Bioaccumulation of heavy metals in the earthworm Eisenia fetida in relation to bioavailable metal concentrations in pig manure

The study investigated the bioaccumulation of Cu, Zn, Pb and Cd in Eisenia fetida fed on pig manure in greenhouse, and its relationship to bioavailability of these elements in pig manure. Metals in exchangeable, carbonates-bound and Fe–Mn oxides-bound fractions obtained by sequential extraction were considered to be bioavailable. The bioaccumulation factors (BAFs) of E. fetida to heavy metals were Cd (2.749 ± 0.441), Zn (0.594 ± 0.200), Pb (0.274 ± 0.101) and Cu (0.076 ± 0.030). Variations in the Pb and Cd concentrations of E. fetida were best explained by the concentration of exchangeable fraction, while that of Cu was best explained by the concentrations of exchangeable and Fe–Mn oxides-bound fractions. The concentration of Zn in E. fetida depended strongly on the concentrations of exchangeable, carbonates-bound and Fe–Mn oxides-bound fractions. Further nonlinear regression analysis revealed the positive logarithmic relationship between the BAF and the exchangeable metal concentration of pig manure.