Case-control cancer mortality study and chlorination of drinking water in Louisiana.

Several Louisiana parishes (counties) using the Mississippi River for their source of public drinking water have the highest mortality rates (1950-69) in the United States for several cancers. Therefore, a case-control mortality study on cancer of the liver, brain, pancreas, bladder, kidney, prostate, rectum, colon, esophagus, stomach, non-Hodgkin's lymphoma, multiple myeloma, leukemia, Hodgkin's disease, lung; breast and malignant melanoma, from 1960 to 1975 in South Louisiana parishes grouped for similarities in industrial characteristics, having approximately equal exposure of the population to surface and groundwater, was conducted. Noncancer deaths were randomly selected as controls and matched to the case death on age, race, sex, and year and parish group of death. Water source at death was assigned based on the residence at death and described as surface or ground and chlorinated or nonchlorinated. A significantly increased risk for surface, chlorinated water use was noted for rectal cancer. No risk could be demonstrated for colon cancer. The risk noted for bladder cancer by other investigators is not substantiated. Brain cancer risk appears to be associated with chlorinated groundwater, but this may be industrial confounding. Breast cancer demonstrated a slight, but significant, risk associated with surface chlorinated water. This risk, however, might be due to confounding of rural life style, early childbearing and large families with nonchlorinated water found in these settings. Chlorination risk for kidney cancer was not significant. No risk was observed in association with surface water for other cancers of the gastrointestinal or urinary tract. Multiple myeloma was significantly associated with a risk from ground water.