Heavy metal availability, bioaccessibility, and leachability in contaminated soil: effects of pig manure and earthworms.

A pot experiment and a leaching experiment were conducted to investigate the effects of earthworms and pig manure on heavy metals (Cd, Pb, and Zn) immobility, in vitro bioaccessibility and leachability under simulated acid rain (SAR). Results showed manure significantly increased soil organic carbon (SOC), dissolved organic carbon (DOC), available phosphorus (AP), total N, total P and pH, and decreased CaCl2-extractable metals and total heavy metals in water and SAR leachate. The addition of earthworms significantly increased AP (from 0.38 to 1.7 mg kg-1), and a downward trend in CaCl2-extractable and total leaching loss of heavy metals were observed. The combined earthworm and manure treatment decreased CaCl2-extractable Zn, Cd, and Pb. For Na4P2O7-extractable metals, Cd and Pb were decreased with increasing manure application rate. Application of earthworm alone did not contribute to the remediation of heavy metal polluted soils. Considering the effects on heavy metal immobilization and cost, the application of 6% manure was an alternative approach for treating contaminated soils. These findings provide valuable information for risk management during immobilization of heavy metals in contaminated soils.