Probing the Enantioselectivity of Chiral Pesticides

U.S. EPA National Exposure Research Laboratory, Athens, GA, USA.
Environmental Science and Technology (Impact Factor: 5.33). 02/2006; 40(1):16-23. DOI: 10.1021/es063022f
Source: PubMed


As much as 25% of the pesticides in use are chiral, but the compounds are typically supplied as racemic mixtures. While one enantiomer may have the desired effect on a target species, the other enantiomer or enantiomers may not. Moreover, the various chiral forms could have different toxicities, degradation rates, and environmental effects. Therefore, a comprehensive risk assessment requires determining the enantiomer selectivity of these pesticides.

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    • "Therefore, providing regulators and managers for herbicides is necessary to assess the direct effects of PSII herbicides on photosynthesis. Chiral herbicide family represents about quarter of the pesticide active ingredients and this ratio has been increased by introducing compounds with more complex structures (Garrison, 2006;Wen et al., 2009;Ye et al., 2009b). Previous studies have reported that chiral herbicides displayed enantioselective disturbance to plants though they share the identical physical and chemical properties due to their different interactions with enzymes and biological receptors in organism (Wang et al., 2007;Qian et al., 2015;Wen et al., 2011;Wen et al., 2010). "
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    ABSTRACT: With the wide application of chiral herbicides and the frequent detection of photosystem II (PSII) herbicides, it is of great importance to assess the direct effects of PSII herbicides on photosynthesis in an enantiomeric level. In the present study, the enantioselective phytotoxicity of bromacil (BRO), typical photosynthesis inhibition herbicide, on Arabidopsis thaliana was investigated. The results showed that S-BRO exhibited a greater inhibition of electron transmission in photosystem I (PSI) of A. thaliana than R-BRO by inhibiting the transcription of fnr 1. S-BRO also changed the chlorophyll fluorescence parameters Y (II), Y (NO), and Y (NPQ) to a greater extent than R-Bro. Transcription of genes psbO2, Lhcb3 and Lhcb6 was down-regulated in an enantioselective rhythm and S-BRO caused more serious influence, indicating that S-BRO did worse damage to the photosystem II (PSII) of A. thaliana than R-BRO. This study suggested that S-BRO disturbed the photosynthesis of plants to a larger extent than R-BRO and provided a new sight to evaluate the phytotoxicity of chiral herbicides.
    Full-text · Article · Apr 2016 · Science of The Total Environment
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    • "Stereoselective transformation and residues have been reported for chiral herbicides(Garrison, 2006; Liu et al., 2009), insecticides(Faller et al., 1991; Müller and Kohler, 2004), and other organic compounds (Wiberg et al., 2000). While most chiral pesticides are usually used as a racemic mix, only a few studies have investigated the effect of the individual enantiomers. "
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    ABSTRACT: Cycloxaprid (CYC) is a novel broad-spectrum neonicotinoid insecticide that has been developed for agricultural pest control. The fate of the (14)C-labeled racemic and enantio-pure CYC isomers in flooded and anaerobic soil was investigated using radioisotope tracing techniques. After 100d of incubation, only a minor portion (<1%) of the applied CYC isomers is mineralized by each of the four tested soil types. The fraction of initially applied radioactive CYC dissipated into the bound or non-extractable residues (BR) increases with increase in the length of the incubation period, reaching up to 53.0-81.6%. The dissipation of the CYC through mineralization or formation of BR is strongly influenced by soil properties, such as humic content, pH value, and retained microbial activity. Amongst the soils studied, the fluvio-marine yellow loamy soil displayed the highest tendency to mineralize CYC while the coastal saline soil exhibited the strongest tendency to form BR. The observation that the water phase retained the large portion(>60%) of the radioactivity attributed to the total extractable residue suggested that under the experimental condition, the initially applied (14)C-labeled CYC residues were readily available for leaching or offsite transport. Additionally, no enantiomer-specific behaviors are observed. The results from this study provide a framework for assessing the environmental impact resulting from the use of this pesticide.
    Full-text · Article · Feb 2016 · Science of The Total Environment
    • "Increasing knowledge of the factors controlling the environmental fate of chiral pesticide enantiomers is a recent matter of concern (Garrison, 2006; Petrie et al., 2015; Sekhon, 2009). Over 25% of pesticides currently in use are chiral, and in China up to 40% of the pesticides in use are classified as chiral compounds (Garrison, 2006; Ye et al., 2009). The presence of chirality in pesticides has received very little attention . "
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    ABSTRACT: A large number of pesticides are chiral and reach the environment as mixtures of optical isomers or enantiomers. Agricultural practices can affect differently the environmental fate of the individual enantiomers. We investigated how amending an agricultural soil with composted olive-mill waste (OMWc) or its biochar (BC) at 2% (w:w) affected the sorption, degradation, and leaching of each of the two enantiomers of the chiral fungicide metalaxyl. Sorption of metalaxyl enantiomers was higher on BC (Kd≈145Lkg(-1)) than on OMWc (Kd≈22Lkg(-1)) and was not enantioselective in either case, and followed the order BC-amended>OMWc-amended>unamended soil. Both enantiomers showed greater resistance to desorption from BC-amended soil compared to unamended and OMWc-amended soil. Dissipation studies revealed that the degradation of metalaxyl was more enantioselective (R>S) in unamended and OMWc-amended soil than in BC-amended soil. The leaching of both S- and R-metalaxyl from soil columns was almost completely suppressed after amending the soil with BC and metalaxyl residues remaining in the soil columns were more racemic than those in soil column leachates. Our findings show that addition of BC affected the final enantioselective behavior of metalaxyl in soil indirectly by reducing its bioavailability through sorption, and to a greater extent than OMWc. BC showed high sorption capacity to remove metalaxyl enantiomers from water, immobilize metalaxyl enantiomers in soil, and mitigate the groundwater contamination problems particularly associated with the high leaching potential of the more persistent enantiomer.
    No preview · Article · Oct 2015 · Science of The Total Environment
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