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.