Gold at the price of health: Multi-metallic soil pollution by artisanal gold mining in Siguiri (Guinea)—ecological risks and human exposure

Artisanal gold mining is the world’s leading anthropogenic emitter of mercury. Despite the intensity of this activity in Siguiri (Guinea), no geochemical or quantitative health assessment has been published. This study carries out a multi-parametric assessment of trace metal contamination in Siguiri’s gold panning soils and quantifies the associated ecological and health risks. Forty-eight samples (0–20 cm; six localities) were analyzed by portable X-ray fluorescence (pXRF) for nine trace metal elements (As, Hg, Cr, V, Co, Ni, Pb, Cu, Zn). Contamination indices (contamination factor [CF], geo-accumulation index [I geo ], pollution load index [PLI]), ecological risk, sources (principal component analysis [ACP], hierarchical agglomerative clustering [HAC]), and health risks were determined. Soils were found to exhibit alkaline to very strongly alkaline pH (8.16–9.57), values unprecedented for tropical ferralsols in West Africa, likely attributable to artisanal gold mining. A ternary geochemical signature was identified: an anthropogenic mercury pole (Hg: 12.1–21.3 mg/kg; 12–21 times the World Health Organization [WHO] threshold), a Birimian arsenopyrite–cobaltite pole (As: 521 mg/kg; Co: 519 mg/kg), and an ultrabasic Cr–V pole (Cr: 635 mg/kg). Ecological risk (RI = 9086–15,240) exceeded the very high threshold at all six sites. Noncarcinogenic risk (hazard index [HI] > 1) was unacceptable for adults at five sites and for children at all six; total carcinogenic risk (TCR > 10 −4 ) was exceeded at four sites in adults and all six in children; the cereal pathway dominates arsenic exposure (+6619% at Koboni). These results fill a major scientific gap and provide the Guinean authorities with the factual basis for implementation of the Minamata Convention, restricting cereal crops and establishing a biomedical monitoring program in Siguiri.