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.

Keywords:

• potentially harmful elements
• artisanal gold mining
• geochemistry
• ecological risk
• pedogeochemical processes

Public interest statement

The study describes the anthropogenic and geogenic sources of artisanal gold mining-derived potentially toxic heavy metals/metalloids and their ecological impacts on semi-arid soils in southwestern Burkina Faso. Even though artisanal gold mining contributes to poverty alleviation in rural communities, it causes several environmental problems such deforestation, soil degradation and water and air pollution. The release and accumulation of large quantities of potentially harmful elements in the surrounding soils can pose serious threat to human health and also to ecosystems. The presence of hundreds of uncontrolled artisanal gold mining sites around rural dwellings and farmlands across the country makes environmental geochemistry and ecological risk assessment of potentially harmful elements in soils highly important.

Competing interests

The authors declares no competing interests.

Acknowledgements

The authors thank Dr Sâga S. Sawadogo for compiling the sampling map. Comments and suggestions from two reviewers and Dr Arno Rein, the editor of the journal, greatly improved the early version of the manuscript.

Additional information

Funding

The authors received no direct funding for this research.

Notes on contributors

Aboubakar Sako

Aboubakar Sako is an environmental geochemist and assistant professor of environment and geosciences from University of Dédougou (Burkina Faso). He holds a PhD in Environmental Sciences from Arkansas State University (Arkansas, USA). His research involves geochemical characterization of heavy metals in surface water, groundwater and soils. Dr Sako is also interested in hydrogeochemical modeling and ecological risk assessment of industrial and artisanal gold mining sites in the West Africa region.

Mamadou Nimi

Mamadou Nimi is a geochemical analyst and presently head of the Geological Survey of Burkina Faso in the regional office of Bobo-Dioulasso. He gained about 13 year experience in natural water, soil and rock sample characterization and analysis for environmental assessment and mineral exploration.