Characterisation of soil-bound residue fractions of the fungicide dithianon by gel permeation chromatography and polyacrylamide gel electrophoresis

The degradation of the C-14-labelled fungicide dithianon in an orthic luvis ol was investigated under standardized conditions in comparison to stimulat ed microbial activity by an amendment of maize straw. The compound is chara cterized by mineralization losses of approximate to 33% and the formation o f non-extractable bound residues of approximate to 63% in 64 days. Despite the major role of microorganisms in mineralizing this compound, the formati on of bound residues is not biotically induced. Gel permeation chromatograp hy and polyacrylamide gel electrophoresis, as different size separation tec hniques of the humic acids fractions, showed differences in the distributio n patterns of non-extractable residues depending on the addition of straw m aterial. The results presented support the existence of humic substances in soil as a micellar system rather than as a biopolymer. (C) 2000 Elsevier S cience Ltd. All rights reserved.