Neurodevelopment Outcomes in Children Exposed to Organic Mercury from Multiple Sources in a Tin-Ore Mine Environment in Brazil

Methylmercury (from fresh-water fish) and ethylmercury [from thimerosal-containing vaccines (TCVs)] are the most prevalent source of neurotoxic exposure during early life in families consuming fish and using these vaccines. But children living in Amazonian mining environments are exposed to additional toxic metals in waste materials. We studied mercury (Hg) exposure and neurodevelopment in 294 children (105 boys and 189 girls) from Bom Futuro (Rondonia, Brazil), the epicenter of a tin-ore open-pit mine. Hair-Hg (HHg) concentrations and total ethylmercury (from TCVs) were taken from infants and respective mothers during pregnancy. We used bivariate analysis to determine the effect of sex and linear mixed models to assess the association of prenatal and postnatal organic Hg exposures with children’s Bayley Scales of Infant Development (BSID) as psychomotor developmental index and mental developmental index (MDI) at 6 and 24 months of age as well as milestones achievements (age of walking and age of talking). Significant differences between boys and girls were observed for both MDI score ( p = 0.0073) and MDI score ( p = 0.0288) at 6 months but not at 24 months. Regression analysis showed that only in boys was there a significant interaction between MDI score with family income ( β = 0.288, p = 0.018) and with birth weight ( β = −0.216, p = 0.036) at 6 months; at 24 months, however, only boys showed a significant association of both MDI score ( β = −0.222, p = 0.045) and MDI score ( β = −0.222, p = 0.045) with neonatal HHg. In boys, age of walking was associated with HHg ( β = 0.188, p = 0.019) and breastfeeding ( β = −0.282, p = 0.000), whereas for girls, age of walking was only associated with breastfeeding ( β = −0.275, p = 0.001). In this mining environment, with only a weak association for prenatal Hg exposure, there was a significant sex difference in neurodevelopment, with boys showing more sensitivity related to BSID delays.