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Drinking Water Chlorination White
Paper
The practice of drinking water chlorination is one of the most significant public health advances of the 20th century. Our quality of life depends on the knowledge that when we turn on the tap, the water will be clean and safe. For that reason, over 98% of water treatment facilities in the United States disinfect with chlorine and chlorine-based chemicals. This paper has been prepared for water utility managers, public health officials and other decision makers to help answer their questions about the role of chlorine in drinking water treatment. The document received the input and guidance of many technical experts from the chlorine industry and was reviewed by select members of the Chlorine Chemistry Council's® Public Health Advisory Board. Chlorination has played a critical role in protecting America's drinking water supply from waterborne infectious diseases for 90 years. Drinking water chlorination is one of the most significant advances in public health protection, having virtually eliminated waterborne diseases such as cholera, typhoid, dysentery and hepatitis A in this country. Over 98% of water supply systems that disinfect drinking water use chlorine because of its germicidal potency, economy and efficiency. In addition, chlorine-based disinfectants are the only major disinfectants with the lasting residual properties that prevent microbial regrowth and provide continual protection throughout distribution from the treatment plant to the tap. Preventing Waterborne Diseases Waterborne diseases continue to present challenges to public health officials and water suppliers. Prevention and control of waterborne diseases through source water protection and proper treatment techniques are critically important. Untreated or inadequately treated drinking water supplies, primarily from surface water sources, contain microorganisms that can cause outbreaks of waterborne diseases. There are new concerns about emerging pathogens, including Cryptosporidium and certain viruses, that might be found even in drinking water treated by conventional methods. In the United States, vulnerable populations - the young, the elderly and those with compromised immune systems - remain at risk for significant illness and even death. The scourge of diarrheal diseases in the developing world, including a five-year cholera epidemic in Latin America, reinforces the conclusions of the American Academy of Microbiology: "The single, most important requirement that must be emphasized is that disinfection of a public water supply should not be compromised."1 The World Health Organization, in its Guidelines for Drinking-Water Quality, further supports the necessity of water disinfection: "Disinfection is unquestionably the most important step in the treatment of water for public supply. ... Efficient disinfection must never be compromised."52 Chlorine Benefits Outweigh Risks In 1974, scientists discovered that during the water treatment process, chlorine reacts with organic matter in raw water to form disinfection by-products (DBPs). Other disinfectants also form DBPs. Concerns that the presence of these compounds in drinking water may present potential health risks led the U.S. Environmental Protection Agency to propose regulations to control DBPs. Nevertheless, 25 years of research have failed to establish a direct link between trace amounts of chlorinated DBPs present in tap water and any additional cancer risk in humans. In 1990, the International Agency for Research on Cancer evaluated the body of research concerning the potential health effects of chlorinated drinking water and concluded that it is "not classifiable as to its carcinogenicity to humans."30 Furthermore, the World Health Organization noted that "the risks to health from disinfection by-products are extremely small in comparison with the risks associated with inadequate disinfection, and it is important that disinfection should not be compromised in attempting to control such by-products."52 According to Regli et al., "the risk of death from known pathogens in untreated surface water appears to be at least 100 to 1000 times greater than the risk of cancer from known DBPs in chlorinated drinking water."36 Controlling Disinfection By-Products Alternatives to chlorination have been suggested, but all alternative methods, with the possible exception of ultraviolet radiation, also form by-products. Little is known about these other by-products compared with our knowledge of chlorine-related DBPs. In addition, because alternative disinfectants cannot provide the residual protection of chlorine-based disinfectants, they must be used in combination with chlorine or chloramines to provide a complete disinfection system. Disinfection by-products can be reduced by removing DBP precursors and protecting source water where possible from the entry of DBP precursors. Removing organic precursors through enhanced coagulation and changing the point of chlorination to later in the treatment process are examples of measures that can help control by-product formation. Establishing Priorities Protecting public health involves establishing priorities. Comparative risk assessment suggests that the prevention of observed waterborne diseases through the control of microbiological contaminants should take precedence over eliminating the hypothetical risks posed by disinfection by-products. To that end, future drinking water regulations should rely on cost-benefit analysis to determine where dollars spent for water treatment will yield the most public health benefits. The Chlorine Chemistry Council supports research on both the efficacy of chlorine as a disinfectant and a better understanding of the health effects of disinfection by-products. Chlorination has played a critical role in protecting America's drinking water supply from waterborne infectious diseases for 90 years. Chlorination began in the early years of this century in Great Britain, where its application sharply reduced typhoid deaths. Shortly after this dramatic success, chlorination and filtration were introduced into the United States, which resulted in the virtual elimination of waterborne diseases such as cholera, typhoid, dysentery and hepatitis A.51 The adoption of drinking water chlorination has been one of the most significant advances in public health protection.52
While chlorine's most important attributes are its broad-spectrum germicidal potency and persistence in water distribution systems, its ability to efficiently and economically address many other water treatment concerns has also supported its wide use. Chlorine-based compounds are the only major disinfectants exhibiting lasting residual properties to provide continual protection against microbial regrowth.51 Water treatment practices vary in the United States, but there are generally accepted basic techniques. Source water quality predicates the kind of treatment required to provide safe water. Therefore, protecting source water quality is a primary goal. The treatment choice depends on a number of factors that are site specific and for which adjustments must be made depending on raw water quality. Source water quality and turbidity (particulate matter) levels, water temperature and pH level, and incidence of pathogenic contaminants must be taken into account for treatment decision making. Conventional, sequential water treatment for surface water proceeds as follows: watershed protection program; pretreatment employing flocculation and sedimentation to remove turbidity, as well as the organic precursors that form by-products; filtration; disinfection at an appropriate concentration (C) for a prescribed time (T) (CT criteria) to destroy harmful organisms; and the addition of chlorine to maintain residual disinfection throughout the distribution system. There may also be a need for prechlorination or rechlorination during storage and/or distribution to ensure that an appropriate residual is maintained throughout the system.
Source: 1989-1990 AWWA Disinfection Committee Survey of Disinfection Practices
Chlorine-based chemicals are the disinfectants of choice for treating drinking water. In fact, some 98% of all systems that treat water employ chlorine-based disinfectants. Facilities use chlorine because it does its job extremely well, is safe to use when handled properly and is very cost-effective. After its initial introduction in 1908 in New Jersey, chlorine was adopted as a disinfectant by most water treatment plants in the United States and Canada. More than 200 million Americans and Canadians receive chlorine-disinfected drinking water every day. Chlorine's popularity in water disinfection is based on many factors. A 1985 study of the role of chlorine in water treatment conducted by J. Carrell Morris of the Harvard University School of Medicine identified many of chlorine's benefits:31 Potent germicide. The demonstrated use of chlorine reduces the level of disease-causing microorganisms in drinking water to almost immeasurable levels. Residual qualities. Chlorine produces a sustained residual disinfection action "unique among available large-scale water disinfectants." Chlorine's superiority as a residual disinfectant remains true today. The presence of a sustained residual maintains the hygienicity of the finished drinking water from the treatment plant to the consumer's tap. Taste and odor control. Chlorination of drinking water reduces tastes and odors. Chlorine oxidizes many naturally occurring substances such as foul-smelling algae secretions and odors from decaying vegetation, resulting in nonodorous, better-tasting drinking water. Biological growth control. Chlorine's powerful germicidal action eliminates slime bacteria, molds and algae. Chlorine controls these nuisance organisms, which typically can grow in reservoirs, on the walls of transmission water mains and in storage tanks. Chemical control. Chlorine in water treatment destroys hydrogen sulfide and removes ammonia and other nitrogenous compounds that have unpleasant tastes and hinder disinfection. Chlorinated drinking water's chief benefit is the protection of public health through the control of waterborne diseases. It plays a paramount role in controlling pathogens in water that cause human illness, as evidenced by the virtual absence of waterborne diseases such as typhoid and cholera in developed countries. Untreated or inadequately treated drinking water supplies remain the greatest threat to public health, especially in developing countries, where nearly half the population drinks contaminated water. In these countries, diseases such as cholera, typhoid and chronic dysentery are endemic and kill young and old alike. In 1990, over three million children under the age of five died of diarrheal diseases. Unfortunately, the availability of safe drinking water supplies in many areas is practically nonexistent, due to poverty, poor understanding of water contamination, and lack of a treatment and delivery infrastructure. International assistance groups, including the World Health Organization and the Pan American Health Organization (PAHO), have long-standing technical assistance and education programs to improve water supply and sanitation practices. It has been estimated that such improvements - including chlorine disinfection - can prevent 25% of all diarrheal outbreaks and reduce childhood mortality by equal levels.17 A recent example of the continuing public health threat from waterborne disease outbreaks occurred in Peru in 1991, where a major causative factor was the absence or inadequacy of drinking water disinfection. This failure to disinfect was partly based on concern about U.S. reports of the detection of disinfection by-products. The result: a five-year epidemic of cholera, its first appearance in the Americas in this century. The epidemic spread to 19 Latin American countries and has been only partially abated through public health interventions supported by PAHO's advice and technical assistance. Nearly a million cases and 10,000 deaths have been reported.17 These statistics strongly reinforce the concept that water disinfection must be a primary tool in protecting public health worldwide. As noted by the American Academy of Microbiology, "The single, most important requirement that must be emphasized is that disinfection of a public water supply should not be compromised."1 At the 1992 First International Conference on the Safety of Water Disinfection, several researchers described the costs associated with microbiological disease as well as the benefits of illness avoided through water treatment. Real health care savings can be realized from preventing and eliminating microbial contamination in drinking water supplies.12 In his conference presentation, Dr. Pierre Payment (University of Quebec) stated that the "social cost of 'mild' gastrointestinal illness in industrialized countries is several orders of magnitude higher than costs associated with acute hospitalized cases." For example, in the United States, annual costs were estimated to be $9.5 billion (1985 dollars) for cases with no consultation with a physician, $2.7 billion for those with consultations, and only $760 million for those requiring hospitalization.35 Dr. Payment presented data estimating that in 1985, about 500,000 hospitalizations and 3,000 deaths were due to gastrointestinal illnesses in the United States, the majority being of unknown origin. His study assumed that these numbers are grossly underestimated due to unreported or unidentified illnesses. Over 13% were due to viral illnesses, 4.9% were bacterial and 1.1% were parasitic. About 80% were presumed noninfectious. One out of ten deaths from gastroenteritis could be due to viruses. Commenting on Dr. Payment's report, the American Academy of Microbiology noted, "A decrease in morbidity and mortality is not the only benefit which should be considered in a cost-benefit analysis ... The benefits of microbiologically safe water ... go beyond the absence of disease, and affect the productivity of industry, as well as the prices of goods and services."1 At the same conference, a paper by Gunther F. Craun et al. discussed the cost-effectiveness of water treatment for pathogen removal.19 An evaluation of five pathogens and treatment costs shows the favorable economic benefits of preventing infectious waterborne diseases. These benefits were determined based on an annual probability of illness and death, assuming no water treatment, and a cost of $3,000 per illness and $500,000 per death. The effectiveness of water treatment in reducing waterborne diseases depends on the quality of the source water and how the treatment system is operated and maintained. The table below shows positive benefit-cost ratios associated with the installation of chlorination and conventional water treatment to remove and control pathogens in drinking water. The ratios were arrived at by comparing the probability of foregone disease, using the difference between the disease probabilities with no water treatment and those for various levels of water treatment in communities with populations of 10,000, 100,000 and 500,000.
Regarding comparison of these benefits with potential cancer risks associated with drinking water disinfection, the group noted that the costs of preventing the relatively small carcinogenic risks may not be warranted in light of many other public health risks that should be reduced.
Waterborne diseases continue to present challenges to public health officials and water suppliers. The presence of disease-causing microorganisms in tap water typically results from poor source water quality, lapses in disinfection and filtration treatment processes, or compromised distribution systems. In most instances, outbreaks of waterborne diseases occur in water systems with inadequate or no disinfection. However, there are new concerns about emerging pathogens, such as Cryptosporidium, that appear even in high-quality water supplies.18 Waterborne pathogens that cause disease fall into three general classes - bacteria, viruses and parasitic protozoa, each with various identified species: Bacteria and viruses contaminate both surface and groundwater, whereas parasitic protozoa appear predominantly in surface water.41
All waterborne microbial pathogens are potentially infectious and capable of causing illness depending on the dose and the physical condition of the individuals exposed. It should be stressed that exposure to waterborne pathogens does not always mean infection, nor does infectivity always lead to clinical illness. Although the dose-response mechanism is still not fully understood, scientists estimate that the risk of waterborne microbial illness in the United States is approximately 1 in 1 thousand individuals. Of those infected in the general population, the mortality risk is 1 in 1 thousand (as compared to a mortality risk of 1 in 1 million for uninfected individuals).41 Bacteria and protozoa generally induce gastrointestinal disorders with a wide range of severity. Bacteria also cause life-threatening diseases such as typhoid and cholera. Viruses cause serious diseases such as aseptic meningitis, encephalitis, poliomyelitis, hepatitis, myocarditis and diabetes.35 In addition, gastrointestinal disorders may be attributed to unidentified or unspecified microorganisms. In terms of occurrence, protozoan infections are the most common, followed by bacterial infections and then viral infections.20 For most pathogens, the severity of illness ranges from mild gastrointestinal upset, fever and vomiting, and intermittent diarrhea to chronic diarrhea, dehydration, liver damage, acute respiratory illness, adverse neurological effects, depressed immune systems and death. Most healthy individuals in the general population usually experience only mild gastroenteritis that is easily controlled and of short duration. On the other hand, certain segments of the population are especially vulnerable to acute illness (morbidity) and can exhibit high death (mortality) rates. These segments include pregnant women, infants, the elderly and those whose immune systems are compromised by cancer, AIDS or the drugs used to treat these and other conditions.16 For example, nursing home studies have shown dramatic increases in diarrheal deaths in individuals over age 55, with mortality rates as high as 1 in 100, or 10 to 100 times greater than in the general population.26 Occurrence Some occurrence statistics exist for outbreaks of waterborne diseases, but public health and water authorities generally must deal with unreliable estimates. Among the difficulties encountered when trying to determine the extent of waterborne disease occurrence in the United States is that illnesses often go unreported or may only be attributed to unknown causes (etiology).29,35
** Not DBPs
Data on waterborne disease outbreaks have been compiled by Gunther F. Craun, a water expert formerly with the U.S. Environmental Protection Agency (EPA). The following tables illustrate occurrence, pathogenic agents identified with cases of illness and causes of outbreaks from 1971 to 1992 in the United States. It should be noted that these data do not include the outbreak of cryptosporidiosis in Milwaukee in 1993.20
Prevention and Control Eliminating and preventing contamination of water supplies is critically important. Under EPA's Total Coliform Rule, maximum contaminant levels (MCLs) and routine monitoring have formed the basis for controlling microbiological contamination of public water supplies. EPA uses the presence or absence of "indicator" bacteria, e.g., E.coli, to verify whether drinking water is pathogen-free and safe. However, epidemiologists have now traced waterborne disease outbreaks to water supplies that did not exceed the MCL for total coliforms or turbidity and met all water quality standards. Cryptosporidium parvum, Giardia lamblia and viruses have been found in disinfected water where indicator bacteria were absent.1 The best-known example of this phenomenon was the 1993 cryptosporidiosis outbreak in Milwaukee that infected over 400,000 residents and killed over 100, most of whom were immunocompromised individuals. That outbreak was traced to a combination of a "spike" of Cryptosporidium oocysts in the raw water, perhaps related to a runoff event from agricultural areas, and process control difficulties. Although turbidity increased in the finished water, the city's water supply did not exceed EPA's coliform MCL, nor were the turbidities in violation at any time. Another outbreak of cryptosporidiosis occurred in Clark County (Las Vegas), Nevada, in 1994, resulting in 78 cases, of which 61 were AIDS patients. Epidemiologists remain puzzled by this outbreak since no Cryptosporidium oocysts could be detected in either raw or finished water supplies, nor were coliform MCLs exceeded. Furthermore, the area's source water is exceptionally high quality, and the Las Vegas water treatment facility is state-of-the-art.9,28 Drinking water facilities work to achieve the goal of minimal risk in water supplies by removing contaminants and mitigating disease outcomes with a coordinated multi-barrier approach to risk management and public health protection. An EPA report, National Drinking Water Program Redirection Strategy, released in June 1996 highlighted the need for a nationwide commitment to water quality improvement.49 EPA's recommended action steps for the delivery of high-quality drinking water include:
The American Academy of Microbiology adds further recommendations:1
Scientific Research Update: Cryptosporidium Inactivation The serious health risks associated with drinking water contaminated by Cryptosporidium have sparked considerable research into ways to control this protozoan parasite. The protective shell of C. parvum oocysts permits their long-term survival in the environment and makes them appear resistant to conventional disinfection methods. Typical control methods have included sequential addition of chlorine-based disinfectants combined with various filtration techniques. Ozone may be applied sequentially with chlorine as well, providing effective inactivation.39 The results of promising new research projects released in the last two years are summarized below. Chlorine and Chloramine Dr. Gordon R. Finch of the University of Alberta, Canada, released a study of chlorine inactivation of Cryptosporidium in May 1996.24 Dr. Finch evaluated a two-step disinfection approach in which different types of chlorine were applied sequentially - i.e., free chlorine (elemental chlorine, hypochlorous acid or hypochlorite ion) pretreatment followed by monochloramine. He also proposed a disinfection model for use by engineers to design C. parvum control processes for water treatment facilities. Dr. Finch theorized that chlorine pretreatment sensitized the oocysts to the effects of monochloramines, increasing levels of inactivation. He also found that hypochlorous acid performed significantly better than hypochlorite ion for inactivation. The study concluded that chlorine followed by chloramines could be used as an alternative methodology with appropriate disinfectant concentrations and contact times. Increasing levels of chlorine pretreatment proportionally reduce the subsequent monochloramine concentration and contact time necessary for a given level of inactivation. Dr. Finch further suggested that the proposed two-step model for sequential chlorine-monochloramine disinfection could provide a potential disinfection barrier to C. parvum for water systems with adequate contact time. Chlorine Dioxide Dr. Finch also described several studies that reported C. parvum inactivation by chlorine dioxide in water at high pH levels and low temperature. More recent evidence suggests that effective inactivation can be achieved with a chlorine dioxide dose followed by free chlorine.25M Ultraviolet Radiation A joint venture in the United Kingdom has proposed an ultraviolet (UV) system to inactivate Cryptosporidium and Giardia in drinking water. Rather than treating the water, the system directly treats the oocysts to achieve inactivation. Water enters a treatment chamber and passes through a screen where the oocysts are trapped and irradiated. Using a two-step process, the water flow is reversed, and the oocysts are trapped and irradiated a second time. While additional development is needed, especially with regard to cost and design requirements, initial animal infectivity studies resulted in no infection to laboratory mice after treatment.22 Ozone Ozone has been used to achieve the inactivation of Cryptosporidium oocysts. After conventional treatment processes (coagulation, flocculation, sedimentation or dissolved air flotation) accomplish 99.0% to 99.9% removal of the oocysts, ozone disinfection can successfully inactivate the rest. Important considerations in designing models for ozone disinfection of Cryptosporidium include water temperature, CT (concentration X time) criteria and residual levels.39 In water systems using ozone, Dr. Finch's research has shown that combining ozone as the primary disinfectant with chlorine or chloramine to furnish a dependable residual disinfectant may provide very effective treatment.23
Drinking water regulatory policy in the United States has, since 1974, focused primarily on mitigating potential health risks associated with chemical contaminants in drinking water supplies. In 1974, EPA scientists determined that chlorine reacts with certain organic materials during water disinfection to create trihalomethanes (THMs), including chloroform in particular and lesser amounts of other THMs. Toxicological studies undertaken on chloroform suggested that it was carcinogenic to laboratory animals, although at levels much higher than those found in drinking water. Fears that THMs could be a potential human carcinogen led EPA to set regulatory limits for these disinfection by-products (DBPs). The agency initiated a review of other chlorination by-products, such as haloacetic acids (HAAs) and haloacetonitriles, with a goal of developing much more comprehensive regulations. Meanwhile, studies also identified by-products associated with other disinfectants - chloramines, chlorine dioxide and ozone.46 Because high levels of disinfection by-products in drinking water are undesirable, cost-effective methods to reduce DBP formation should be employed. However, the microbiological quality of drinking water must always be the top priority. Even as EPA has moved forward to regulate disinfection by-products, health effects research results have proven to be largely inconclusive. In 1990, the International Agency for Research on Cancer (IARC) convened an expert workshop to evaluate the possible carcinogenicity of chlorinated drinking water. IARC is an investigative research branch of the World Health Organization, and regularly evaluates the human carcinogenicity of different materials. The IARC working group evaluated every available major scientific analysis of the potential health effects of chlorinated drinking water. They concluded that chlorinated drinking water is "not classifiable as to its carcinogenicity to humans."30 The National Toxicology Program (NTP) of the U.S. Department of Health and Human Services reached a similar conclusion in 1990. The NTP study examined the carcinogenicity of chlorinated and chloraminated water in laboratory rats and mice. It is important to note that the water used in this study was chlorinated orders of magnitude above the chlorination levels found in public water supplies. The results of the NTP study reported that there was no evidence of carcinogenic activity in male and female mice or male rats from the consumption of chlorinated and chloraminated water. Equivocal evidence of carcinogenic activity was noted in female rats.34 Morris et al. (1992) published a meta-analysis study statistically combining the results of ten previous epidemiological studies.32 This meta-analysis purported to show increased risks of bladder and colon cancer associated with chlorinated drinking water. Subsequent reviews of the Morris report revealed inconsistencies and errors in methodology and approach. Dr. Patricia Murphy of the EPA Office of Research and Development questioned this application of meta-analysis to risk assessment for cancer and chlorinated drinking water due to the many confounding variables and inconsistent quality of the studies. She cited 12 specific problem areas with the Morris conclusions, noting that "a single summary estimate of a very complex problem in this specific instance may be a precise estimate of a meaningless (or at least uninterpretable) relative risk."33 Comparative Risks: Microbial versus Chemical Contaminants The task for regulators is to maximize public health protection by managing the relative human health risks of microbiological and chemical contaminants in drinking water. To a considerable degree, EPA regulations have given greater weight to chemical risks, historically expressed as potential cancer risk, than to microbial risks. For example, the current debate centers on hypothetical cancer risks associated with chlorine disinfection by-products created during the water treatment process. However, continuing evidence of waterborne disease occurrence suggests that microbial risks should receive a much higher level of attention. This became increasingly relevant as improved detection techniques confirmed the presence in water supplies of microbial pathogens other than bacteria, such as viruses and protozoa. For this reason, the American Academy of Microbiology has recommended that "the health risks posed by microbial pathogens should be placed as the highest priority in water treatment to protect public health."1 In a 1993 study submitted to EPA during negotiations over the DBP rule, Dr. Robert Tardiff reported results of applying five essential criteria for determining the comparative health risks of microbial and chemical contamination. The five criteria for assessing water-related diseases are
Dr. Tardiff's report concluded that the risk of microbial disease is much greater than the risk posed by chemicals suspected of causing cancer in humans. Importantly, there are significant differences in the incidence of disease, the amount of time (latency) between exposure and clinical illness, and the certainty that many people will become ill. Compared with chemical risks, microbial risks are much greater (1,000 to 100,000 times), their latency is very much shorter (days versus decades) and they will almost certainly cause illness in humans. It is clear that a great deal more research needs to be done, especially in the development of improved risk assessment methodologies that provide a clearer picture of the comparative health risks of microbial and chemical con-taminants. Currently, EPA is developing the tools that will achieve these goals. Some investigators believe it is not possible to assess the risks associated with various disinfection by-products without more knowledge about their occurrence and health effects. Thus far, toxicological studies (dose-response evidence in laboratory animals) have revealed adverse health effects from DBPs at high doses, usually several orders of magnitude greater than those found in drinking water. Epidemiological evidence (statistical correlation between observed human illness and exposures) is inconclusive.7 By-products of disinfectants other than chlorine have been studied far less than those from chlorine.4,16 (See Chapter 6, Control of Disinfection By-Products.) Therefore, at present, available scientific data cannot reasonably justify the extrapolation of cancer risks from laboratory animals to humans. In other words, data have been so limited and research results so inconsistent that there may well be no human cancer risk whatever from the low levels of chlorination by-products typically found in drinking water supplies.18 A 1994 report published by the International Society of Regulatory Toxicology and Pharmacology stated that "the reduction in mortality due to waterborne infectious diseases, attributed largely to chlorination of potable water supplies, appears to outweigh any theoretical cancer risks (which may be as low as zero) posed by the minute quantities of chlorinated organic chemicals reported in drinking water disinfected with chlorine."14 This view is supported by the American Academy of Microbiology: "It is important to point out that there is no direct and conclusive evidence that disinfection by-products affect human health at concentrations found in drinking water. ... Concerns over the toxicology of DBPs should not be allowed to compromise successful disinfection of drinking water, at least without data to support such decisions."1 Scientific Research Update: Chloroform Reassessment New research indicates that the health risks associated with chloroform, the primary component of THM by-products, are significantly lower than once believed, perhaps 2,000 times less than EPA's previous estimates. Since 1985, when EPA first established a very low "virtually safe dose" of 60 parts per billion (ppb) for chloroform, scientists have conducted numerous inhalation and ingestion studies of chloroform.37 These recent studies developed mechanistic data and biologically based models that allowed reevaluation of the original studies (NCI, 1976, 1985) relied on by EPA. The new results yield virtually safe doses ranging from 1,800 ppb to 56,000 ppb. Reassess-ments of the earlier research showed that chloroform's carcinogenic potential was found in laboratory rats only when ingested at extremely high doses and, in most cases, only if vital tissues were damaged first. There was no direct damage to genetic material (DNA) from chloroform ingestion. Considerable uncertainty remains about accurately extrapolating the cancer potency of chloroform from laboratory animals to humans. One factor is the high toxic doses consumed by laboratory animals compared with the low levels to which humans are exposed in drinking water. Another uncertainty relates to the unknown degree of similarity between how inhaled chloroform affects rodents and how it affects humans. Different risk models and biologically based models likely will yield a clearer picture of human dose-response and, therefore, a more realistic low-dose cancer risk assessment. EPA is already moving in this direction based on the new chloroform data.8,37
Alternatives to chlorination have been studied throughout the history of water treatment, and various disinfection methods have been proposed. Some treatment techniques have questionable value in drinking water treatment. Studies by Richard J. Bull and others indicated that alternative disinfectants produced a series of by-products. These findings demonstrated that all known methods (with the possible exception of ultraviolet radiation) of drinking water disinfection involve the use of reactive chemicals and, as such, lead to by-product formation.6 The water industry has been assessing alternatives to chlorine-based disinfectants. While each alternative has its advantages and disadvantages, all must be assessed on the basis of risks and uncertainties, as well as benefits. This is especially important in light of the limited experience and scientific knowledge associated with these processes. Compared with chlorination, relatively little is known about the potential by-products of alternative disinfectants. The known advantages and disadvantages associated with chlorine-based and alternative disinfection procedures are described below.13,15,40,45,51 Chlorine-based Disinfectants Chloramines This process involves the addition of ammonia and chlorine compounds to a water filtration plant. When properly controlled, the mixture forms chloramines. They are commonly used to maintain a residual in the distribution system following treatment with a stronger disinfectant, such as free chlorine. Chloramine advantages
Chloramine disadvantages
Chlorine Dioxide Chlorine dioxide is generated on-site at water treatment facilities. The popularity of chlorine dioxide as a water disinfectant increased in the 1970s when it was discovered that it did not promote THM formation. Chlorine dioxide advantages
Chlorine dioxide disadvantages
Ozone Ozone has been used for several decades in Europe for taste and odor control, color removal and disinfection. Ozone advantages
Ozone disadvantages
Ultraviolet Radiation
This process involves exposing water to ultraviolet (UV) radiation, which inactivates various microorganisms. The technique has enjoyed increased application in wastewater treatment but very limited application in potable water treatment. Ultraviolet radiation advantages
Ultraviolet radiation disadvantages
Scientific investigation of risk associated with alternative disinfectants and alternative disinfection by-products is limited. A decision by water facilities to switch from chlorination could be risky because scientists know so little about DBPs from processes other than chlorination.
*In Europe, 50% of water distribution systems use
chlorine dioxide as the residual disinfectant
EPA acknowledged during the development of disinfectant and disinfection by-product regulations that "we [EPA] currently do not have a good understanding of the by-products formed from alternate disinfectants and some of their associated health risks."48 Determining the health risks associated with disinfectants and disinfection by-products requires additional research especially focused on the major disinfection alternatives. According to William H. Glaze et al. (including Dr. Bull), research is needed to 1) assess the relative toxicological hazards of the disinfectants and their by-products, and 2) develop biologically based models for the dose-response relationships of these chemicals.27
Disinfectants react with natural organic matter (NOM) to form organic disenfection by-products (DBPs). Treatment techniques are available that provide water suppliers with the opportunity to maximize potable water safety and quality while minimizing the risk of DBP formation. One of the best methods to control DBPs from any disinfection process is to remove NOM precursors prior to disinfection. Other conventional methods include changing the point of chlorination, using chloramine in the distribution system and lowering the chlorine feed rate, although this may lead to unacceptable increases in microbial risk. An October 1991 American Water Works Association (AWWA) Water Quality Committee report identified effective procedures for reducing the formation of trihalomethanes (THMs), as follows:3 Organic Precursor Removal There are three ways to effectively remove NOM precursors:
In 1988, the American Chemistry Council launched Responsible Care®, the most ambitious and innovative health, safety and environmental improvement initiative in American industrial history. The initiative requires continuous performance improvement in the areas of community awareness and emergency response, pollution prevention, process safety, distribution, employee health and safety, and product stewardship. Every Responsible Care member is expected to improve performance in the following areas:
The chlorine industry is committed to continuous performance improvement in safety, health and environmental protection in the production, distribution and use of chlorine. The chlorine industry demonstrates this commitment through the active participation of member companies in the American Chemistry Council's Responsible Care® initiative and in the safety programs of the Chlorine Institute, Inc. Since 1924, the Chlorine Institute, Inc., has been the focal point of the North American chlorine industry's efforts to promote safety, health and environmental protection by being the source of technical and safety information on chlorine. The Institute's North American members account for over 98% of chlorine production and the vast majority of repackaged chlorine. The Institute has available over 150 items - pamphlets, drawings and audiovisual productions - developed by and for its members and for chlorine users. Many of these items are directly related to the use of elemental chlorine in drinking water disinfection and are utilized by many treatment facilities. The Chlorine Institute manages the Chlorine Emergency Plan (CHLOREP) to respond to chlorine emergencies. CHLOREP maintains a network of more than 200 highly trained mutual aid teams to deal with chlorine incidents across North America. CHLOREP teams respond to any emergencies in their sector, regardless of who owns the chlorine.10,11 In 1993, the Chlorine Chemistry Council (CCC) was created to promote science-based public policy regarding chlorine chemistry. CCC sponsors research projects, seminars and conferences designed to further society's knowledge of chlorine chemistry. CCC activities include:
The Research Foundation for Health and Environmental Effects, created by CCC, sponsors scientific research concerning the potential health and environmental effects of chlorine and other substances containing chlorine. Studies are submitted for publication in peer-reviewed journals. Research supported by CCC reflects its guiding principles of comparative risk assessment, risk management to promote the health and safety benefits and uses of chlorine chemistry, and responsible stewardship practices to prevent pollution. CANADIAN CHLORINE COORDINATING COMMITTEE The Canadian Chlorine Coordinating Committee (C4) was formed in the autumn of 1993 to facilitate and promote coordinated dialogue and action in Canada among key stakeholders in order to provide a balanced view of chlorine chemistry to enable society to make informed, science-based decisions on issues involving chlorine. Operating under a set of key principles, C4 and its members will
A large portion of C4's budget is used to sponsor research aimed at promoting science-based decision making on these issues. References
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