DRINKING-WATER SOURCE AND CHLORINATION BY-PRODUCTS-I - RISK OF BLADDER-CANCER

We conducted a population-based case control study of bladder cancer i n Iowa in 1986-1989 to evaluate the risk posed by tapwater containing chlorination byproducts. We combined information about residential his tory, drinking water source, beverage intake, and other factors with h istorical data from water utilities and measured contaminant levels to create in dices of past exposure to chlorination byproducts. The stud y comprised 1,123 cases and 1,983 controls who had data relat ing to a t least 70% of their lifetime drinking water source. After we adjusted for potential confounders, we calculated odds ratios for duration of chlorinated surface water of 1.0 (referent), 1.0, 1.1, 1.2, and 1.5 fo r 0, 1-19, 20-39, 40-59, and greater than or equal to 60 years of use. We also found associations with total and average lifetime byproduct intake, as represented by trihalomethane estimates. Positive findings were restricted to men and to ever-smokers. Among men, odds ratios wer e 1.0 (referent), 1.1, 1.3, 1.5, and 1.9, and among ever smokers, 1.0, 1.1, 1.3, 1.0, and 2.2, after adjustment for intensity and timing of smoking. Among nonsmoking men and women, regardless of smoking habit, there was no association. Among men, smoking and exposure to chlorinat ed surface water mutually enhanced the risk of bladder cancer. The ove rall association of bladder cancer risk with duration of chlorinated s urface water use that we found is consistent with the findings of othe r investigations, bur the differences in risk between men and women, a nd between smokers and nonsmokers, have not been widely observed.