Redistribution of residual Pb, Zn, and Cd in soil remediated with EDTA leaching and exposed to earthworms (Eisenia fetida)

Abstract

After soil remediation with ethylenediamine tetraacetate (EDTA) leaching/washing, the residual Pb, Zn, and Cd species are left in the soil in non‐labile forms. The effect of earthworms as main soil biotic factors on the residual Pb, Zn, and Cd fraction lability (mobility, bioavailability to plants, and oral‐availability) was investigated. Contaminated soil from a smelter site was treated with increasing EDTA concentrations (2.5 to 4‐times 40 mmol kg−1) to gradually reduce the heavy metal content and lability. Leached soils were processed by Eisenia fetida and heavy metal lability and fractionation determined in casts and earthworm‐processed soils. In general E. fetida increased heavy metal accessibility/mobility, but the induced changes diminished with the intensity of soil EDTA treatment. Fractionation results indicate the possibility of a time‐dependent complexation of heavy metals to carbonates favoured by earthworms’ gut processes. The transition of residual heavy metals in time (ageing) should be considered.