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A correlation was found between the formation of benrimidazol-2-ylcarbamate esters from the thiophanate fungicides [ thiophanate, thiophanate-methyl and 2-(3-methoxycarbonylthioureido)aniline] and the fungitoxic activity of these ficngicides. Fungitoxic activity of the thiophanates is increased by ageing in aqueous media, while fungitoxicity as well as conversion rate decrease at lower pH. It is concluded that it is not the thiophanates themselves but the corresponding benrimidazol-2-ylcarbamate esters that are responsible for the fungitoxic effect. Hence thiophanate-methyl, like benomyl, is a precursor of the fungitoxic agent methyl benzimi&zol-2-ylcarbamate (MBC). Zndications were obtained that fungal metabolic activity can increase the rate of conversion of thiophanate-methyl into MBC.

The degradation of bi~(tri[1-1~C]butyltin) oxide in two soils (1 mg tin kg-l) has been studied under laboratory conditions. Half of the applied compound disappeared from unsterilised silt loam and sandy loam in approximately 15 and 20 weeks, respectively; it disappeared also from the sterilised soils but to a lesser extent. The formation of small amounts of dibutyltin derivatives was established by thin-layer chromatography both in the unsterilised and sterile soils. The amount of unextractable radioactivity increased with time in the unsterilised and sterile soils. In the unsterilised soils 14C was released as [Wlcarbon dioxide in amounts equivalent to 20% of the applied radioactivity for silt loam and 10.7 % for sandy loam over a period of 42 weeks. Almost no [14C]carbon dioxide was released from the sterile soils, confirming microbial participation in the degradation of the compound in the unsterilised soils.

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