Exposure to manganese from drinking water and IQ in school-age children

Abstract

Background: Manganese is a naturally occurring element and can be found in underground water at high concentrations. This element is a known neurotoxicant, although this has mostly been documented with workplace airborne exposure. A growing body of data suggests that exposure to manganese in drinking water could be neurotoxic. Our objective was to examine the association between exposure to manganese from drinking water and cognitive function in children. Methods: We recruited 262 children consuming groundwater, and assessed their cognition with the WASI (yielding Performance, Verbal and Full Scale IQ scores). To estimate exposure, we measured manganese concentration in home tap water and in children’s hair and toenail. We used linear regression analysis to assess the relation between log10 manganese exposure indicators and IQ scores in boys and girls, adjusting for potential confounders. Results: Drinking water manganese concentrations were generally low, with 48% of children consuming water below 5 μg manganese/L, 25% above 50 μg/L, and 4% above 400 μg/L. In girls, higher levels of exposure as indicated by all indicators (manganese concentration in water, hair, and toe nail) were consistently associated with poorer Performance IQ scores. However, these relations were not statistically significant after covariate adjustment, except for the association between log10 toe nail manganese concentration and Performance IQ (: -5.9, 95% CI: -11.8, -0.04). In boys, there was no clear association between manganese exposure indicators and IQ scores. Conclusions: Drinking water manganese levels were considerably lower than in previous studies reporting neurotoxic effects. Manganese exposure appeared associated in a dose-dependent way with lower Performance IQ scores in girls but not in boys. Studies should further examine the risks of manganese-contaminated drinking water, with a sample size sufficient to detect sex-specific effects.