Intellectual Function in Mexican Children Living in a Mining Area and Environmentally Exposed to Manganese

BACKGROUND: Excessive exposure to manganese (Mn), an essential trace element, has been shown to be neurotoxic, especially when inhaled. Few studies have examined potential effects of Mn on cognitive functions of environmentally exposed children. OBJECTIVE: This study was intended to estimate environmental exposure to Mn resulting from mining and processing and to explore its association with intellectual function of school-age children. METHODS: Children between 7 and 11 years of age from the Molango mining district in central Mexico (n = 79) and communities with similar socioeconomic conditions that were outside the mining district (n = 93) participated in the cross-sectional evaluation. The revised version of the Wechsler Intelligence Scale for Children adapted for the Mexican population was applied. Concentrations of Mn in blood (MnB) and hair (MnH) were used as biomarkers of exposure. RESULTS: Exposed children had significantly higher median values for MnH (12.6 mu g/g) and MnB (9.5 mu g/L) than did nonexposed children (0.6 mu g/g and 8.0 mu g/L, respectively). MnH was inversely associated with Verbal IQ [beta = -0.29; 95% confidence interval (CI), -0.51 to -0.08], Performance IQ (beta = -0.08; 95% CI, -0.32 to 0.16), and Total Scale IQ (beta = -0.20; 95% CI, -0.42 to 0.02). MnB was inversely but nonsignificantly associated with Total and Verbal IQ score. Age and sex significantly modified associations of MnH, with the strongest inverse associations in young girls and little evidence of associations in boys at any age. Associations with MnB did not appear to be modified by sex but appeared to be limited to younger study participants. CONCLUSIONS: The findings from this study suggest that airborne Mn environmental exposure is inversely associated with intellectual function in young school-age children.