Evaluation of heavy metals in soils around auto mechanic workshop clusters in Gboko and Makurdi, Central Nigeria

摘要

The concentration levels of selected heavy metals (Cd, Cu, Mn, Ni, Pb and Zn) in soils around two major auto mechanic workshop clusters in Benue State, Central Nigeria was investigated to ascertain the possible environmental impact of these clusters. Results of the atomic absorption spectrophotometric (AAS) analysis of samples of the soils revealed that for the majority of heavy metals, the concentrations in the soils are above background levels and permissible limits recommended for soils in some countries as indicated by the following ranges (mg/kg): Cu, 254-1,348; Pb, 283 - 665; Zn, 295-553; Mn, 58.8-272.; Ni, 18.0 - 41; and Cd, 10.50-12.7, with a variation pattern in the order: CuPdZnMnNiCd. The order of accumulation of metals in the auto mechanic workshop locations is: GbokoApir. Factors which appear to significantly influence the mobility of metals in the soils were the pH, cation exchange capacity (CEC), organic matter (OM) content and texture of the soils. Contamination factors for Pb and Cu in the areas under investigation ranged from considerable to very high contamination, while Zn, Mn and Cd had minimal to moderate enrichment and Ni demonstrated moderate to considerable enrichment. Geo-accumulation index values for the metals in the soils also showed that the environment surrounding the workshops is highly polluted with Pb and Cu, and to a lesser degree with Ni. Both Cd and Mn showed moderate pollution status while the soils remain unpolluted with Zn.