Chlorination disinfection by-products in drinking water and the risk of adult leukemia in Canada.

The authors conducted a population-based case-control study of 1,068 incident leukemia cases and 5,039 controls aged 20-74 years during 1994-1997 to examine the association between exposure to drinking water chlorination disinfection by-products and adult leukemia risk in Canada. Residence and drinking water source histories and data from municipal water supplies were used to estimate individual chlorination disinfection by-product exposure according to water source, chlorination status, and chlorination disinfection by-product levels during the 40-year period before the interview. The analysis included 686 cases and 3,420 controls for whom water quality information was available for at least 30 of these years. Increased risk of chronic myeloid leukemia was associated with increasing years of exposure to different chlorination disinfection by-product indexes, with an adjusted odds ratio of 1.72 (95% confidence interval: 1.01, 3.08) for the highest exposure duration to total trihalomethanes of more than 40 microg/liter. In contrast, the risk of the other studied leukemia subtypes was found to decrease with increasing years of exposure to chlorination disinfection by-products. A protective effect was noted for chronic lymphoid leukemia (odds ratio = 0.60, 95 percent confidence interval: 0.41, 0.87) associated with the highest exposure duration to total trihalomethanes of more than 40 microg/liter. More studies with long-term exposure measures and large enough to evaluate leukemia subtypes are needed to further understanding of the issue.