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Chemistry International
Vol. 23, No. 6
November 2001


New Publications from the World Health Organization

Disinfectants and Disinfectant By-products, Environmental Health Criteria No. 216, 2000, xxvii + 499 pages (English, with summaries in French and Spanish), ISBN 92-4-157216 -7, CHF 102.-/ USD 91.80; In developing countries: CHF 71.40, Order No. 1160216. WHO Marketing and Dissemination, CH-1211 Geneva 27, Switzerland; E-mail: [email protected]; Tel.: +41 22 791 24 76; Fax: +41 22 791 48 57.

This book evaluates the risks to human health posed by disinfectants and disinfectant by-products found in treated drinking-water. Noting that chlorine and other widely used disinfectants were approved for use almost 100 years ago, when toxicological data were limited, the report responds to the need for reassurance that consumption of treated drinking-water will not have adverse effects on health. Particular concern centers on the potential of chlorine to react with natural organic matter and form a large number of by-products, some of which have been intensively studied as potential human carcinogens. With these concerns in mind, the report evaluates over 800 recent studies in an effort to clarify understanding of the chemistry and toxicology of disinfectants and disinfectant by-products, and provide a balanced assessment of the associated risks to human health.

The report is issued at a time when public health authorities and utilities providers in several countries are considering alternative methods of disinfection aimed at reducing the formation of specific by-products. In this context, the report stresses the overriding importance of microbiological safety, and warns that adequate disinfection must not be compromised by efforts to control chemical by-products.

The first chapter, on the chemistry of disinfectants and disinfectant by-products, examines the many complex factors, including methods of water treatment, that govern the formation of by-products and influence their type and amount. Of special interest to utilities providers, the chapter explains the physical and chemical properties that influence the behavior of specific by-products in drinking-water and determine their toxic actions. By-products of greatest concern are identified as trihalomethanes, including chloroform and bromodichloromethane; haloacetic acids, including dichloroacetic acid and trichloroacetic acid; bromate; and chlorite. The chapter concludes that the adoption of alternative disinfecting chemicals often amounts to nothing more than a trade-off between one group of byproducts and another. Removal of natural organic matter is singled out as the most effective control strategy. Chapter 2 reviews what is known about the toxic effects of the principal disinfectants: chlorine and hypochlorite, chloramine, and chlorine dioxide. On the basis of this evaluation, the report concludes that disinfectants probably do not increase the risk of cancer or have other significant adverse effects on health. Chapter 3 evaluates the toxic effects of 14 by-products, concentrating on the large number of studies of carcinogenicity and mutagenicity.

Epidemiological studies are reviewed in Chapter 4, which considers extensive investigations of possible associations with cancer, cardiovascular disease, and adverse effects on reproduction and development. While most studies have concentrated on an increased risk of bladder cancer, risks of colon, rectal, and other cancers have also been investigated. Noting the uncertainties surrounding many of these studies, the report cautions against a simple interpretation of observed associations and concludes that more comprehensive water quality data must be collected to improve exposure assessments. Evidence was considered insufficient to determine whether observed associations are causal and which specific by-products or other contaminants play a role. In the final chapters, focused on risk characterization and assessment, the report concludes that the risks to health from disinfectant by-products, at the levels at which they occur in drinking-water, are extremely small in comparison with the risks associated with inadequate disinfection. In supporting efforts to minimize the formation of by-products, the report further concludes that protection of source waters, aimed at reducing the presence of natural organic matter, is often the most efficient approach to control.




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