Faster degradation of herbicidally-active enantiomer of imidazolinones in soils

Ramezani, Mohammad Kazem; Oliver, Danielle P.; Kookana, Rai S.; Lao, Wenjian; Gill, Gurjeet; Preston, Christopher

doi:10.1016/j.chemosphere.2010.03.046

Cited by 40 publications

(33 citation statements)

References 36 publications

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“…in chiral environments. For example, chiral pesticide enantiomers can differ in their toxicity and biological degradation due to the fact that the molecular receptor responsible for the toxicity or biological degradation of a pesticide is often an enzyme, the active center of which is also chiral and in turn enantioselective [2,[11][12][13][14][15]. Abiotic processes such as chemical, distribution, or transport processes are supposed to affect both enantiomers equally and are generally assumed to be non-enantioselective [10,16,17].…”

Section: Optical Isomers or Enantiomers Have Practically Identical Chmentioning

confidence: 99%

Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications

Celis

Gámiz

Facenda

et al. 2015

Journal of Hazardous Materials

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Mechanisms governing the enantioselectivity of the processes that determine the behavior of chiral pollutants in the environment need to be better understood. Understanding these mechanisms should help improve predictions of the hazards and risks chiral compounds can pose to people and the environment. We report the results of batch sorption experiments indicating that the sorption of the chiral fungicide metalaxyl on soil from non-racemic initial solutions was enantioselective. While from a racemic initial solution the two enantiomers of metalaxyl were sorbed on the soil to the same extent, increasing the fraction of R-enantiomer in the initial solution led to enhanced sorption of this enantiomer and to reduced sorption of the S-enantiomer. Considering the shape of the sorption isotherms (S-type) and the sorption behavior of model sorbents, we attributed this effect to molecular interactions between metalaxyl enantiomer species at the sorbed state, where R-R metalaxyl interactions appeared to be more favorable than R-S metalaxyl interactions. We discuss important environmental implications of the proposed mechanism, such as those related to the fact that the biological degradation of metalaxyl is known to be an enantioselective process that can yield non-racemic residues in soils shortly after application of the fungicide as a racemic mixture.

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Section: Optical Isomers or Enantiomers Have Practically Identical Chmentioning

confidence: 99%

Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications

Celis

Gámiz

Facenda

et al. 2015

Journal of Hazardous Materials

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“…It is well known that the degradation of chiral pesticides in soil is usually enantioselective, primarily due to the enantioselectivity of soil biological degradation processes (Buerge et al, 2006;Garrison et al, 1996;Kurt-Karakus et al, 2005;Li et al, 2006;Ramezani et al, 2010); however, information on factors influencing such enantioselective degradation is still scarce (Buerge et al, 2003;Garrison, 2006;Lewis et al, 1999;Romero et al, 2001;Tan et al, 2008).…”

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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“…These concentrations would not represent a risk for freshwater algae considering the EC50 for P. subcapitata obtained in our study, which was 1,000 times greater than that concentration. However, imazethapyr is degraded slowly in soils, having a half-life between 30 and 60 days under laboratory conditions and between 2.6 and 10.6 months under field conditions (Ramezani et al 2010). While there is no information about its degradability in water, it would be relatively slow as in soil and thus may remain for some time in the aquatic ecosystems, increasing algae exposure.…”

Section: Resultsmentioning

confidence: 98%

Phytotoxicity and genotoxicity assessment of imazethapyr herbicide using a battery of bioassays

Magdaleno

Gavensky

Fassiano

et al. 2015

Environ Sci Pollut Res

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The imazethapyr herbicide (formulation Verosil(®)) was evaluated for phytotoxicity and genotoxicity using a battery of bioassays: (1) the growth inhibition of the green alga Pseudokirchneriella subcapitata, (2) the root growth and germination of the higher plant Lactuca sativa, (3) the genetic damage using the Salmonella/microsome test, and (4) the aneugenic and clastogenic effects on Allium cepa. The Verosil(®) formulation was highly toxic to the non-target green alga (median effective concentration (EC50) = 1.05 ± 0.05 mg active ingredient (a.i.) L(-1)), and concentrations above 10 mg a.i. L(-1) inhibited root elongation in lettuce: relative growth index (RGI) between 0.28 ± 0.01 and 0.66 ± 0.10. No genotoxic effect was observed in S almonella typhimurium at 100 mg a.i. L(-1), either with or without the microsomal fraction. However, significant differences in the frequency of chromosomal aberrations in anaphases and telophases (bridges, chromosome fragments, and vagrants) were observed in A. cepa at concentrations between 0.01 and 1 mg a.i. L(-1) with respect to the control. The frequencies of micronuclei showed significant differences with respect to the control at concentrations between 0.001 and 0.1 mg a.i. L(-1). A very high mitotic index (MI = 93.8 ± 5.8) was observed associated with a high number of cells in the prophase stage at 100 mg a.i. L(-1), indicating cytotoxicity. These results showed that imazethapyr is toxic to the non-target populations in both aquatic and terrestrial ecosystems. This herbicide might also exert clastogenic and aneugenic mitotic damage in higher plants. Therefore, the imazethapyr formulation may constitute an environmental risk to plants.

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Faster degradation of herbicidally-active enantiomer of imidazolinones in soils

Cited by 40 publications

References 36 publications

Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications

Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications

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

Phytotoxicity and genotoxicity assessment of imazethapyr herbicide using a battery of bioassays

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