Mercury Exposure, Gene Expression, and Intelligence Quotient in Afro-Descendant Children from Two Colombian Regions

The impact of mercury (Hg) on biological systems is well documented; however, the long-term effects of low-level exposure in children remain unclear, particularly with respect to oxidative stress and cognitive outcomes. This study evaluated Hg exposure and its associations with the gene expression and intelligence quotient (IQ) in two Afro-descendant child populations in Colombia. Hair total mercury (T-Hg) was quantified in 163 children under 7 years old, along with their sociodemographic data. Significant differences (<i>p</i> < 0.05) were found in fish consumption and mean hair T-Hg concentrations between children from Mahates (2.66 ± 0.30 meals/week; 0.32 ± 0.03 µg/g) and Zanjón (1.24 ± 0.09 meals/week; 0.24 ± 0.01 µg/g). The gene expression analysis revealed higher SOD1 expression in Mahates. The mean IQ scores were higher in Zanjón (74.7) than those in Mahates (71.7). Overall, Spearman's correlation analysis showed no significant associations (<i>p</i> > 0.05) between T-Hg and the measured variables. The principal component analysis (PCA) revealed a clear separation between populations: Mahates, associated with a higher mercury burden and the upregulation of stress-response genes, and Zanjón, characterized by a better cognitive performance and lower mercury exposure. These findings suggest that despite the low overall exposure and non-significant bivariate correlations, the communities displayed distinct profiles, highlighting the value of integrated molecular-cognitive biomonitoring and motivate longitudinal studies addressing co-exposures and socioeconomic confounding.