ABSTRACT

The German Sewage Sludge Regulation of 1983 issued following the Federal Waste Disposal Law of 1972 gives values for the maximum concentration of heavy metals, that may be tolerated in soils. Before sewage sludge is added to soils, the total concentration of Cd, Ni, Hg, Cu, Pb, and Zn are to be determined in both soil and sludge after digestion in hot aqua regia. It is assumed, that this procedure will show the potential maximum, long-term hazard with respect to heavy metals. But the different sources and thus the solubility of heavy metals are not considered, nor are the properties of the soils (pH, clay, iron, and organic matter content) and plant species that influence these. This is inadequate from a pedological and ecological/ chemical viewpoint.