Heavy metal (copper, lead, and zinc) accumulation and excretion by the earthworm, Dendrobaena veneta

To obtain knowledge about heavy metal kinetics in earthworms (Dendrobaena veneta), we performed accumulation and excretion experiments under laboratory conditions using soils from a heavy metal (Cu, Pb, and Zn)- contaminated site. To determine heavy metal accumulation rate, earthworms were exposed for 1, 2, 3, 7, 14, 28, 56, or 112 d to soil MH (Cu: 815 mg kg-1, Pb: 340 mg kg-1, and Zn: 225 mg kg-1). After exposure for 28 d to soil LB (Cu 242 mg kg-1, Pb: 109 mg kg-1, Zn 72 mg kg-1) or for 112 d to soil MH, D. veneta were transferred to uncontaminated soil and sampled after 1, 2, 3, 7, 14, 28, or 56 d to determine heavy metal excretion rates. Fourteen days after the transfer to the uncontaminated soil, some earthworms were transferred back to soil LB to determine the accumulation after a short recovery period. The Cu accumulation until Day 56 could be described by a one-compartment model. At Day 112, however, we observed an unexpected further increase in tissue Cu concentration (C(Cu)). We observed a significant increase in C(Zn), only at Day 112. Excretion of Cu could be described excellently by a two compartment model, the half-life times being t(1/2;1) ≃ 0.36 d, and t(1/2;2) = 37 d. Excretion of Pb could be described with a one- compartment model. After a fast initial excretion (t(1/2) ≃ 0.70 d), Pb excretion stagnated. The Cu accumulation after a 14-d recovery period appeared to be significantly less than the initial accumulation. The Pb accumulation appeared to be slower after recovery than before.