Heavy metal contamination and health risks in Katoro's artisanal gold mining soils, Tanzania

This study assessed heavy metal contamination in surface soils from artisanal gold mining areas in Katoro, Tanzania, evaluating ecological and human health risks. Thirty-six soil samples were systematically collected from three mining villages (Bingwa, Isenye, and CCM) at varying distances ranging from 30 to 90 m from active mining pits alongside twelve control samples from a non-mining area for comparison purposes. Concentrations of Cr, Cu, Ni, Zn, Pb, and As in soil samples were analyzed using energy-dispersive X-ray fluorescence spectrometry (EDXRF). Results revealed severe contamination, with Cr (117–1255 mg/kg), Cu (81–104 mg/kg), and Ni (89–271 mg/kg) exceeding permissible limits. The geoaccumulation (Igeo) index indicated moderate to heavy contamination (Class II-III) for Cr, Cu and Ni. Meanwhile, the ecological risk assessment showed moderate risk (ERI = 154.41) across the study area highest being in Isenye village (ERI = 204.46). Health risk models identified ingestion as the primary exposure pathway, with hazard indices (HI) below 1, suggesting negligible non-carcinogenic risks. However, lifetime cancer risks for As (1.21×10⁻⁴) and Cr (3.59×10⁻³) surpassed acceptable thresholds (1×10⁻⁴), indicating significant carcinogenic concerns, particularly for children. These findings underscore the urgent need for remediation and stricter regulations to mitigate contamination from artisanal mining activities.