Derivation of soil to plant transfer functions for metals and metalloids: impact of contaminant’s availability

Abstract

Background Soil to plant transfer models (SPT) are needed to predict levels of potentially toxic elements (PTE’s) in crops in view of risk assessment. Methods Here we developed a field study to test the suitability of empirical SPT models based on the reactive soil content in combination with soil properties versus a 0.01 M CaCl2 extraction to predict levels of metals and metalloids in ryegrass (Lolium perenne). Results Both empirical SPT models and the 0.01 M CaCl2 extraction explained between 14 and 68 % of the variation of Cd, Zn, Pb, Cu, Hg, As, Co and Ba in the ryegrass. Organic carbon and pH were the main variables explaining levels of elements in ryegrass. For Hg and Pb, amorphous aluminium oxides (Alox) played a significant role. For B, Cr, Mo, Ni, Sb and U no significant relationship could be derived. Conclusions Despite a range in the predictive quality of empirical SPT models reasonable to good estimates of As, Ba, Cd, Co, Cu, Hg, Pb and Zn in ryegrass could be obtained. The main advantage of SPT models is that they allow to account for differences in the availability of PTE’s. Ultimately either SPT’s or fixed crop levels can be the basis of a more realistic risk assessment framework addressing the transfer of contaminants from soil into the food chain.