Hydropower vs Gold Mining: Unexpected Mercury Human Exposure Patterns in the Amazon

High Resolution Image Download MS PowerPoint Slide Mercury pollution remains a critical global health issue, with the Amazon region among the most affected areas due to gold mining using mercury (GMUM), deforestation, forest fires, and large-scale hydroelectric projects that may favor the formation of methylmercury (MeHg). This study presents the largest hair-based biomonitoring assessment of mercury exposure conducted to date across different regions of the Brazilian Amazon, analyzing nearly 900 samples from two representative scenarios: the Tapajós River basin (GMUM-impacted) and the Tucuruı́ area, influenced by one of the world’s largest hydroelectric power plants. Populations living in Tucuruı́, despite the absence of GMUM activity, exhibited median hair mercury concentrations more than twice those found in Tapajós, challenging the assumption that mercury exposure is confined to mining-affected areas. MeHg accounted for around 90% of total mercury, supporting fish consumption as the primary exposure route. Hydrological seasonality influenced exposure patterns, with significantly higher mercury levels during the wet season in Tapajós and no seasonal variation in Tucuruı́, suggesting more stable, year-round exposure patterns in the reservoir system. Regional, seasonal, and physiological factors significantly affected mercury levels. Notably, 63% of women of reproductive age in Tucuruí exceeded the 5 μg/g threshold associated with the increased risk of fetal neurodevelopmental impairment. Selenium concentrations were generally within the World Health Organization recommended ranges, but 90% of participants had Se:Hg molar ratios below 1, indicating limited potential for selenium-mediated mitigation of mercury toxicity. These findings underscore the urgent need for expanded biomonitoring beyond GMUM zones and for targeted public health interventions to mitigate mercury exposure in vulnerable Amazonian populations.