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Toxicity of Triadimefon Racemate and Enantiomers to Black Fly Larvae
Citation:
Kellock, K., J. Overmyer, A. W. GARRISON, AND J. K. AVANTS. Toxicity of Triadimefon Racemate and Enantiomers to Black Fly Larvae. Presented at SETAC North America 30th Annual Meeting, New Orleans, LA, November 19 - 23, 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.
Description:
Triadimefon is a conazole fungicide commonly used for commercial and agricultural fungal control on trees, ornamentals and fruits. It is a chiral compound, existing as R-(-) and S-(+) enantiomers and used as the racemate. This is of interest since the triadimefon enantiomers can have varying degrees of toxicity to non-target organisms. Results of earlier 48 hr LC50 tests at pH 7.6, reported as the median with fiducial limits, showed that triadimefon racemate (+/-) is toxic to the black fly larvae. In the current study, the triadimefon racemate and its enantiomers were evaluated separately to determine their respective 48 hr LC50 values to black fly (Diptera: Simuliidae) larvae using an orbital shaker toxicity bioassay. Previous research had shown that triadimefon enantiomerizes in water at near neutral pHs, so the pH was maintained at near 5 to prevent enantiomer conversion. Preliminary data at pH 5 indicates the (-) enantiomer to be two-fold more toxic than the racemate, while the (+) enantiomer LC50 falls in between the racemate and (-) values. Future work will focus on final LC50 toxicity assessments of triadimefon, its enantiomers, and its metabolites, as well as investigations into triadimefon metabolic pathways and mechanisms relative to black fly larvae.