MODELLING SOIL TO SNAIL METAL TRANSFER USING EDAPHIC PARAMETERS
Résumé
Environmental risk management associated to soil contamination requires an understanding of the mechanisms that control pollutant fate in this medium. However, the current procedures for risk assessment ignore that soil variability may result in substantial differences in contaminant uptake and effects in organisms. The first aim was to identify the soil parameters that modulate bioavailability and transfer of metals (cadmium (Cd), lead (Pb) and zinc (Zn)) from the soil to the landsnail Helix aspersa. The second was to evaluate the chemical method of environmental availability assessment (soil pollutant partitioning) best able to simulate the labile pool, usually assumed to be available for uptake by organisms. Snails were exposed for 2 to 28 days to 17 contaminated soils. Assimilation fluxes, adsorption and excretion rates of metals were determined using a one-compartment kinetic model. Five chemical extraction methods and two estimations of ionic activity were tested on these soils to simulate the labile pool. Differences in accumulation patterns during exposure were observed between Cd (linear), Pb (steady-state concentration reached) and Zn (intermediate behaviour), reflecting the variability of uptake and metabolism of each of the metals. Multivariate regressions showed that soil pH, organic mater and iron oxides were the main parameters influencing the environmental availability and bioavailability to Helix aspersa. Single extraction (NaNO3, NH4NO3, and CaCl2) as well as ionic activity and dissolved concentration were found to be reliable estimators to predict metal bioavailability and transfer from soil to snails. These original data for Helix aspersa are helpful to improve risk assessment procedures.