Water chlorination, mutagenicity, and cancer epidemiology

Studies of drinking water chlorination and mutagenicity should be interpreted with caution. A Finnish study by links water chlorination with bladder and kidney cancer. Chlorination of public drinking water supplies over almost 90 years in the US has resulted in safe, disinfected water which prevents transmission of water-borne diseases. Byproducts of chlorination such as trihalomethanes were first discovered in drinking water supplies 20 years ago, and since then, hundreds of nonvolatile chlorinated hydrocarbons of higher molecular weight have been detected. Linking such substances with occurrence of cancer should be done only after analyzing carefully done case-controlled interview studies or cohort studies. Historical records of drinking water supplies are more comprehensive in Finland than in the US, so extrapolating Finnish results to the US may be difficult.