Bioavailability of heavy metals from polluted soils to plants
The aim of this work was to estimate, on the basis of soil extraction procedures, whether a given soil is suitable for cultivation of plants used as food or feed. The paper discusses the transfer of metal ions (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn) from contaminated soils to plants in terms of transfer factors (TF). The knowledge of transfer factors for a given element should enable prediction, before plants are sowed, whether a given soil is suitable for the cultivation of plants for consumption purposes. TF can only be evaluated when a linear relationship is observed between soil and plant composition for a given element. Such a relationship is rarely observed between the total soil content of a given metal and that of the plant. For this reason, it was necessary to develop an extraction procedure that would represent the content of metal available to plants during growing season. Several extracting agents were tested. The extracting agent that fulfilled these criteria was 2% (w/v) ammonium citrate. Statistically significant correlation coefficients were determined between the citrate-soluble fraction of soil and content in plant in the case of all the elements studied, except Ni. If a statistically significant correlation exists, it is then possible to evaluate the soil–plant transfer factor for a given metal in plants.