Evaluation of Heavy Metal Pollution Levels in Agricultural Soils Around the Kalsaka Gold Mine, Burkina Faso

Abstract

This study evaluated heavy metal pollution levels in agricultural soils around the Kalsaka gold mine in Burkina Faso. Sixteen surface soil samples were collected from agricultural areas near the former mining site and analysed for chromium, nickel, copper, zinc, arsenic, mercury, and lead. The soil samples were sieved, digested using aqua regia, and analysed by atomic absorption spectrophotometry. Soil contamination was assessed by comparing concentrations with reference limits and by calculating the contamination factor, Pollution Load Index, and geo-accumulation index. The mean concentrations of the analysed metals were 206.56 mg/kg for chromium, 52.68 mg/kg for nickel, 132.82 mg/kg for copper, 129.24 mg/kg for zinc, 276.94 mg/kg for arsenic, 5.13 mg/kg for mercury, and 44.22 mg/kg for lead. The average concentrations followed the order As > Cr > Cu > Zn > Ni > Pb > Hg. Chromium, nickel, copper, arsenic, and mercury exceeded the reference limits used in the study, whereas zinc and lead remained below the corresponding limits based on mean values. Arsenic and mercury had the highest contamination factor and geo-accumulation index values, indicating that they were the main contributors to soil pollution in the study area. Pollution Load Index values were greater than one for all sampled soils, showing that the agricultural soils around the Kalsaka mine were affected by heavy metal contamination. The findings indicate degraded soil quality in the study area and highlight the need for continued monitoring, improved environmental management, and further assessment of metal mobility and potential transfer into crops.