The acute toxicity of nickel to freshwater ciliates

The degradation of the (14)C-labelled fungicide dithianon in an orthic luvisol was investigated under standardized conditions in comparison to stimulated microbial activity by an amendment of maize straw. The compound is characterized by mineralization losses of approximately 33% and the formation of non-extractable bound residues of approximately 63% in 64 days. Despite the major role of microorganisms in mineralizing this compound, the formation of bound residues is not biotically induced. Gel permeation chromatography and polyacrylamide gel electrophoresis, as different size separation techniques of the humic acids fractions, showed differences in the distribution patterns of non-extractable residues depending on the addition of straw material. The results presented support the existence of humic substances in soil as a micellar system rather than as a biopolymer.