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CHIRAL PESTICIDES: OCCURRENCE AND SIGNIFICANCE
Citation:
Falconer, R L., M K. Morgan, A W. Garrison, A. D. Leone, T. Bidleman, AND L. M. Jantunen. CHIRAL PESTICIDES: OCCURRENCE AND SIGNIFICANCE. Presented at Rocky Mountain Conference on Analytical Chemistry, Denver, CO, July 29-August 2, 2001.
Impact/Purpose:
The goal of this task is to contribute to a better understanding of human exposure to pesticides, especially for small children by developing methods to characterize sources and pathways in and around the residential environment. We will support the science behind FQPA and assist the Office of Pesticide Programs (OPP) in the development of guidelines for the assessment of residential exposure to pesticides. Specific research objectives include: (i) to evaluate and develop methods for measuring pesticides in air using passive/diffusive samplers. Assess and refine devices for the collection of surface transferable pesticide residues and to establish transfer efficiencies; (ii) to develop and apply analytical methods for new and emerging pesticides using both gas and liquid chromatographic methods in support of the National Exposure Research Laboratory's (NERL) Human Exposure Measurement Project; and, (iii) to conduct pilot studies investigating chiral chromatographic methods.
Description:
Like amino acids, certain pesticides exist in "left-handed" and "right-handed" (chiral) forms. Commercially available chiral pesticides are produced as racemic mixtures in which the ratio of the two forms (or enantiomers) is 1:1. Enantiomers have the same physical and chemical properties, therefore transport processes (leaching, volatilization) and abiotic reactions (hydrolysis, photolysis) do not discriminate between the enantiomers. However, since enzymes themselves are chiral molecules, they can react selectively with one of the forms. Thus, metabolism by microorganisms in water and soil and in higher organisms often leads to non-racemic residues. Examining the enantiomeric patterns of pesticides thus provides a sensitive indicator of biological degradation. Several classes of insecticides and herbicides have members that are chiral, including four of the eight OC pesticides on the United Nations Environmental Program list (o,p'-DDT, chlordane, heptachlor and toxaphene). Pesticide enantiomers have been separated by gas and liquid chromatography and capillary electrophoresis. With GC-MS, it is possible to determine the fraction of enantiomers within 1-2% relative standard deviation or less, more precisely than individual concentrations. Numerous studies have been done looking at chiral pesticides and their metabolites in the environment and several researchers have reported preferential degradation/accumulation of pesticide enantiomers in biota. Unfortunately, very little work has been done to date on chiral pesticides in the human body even though past research has shown that enantiomers of biologically active chiral molecules can differ in potency, pharmacological action, metabolism, toxicity and kinetics. In our current work, we are studying the enantiomeric patterns of chiral pesticides and their chiral metabolites in human breast milk and adipose tissue as well as in ambient and indoor media.
This work has been funded wholly or in part by the United States Environmental Protection Agency and has been subjected to Agency review and approved for publication.