THE ASSOCIATION OF DRINKING-WATER SOURCE AND CHLORINATION BY-PRODUCTSWITH CANCER INCIDENCE AMONG POSTMENOPAUSAL WOMEN IN IOWA - A PROSPECTIVE COHORT STUDY

Objectives. This study assessed by the association of drinking water s ource and chlorination by-product exposure with cancer incidence. Meth ods. A cohort of 28237 Iowa women reported their drinking water source . Exposure to chlorination by-products was determined from statewide w ater quality data. Results. In comparision with women who used municip al groundwater sources, women with municipal surface water sources wer e at an increased risk of colon cancer and all cancers combined. A cle ar dose-response relation was observed between four categories of incr easing chloroform levels in finished drinking water and the risk of co lon cancer and all cancers combined. The relative risks were 1.00, 1.0 6, 1.39, and 1.68 for colon cancer and 1.00, 1.04, 1.24, and 1.25 for total cancers. No consistent association with either water source or c hloroform concentration was observed for other cancer sites. Conclusio ns. These results suggest that exposure to chlorination by-products in drinking water is associated with increased risk of colon cancer.