Epidemiologic Study of Drinking Water Chlorination and Wisconsin Female Cancer Mortality2

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Abstract
The association between gastrointestinal, urinary tract, brain, lung, and breast cancer mortality and drinking water trihalomethane exposure, as estimated by average daily chlorine dosage of water source 20 years past, was investigated for Wisconsin white females by use of a death certificate-based case-control study design. A total of 8,029 cancer deaths and 8,029 controls (noncancer deaths) matched on county of residence, year of death, and age were taken from mortality records of 28 counties for the years 1972–77. Data on characteristics and treatment of municipal water supplied to the residences of cases and controls were obtained from questionnaires sent to the water superintendents of the 202 waterworks associated with the sample. By the use of logistic regression analysis, odds ratios for site-specific cancer death associated with high, medium, and low chlorine-dosed water as compared to unchlorinated water exposure were determined; the control variables were urbanicity, marital status, and occupation. With the exception of cancer of the colon, no anatomic cancer site was significantly associated with any chlorine dose exposure category. For colon cancer, odds ratios of 1.51 [95% confidence interval (CI) = 1.06–2.14], 1.53 (95% CI = 1.08–2.00), and 1.53 (95% CI = 1.11––2.11) were obtained for high-, medium-, and low-dose chlorination, respectively (P≤0.02). For colon cancer cases and controls exposed to water sources affected by rural runoff, odds ratios of 3.30 (95% CI = 1.45–7.48), 3.60 (95% CI = 1.57–8.26), and 2.74 (95% CI = 1.10–6.88) were observed for high, medium, and low chlorine dosages 20 years past (P≤0.025).

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