Effect of solid waste source (dumpsite type) on heavy metal contaminations in urban soils of Bauchi, Nigeria

Heavy metals constitute a major threat to humans due to the fact that they unlike some other pollutants are not biodegradable. Different Sources of these metals when dumped with municipal solid wastes raise the level of heavy metals in dumpsites. A study of the effect of solid waste source on heavy metal contaminations in urban soils of Bauchi, Nigeria was carried out using Atomic Absorption Spectrophotometer. Single and integrated pollution indices were used to assess the impact of human activities on the concentration of heavy metals in soils. The results obtained show that heavy metal contamination of urban soils in Bauchi is strongly affected by the source area of waste materials or the dumpsite type. Heavy metal contaminations based on single pollution indices used give the following trend: Pb > Cd > Ni > Zn > Cr > Mn > Cu >Fe for residential soils; Pb > Ni > Cd > Zn > Cr > Mn > Cu > Fe for commercial soils and Pb > Cd > Ni > Zn > Cu > Cr > Mn > Fe for industrial soils. In view of the discrepancies in results obtained when different reference values are used, the development of a unified contamination classification model named Unified Contamination Classification by Eze at Bauchi (UCCEB) was undertaken resulting in interesting coherence among single pollution indices. The application of UCCEB model enabled the differentiation of anthropogenic-related contaminations from lithogenic-related inputs. The studied sites gave the following results using UCCEB: Residential dumpsite (RES): moderate pollution with respect to Cd, Ni, Pb, Zn; low pollution with respect to Cr, Cu, Mn; and deficient pollution with respect to Fe. Commercial dumpsite (COM): moderate pollution with respect to Cd, Cr, Ni, Pb, Zn; low pollution with respect to Cu, Mn; and deficient pollution with respect to Fe. Industrial dumpsite (IND): moderate pollution with respect to Cd, Cr, Cu, Ni, Pb, Zn; low pollution with respect to Mn; and deficient pollution with respect to Fe. Thus the order of multi-element contamination can be summarized as IND>COM>RES.