Evidence From Humans
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Case-control cancer mortality study and chlorination of drinking water in Louisiana
Gottlieb, M. S., Carr, J. K. Environ Health Perspect. 1982. 46, 169-77.
Topic area
Environmental pollutant - Drinking water, chlorination byproducts
Study design
Other: Case-control mortality
Study Participants
Menopausal Status
The menopausal status of women included in this study is listed here.
Post menopausal
Pre menopausal
Number of Controls
Controls: 847
Participant selection: Inclusion and exclusion criteria
Criteria used to select participants in the study.
Death certificate from selected Louisiana parishes for 1960-1975 and noncancer deaths matched by race, sex, year of death, and age.
Exposure Investigated
Exposures investigated
Address at death categorized by drinking water that was nonchlorinated (groundwater), chlorinated at a level below the mean (1.09 ppm), and chlorinated above the mean.
How exposure was measured
GIS/geographic location
Exposure assessment comment
Chlorination was associated with year of death, suggesting changes in chlorination practices during the study period. Chlorination at the source may not reflect chlorination at the tap at various locations in the distrubtion system.
Statistical Analysis
Breast cancer outcome investigated
Mortality from breast cancer
Ethnic groups with separate analysis
If this study provided a separate analysis by ethnic or racial group, the groups are listed here.
Confounders considered
Other breast cancer risk factors, such as family history, age at first birth, and hormone replacement therapy use, that were taken into account in the study.
Age, race, sex, year and parish of death controlled by matching.
Genetic characterization included
If the study analyzed relationships between environmental factors and inherited genetic variations, this field will be marked “Yes.” “No”, if not.
Description of major analysis
Multidimension contingency table analysis based on log-linear model and using maximum likelihood estimations to evaluate effect modification by matching variables.
Strength of associations reported
High chlorine OR 1.58 (1.09-2.29)
Low chlorine OR 1.61 (1.13-2.30)
No effect seen in urban parishes.
Results Comments
Authors suggest that elevated risk is due to confounding: nonchlorinated groundwater is associated with nonurban lifestyle, which is associated with lower breast cancer risk from established risk factors (e.g. reproductive history)
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.
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