Center for Environment and Energy Research and Studies (CEERS)
Abstract
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
<citric acid <tartaric acid <unwashed soil.
Ethylenediaminetetraacetic acid and citric acid appeared to offer
greater potentials as chelating agents to use in remediating the high
permeability soil. Tartaric acid, however, is recommended in events of
moderate contamination