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Stereoselective Microbial Transformation of Triadimefon to Triadimenol in Soils: Varying Production Rates of Triadimenol Stereoisomers Could Impact Risk Assessment
Citation:
GARRISON, A. W., J. K. AVANTS, AND W. J. JONES. Stereoselective Microbial Transformation of Triadimefon to Triadimenol in Soils: Varying Production Rates of Triadimenol Stereoisomers Could Impact Risk Assessment. Presented at Chirality 2009, Breckenridge, CO, July 12 - 15, 2009.
Impact/Purpose:
The main objective of this research is to determine the environmental occurrences, fate, and exposure of the enantiomers of selected chiral pesticides and other chiral organic pollutants. Chiral compounds, which exist as mixtures of enantiomers, include important environmental pollutants.
Description:
The microbial transformation of triadimefon, an agricultural fungicide of the 1,2,4-triazole class, was followed over several months under aerobic conditions in 3 different soil types to observe rates and products of transformation as well as enantiomer fractions of parent and products. The transformation was stereoselective. The primary transformation involves reduction of the prochiral ketone moiety of triadimefon to an alcohol, triadimenol, which has 2 chiral centers and 4 stereoisomers. The ratios of the 4 stereoisomers, while different from each other, were similar for each soil type. The triadimenol formed by soil transformation of triadimefon, however, showed no such stereoisomer pattern; instead, varying production rates were observed for each of the 4 triadimenol stereoisomers, resulting in all stereoisomer ratios being different from each other. This result is important in risk assessment if toxicity of the environmental transformation products were to be compared to that of the commercial triadimenol. In addition, since it is known that the stereoisomers of triadimenol differ in their toxicities, at least to fungi and rats, and that their relative abundance can vary with metabolism of the exposed species, the biological activity of the triadimenol that is formed by microbes in soils and, indeed, by any biological species, probably depends on the relative abundance of its 4 stereoisomers. This is a risk assessment issue that, in principle, applies to any chiral pesticide and its metabolite.