Trace metal transfer in a soil-plant-snail microcosm field experiment and biomarker responses in snails

A microcosm experiment was performed to investigate temporal (up to 16 weeks) and spatial variation in metal transfer in a soil-food (nettle)-snail (Cepaea nemoralis) food chain and biomarker responses in the digestive gland of the same snails. Adult snails were sampled from an uncontaminated site and transferred to five sites located 0.5, 2.5, 3, 5, and 10 km from a historically polluted point source. All sites were park areas where grasslands interfered with patches of deciduous forest. Soil physicochemical properties (pH, clay%, OC%) significantly explained the uptake of metals by nettle. Concentrations of metals in the digestive gland (DG) of snails were significantly related to those in nettle, but rarely to soil physicochemical properties. In general metal concentrations in the DG fluctuated while As, Ni, Pb and Zn showed a site dependent increase with time. Despite the long term exposure, biomarker concentrations (lipid, glycogen, proteins, glutathione-S-transferases), and shell morphology, were not related to DG metal concentrations. Our investigation emphasizes the need for controlled long-term studies on the transfer and effects of metals in food chains since short term studies might only show temporary physiological changes due to experimental acclimation.