Accumulation of potentially toxic elements in plants and their transfer tohuman food chain

Contaminated soils can be a source for crop plants of such elements like As , Cd, Cr, Cu, Ni, Pb, and Zn. The excessive transfer of As, Cu, Ni, and Zn to the food chain is controlled by a "soil-plant barrier"; however, for som e elements, including Cd, the soil-plant barrier fails. The level of Cd ing ested by average person in USA is about 12 mu g/day, which is relatively lo w comparing to Risk Reference Dose (70 mu g Cd/day) established by USEPA. F ood of plant origin is a main source of Cd intake by modern society. Fish a nd shellfish may be a dominant dietary sources of Hg for some human populat ions. About half of human Pb intake is through food, of which more than hal f originates from plants. Dietary intake of Cd and Pb may be increased by a pplication of sludges on cropland with already high levels of these metals. Soils amended with sludges in the USA will be permitted (by USEPA503 regul ations) to accumulate Cr, Cd Cu, Pb, Hg, Ni, and Se,and Zn to levels from 1 0 to 100 times the present baseline concentrations. These levels are very p ermissive by international standards. Because of the limited supply of toxi city data obtained from metals applied in sewage sludge, predictions as to the new regulations will protect crop plants from metal toxicities, and foo d chain from contamination, are difficult to make.