Mobility of Some Heavy Metals in Soil-Plant Systems Studied on Soil Monoliths

The soil can act as a natural buffer by retaining toxic materials present in municipal and industrial wastes and sewage sludges. Countries of Eastern Europe currently have a limited industrial infrastructure for recycling wastes. One of the most rational and economic ways for these countries to dispose of their waste waters and sludges is to apply them to agricultural fields, thereby utilizing also their nutrient content. A U.S.-Hungarian research project was recently started with the aim of studying the fate and transport of selected heavy metals in the soil profile of cropped undisturbed soil monoliths. Preliminary experiments were carried out to study the adsorption-desorption processes of these chemicals on disturbed soil samples, and to investigate the plant-availability of different metal forms. Concentrations of Zn, Pb, Cr and Cd in the soil solution were found to decrease with increasing soil moisture content and length of the adsorption period, both showing hyperbolic relationships. Lower soil moisture contents increased both the solution concentrations and the adsorbed concentrations of the elements. Release of adsorbed Zn and Cd was higher than that of Pb and Cr. Higher plant-availability of inorganic forms of Ni correlated with a higher phytotoxicity as compared to Ni applied in sewage sludge.