Effects of prenatal lead, mercury, cadmium, and arsenic exposure on children's neurodevelopment in an artisanal small-scale gold mining area in Northwestern Tanzania using a multi-chemical exposure model.

An estimated 250 million children under five fail to reach their cognitive development potential in Africa. Growing evidence suggests reduced neurodevelopments for children from environmental exposures, yet research on this topic in Sub-Saharan Africa remains limited. This study examined the effects of multi-chemical prenatal exposure to heavy metals on developmental milestones for children aged 3-4 in artisanal and small gold mining areas in northwestern Tanzania. This longitudinal follow-up study of children whose mothers were enrolled in the Tanzania Mining and Health Cohort in Geita District in 2015 were assessed at 3-4 years of age for the current study between June 2019 - June 2020. Developmental outcomes (cognitive, social, motor, and language skills) were assessed using the Malawi Developmental Assessment Tool (MDAT). A quantile g-computation model evaluated the linkage between multi-chemical exposures and developmental milestones. Of the 310 children in the follow-up, a majority had at least one form of developmental impairment (50.7%; n = 157) across four domains: gross motor (20.3%), fine motor (23.9%), language (28.3%), and social skill (16.2%). Increased Pb, Hg, Cd, and As exposure jointly reduced gross motor by 17.78% (aPR = 0.822; 95% CI: 0.6994, 0.966). Joint exposure to these heavy metals decreased language ability by 55.36% (aPR = 0.446; 95% CI: 0.313, 0.636) and decreased general developmental milestones by 13.36% (aPR = 0.866; 95% CI: 0.747,1.005). However, the combined effect on the fine motor (aPR = 0.943; 95% CI: 0.754, 1.180) and social skills 6.71% (aPR = 1.067; 95% CI: 0.694, 1.641) were not statistically significant. Exposure to heavy metals while in utero reduced children neurodevelopmental milestones at 3-4 years of age. The cumulative impact of Pb, Hg, Cd, and As was significant for gross motor, language ability, and general impairment. The independent effects of Pb and Hg were amplified beyond what would be expected under the additive assumption with Cd and As, suggesting synergistic effects.