Enantioselective Breakdown of .alpha.-Hexachlorocyclohexane in a Small Arctic Lake and its Watershed

Falconer, Renee L.; Bidleman, Terry F.; Gregor, D.J.; Semkin, R. G.; Teixeira, Carlos

doi:10.1021/es00005a023

Cited by 74 publications

(80 citation statements)

References 23 publications

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“…Enantioselectivity increased with depth in the Canada Basin and eastern Arctic Ocean, with greater proportions of (+)-R-HCH being depleted below the polar surface water (PSW) (6,7). Preferential loss of (+)-R-HCH was also reported in arctic lakes and wetlands (11,12).…”

Section: Introductionmentioning

confidence: 92%

Enantiomer Fractions of Organic Chlorinated Pesticides in Arctic Marine Ice Fauna, Zooplankton, and Benthos

Borgå

Bidleman

2005

Environ. Sci. Technol.

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Stereoisomers of chiral chlorinated pesticides (R-HCH (HCH ) hexachlorocyclohexane), transand cis-chlordane, MC5, o,p′-DDT) were quantified in arctic marine invertebrates (ice-associated amphipods Gammarus wilkitzkii, pelagic copepods Calanus hyperboreus, krill Thysanoessa inermis, and amphipods Themisto libellula, and benthic amphipods Paramphithoe hystrix). Enantiomer fractions (EFs) were calculated to investigate the influence of habitat, geographic area, and diet on selective bioaccumulation of the (-)or (+)-enantiomer. Depletion of the (+)-R-HCH enantionmer increased from ice fauna to zooplankton to benthos, corresponding to previous reports of EF variations with depth. Chlordanes and o,p′-DDT also showed the strongest enantioselective bioaccumulation in benthic amphipods and less so in zooplankton and ice fauna, which had closer to racemic EFs. Neither diet nor geographic area explained EF differences among samples. Nonracemic EFs in benthos may be related to stereoselective biotransformation, but is most likely reflecting vertical distribution of EFs in the water column and sediments, as demonstrated earlier for R-HCH in the Canadian and European Arctic.

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Section: Introductionmentioning

confidence: 92%

Enantiomer Fractions of Organic Chlorinated Pesticides in Arctic Marine Ice Fauna, Zooplankton, and Benthos

Borgå

Bidleman

2005

Environ. Sci. Technol.

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“…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.…”

mentioning

confidence: 99%

“…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.…”

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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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“…15) (ϩ)-Enantiomer of fipronil (4), a phenylpyrazole broad-spectrum insecticide, was more toxic to C. dubia than the (Ϫ)-enantiomer 16) but in other studies the (Ϫ)-enantiomer was shown to have significantly more androgen and progesterone activity than the (ϩ) form. 3) Enantioselective degradation occurred in human breast milk for o,pЈ-DDT (17), trans-chlordane (18), cis-chlordane (19), oxychlordane (20) and hexachlorocyclohexane (21) (Fig. 5), although pesticide levels were near or at detection limits for most compounds, 17) however, changes in enantiomeric composition are still not well understood, and further investigation in this direction is recommended.…”

Section: Biological Significance Of Chiral Isomersmentioning

confidence: 99%

“…Studies on chiral pesticides started to appear in the early 1990s. [19][20][21][22][23][24][25][26][27][28] Companies have been deeply interested in selling synthetic chiral pesticides as single enantiomers in the past decade. The key reasons why single isomers are less common than they could be are probably limited access to chiral raw materials and economic synthetic routes.…”

Section: Chirality and Potential For Pesticide Reductionmentioning

confidence: 99%

Chiral pesticides

Sekhon

2009

Journal of Pesticide Science

108

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The enantiomers of chiral pesticides are often metabolized at different rates. In agriculture, the preferred chiral form of a pesticide is more effective at lower application rates or more specific toward a targeted pest. Other advantages of chiral pure pesticides include greater environmental safety, reduced cost, greater specificity and extended patent life. Recent progress in optical resolution, asymmetric synthesis and biocatalysis of chiral pesticides has been described. Techniques to separate enantiomers with chiral HPLC and GC columns, electrophoresis and mass spectrometry have been reported. Chiral chase is actively pursuing asymmetric hydrogenation for the manufacture of a pure single-enantiomer pesticide. Enantioselectivity occurs in pesticidal activities toward target organisms as well as non-targeted organisms. There is a need to characterize both enantiomers of chiral pesticides in order to have an accurate understanding of their distribution and fate in the environment. Enantiomeric analysis can be useful in this aim and this is an important consideration in the risk assessment of pesticides. Use of only the target-active enantiomer of pesticides should be encouraged as it will reduce the pollutant load, provided it has no adverse impact on non-target organisms.

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Enantioselective Breakdown of .alpha.-Hexachlorocyclohexane in a Small Arctic Lake and its Watershed

Cited by 74 publications

References 23 publications

Enantiomer Fractions of Organic Chlorinated Pesticides in Arctic Marine Ice Fauna, Zooplankton, and Benthos

Enantiomer Fractions of Organic Chlorinated Pesticides in Arctic Marine Ice Fauna, Zooplankton, and Benthos

Enantioselectivity in environmental safety of current chiral insecticides

Chiral pesticides

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