Temporal changes and sociodemographic determinants of mercury exposure in Madeira River communities, Brazilian Amazon

Riverine populations in the Brazilian Amazon are chronically exposed to mercury (Hg), primarily through fish consumption. This study assessed temporal trends, sociodemographic determinants, and health risks associated with Hg exposure in three riverside communities (Nazaré, Calama, and São Carlos) in the Madeira River basin (Western Amazon). Total mercury (THg) was quantified in hair samples from 618 adults collected in 2022 and compared with data obtained two decades earlier by our research group. Mean THg concentration was 7.82 ± 8.18 mg kg^-1, with 90% of individuals exceeding the U.S. EPA safety threshold and 76% surpassing the FAO/WHO guideline. A significant temporal decline was observed only in Nazaré, but exposure levels remained persistently above international health thresholds in all communities. Lower educational attainment and exclusive fish consumption were consistently associated with higher THg concentrations. Age and length of residence further influenced exposure patterns in specific communities. Risk assessment based on the most frequently consumed fish species showed estimated weekly intakes exceeding the provisional tolerable weekly intake for nearly all trophic groups, particularly omnivorous and piscivorous species. Hazard quotient values were significantly greater than 1, suggesting potential non-carcinogenic health risks. Although herbivorous species presented comparatively lower exposure risks, current consumption rates still exceed safe limits. Our findings demonstrate that biomagnification within aquatic food webs, combined with socioeconomic vulnerability and dietary dependence on fish, sustains elevated Hg exposure despite reductions in regional gold mining. These results underscore the urgent need for culturally appropriate public health interventions that promote safer fish consumption patterns while preserving the nutritional importance of fisheries for Amazonian riverine populations.