

@article {16029,
	title = {Chapter 7: Drinking water and wastewaters},
	journal = {Regulatory Toxicology and PharmacologyRegulatory Toxicology and Pharmacology},
	volume = {20},
	number = {1, Part 2},
	year = {1994},
	pages = {S416-S539},
	abstract = {The following chapter provides an assessment of the possible human and environmental health effects associated with exposure to chemicals arising from the disinfection of drinking water and wastewater using chlorine. In addition, the benefits associated with disinfection of water using chlorine and the potential risks and benefits associated with other disinfection processes are discussed. The overall conclusions of this interpretive review are that the disinfection of drinking water and wastewaters with chlorine continues  to be the treatment of choice. The recent concern over trihalomethanes and other chlorinated organic chemicals in drinking water has resulted in a better understanding of chlorine chemistry in disinfection/oxidation processes. This has led to improvements in water treatment processes to remove precursors of the chlorinated organics and minimize chlorine contact time resulting in significant reductions in the  chlorinated by-products formed. These advances in water treatment technology using chlorine will further reduce estimated exposures to chlorinated organic chemicals through consumption of drinking water. The treatment of water supplies by chlorination has proven highly effective in destroying or inactivating human pathogenic microorganisms, as indicated by reported reductions of cholera incidences by 90\%, leptospirosis and typhoid fever by80\%,amoebic dysentery by 50\%, and ascariasis by 40\% following conventional water treatment including chlorine. In terms of concentration-contact time, chlorine provides one of the most effective water disinfection methodologies available. However, human health concerns over the detection of trace concentrations (ppb or less) of chlorinated chemicals (e.g., trihalomethanes) in the finished drinking water have raised the interest in alternative disinfection processes. Alternative methods for water disinfection that have been tested to varying degrees include the use of ozone,  chlorine dioxide, chloramine, ultraviolet (uv) light, and ultrasonic waves. To be an effective drinking water treatment, the agent must not only demonstrate excellent biocidal activity against pathogenic bacteria, viruses, and other microorganisms, but it should also improve the organoleptic qualities of raw water and provide residual disinfectant action throughout the  water distribution system. Few of the present alternative methodologies to chlorination meet all three requirements. The major conclusions of the  comparative review of the alternative disinfection methods to chlorine are: (i) Compared to chlorine, ozone has a greater oxidation potential requiring shorter contact times and lower concentrations to achieve 99\% destruction of bacteria, viruses, and other pathogenic microorganisms, has a greater potential for the removal of odorand taste-producing chlorophenolics, and does not react with ammonia. The primary disadvantages in the use ofozonation in the treatment of drinking water are the inability to retain residual concentrations of ozone, and therefore, disinfection, in water in the distribution system, and potential adverse effects associated with by-products formed during ozonation. Consequently, the treatment of potable waters in modem distribution systems cannot be achieved through ozonation alone. Rather, some other form of disinfection (i.e., chlorine, chlorine dioxide, chloramine, or other technology) must be used to prevent recontamination of the water supply during distribution. Furthermore, the potential adverse health effects associated with ozonation disinfection by- products are poorly understood and some may be potentially more potent inducers of adverse effects than chlorine disinfection by-products. (ii) Chlorine dioxide for drinking water disinfection provides excellent biocidal efficacy and long-lasting residual concentrations in the distribution system. Unlike chlorine, chlorine dioxide does not react with ammonia to form chloramines. Chlorine dioxide treatment also produces much lower concentrations of chlorinated organic chemicals than chlorine and little if any trihalomethanes. However, two inorganic breakdown products of chlorine dioxide (chlorate and chlorite) remain in the treated water. Extreme exposures of animals under laboratory conditions to chlorates/chlorites have been associated with adverse effects; however, there are questions as to whether these concerns would occur at the chlorate/chlorite concentrations typically found in drinking water disinfected with chlorine dioxide. (iii) Compared to chlorination, chloramination treatment procedures result in lower concentrations of chlorinated organic by-products (e.g., virtually no trihalomethanes, haloacetic acids, or haloketones are produced). However, there are serious concerns regarding the potential toxicity of the chloramine itself. Chloramine does not dissociate in water; therefore, the potential exists for direct human exposure to substantial quantities of chloramine from consumption of treated water. Positive hepatotoxicity in laboratory studies and an increased incidence of monocellular leukemia reported in female rats consuming chloramine in drinking water have been interpreted as "equivocal evidence of cancer" and have raised concerns regarding the potential adverse effects from human exposures to chloramine. (iv) The effectiveness of physical treatments such as uv and ultrasonic radiation, is dependent on the physical characteristics of the source water. In addition, these technologies do not provide for residual disinfection that is important in maintaining water quality in the distribution system. Concerns about the formation of various chlorinated organic chemicals during the disinfection of drinking water and wastewaters with chlorine have focused attention on these chemicals. The remainder of the assessment focused on specific chlorinated chemicals that were selected in the chemical selection process. The major conclusions from this assessment were: (i) The assessment demonstrated that no human health impacts would be expected to be associated with the chlorinated by-products from the chlorinated acid, aldehyde, alkane, or phenol classes of chemicals assessed. (ii) The assessment of the potential adverse health effects from the concentrations of chlorinated ketones and nitrogen chemicals that are produced during the disinfection of drinking water with chlorine was inconclusive. The assessment of potential adverse effects from possible exposures to these chemicals was limited by the inadequacies of S418 the toxicological data available and the limited information on their concentrations in drinking water. However, even with these limitations, it was considered unlikely that the low ppb concentrations of chlorinated ketones and nitrogen compounds would result in measurable adverse impacts on human health. Any possible adverse effects from chlorine disinfection of wastewaters would be limited to exposures of wildlife to chlorination by-products in surface waters receiving wastewater discharges. The assessment of these possible effects was limited by the lack of information on whether the chlorinated organic chemicals identified were chlorination by-products or were present in the wastewaters prior to disinfection or were present in receiving waters from another source. Comparisons were made among end-of-pipe concentrations and concentrations of chemicals that have been associated with adverse effects in fish, in piscivorous wildlife, or in terrestrial wildlife. Waterborne concentrations were considerably lower than concentrations associated with adverse effects. However, for chemicals that have very low solubility in water and bioaccumulate in the food chain, the concentrations in tissues of their prey rather than waterborne concentrations are better indicators of the potential for adverse effects. Consequently, chemicals with a log octanol/water partition coefficient (Kow) of >4 were assessed using a food chain approach. Ambient chemical concentrations in fish were used in this approach since concentrations in fish directly related to wastewater were not available. The assessments of these chemicals indicated that past concentrations of hexachlorobenzenes, pentachlorophenol, and polychlorihated dibenzo-p-dioxins and dibenzofurans were sufficiently high to raise concerns about possible adverse reproductive effects in piscivorous wildlife. Current concentrations are significantly lower than those observed in the late 1970s and early 1980s, resulting in significantly lower exposures to piscivorous wildlife. },
	isbn = {0273-2300}
}
