Geochemistry and geostatistics for the assessment of trace elements contamination in soil and stream sediments in abandoned artisanal small-scale gold mining (Bétaré-Oya, Cameroon)

Abstract

Soil and stream sediment contamination from abandoned artisanal mines is of prime importance due to the associated potential for heavy metal and metalloid contamination. Indeed, mine wastes are an evident source of soil and stream sediment contamination. The aim of the current study is to propose a conceptual approach to assess the contamination degree and the spatial distribution of trace elements in soils and stream sediments around mine sites. The abandoned artisanal gold mine of Bétaré-Oya in Cameroon was considered as a case study. In order to separate anthropogenically contaminated soils and stream sediments from the un contaminated ones, representative soil, stream sediment and mine wastes samples were collected and analyzed for the pH, Electrical Conductivity (EC), mineralogical paragenesis, major elements and trace elements. Very acidic pH values and high EC values ranging from 3.2 to 5.8 and from 44 to 315 μs cm−1, respectively were obtained for the analyzed samples. Based on the enrichment factor (EF) calculation, four elements of interest (Co, Cd, Cu and As) were selected for soils and seven elements of interest (Co, Cd, Cu, As, Cr, Pb and Zn) were selected for stream sediments. The Geochemical Background (GB) of these elements was determined with the normal Q-Q plot, the Geo-accumulation index (Igeo) was calculated and the geochemical maps for soils and stream sediments were elaborated using geostatistics in Geographic Information System (GIS) environment.The obtained results show that Bétaré-Oya soils and stream sediments are contaminated with metals and metalloid that exceed the established GB values for soil (Co ≈ 17.73 mg/kg, Cd ≈ 0.36 mg/kg, Cu ≈ 146.81 mg/kg and As≈48.82 mg/kg) and GB values for stream sediments (Co ≈ 30.90 mg/kg, Cd ≈ 0.24 mg/kg, Cu ≈ 173 mg/kg, As≈51.59 mg/kg, Cr ≈ 137 mg/kg, Pb ≈ 7.56 mg/kg, and Zn ≈ 39.48 mg/kg). The Igeo calculation revealed that soils and stream sediments were highly influenced by anthropogenic activity. The maximum values of the Igeo, especially for Cd ≈ 4.59, Pb ≈ 2.83, and Zn ≈ 2.97, highlighted the highly contaminated samples and therefore quantify accurately the contamination degree. Finally, geochemical maps of soils and stream sediments show clearly that mine wastes are the main source of trace elements contamination in the study area.