Assessment of anthropogenic influence on the level of selected heavy metals (Cu, Zn, Cd and Pb) in soil

Abstract

The study aimed at assessing potential influence of anthropogenic activities on the level of selected toxic heavy metals in soil in Tsumeb Township, Namibia. This was with a view of evaluating possible implications on human health and across the food chain. Soil samples were randomly collected from stratified areas and taken to the laboratory for pre-treatment and analysis. Soil metallic contents were extracted using acid digestion technique and were quantified using ICP-OES. Experimental protocol was validated using the standard metal addition techniques and was found to be applicable with quantitative metallic recoveries (n= 3) in the range of 85-90%. The overall mean concentration of analysed metals in soil samples ranged from 39.0 - 2532.8 mg/kg (Cu); 59.5- 1994.8 mg/kg (Zn); 1.7-21.3 mg/kg (Cd) and 1.2-141 mg/kg (Pb) across SCP1-SCP4. The analysed metals increased variedly at the SCPs in the order Cu: SCP1>SCP2>SCP4>SCP3; Zn: SCP1>SCP2>SCP4> SCP3; Cd: SCP1>SCP2>SCP3>SCP4; Pb: SCP1>SCP2>SCP3>SCP4. Hence, highest or most profound anthropogenic influence was observed at SCP1 for all metals while the lowest was as SCP4. Strong metallic correlation (r > 0.99) was obtained between all analysed metals and some significant above threshold metallic levels in soil were obtained for Cu and Zn but most worrisome was the high level of Cd obtained in soil. Possible uptake of these metals by plants and transfer across the food chain is highly probable. Key words: Heavy metals, soil, human health, anthropogenic, ICP-OES, Namibia.