Interaction effects of salinity, sewage sludge, and earthworms on the fractionations of Zn and Cu, and the metals uptake by the earthworms in a Zn- and Cu-contaminated calcareous soil.

This study assessed the effects of salinity and sewage sludge on the fractionation of Zn and Cu in a soil around a lead-zinc mine as well as their uptake by earthworms (Eisenia fetida) in order to identify novel methods for employing the earthworms in waste management techniques. Eisenia fetida specimens were kept under laboratory conditions for 42 days. The first treatment involved the addition of 0%, 2%, 4%, and 8% (w/w) sewage sludge to contaminated soil. In the second treatment, NaCl was added to the soil at concentrations of 0, 1170, 2340, 3510, and 4680 mg L-1. The results indicated that the combined application of high salinity and sewage sludge had adverse effects on the survival of the earthworms. The presence of the earthworms increased the amount of Zn and Cu bound to organic matter. The organic fraction of Zn and Cu also significantly aggregated with increasing salinity levels. The interaction of salinity and earthworm showed that the residual Cu fraction increased with the presence of earthworm and decreased with increasing salinity. The residual fraction of Cu was significantly affected by the interactions of salinity and sewage sludge, where the highest amount was seen in the EC0 (distilled water) × SS8 (8% sewage sludge) treatment. The Zn and Cu contents increased with the earthworms when exposed to higher levels of salinity and sewage sludge.