Cadmium and Chromium Fractions on Different Soils as Affected by Communal Sewage Sludge Loads.

A pot experiment was set up in 1999 for examining the effect of sewage sludge loads on soils and plants. Four soils were used. Soils can be classified as the following: Őrbottyan, calcareous sandy soil; Nagyhorcsok, calcareous silty soil; Gyongyos, acidic silty soil; and Nyirlugos, acidic sandy soil. Applied sewage sludge loads were 0, 2.5, 5, 10, and 20 g sludge DM/kg air-dry soil. From the soil samples, total recoverable [cc. nitric acid (HNO3) + hydrogen peroxide (H2O2) digestion], extractable [0.5 M ammonium acetate + 0.02 M ethylenediaminetetraacetic acid (EDTA)-extractable], and the mobile [1 M ammonium nitrate (NH4NO3)-extractable] elemental concentrations were measured. There was an increase in all of three fractions after sewage sludge application for both cadmium (Cd) and chromium (Cr); the extent of changes was varied. To quantify the Cd and Cr response to sewage sludge loads, sewage sludge loads vs. elemental concentration functions were plotted, and the slope of these functions means sensitivity of soils in the given fraction. After examining the sensitivity of four soils in the three fractions for elements investigated, it can be stated that the most sensitive fraction was the total recoverable fraction. The ammonium acetate + EDTA-extractable fraction has the second greatest sensitivity, whereas NH4NO3 extraction was a good indicator for treatments only on sandy soils. However, the strongest correlation was found between mobile Cd and Cr and the plant element uptake. So there is an obvious contradiction: the fraction that is less sensitive to sewage sludge treatments has the strongest correlation with plant uptake. [ABSTRACT FROM AUTHOR]