Chemical activity and biological effect of sludge-borne heavy metals and inorganic metal salts added to soils

Summary A greenhouse experiment was conducted in order to evaluate the chemical activity and the uptake by Italian ryegrass (Lolium perenne cv. S24) of Zn, Cu, Cd and Ni added to a sandy and a heavy clay soil in two different forms: as inorganic salts and sludge-borne.The chemical activity of heavy metals as evaluated with different extractants was higher for the inorganic salt treatment and for the sandy soil, indicating that the chemical form of the metal and soil characteristics largely affect their extractability.The different chemical activity was also reflected in plant uptake. For all metals the degree of plant accumulation decreased in the following order: sandy soil-salt sandy soil-sludge> clay soil-salt>clay soil-sludge.These findings indicate that caution must be used when using results of inorganic salt treatments and different soil types to evaluate plant uptake of heavy metals from sludge amended soils.