Effects of soil amendments on the bioavailability of lead, zinc, and cadmium to earthworms

This research investigated the effectiveness of phosphorus (P) and organic matter (OM) as possible in situ remediation techniques for metal contaminated soils. The study was designed to determine the bioavailability of ph, Zn, and Cd individually and in combination to the earthworm Eisenia fetida in an artificial soil amended with varying levels of P and OM, A toxicokinetic approach using bioaccumulation factors and uptake rate coefficients was used to assess the bioavailability of the heavy metals. Overall, earthworms in P-amended soils showed significantly reduced Pb levels in the individual and mixture experiments, while Zn and Cd bioavailability was not reduced. X-ray diffraction analyses indicated that pyromorphites were formed with P amendment, thereby reducing the solubility and bioavailability of Pb within the soil. In contrast, the OM soil amendments increased bioavailability of Pb in the individual experiment and decreased it in the mixture experiment. The results of this study suggest that P amendments may be a viable technique to remediate Pb contaminated residential soils and that earthworm bioassays represent a biologically relevant measure of metal availability in soil.