Chemical speciation and mobility study of some heavy metals in soils around municipal solid waste dumpsites in Benin City metropolis, Nigeria

Abstract

This paper examined chemical fractionation of selected heavy metals (Cu, Pb, Mn and Ni) in soils around municipal solid waste dumpsites in Benin City, Nigeria, using the multi-step phase-selective extraction schemes for metal speciation. Total concentration levels of the heavy metals were done using atomic absorption spectrophotometry. The results showed that the analysed heavy metals were more abundant in their stabile fractions with the residual fraction dominating the non-bioavailable fractions. The potentially mobile and bioavailable fraction of Cu ranged from 21 to 40%, of Pb ranged from 20 to 30%, of Mn ranged from 16 to 30%, while that of Ni ranged from 18 to 29% in soils around the studied dumpsites. The percentage of bioavailability/mobility of the analysed heavy metals in soils around each studied dumpsite were in the order: dumpsite (I), Pb > Cu > Mn > Ni; dumpsite (II), Cu > Ni > Pb > Mn; and dumpsite (III), Cu > Mn > Pb > Ni. The relative low mobility factors shown by each heavy metal in the studied sites were quite in agreement with the low bioavailable fractions recorded from their fractionation analysis. The overall result shows that large fractions of the analysed heavy metals were in geochemical forms and not readily released into soil solution for bioavailability.