Characterization of non-extractable residues of the fungicide dithianon in soil using 13C/14C-labelling techniques

The fate of the 14C-labelled fungicide dithianon in soil is characterized by the formation of non-extractable, “bound” residues of ≈63% of applied amount in 64 d. Humic acids containing these “bound” residues were isolated after conducting degradation studies of the active ingredient in an orthic luvisol under standardized conditions. In the same way, 13C-labelled dithianon was incubated in an artificial soil which was produced by humification of 13C-depleted straw in an incinerated soil. The “bound” residues of the 13C-labelled dithianon in the humic acid fraction of the artificial soil were analyzed using 13C-NMR techniques. There was no evidence of a covalent bonding of the residues to the humic substances. Results of polarity gradient high performance thin layer chromatography (AMD-HPTLC) of “bound” residues of the 14C-labelled dithianon in the humic acid fraction indicate a sequestration process of metabolites into the humic substance as a possible binding mechanism.