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.