EFFECT OF INDUSTRIAL-COMMUNAL SEWAGE SLUDGE TREATMENT ON THE Cd AND Cr FRACTIONS OF SOIL AND ON PLANT UPTAKE
The Cd and Cr fractions (mobile: 1M NH4NO3-soluble, mobilisable: ammonium acetate + EDTA-soluble, “total”: cc. HNO3 + cc. H2O2-soluble) of the experimental soils and the Cd and Cr contents of spring barley grain and straw were examined in a pot experiment to investigate the effect of applying industrial-communal sewage sludge with metal contents exceeding the authorised limit. The four experimental soils were acidic sand, calcareous sandy soil, calcareous chernozem loamy soil and brown forest soil, or acidic loam. The sludge was applied at rates of 0, 2.5, 5, 10 and 20 g sludge D.M. /kg air-dry soil in four replications. The mobile fraction of both elements changed only on sandy soils significantly. Regression analysis on the soil Cr and Cd fractions and the barley grain and straw element contents revealed that in the case of Cd the soil mobile fraction is the most suitable to predict the plant concentration. The changes in plant Cr concentrations were not coherent, thus the regression with soil Cr concentration did not give reliable results. Only a negligible proportion of the elements added with the sludge appeared in mobile form in the soil. This ratio is smaller in the case of Cr where only 0.02 % of the sludge Cr content can be found in the soil mobile Cr fraction. Since Cd is more mobile element 2.5 % of the added Cd can be found in the mobile fraction. Our results indicated that in case of sewage sludge application on field it is important to consider not only the element contents, but also other parameters (pH, texture, organic matter), as these may influence the dissolution of contaminants. The Cd and Cr content of the investigated sludge may cause adverse effects principally on light textured soils.
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