FEMALE BREAST-CANCER AND TRIHALOMETHANE LEVELS IN DRINKING-WATER IN NORTH-CAROLINA

Some studies indicate that chlorination by-products in drinking water may contribute slightly to breast cancer risk. This ecologic study des cribes the association between total trihalomethane levels in publicly supplied water and the incidence of female invasive breast cancer. We included 71 North Carolina water suppliers serving at least 10,000 cu stomers in the summer of 1995 as the units of analysis. We estimated i ncidence rates using 6,462 cases who were either white or black and be tween 35 and 84 years old and were linked by zip codes to the water su pplier. We treated ecologic measurements of age, income, education, ur ban status, and race as potential confounders. Total trihalomethane le vels were not associated materially with breast cancer risk, adjusting for potential confounders. The rate ratio for 80.0 parts per billion (ppb) or more us less than 40.0 ppb total trihalomethanes was 1.1 [95% confidence interval (CI) = 0.9-1.2]. When stratified by race, the obs erved association for the aforementioned total trihalomethane category was not very different in black women (rate ratio = 1.2; 95% CI = 0.8 -1.8) than in white women (rate ratio = 1.1; 95% CI = 0.9-1.3). These ecologic data are compatible with trihalomethanes in drinking water be ing either unrelated or weakly related to breast cancer risk.