Mercury contamination in Brazil related to (historical) artisanal and small-scale gold mining activity: a narrative...

Artisanal and Small-Scale Gold Mining (ASGM, known as garimpo in Brazilian Portuguese) remains a significant source of mercury (Hg) contamination worldwide, posing threats to both environmental integrity and One Health. Elevated Hg levels in affected regions typically arise from three interconnected pathways: (1) direct anthropogenic inputs of new mercury, such as elemental Hg released during gold amalgamation; (2) anthropogenic mobilization of existing Hg stocks through the mechanical disturbance of soils and sediments, including both legacy mining residues and naturally stored mercury; and (3) naturally occurring background mercury, derived from geogenic substrates and long-term atmospheric deposition into forested and aquatic ecosystems. This review synthesizes findings from peer-reviewed studies on garimpo-related Hg contamination in Brazil across multiple matrices, including human tissues, soils, sediments, water, air, and biota-and identifies the Amazon as a critical hotspot where high natural Hg backgrounds converge with historical and ongoing garimpos. Human exposure occurs primarily through occupational inhalation of elemental Hg vapor and dietary intake of methylmercury (MeHg) via fish consumption, particularly among riverine and Indigenous populations. Environmental compartments such as sediments, soils, and suspended particulate matter frequently exceed national prevention limits, underscoring mercury's persistence, mobility, and remobilization potential. Bioaccumulation is evident across trophic levels, with MeHg formation intensified under flooded, anoxic conditions typical of Amazonian wetlands and reservoirs. This complex interplay of geogenic, legacy, and active sources poses a sustained threat to ecological and human health. While Brazil's 2017 ratification of the Minamata Convention marks progress, reductions in fish MeHg may take decades, as stored Hg in floodplains continues to methylate. Effective mitigation will require mercury-free mining technologies, rigorous law enforcement, culturally appropriate health responses, and expanded monitoring tailored to geological and biogeochemical variability. Collectively, this integrated assessment highlights the multi-faceted nature of garimpo-related Hg contamination and provides insights to guide research priorities, policy frameworks, and stakeholder actions aimed at safeguarding human well-being and ecosystem health across Brazil.