Spatial Distribution, Ecotoxicological and Health Risks Assessment of Mercury in Topsoil within Tarkwa-Nsuaem Municipality, Ghana

Tarkwa-Nsuaem Municipality continues to benefit from Artisanal and Small-Scale Gold Mining (ASGM) but faces severe mercury (Hg) contamination risks. This study integrates geospatial analysis with ecotoxicological and human health risk assessment to unravel Hg distribution patterns and exposure pathways. Fifteen topsoil samples (A-O), were collected and analysed from the study sites. The analyses of the fifteen samples revealed extreme Hg pollution (mean 8,951 μg/kg), exceeding WHO limits (300 μg/kg) at all sites, with a distinct NW-SW contamination corridor near ASGM operational zones. Crucially, acidic soils (pH 4.68 - 6.54) in these hotspots amplified Hg mobility and bioavailability. For ecotoxicological risks, geo-accumulation indices (Igeo: 0.02 - 5.98) classified 14 sites as extremely polluted, and Ecological Risk Indices (ERI: 61 - 3,796) indicated very high risk at 14 sites, where site M near UMaT campus showed moderate risk (ERI = 61) and uncontaminated (Igeo: 0.02), aligning with the absence of ASGM activities. For health risks, children exhibited significant non-carcinogenic effects (Hazard Index, HI = 0.11 - 4.99) at 9 hotspots—predominantly via soil ingestion (>75% of total risk). Adults showed lower risks (HI ≤ 0.80) but faced inhalation exposure at processing sites (e.g., Site H). Acidic conditions (pH 2+ solubility and methylmercury formation potential by 60% - 80%, creating unquantified dietary threats. Spatial interpolation confirmed pH-Hg synergy maximized risks in the central mining belt. Based on outcomes, precision remediation of liming acidic hotspots (pH < 6.0), capping extreme-pollution sites (e.g., H, I, A), and restricting agriculture in the NW-SW corridor is recommended. This approach shifts Hg management from broad policies to source-targeted interventions, addressing Tarkwa’s biogeochemical crisis.