The hypothesis tested in this study was that low level exposure to manganese in children through drinking water is associated with impaired cognitive performance on standardized tests of intellectual function. The study was based on the pathological and toxicological effects of exposure to manganese in laboratory animals and recent epidemiologic evidence showing an association between exposures to manganese in drinking water and decreased intellectual function (IQ) as well as hyperactive behaviors in children. A clear analogy with lead exists. California has a statewide monitoring system for drinking water manganese which was used to identify school districts for water sampling and analysis. Target school districts were identified for sampling from the California Department of Public Health Drinking Water Program. 100 schools within those cities were identified with manganese concentrations ranging from 20 mug/L to over 900 mug/L. Water samples were collected (n=81), analyzed for manganese concentration (ppb), and grouped into three exposure categories High (>30mug/L), Low (2-29mug/L), and ND (< 2mug/L). Cognitive assessment was determined from standardized test score data for 3rd, 4th, and 5th grade children from the California Standardized Testing and Reporting Program (STAR) for each school. Analysis of Variance, Analysis of Covariance, and Mixed Effect General Linear Regression analyses were used to analyze the data and adjusted for covariates including age, gender, ethnicity, parental education and economic status. The results of this study did not suggest mean test scores to be significantly different between high, low, and non-detect manganese exposure groups when adjusted for confounders. Mean test scores were not highest in the non-detect exposure group and lowest in the high exposure group as predicted.
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