title: Case-control study of colon and rectal cancers and chlorination by-products in treated water.
abstract: This population-based case-control study was conducted in southern Ontario, Canada from 1992 to 1994 to assess the relationship between chlorination by-products in public water supplies and cancers of the colon and rectum. Interviews providing residence and water source histories were completed by 76% of eligible cancer cases and 72% of eligible controls. Supplemental data from municipal water supplies were used to estimate individual exposure to water source, chlorination status, and by-product levels as represented by trihalomethanes (THMs) during the 40-year period before the interview. The analyses included 767 colon cases, 661 rectal cases, and 1545 controls with exposure information for at least 30 of these years (75% of subjects with completed interviews). Among males, colon cancer risk was associated with cumulative exposure to THMs, duration of exposure to chlorinated surface water, and duration of exposure to a THM level > or = 50 microg/liter and 75 microg/liter. Males exposed to chlorinated surface water for 35-40 years had an increased risk of colon cancer compared with those exposed for < 10 years (odds ratio, 1.53; 95% confidence interval, 1.13-2.09). Males exposed to an estimated THM level of 75 microg/liter for > or = 35 years had double the risk of those exposed for < 10 years (odds ratio, 2.10; 95% confidence interval, 1.21-3.66). In contrast, these relationships were not observed among females. No relationship was observed between rectal cancer risk and any of the measures of exposure to chlorination by-products. The results of this study should be interpreted with caution because they are only partially congruent with the limited amount of literature addressing this issue.
authors.affiliation: Department of Community Health and Epidemiology, Queen's University, Kingston, Ontario, Canada. kingw@post.queensu.ca
authors.forename: W D
authors.initials: WD
authors.lastname: King
authors.forename: L D
authors.initials: LD
authors.lastname: Marrett
authors.forename: C G
authors.initials: CG
authors.lastname: Woolcott
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D002713:Chlorine / Q000009:adverse effects*; D003110:Colonic Neoplasms / Q000453:epidemiology / Q000209:etiology*; D004326:Drinking; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D009864:Ontario / Q000453:epidemiology; D012004:Rectal Neoplasms / Q000453:epidemiology / Q000209:etiology*; D012307:Risk Factors; D012737:Sex Factors; D011795:Surveys and Questionnaires; D022882:Trihalomethanes / Q000032:analysis; D018508:Water Purification / Q000379:methods; D014881:Water Supply / Q000032:analysis
chemical_list: D022882:Trihalomethanes; D002713:Chlorine