Degradation of Racemic and Enantiopure Metalaxyl in Tropical and Temperate Soils

Monkiédjé, Adolphe; Spiteller, Michael; Bester, Kai

doi:10.1021/es020123e

Cited by 98 publications

(85 citation statements)

References 12 publications

(15 reference statements)

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“…[26,[29][30][31][32] The sorption of the two fungicides by Soils 1, 3, 4 and 5 were considerably greater than that of the other soils, most likely as a result of their greater organic matter and clay contents ( Table 1). The mineralogy of the clay fraction in the soils also affects the sorption of organic compounds which preferentially adsorbed on mineral surfaces.…”

Section: Environmental Behavior Of Benalaxyl and Furalaxylmentioning

confidence: 98%

Environmental behavior of benalaxyl and furalaxyl enantiomers in agricultural soils

Fang

Gao

Guo

et al. 2014

Journal of Environmental Science and Health, Part B

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The enantioselective environmental behavior of the chiral fungicides benalaxy and furalaxyl in agricultural soils in China was studied. Although sorption onto soils was non-enantioselective, the leaching of benalaxy and furalaxyl was enantioselective in soil columns. The concentrations of the S-enantiomers of both fungicides in the leachates were higher than the R-enantiomers. This can be attributed to enantioselective degradation of the two fungicides in the soil column. Enantioselective degradation of the two fungicides was verified by soil dissipation experiments, and the R-enantiomers degraded faster than the S-enantiomers in partial soils. The half-life was 27.7-57.8 days for S-benalaxyl, 20.4-53.3 days for R-benalaxyl, 19.3-49.5 days for S-furalaxyl and 11.4-34.7 days for R-furalaxyl. The degradation process of the two fungicide enantiomers followed the first-order kinetics (R 2 > 0.96). Compared to furalaxyl, benalaxyl degraded more slowly and degradation was less enantioselective. These results are attributed to the influence of soil physicochemical properties, soil microorganisms, and environmental factors.

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Section: Environmental Behavior Of Benalaxyl and Furalaxylmentioning

confidence: 98%

Environmental behavior of benalaxyl and furalaxyl enantiomers in agricultural soils

Fang

Gao

Guo

et al. 2014

Journal of Environmental Science and Health, Part B

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“…However, if the adverse effects are caused only by or mostly by the excluded enantiomer, using enantiomer-enriched products may offer great environmental benefits. In addition, studies show that enantioselectivity may closely depend on environmental conditions and may vary significantly even for the same compound (4,14,24,25). Further studies are needed to characterize interactions of environmental factors, such as soil͞sediment properties, vegetation types, redox conditions, and microbial structures, with enantioselectivity in the behavior of chiral pesticides.…”

Section: Enantioselectivity In Degradationmentioning

confidence: 99%

Enantioselectivity in environmental safety of current chiral insecticides

Liu

Gan

Schlenk

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

457

395

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Chiral pesticides currently constitute about 25% of all pesticides used, and this ratio is increasing as more complex structures are introduced. Chirality occurs widely in synthetic pyrethroids and organophosphates, which are the mainstay of modern insecticides. Despite the great public concerns associated with the use of insecticides, the environmental significance of chirality in currently used insecticides is poorly understood. In this study, we resolved enantiomers of a number of synthetic pyrethroid and organophosphate insecticides on chiral selective columns and evaluated the occurrence of enantioselectivity in aquatic toxicity and biodegradation. Dramatic differences between enantiomers were observed in their acute toxicity to the freshwater invertebrates Ceriodaphnia dubia and Daphnia magna, suggesting that the aquatic toxicity is primarily attributable to a specific enantiomer in the racemate. In field sediments, the (؊) enantiomer of cis-bifenthrin or cispermethrin was preferentially degraded, resulting in relative enrichment of the (؉) enantiomer. Enantioselective degradation was also observed during incubation of sediments under laboratory conditions. Enantioselectivity in these processes is expected to result in ecotoxicological effects that cannot be predicted from our existing knowledge and must be considered in future risk assessment and regulatory decisions. chiral contaminants ͉ chirality ͉ enantiomers ͉ chiral pesticides ͉ chiral selectivity T he significance of molecular chirality is widely recognized in life sciences (1, 2). A lesser-known fact is that many modern pesticides also contain chiral structures and thus consist of enantiomers (3, 4). About 25% of currently used pesticides are chiral, and this ratio is increasing as compounds with more complex structures are introduced into use (3). Enantiomers of the same compound have identical physical-chemical properties and thus appear as a single compound in standard analysis. For economic reasons, chiral pesticides are primarily used as mixtures of enantiomers, or racemates. However, enantiomers are known to selectively interact with biological systems that are usually enantioselective and may behave as drastically different compounds. The role of enantioselectivity in environmental safety is poorly understood for pesticides, and the knowledge gap is reflected in that the great majority of chiral pesticides are used and regulated as if they were achiral, that is, single compounds.Studies on chiral pesticides started to appear in the early 1990s (4,(5)(6)(7)(8)(9)(10)(11)(12). Studies so far show that microbial degradation of chiral pesticides is commonly enantioselective. As one enantiomer is preferentially degraded, the enantiomer ratio (ER), defined as the ratio of (ϩ) enantiomers to (Ϫ) enantiomers, increasingly deviates from the original value (typically 1.0) (8, 9). Enantioselectivity was found to result in changes of ER in ␣-HCH along the polar bear food chain, causing ER to increase from Ϸ1.0 in cod to 2.3 in liver samples of polar be...

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“…Enantioselectivity of soil degradation processes can be affected by environmental conditions, such as soil type, pH, and microbial populations, so that agricultural practices affecting those parameters can influence the enantioselective degradation of chiral pesticides (Buerge et al, 2003(Buerge et al, , 2006Lewis et al, 1999;Monkiedje et al, 2003;Romero et al, 2001). …”

Section: Introductionmentioning

confidence: 99%

Environmental behavior of the enantiomers of the chiral fungicide metalaxyl in Mediterranean agricultural soils

Celis

Gámiz

Adelino

et al. 2013

Science of The Total Environment

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Improving the existing knowledge on the enantioselectivity of processes affecting chiral pesticide enantiomers in the environment is necessary to maximize the efficacy and minimize the environmental impact caused by the use of pesticides with chiral properties. In this work, the enantioselectivity of the sorption, degradation, and leaching processes of the chiral fungicide metalaxyl in three slightly alkaline, agricultural soils from southern Spain was studied. Batch sorption experiments indicated that the sorption of racemic-metalaxyl on soils, their clay (< 2 µm) fractions, and a number of model sorbents simulating naturally-occurring soil colloidal particles was non-enantioselective; the S-enantiomer was sorbed to the same extent as the R-enantiomer on all soil materials. Soil incubation experiments revealed that the R-enantiomer of metalaxyl was degraded faster than the S-enantiomer in all three soils, but the extent and enantioselectivity of metalaxyl degradation was soil-dependent, occurring more slowly and with less enantioselectivity in the fine-textured soil (soil 1) than in the coarsetextured soils (soils 2 and 3). For soils 2 and 3, S-and R-metalaxyl dissipation data were very well described by single first-order kinetics, whereas for soil 1 dissipation data were better fitted by two coupled first-order equations. It is suggested that sorption and entrapment of metalaxyl enantiomers in the abundant small-size pores of soil 1 (i.e., pore radius < 100 nm) could have resulted in a fraction of the fungicide of reduced bioavailability, and consequently, protected from enantioselective degradation. Metalaxyl leaching through soil columns was also enantioselective; the concentration of S-metalaxyl in all leachates collected was greater than that of R-metalaxyl. Despite being non-enantioselective, sorption influenced the enantioselectivity of metalaxyl leaching, as it determined the residence time of the fungicide within the soil column, and consequently, the extent and enantioselectivity of its degradation during leaching.

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Degradation of Racemic and Enantiopure Metalaxyl in Tropical and Temperate Soils

Cited by 98 publications

References 12 publications

Environmental behavior of benalaxyl and furalaxyl enantiomers in agricultural soils

Environmental behavior of benalaxyl and furalaxyl enantiomers in agricultural soils

Enantioselectivity in environmental safety of current chiral insecticides

Environmental behavior of the enantiomers of the chiral fungicide metalaxyl in Mediterranean agricultural soils

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