Transfer of Cd, Cu, Ni, Pb, and Zn in a Soil-plant-invertebrate Food Chain: a Microcosm Study

The transfer of Cd, Cu, Ni, Pb, and Zn was evaluated in a soil-plant (lettuce, Lactuca sativa)-invertebrate (snail, Helix aspersa) food chain during a microcosm experiment. Two agricultural soils, polluted and unpolluted, were studied. Lettuce was cultivated for eight weeks before introduction of snails into the microcosms (M-snails). In a parallel experiment, snails were exposed to lettuce only (i.e., without soil) in simpler exposure devices called containers (C-snails). Snail exposure duration was eight weeks for both M- and C-snails. No effects on snail survival were found. Both M- and C-snails exposed to polluted soil showed a growth reduction, but only after two weeks of exposure. Time-dependent accumulation in M-snails exposed to the polluted environment showed a regular increase of Cd and Zn concentrations over time and a rapid increase of Pb concentrations within the first two weeks, which then remained stable. Copper and Ni concentrations did not increase during any of the experiments. Concentrations in M- and C-snails were compared to estimate the relative contribution of soil and plant to the total bioaccumulation. The results suggest that the soil contribution may be higher than 80% for Pb, from 30 to 60% for Zn, and from 2 to 40% for Cd.