry of chlorination The reactions of chlorine with or ganic materials in natural waters are extremely complex. In general, organic materials in natural waters (loosely referred to as humic substances) and other organic materials derived from natural sources are responsible for most of the observed reactions of chlorine with surface waters. Roger Bean of Battelle, Pacific Northwest Laboratories cleared up some of the confusion about chlorine chemistry by presenting a table called Low Level Chlorination of Natural Waters (see box). Before the conference, it was
Low level chlorination of natural waters (where does the chlorine go?) a Process
Haloform formation Organic oxidation to C02 Haloacetonitrile formation Formation of nonhaloform organic halogens (eg., trihalomethane precursors, de polymerized organohalogens, etc.) Halogenated phenol formation Other reactions
Percent of chlorine used
0.5-5 50-80 0-5 1-6
~0.1 remainder
a A rough estimate of the percent of chlorine used by each type of reaction.
thought that approximately 80% of the chlorine was used to oxidize organic matter to CO2. However, George Helz of Stanford University reported ex periments that suggest the figure is closer to 50%. He postulated that at tack at certain labile amino acids in the peptide chains initiated a series of re actions resulting in CO2 production. Another reaction that requires a weak link in the peptide chain is the forma tion of haloacetonitriles, reported by Theodore Bieber of Florida Atlantic University (Boca Raton, La.). In the past, several scientists sug gested that phenolic components in humic materials are the primary sources of haloforms from water chlorination. At this conference, Scott Boyce of the California Institute of Technology reported work with resorcinol, a 13 C-labeled phenolic com pound, showing that the aromatic carbon atom between two meta-hydroxy groups is the one incorporated into the haloform product. Barry Ol iver (Canada Centre for Inland Wa ters) reported that the amount of T H M s produced from humic sub stances can be correlated with in creasing color if the primary T H M producers in a water sample are humics. Bean reported that his own work suggested that phenols are important substrates in water chlorination reac tions. He found more than 30 different halogenated phenols produced by the low level chlorination of power plant cooling waters. Jolley presented work showing that bromochloramines should be included along with monochloramine, dibromamine, and tribromoamine as im portant haloamines in chlorinated seawater. Donald Johnson and coworkers of the University of North Carolina chlorinated natural aquatic humic material and analyzed the products. They found that except for chloroform and choral, all chlorinated components were carboxylic acids. Also, the ma jority of the components contained chlorine; no chlorinated aromatics were present. The experiment revealed a great deal but did not tell how the total amount of other chlorinated organics relates to the amount of chlo roform nor whether any of them are present in actual drinking water. Johnson said that "if it is shown that trihalomethanes are not the most abundant chloro derivatives of aquatic humic material which occur ubiqui tously, then health effects data on compounds such as di- and trichloro acetic acid will be needed in order to state more definitely the human health Environ. Sci. Technol., Vol. 16, No. 1, 1982
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risks from the consumption of chlori nated water." Although the reactions of chlorine are complex, Bean speculated "it is possible that only one or two key re actions with a few key structural components will be required to explain the initiation of the reaction sequences involved." Obviously much work re mains to be done in this area before even the most important reactions of chlorine in natural environments can be reasonably understood. Aquatic ecosystems Because the discharge of chlorine into surface waters and the ocean damages aquatic organisms, some areas of the U.S. are seriously consid ering banning wastewater chlorination. The EPA is now working on chlorine water quality criteria for the protection of aquatic life. It is anticipated that draft chlorine criteria will be com pleted early this year. Presently, many regulators and environmental man agers feel sufficient research has been completed to identify the hazards of chlorination for aquatic life. This chlorination conference, how ever, highlighted the fact that a great deal is still unknown. Richard Vanderhorst of Battelle, Pacific Northwest
Laboratories performed a study that examined the effects of low level chlorination on open microcosms in Puget Sound, Washington. He found statistically significant differences in the rates of growth; however, the meaning of these findings is question able because the "systems were clearly in a growth phase and had not reached steady state at the experiment's con clusion." David Anderson of Envirotest (Redmond, Wash.) presented infor mation to show that the interaction of chlorination with nickel resulted in increased accumulation of nickel in rainbow trout. His data show how important it is to evaluate the inter action of chlorination with other chemicals known to have environ mental effects. An overview of the effects of chlo rine-produced oxidants and THMs on marine invertebrates was presented by Geoffrey Scott of Research Planning Institute (Meggett, S.C.). The mate rials he reviewed showed that many of the effects are irreversible and that the juvenile stages of the organisms are more sensitive than the adult stages. Scott also presented information on the bioconcentration of bromoform in American oysters.
Fava and Davis said that the "inte gration of marine biological research with identified technical needs could be one of the true progressive steps to achieve the benefits of chlorination while at the same time helping to pro tect sensitive environmental systems." An example is using marine organisms such as oysters to monitor for human pathogens in the effluent from waste treatment plants. Many investigators said that additional field experiments concerning the effects of chlorine on aquatic life are needed to confirm what has been learned in the laboratory. Fava and Davis pointed out the need for additional research when they said: "As the use of chlorine continues to grow, so does the potential for aquatic effects. Ignoring the problem is not the proper response from an intelligent society. Instead, we need to be pre pared to make educated technical de cisions based on experimentally proven facts—not on ignorance and unproven assumptions." The proceedings of the conference will be published this year by Ann Arbor Science (Mich.). The next chlorination conference is scheduled for October 1983 in the MarylandVirginia area. —Bette Hileman
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