Contamination and risk assessment of trace metals and As in surface sediments from abandoned gold mining sites of Bekao, Adamawa-Cameroon

This paper assesses the spatial distribution and the trace metal and As contamination in surface sediments along the Lom River in the abandoned gold mining sites of Bekao (Adamawa Cameroon). A total of thirty one (31) surface sediment samples is collected and analyzed to determine the concentrations of Cr, Mn, Fe, Ni, Cu, Zn, Sn, Pb and As. The results obtained are compared with the Average Shale Values (ASVs) and Sediment Quality Guidelines (SQGs) as the threshold effect concentration (TEC), the probable effect concentration (PEC), the Effect Range Low (ERL) and the Effect Range Median (ERM). To assess the trace metal and As pollution level in sediments, nine environmental pollution indices, namely geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (CF), contamination degree (CD), modified degree of contamination (mCD), Nemerow index (NI), contamination severity index (CSI), probability of toxicity (MERMQ) and potential ecological risk (RI) are used. In addition, Pearson's correlation matrix and General Linear Model (GLM) are used to determine the pollution indices which adjust better with the trace metals and As concentrations. The results reveal that the sequence of trace metals and As mean concentrations was Fe > Mn > Cu > Ni > Sn > Cr > Zn > Pb > As, and the mean concentrations of Zn, Ni, Sn, and Cu exceed the ASVs. Based on the sediments quality guidelines (SQGs), sediments are polluted in Ni and Cu. According to the Igeo, EF and CF, Sn and Cu reveal a high level of contamination with significant enrichment and Ni a moderate level of contamination and enrichment. The results of the calculation of CD, mCD, and NI indices suggest significant contamination, high contamination and high pollution of trace metals and As in sediments, respectively. Globally, CSI demonstrates an ultra-high severity contamination, MERMQ a high-medium priority with a toxic probability of 49% and RI show a moderate ecological risk. Pearson's correlation matrix and GLM suggest that CSI and MERMQ are the indices which adjust better with trace metals and As in sediments.