Trace metals distribution in different geochemical phases of soils around automobile junk markets in southern Nigeria

Abstract

Chemical forms of some trace metals in soils around some selected automobile junk markets were studied using five step sequential extraction procedure. The results revealed that nickel, chromium and iron were of lithogenic origin while copper, lead, manganese and cadmium were from anthropogenic sources. The residual fraction was the most important phase for nickel, chromium and iron with the average amounts of 20.38%, 29.93% and 31.09% respectively. Copper and lead were mainly associated with the organic fraction having the average amounts of 24.06% and 22.89% respectively. Manganese predominated in Iron-Manganese oxide phase with an average amount of 23.76% while cadmium existed mainly in the exchangeable phase with an average amount of 30.36%. These results suggest that nickel, chromium and iron cannot be mobilized while cadmium is the most mobile and is easily available for plant uptake. Lead, manganese and copper are relatively stable but may become mobile if there are changes in soil pH or redox potential. The amounts of the metals in the non exchangeable phases were generally high but with relative high mobility factor values obtained for all the metals, changes in the soils physicochemical conditions may lead to remobilization of the metals and they may become bioavailable to plants and may enter food chain which implies a contamination risk for the metals.