Prediction of heavy metal solubility in agricultural topsoils around two smelters by the physico-chemical parameters of the soils

Solubility of heavy metals in soils is one of the main parameters causing their transfer into the hydrosphere and into the biosphere. It is thus important to understand its mechanisms in order to improve the current methodologies of risk assessment. Leaching tests were performed to investigate the solubility of Cd, Pb and Zn in 458 contaminated agricultural soils sampled around two smelters in Northern France. Distilled water and acetic acid were used consecutively to characterize two strengths of heavy metal extractability. Results showed very different behaviours of heavy metals based on the soil parameters, and statistical analysis pointed out the combined influence of these parameters on the solubility of each metal. An empirical and mathematical approach of their solubilities yielded significant results with a few soil parameters as predictors (pH, texture, CaCO3 content, total organic matter content and phosphorus content). Heavy metal mobility maps of the area were drawn according to these models and validated by comparison maps of soil types and isoconcentrations of total heavy metal contents. However, as the soils were mostly sampled in the same area, these statistical models for Cd, Pb and Zn solubility should be validated on other soil types, and compared with results of bioavailability and ecotoxicity assays.