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...

Bisphenol A (BPA) is a ubiquitous environmental contaminant with endocrine disruption potential. In this study, exploiting the outstanding oxidative capacity of manganese dioxide (delta-MnO2), we explored forthe firsttime the efficacy and mechanisms of BPA removal by MnO2. In aqueous solutions, MnO2 demonstrated an extremely efficient capacity to remove BPA. Nearly all BPA (>99%) was eliminated in 6 min in a pH 4.5 solution initially containing 800 microM MnO2 and 4.4 microM BPA. While humic acid showed negligible inhibition on BPA removal, coexisting metal ions such as Mn2+, Ca2+, Mg2+, and Fe3+ displayed suppressive effects and the inhibitive capacityfollowed the order Mn2+ > Ca2+ > Mg2+ approximately Fe3+. A total of 11 products or intermediates were indentified and a detailed reaction scheme was suggested. The products could be ascribed to a suite of reactions of radical coupling, fragmentation, substitution, and elimination, triggered by the BPA radical formed through electron transfers to MnO2. The exceptional efficiency of MnO2 in removing BPA represents a potential use of MnO2 to treat waters containing phenolic compounds and also suggests a potentially important role of oxide-facilitated abiotic transformations in BPA attenuation in natural soil and sediment environments.

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Despite the fact that the biological processes of chiral compounds are enantioselective, the endocrine disruption activity and uptake of chiral contaminants with respect to enantioselectivity has so far received limited research. In this study, the estrogenic potential and uptake of the enantiomers of a newer pyrethroid insecticide, bifenthrin (BF), were investigated. Significant differences in estrogenic potential were observed between the two enantiomers in the in vitro human breast carcinoma MCF-7 cell proliferation assay (i.e., the E-SCREEN assay) and the in vivo aquatic vertebrate vitellogenin enzyme-linked immunosorbent assay (ELISA). In the E-SCREEN assay, the relative proliferative effect ratios of 1S-cis-BF and 1R-cis-BF were 74.2% and 20.9%, respectively, and the relative proliferative potency ratios were 10% and 1%, respectively. The cell proliferation induced by the two BF enantiomers may be through the classical estrogen response pathway via the estrogen receptor (ER), as the proliferation induced by the enantiomers could be completely blocked when combined with 10-6 mol/L of the ER antagonist ICI 182,780. Measurement of vitellogenin induction in Japanese medaka (Oryzias latipes) showed that, at an exposure level of 10 ng/mL, the response to 1S-cis-BF was about 123 times greater than thattothe Renantiomer. Significant selectivity also occurred in the uptake of BF enantiomers in the liver and other tissues of J. medaka. These results together suggest that assessment of the environmental safety of chiral insecticides should consider enantioselectivity in acute and chronic ecotoxicities such as endocrine disruption.

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Birnessite (delta-MnO2) is a naturally occurring soil and sediment component that has been shown to oxidize organic compounds containing phenolic or aniline moieties. In this study, for the first time we explored the oxidation reaction of tetrabromobisphenol A (TBBPA), the most heavily used brominated flame retardant, with MnO2. TBBPA rapidly dissipated from the reaction solution and the process was accompanied by the dissolution of Mn2+. Dissipation of 50% of TBBPA occurred in less than 5 min in a system (pH 4.5) containing 625 microM MnO2 and 3.50 microM TBBPA at 21 degrees C, and the removal further increased to as high as 90% when the reaction was prolonged to 60 min. Analysis of initial reaction kinetics showed that the reaction orders with respect to TBBPA, MnO2, and H+ were 1.0, 0.8, and 0.25, respectively. Higher initial concentrations of TBBPA and MnO2 both enhanced the reaction. In addition, reaction rates increased as pH decreased. A retarded first-order model was found to closely describe the long-term reaction kinetics (R2 > or = 0.99), from which initial half-lives of TBBPA under different reaction conditions were estimated. A total of 7 reaction products were identified and a tentative reaction scheme was proposed. This study suggests that oxidative transformation of TBBPA by MnO2 may play an important role in the natural attenuation of TBBPA. The reaction may be further optimized for treatment of TBBPA-containing wastewater or remediation of TBBPA-polluted environmental matrices.

Pyrethroids are commonly used insecticides in both agricultural and urban environments. Recent studies showed that surface runoff facilitated transport of pyrethroids to surface streams, probably by sediment movement. Sediment contamination by pyrethroids is of concern due to their wide-spectrum aquatic toxicity. In this study, we characterized the spatial distribution and persistence of bifenthrin [BF; (2-methyl(1,1'-biphenyl)-3-yl)methyl 3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate] and permethrin [PM; 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid (3-phenoxyphenyl)methyl ester] in the sediment along a 260-m runoff path. Residues of BF and PM were significantly enriched in the eroded sediment, and the magnitude of enrichment was proportional to the downstream distance. At 145 m from the sedimentation pond, BF was enriched by >25 times, while PM isomers were enriched by >3.5 times. Pesticide enrichment along the runoff path coincided with enrichment of organic carbon and clay fractions in the sediment, as well as increases in adsorption coefficient K(d), suggesting that the runoff flow caused selective transport of organic matter and chemical-rich fine particles. Long persistence was observed for BF under both aerobic and anaerobic conditions, and the half-life ranged from 8 to 17 mo at 20 degrees C. The long persistence was probably caused by the strong pesticide adsorption to the solid phase. The significant enrichment, along with the prolonged persistence, suggests that movement of pyrethroids to the surface water may be caused predominantly by the chemically rich fine particles. It is therefore important to understand the fate of sediment-borne pyrethroids and devise mitigation strategies to reduce offsite movement of fine sediment.

Bisphenol S (4-hydroxyphenyl sulfone, BPS) is increasingly used as a bisphenol A (BPA) alternative. The global usage of BPS and its analogues (BPSs) resulted in the frequent detection of their residues in multiple environmental media. We investigated their potential endocrine-disrupting effects toward thyroid hormone receptor (TR) β. The molecular interaction of BPSs toward TRβ ligand binding domain (LBD) was probed by fluorescence spectroscopy and molecular dynamics (MD) simulations. BPSs caused the static fluorescence quenching of TRβ LBD. The 100 ns MD simulations revealed that the binding of BPSs caused significant changes in the distance between residue His435 at helix 11(H11) and residue Phe459 at H12 in comparison to no ligand-bound TRβ LBD, indicating relative repositioning of H12. The recombinant two-hybrid yeast assay showed that tetrabromobisphenol S (TBBPS) and tetrabromobisphenol A (TBBPA) have potent antagonistic activity toward TRβ, with an IC of 10.1 and 21.1 nM, respectively. BPS and BPA have the antagonistic activity with IC of 312 and 884 nM, respectively. BPSs significantly altered the expression level of mRNA of TRβ gene in zebrafish embryos. BPS and TBBPS at environmentally relevant concentrations have antagonistic activity toward TRβ, implying that BPSs are not safe BPA alternatives in many BPA-free products. Future health risk assessments for TR disruption and other adverse effects should focus more on the structure-activity relationship in the design of environmentally benign BPA alternatives.