Heavy Metals Content of the Grassland Soil around Katima Mulilo Municipal Solid Wastes Dumpsite, Namibia

Abstract

The effects of open wastes dumpsites on the immediate vicinity continue to generate safety concern. This study determined the levels of lead, chromium, cadmium, arsenic, nickel, cobalt, copper and manganese in soil samples collected at two depths: 0-15 and 15-30 cm within and around Katima Mulilo municipal solid wastes dumpsite and a control site. The samples were digested according to EPA method 3050 B and analyzed using Inductively Coupled Plasma-Optical Emission Spectrophotometer (ICP: Perkin Elmer Optima 7000 DV). The results obtained revealed that manganese recorded the highest mean concentrations varying between 21.95-91.10 and 15.12-122.30 mg kg^-1 within the 0-15 and 15-30 cm soil depths respectively while Cd (BDL-0.51 mg kg^-1 and BDL-0.86 mg kg^-1) recorded the least. The analysis of variance between the mean levels of the heavy metals was statistically significant (p<0.05). Assessment of the sampling sites contamination revealed that the Wastes dumpsite > Grassland A > Grassland B > Control site but the current ecological risk indices (0.004-0.824) revealed environmental low risk levels (Er < 40). The correlation coefficients of the heavy metals revealed mainly extremely positive correlations (r > 0.9). These suggest common source of anthropogenic inputs of the heavy meals. Generally, the mean concentrations of the heavy metals were lower than their corresponding maximum permissible limits recommended by WHO for the protection of human and ecosystem’s health. However, the presence of heavy metals in the human ecosystem is regarded as a potential toxin because metals are persistence, non-degradable and bio-accumulative in nature. Therefore, we recommend periodic monitoring of the heavy metals in the soils and advice precautionary measures to limit excessive human exposures to the metal contents.