Speciation and bioavailability of potentially toxic element in soils and sediments of mining areas in Meiganga Adamawa plateau (Cameroon).

Contamination by potentially toxic elements (PTEs) is a major environmental concern, especially in mining sites, given the often-increasing concentrations in soil and sediments. Under certain conditions, such contamination may expand beyond the mining area, posing risks to human health. This study investigates the environmental hazard associated with PTEs in soils and river sediments from the Meiganga gold district by evaluating their speciation and mobility. A total of 60 samples (48 soils and 12 sediments) were collected for total digestion analysis. Among these, 10 samples identified as contaminated with PTEs were selected for further speciation analysis using single and sequential (BCR) extraction methods, alongside SEM/EDS. The total concentration of Cr, Ni, Cu, Zn, As, Pb and Cd in the selected samples exceeded the average upper continental values. Cd and Zn exhibited the highest extraction rates (83.33% and 61% respectively), indicating high mobility and potential environmental risk, particularly due to their association with the acid-soluble fraction. In contrast, Cr, As, Cu, Ni and Pb were mainly bound to the residual and reducible fractions, indicating lower mobility and reduced environmental risk. In addition. SEM/EDS analysis confirmed strong associations between several PTEs (Cr, Ni, Pb, As and Zn) and Fe-Mn oxyhydroxides, which could release these elements under changing redox conditions. Both the enrichment factor and geo-accumulation index confirm significant contamination while the high mobility of several PTEs indicates considerable ecological risk. Therefore, ongoing monitoring and appropriate remediation measures are strongly recommended for the Meiganga gold district.