Environmental geochemistry and ecological risk assessment of potentially harmful elements in tropical semi-arid soils around the Bagassi South artisanal gold mining site, Burkina Faso

Abstract This study investigates geochemistry and ecological risk of artisanal gold mining-derived potentially harmful elements in semi-arid soils in Burkina Faso. R-mode factor analysis, which reduces the variables (elements) to few factors, was applied to explain the dominant variance in the data. Three factors, which account 80% of the total variance, described differences in soil geochemistry resulting from anthropogenic and geogenic sources. High loadings of factor 1 on As, Au, Bi, Cd, Hg, Mo, Pb, Sb, Te, W and Zn suggest that the artisanal gold mining was the most important factor controlling the soil geochemistry. Factor 2 had high loadings on Al, Fe, Mn, Ti, Co, Cr, Cu, Ni, Sc, Sr, Tl and V, representing their geogenic origin. With high loadings on Ca, Mg, S and La, factor 3 describes contribution of biogeochemical cycling to the elements’ abundance in the soils. Lead isotope compositions identified atmospheric deposition as the main source of Pb in farmland soils, whereas topsoil and soil profiles were primarily influenced by the mining activities. Mercury, As and, to a lesser degree, Cd posed the most serious ecological threat to the soils collected around the mining site relative to those of the farmland. Based on the findings of this study, a best pollution control plan of potentially harmful element loadings into soils is urgently required around artisanal gold mining sites across the country.