Changes in heavy metal speciation and uptake by maize in a soil before and after washing with
chelating organic acids, citric acid, tartaric acid and ethylenediaminetetraacetic acid were assessed. A sandy loam
was collected from the vicinity of the Benue industrial layout, Makurdi, Nigeria and spiked with a quinternary
mixture of nickel, copper, zinc, cadmium and lead nitrates to achieve higher levels of contamination. Batch soil
washing experiments performed on 1.0 g portions of the spiked soil using 0.05 M chelating agents at a solid:liquid
ratio of 1:25 showed that washing efficiencies varied in the order: ethylenediaminetetraacetic acid> citric acid>
tartaric acid with metal extraction yields typically following the sequence, copper> nickel> zinc> cadmium> lead.
Sequential extractions proposed by the European Communities Bureau of Reference method used to assess the
redistribution of heavy metal forms in the soil showed that apparent metal mobilities were reduced upon soil
washing. Citric acid removed most of the metals hitherto associated with the exchangeable and reducible fractions;
tartaric acid, the exchangeable metal pools; and ethylenediaminetetraacetic acid, the non-residual metal pools.
Heavy metal assay of harvested biomass of maize grown on unwashed and washed soil samples indicated that
metal transfer coefficients, decreased in the order of treatment: ethylenediaminetetraacetic acid
Keywords
Chemical speciation; Contaminated soil; Ethylenediaminetetraacetic acid; Plant uptake; Soil washing
