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Enantiomer‐specific measurements of current‐use pesticides in aquatic systems
Citation:
Ulrich, E., P. TenBrook, L. McMillan, O. Wang, AND W. Lao. Enantiomer‐specific measurements of current‐use pesticides in aquatic systems. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 37(1):99-106, (2018).
Impact/Purpose:
The manuscript describes new experimental data: a new method has been developed and applied to environmental samples that have never been analyzed for the target pesticide enantiomers. The work is significant because we have measured enantiomer fractions (EFs) for fipronil, permethrin, and bifenthrin in known standards and six samples sets of varied origin, including from the natural aquatic environment and laboratory studies related to transport from application sites to local waterways and uptake by fish. These compounds are of particular relevance in California where they are often found in water and sediment in such concentrations to cause toxicity to sentinel species. Measuring EFs for the target analytes is uncommon in aquatic samples, but has the potential to decrease uncertainty in risk assessments.
Description:
Some current‐use pesticides are chiral and have nonsuperimposable mirror images called enantiomers that exhibit identical physical–chemical properties but can behave differently when in contact with other chiral molecules (e.g., regarding degradation and uptake). These differences can result in variations in enantiomer presence in the environment and potentially change the toxicity of pesticide residues. Several current‐use chiral pesticides are applied in urban and agricultural areas, with increased potential to enter watersheds and adversely affect aquatic organisms. The present study describes a stereoselective analytical method for the current‐use pesticides fipronil, cis‐bifenthrin, cis‐permethrin, cypermethrin, and cyfluthrin. We show use of the method by characterizing enantiomer fractions in environmental sample extracts (sediment and water), and laboratory‐dosed fish and concrete extracts previously collected by California organizations. Enantiomer fractions for most environmental samples are the same as racemic standards (equal amounts of enantiomers, enantiomer fraction = 0.5) and therefore are not expected to differ in toxicity from racemic mixtures typically tested. In laboratory‐derived samples, enantiomer fractions are more frequently nonracemic and favor the less toxic enantiomer; permethrin enantiomer fractions range from 0.094 to 0.391 in one type of concrete runoff and enantiomer fractions of bifenthrin in dosed fish range from 0.378 to 0.499. We use enantiomer fractions as a screening tool to understand environmental exposure and explore ways this uncommon measurement could be used to better understand toxicity and risk.
