Trace metals uptake and distribution in corn plants grown on a 6-year urban waste compost amended soil

A 6-year field study was performed to evaluate heavy metal accumulation in the top 20 cm of a clay-loam calcareous soil (Fluventic Xerochrept) amended with urban waste compost and to determine heavy metal uptake and distribution in corn plants grown in this soil. Compared with untreated soils, amended soils showed a significant increase only in Cu, Zn, Pb and, in the last 2 years, Cr concentrations. The corn plants grown on the amended soil showed a general increase in metal uptake, which was about three times greater for Pb and two times greater for the other heavy metals than in plants grown on untreated soil. At times, the diluting effect resulting from enhanced growth rates of the plants with compost application resulted in lower concentrations in the plants grown on treated plots. Cr and Pb were less mobile in the corn plant and were accumulated only in root tissues. Only in the last 3 years of the experiment were traces of Pb found also in the stalks. The limited mobility of Pb was confirmed in a contemporary hydroponic greenhouse experiment. The values of the plant/soil transfer coefficients were within the lower range reported in the literature, indicating that in the soil studied (which contained 14% CaCO3) there was limited transfer of heavy metal ions from the soil to the corn plants. It is concluded that the long-term application of large amounts of urban waste compost to CaCO3-containing soils does not necessarily cause medium-term problems to plant, animal or human health.