Epidemiology of drinking water contaminants: inferring exposure through population biomarkers

Abstract

Background: In using drinking water contamination as an exposure indicator for environmental epidemiology, it is important to know how important an exposure route is drinking water. If the water concentrations contribute a low proportion of total intake, they are of little value in etiological studies of that contaminant. But can nevertheless be of use if the goal of the study is the estimate the effect of the drinking water component specifically, for example to underpin setting drinking water standards. The main focus of this talk is a study of perfluoro-octanoic acid (PFOA) exposure where drinking water is the overwhelming route of exposure. Methods: In the Mid-Ohio Valley approximately 80,000 people were exposed to PFOA contaminated drinking water for many years and many health effects were studied in these “C8 studies”. Most of the exposure came from 6 district water supplies with varying degrees of contamination. Within each district the water distribution led to fairly uniform concentrations but these varied over time. Over 60,000 people provided blood samples and PFOA measures in serum provided another metric for assessing exposure by water distribution area which integrated intake for each community. Water concentrations and serum concentrations were both collected in these communities Results: Geometric mean serum concentrations for PFOA ranged from 10 to 200 ng/ml by district, reflecting differences in water concentration, and these mean values have been used to assess the evidence of associations with several outcomes including cholesterol and thyroid hormones. Discussion: PFOA has the advantage of a very long half life in serum, about 3 years. Food related intake is significant as an exposure route in most communities. Where the water concentrations are high enough to dominate exposure, biomonitoring offers an efficient alternative to water measurements to assess exposure, integrating intake over recent years. Keywords: Water, water quality, biomarkers, perfluoro-octanoic acid, environmental epidemiology