SCIENCE/HEALTH ABSTRACTS
Vol. 2, No. 4
Copyright 1983 Phylis Austin

The President's Council on Environmental Quality has released studies that suggest an association between rectal, bladder, and colon cancer and chlorinated water. The report indicated that people who drink chlorinated water have a greater risk of developing one of these forms of cancer than do people who drink well water. The increased risk ran from 19 to 93 percent. Carcinogens produced by the action of the chlorine on naturally occurring compounds in the water is felt to be the cause, rather than the chlorine itself. (Science 211:694, February 13, 1981)

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Environmental Health Monthly
Volume 7, Number 11 - August 1995

Koivusalo, M., Jaakkola, J., Vartianinen, T., et. al. Drinking water mutagenicity and gastrointestinal and urinary tract cancers: an ecological study in Finland. American Journal of Public Health, 84(8): 1123-[?] (August, 1994).

Abstract: Water Chlorination, Mutagenicity and Cancer

Chlorination is the disinfectant of choice in U.S. public water supplies and has no doubt prevented much widespread illness and disease over the years. Yet, for more than 20 years scientists have known that chlorination causes the formation of carcinogenic and mutagenic substances, notably chloroform and other trihalomethanes (bromoform, dibromochloromethane and bromochloromethane). In 1979, the US Environmental Protection Agency (EPA) set a limit of 100 ug/liter (parts per billion) for trihalomethanes in drinking water. More recently hundreds of nonvolatile chlorinated substances have been identified in municipal drinking water including chlorinated ketones, aldehydes, carboxylic acids and alcohols. These substances form when chlorine reacts with organic matter, mostly naturally occurring humic and fulvic acids, in untreated water. Many of these substances are mutagenic.

The article by Koivusalo et al. in this issue examined the relationship between mutagenic drinking water and cancer of the gastrointestinal and urinary tract in 56 Finnish communities. The authors found a statistically significant exposurerelated association between exposure and the incidence of bladder, kidney and stomach cancers.

The authors looked at cancer occurring during two time periods (1967 to 1976 and 1977 to 1986). Age, sex, social class, urban living and time period were taken into consideration. The relative risk was defined as 1.2 for bladder cancer and 1.2 to 1.4 for kidney cancer for municipalities that rely on surface water that is chlorinated compared to municipalities where nonmutagenic drinking water was consumed. The authors concluded that "acidic mutagenic compounds present in chlorinated drinking water may play a role in the etiology of kidney, bladder and possibly stomach cancer." This finding is consistent with results from earlier studies that found similar associations between consumption of drinking water and increases in gastrointestinal and urinary tract cancers.

A unique approach to estimating exposure was used in this study. The authors measured the mutagenicity of recent drinking water samples and then used computer models to estimate the mutagenic activity of the water in the years 1955 to 1970. The applicability of this approach to U.S. water treatment systems seems promising and warrants attention.

The accompanying editorial by Kenneth Cantor of the National Cancer Institute, supports recent EPA efforts to require water treatment utilities to reduce chlorination practices. Cantor comments that "the available information supports the concern over an elevated carcinogenic risk, and is more than adequate to motivate water utility operators to minimize exposure to chlorinated byproducts while maintaining control of microbiological contamination."

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Chlorinating: Linked To Increased Cancer Risk

Women exposed to elevated levels of chlorination by-products in drinking water are at an increased risk of developing colon cancer, according to a report in Reuters this week.

In the July American Journal of Public Health, Dr. Wei Zheng of the University of Minnesota in Minneapolis explains that water supplied to community residents by municipalities can be "...100% ground water, a mixture of ground water and surface water, or 100% surface water." Surface water supplies, they say "...have consistently been shown to have higher concentrations of chlorination by-products." These by-products, including trihalomethanes, have been linked with an elevated risk of cancer. With that in mind, Dr. Zheng's team assessed "...the association of drinking water source and chlorination by-product exposure with cancer incidence," in 28,237 participants of the Iowa Women's Health Study. Dr. Zheng reports that "...women who resided in areas supplied with municipal surface water or water with higher levels of chloroform were at significantly increased risk for colon cancer and total combined cancer." After adjusting for potential confounders, there was a dose-dependent increase in the risk of these cancers with increasing levels of chloroform. The relative risk for colon cancer was 1.68 times greater for the highest levels of chloroform compared with the lowest level. Although " mechanisms of carcinogenesis caused by exposure to chlorination by-products are not fully understood," Dr. Zheng says that they "...are likely to be due to a tumour promotion effect on mucosal epithelial tissue via direct contact."