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THE ENANTIOMERS OF CHIRAL POLLUTANTS POSE DIFFERENT RISKS
Citation:
Garrison, A W., W J. Jones, T. E. Wiese, B. J. Konwick, M A. Tapper, AND M K. Morgan. THE ENANTIOMERS OF CHIRAL POLLUTANTS POSE DIFFERENT RISKS. Presented at 24th Annual Society of Environmental Toxicology and Chemistry Meeting, Austin, TX, November 9-13, 2003.
Impact/Purpose:
Extend existing model technologies to accommodate the full range of transport, fate and food chain contamination pathways, and their biogeographical variants, present in agricultural landscapes and watersheds. Assemble the range of datasets needed to execute risk assessments with appropriate geographic specificity in support of pesticide safety evaluations. Develop software integration technologies, user interfaces, and reporting capabilities for direct application to the EPA risk assessment paradigm in a statistical and probabilistic decision framework.
Description:
In order to make more accurate risk assessments for chiral pesticides and other pollutants, it is necessary to understand the relative persistence and effects of their enantiomers. A major effort is underway in the USEPA to measure exposure in the home environment to various pesticides and PCB congeners. As an adjunct to this study, extracts of various samples previously shown to contain target pesticides and PCBs were analyzed for the enantiomers of certain of these which are chiral. Preliminary results show that PCB 95 occurs enantioselectively in house dust but not in yard soil: enantiomer ratios (ER) range from 0.51 to 0.98 with an average ER of 0.77 in floor dust compared to near racemic values in yard soil. The toxic effects of enantiomers have been scarcely examined. The effects of the enantiomers of cis-chlordane to the reproduction and survival of potworms (Enchytraeus crypticus) will be reported; these tests are currently underway. In addition, a summary of test results for various toxicity endpoints including Ceriodaphnia toxicity tests and in vitro endocrine activity determinations for the racemate and the separate enantiomers of the modern insecticide fipronil will be presented and compared with data on fipronil enantioselective microbial degradation. Preliminary results indicate high toxicity of racemic fipronil to Ceriodaphnia dubia with an LC50 of 25ug/L. While no estrogen activity was observed for the fipronil racemate or enantiomers, the racemate and (-) enantiomer were shown to have significant androgen receptor and progesterone receptor antagonist activity. Regarding microbial degradation, preliminary studies show that the direction of enantioselectivity can be different in soils with apparently different redox character.