Integrative assessment of enantioselectivity in endocrine disruption and immunotoxicity of synthetic pyrethroids.

The increasing release of chiral chemicals into the environment dictates attention to a better understanding of enantioselectivity in their human and ecotoxicological effects. Although enantioselectivity has been considered in many recent studies, there is little effort for discerning the connection between different processes, and as such, our current knowledge about chiral contaminants is rather scattered and incoherent. In this study, we simultaneously evaluated enantioselectivity of two chiral pesticides, lambda-cyhalothrin (LCT) and (Z)-cis-bifenthrin (cis-BF), in immunotoxicity to macrophage cells (RAW264.7), and endocrine disruption activity in human breast carcinoma cell line MCF-7. Analysis of cell proliferation, cell viability, apoptosis, and receptor gene expression showed significant differences between the enantiomers of LCT or cis-BF in estrogenic potential and immunocytotoxicity. The selectivity in these effects consistently followed the same direction, with (-)-LCT or 1S-cis-BF displaying a greater activity than its counterpart. The consistency was attributed to interplaying mechanisms in the closely interacting immune and endocrine systems. The underlying interplays suggest that other chiral xenobiotics may also show a directional enantioselectivity in immunotoxicity and endocrine toxicity. Given that many biological processes are inter-related, enantioselectivity may follow specific patterns that can be revealed via integrative assessments as demonstrated in this study.

Measuring pyrethroids in sediment pore water using matrix-solid phase microextraction.

Pyrethroids are hydrophobic insecticides commonly used in both agricultural and urban environments. Their high toxicity to aquatic organisms, including benthic invertebrates, and detection in the sediment at many locations in California, U.S.A., have spawned interest in understanding their bioavailability in bed sediments. A recent study showed good correlation between uptake of 14C-permethrin in Chironomus tentans and solid-phase microextraction (SPME) fibers in sediments. The present study was directed at the development of an SPME technique applicable to trace levels of nonlabeled pyrethroids in sediment. Disposable polydimethylsiloxane fibers were used to detect freely dissolved pore-water concentrations of bifenthrin, fenpropathrin, cis-permethrin, trans-permethrin, cyfluthrin, cypermethrin, and esfenvalerate under agitated and static conditions. Partition equilibrium between fiber and sediment was reached in <5 d when the samples were agitated on a shaker at low speed, while much longer times (>23 d) were needed without agitation. Polydimethylsiloxane to water partition ratios (K(PDMS)) of the seven pyrethroids were measured separately and ranged from 2.83 x 10(5) to 1.89 x 10(6). When applied to field-contaminated sediments, agitated matrix-SPME was able to detect pore-water concentrations as low as 0.1 ng/L. The method developed in the present study may be coupled with bioassays to gain mechanistic understanding of factors affecting pyrethroid toxicities, and applied to field samples to better predict sediment toxicities from pyrethroid contamination.

Enantioselective estrogenicity of o,p'-dichlorodiphenyltrichloroethane in the MCF-7 human breast carcinoma cell line.

Research increasingly suggests that selectivity between enantiomers may exist in acute and chronic toxicological effects of chiral contaminants. In this study, we used the human breast carcinoma MCF-7 cell line to evaluate enantioselectivity of o,p'-dichlorodiphenyltrichloroethane (o,p'-DDT). Baseline separation of o,p'-DDT enantiomers was achieved on the Chiralcel OJ chiral column by high-performance liquid chromatography, and the absolute configuration and optical rotation of the resolved enantiomers were further identified. Significant differences in estrogenic potential were observed between the two enantiomers of o,p'-DDT in the MCF-7 cell proliferation assay (i.e., the E-Screen assay) and the real-time quantitative polymerase chain reaction (PCR). In the E-Screen assay, the relative proliferative effect ratios of R-(-)-o,p'-DDT and S-(+)-o,p'-DDT were 89.4 and 27.9%, respectively, and the relative proliferative potency ratios were 0.1 and 0.001%, respectively. Compared to the solvent control, R-(-)-o,p'-DDT induced the maximal increase of 2.31-fold at a concentration of 10(-6) mol/L, while S-(+)-o,p'-DDT at 10(-5) mol/L induced the maximal increase of 1.65-fold in estrogenic biomarker pS2 mRNA level. The maximal down-regulation of the transcription levels of estrogen receptor alpha (ERa) and ER3 by R-(-)-o,p'-DDT were 49 and 40% at the concentration of 10(-6) mol/L, while those by S-(+)-o,p'-DDT were 24 and 26% at the concentration of 10(-5) mol/L. The cell proliferation, the up-regulation of pS2, and the down-regulation of ERalpha and ERbeta gene expressions induced by the racemate and enantiomers of o,p'-DDT were all reversed by cotreatment with 10(-6) mol/L ICI 182,780. Therefore, the enantioselective estrogenicity of o,p'-DDT was likely through the ERalpha and ERbeta signaling pathways. Results from this study suggest the need for considering enantioselectivity of chiral contaminants in chronic ecological toxicities.

Estrogenic activity of lambda-cyhalothrin in the MCF-7 human breast carcinoma cell line.

Synthetic pyrethroids are widely used in both agricultural and urban environments for insect control. Lambda-cyhalothrin (LCT) is one of the most common pyrethroids and is used mainly for controlling mosquitoes, fleas, cockroaches, flies, and ants around households. Previous studies have addressed the environmental behaviors and acute toxicities of LCT, but little is known about its chronic toxicity, such as estrogen-like activity. In the present study, the estrogenic potential of LCT was evaluated using the MCF-7 human breast carcinoma cell line. The in vitro E-screen assay showed that 10(-7) M LCT could significantly promote MCF-7 cell proliferation, with a relative proliferative effect ratio of 45%. The cell proliferation induced by LCT could be blocked completely, however, by the addition of 10(-9) M of the estrogen receptor (ER)-antagonist ICI 182,780. The semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) results showed that the Trefoil factor 1 (pS2) and progesterone receptor gene expression were up-regulated by 10(-7) M LCT for 2- and 1.5-fold, respectively. On the other hand, RT-PCR, Western blot analysis, and immunofluorescent assay demonstrated that LCT significantly repressed the mRNA and protein expression levels of ERalpha and ERbeta. These observations indicate that LCT possesses estrogenic properties and may function as a xenoestrogen, likely via a mechanism similar to that of 17beta-estradiol. The endocrine-disruption potential of LCT should be considered when assessing the safety of this compound in sensitive environmental compartments.

Analysis of pyrethroids in sediment pore water by solid-phase microextraction.

Sediment toxicity from trace contamination of pyrethroid insecticides is an emerging water quality concern. Pyrethroids are highly hydrophobic, and their sediment toxicity is related to the freely dissolved concentration in pore water. Solid-phase microextraction (SPME) was evaluated as a selective method to analyze free concentrations of eight pyrethroids in sediment pore water, and SPME measurements were compared to total pore-water concentrations measured using a conventional liquid-liquid extraction (LLE) method. Free pore-water concentrations detected by SPME (C(w-SPME)) were 4.1 to 37% of the total concentration given by LLE (C(w-LLE)) in pore water prepared from a freshwater sediment and only 3.2 to 13.3% in the pore water of a marine sediment. The difference suggested predominant partitioning of pyrethroids into the dissolved organic matter phase in pore water. The method detection limits of the SPME method were lower than the 10th percentile of the reported median lethal concentrations for aquatic organisms, with relative standard deviation <20% as determined over 200 analyses. The SPME method was further used to analyze field-contaminated sediment samples. Those analyses showed that the phase distribution of pyrethroids in sediment was influenced by sediment type and other conditions. Our results show that SPME provides a sensitive, reproducible, and practical method for screening sediment toxicity from potential pyrethroid contamination.

Enantioselectivity in estrogenic potential and uptake of bifenthrin.

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.

Abiotic enantiomerization of permethrin and cypermethrin: effects of organic solvents.

All synthetic pyrethroids are chiral compounds, and isomerization has been frequently observed from exposure to certain solvents. However, so far, pyrethroid isomerization caused by solvents has not been characterized at the enantiomer level. In this study, we evaluated the occurrence of enantiomerization of two commonly used pyrethroids, permethrin and cypermethrin, in various organic solvents and solvent-water systems. The four stereoisomers of permethrin were stable under all test conditions. Rapid enantiomerization of cypermethrin was observed in isopropanol and methanol but not in n-hexane, acetone, or methylene chloride. After 4 days at room temperature, 18-39% conversions occurred for the different cypermethrin stereoisomers in isopropanol and methanol, and the enantiomerization invariably took place at the alpha-carbon position. The extent of enantiomerization was affected by temperature dependence and was also influenced by water as a cosolvent. In solvent-water mixtures, cypermethrin underwent gradual enantiomerization in acetone-water and rapid enantiomerization in isopropanol-water or methanol-water. The extent of enantiomerization varied among the solvents and as a function of the solvent-to-water ratio. Results from this study suggest that exposure to certain solvents and water may cause artifacts in chiral analysis and that for isomer-enriched pyrethroid products, such abiotic enantiomerization may render the products less effective because the conversion leads to the formation of inactive stereoisomers.

Sorption and degradation of pesticides in nursery recycling ponds.

Knowledge of pesticide distribution and persistence in nursery recycling pond water and sediment is critical for preventing phytotoxicity of pesticides during water reuse and to assess their impacts to the environment. In this study, sorption and degradation of four commonly used pesticides (diazinon, chlorpyrifos, chlorothalonil, and pendimethalin) in sediments from two nursery recycling ponds was investigated. Results showed that diazinon and chlorothalonil were moderately sorbed [K(OC) (soil organic carbon distribution coefficient) from 732 to 2.45 x 10(3) mL g(-1)] to the sediments, and their sorption was mainly attributable to organic matter content, whereas chlorpyrifos and pendimethalin were strongly sorbed (K(OC) > or = 7.43 x 10(3) mL g(-1)) to the sediments, and their sorption was related to both organic matter content and sediment texture. The persistence of diazinon and chlorpyrifos was moderate under aerobic conditions (half-lives = 8 to 32 d), and increased under anaerobic conditions (half-lives = 12 to 53 d). In contrast, chlorothalonil and pendimethalin were quickly degraded under aerobic conditions with half-lives < 2.8 d, and their degradation was further enhanced under anaerobic conditions (half-lives < 1.9 d). The strong sorption of chlorpyrifos and pendimethalin by the sediments suggests that the practice of recycling nursery runoff would effectively retain these compounds in the recycling pond, minimizing their offsite movement. The prolonged persistence of diazinon and chlorpyrifos, however, implies that incidental spills, such as overflows caused by storm events, may contribute significant loads of such pesticides into downstream surface water bodies.

Enantioselective degradation and chiral stability of pyrethroids in soil and sediment.

Synthetic pyrethroids contain two or three chiral centers, making them a family of chiral pesticides with a large number of stereoisomers. Recent studies showed significant differences in aquatic toxicity between enantiomers from the same diastereomers of pyrethroids. To better understand the ecotoxicological effect and fate of pyrethroid insecticides, chirality in biodegradation must also be considered. In this study, we examined enantiomer compositions of selected pyrethroids in field sediment samples taken from various locations in southern California. Enantioselective degradation was frequently observed for cis-bifenthrin, permethrin, and cyfluthrin under field conditions. We further conducted long incubation experiments under laboratory-controlled conditions using single enantiomers of cis-bifenthrin, cis-permethrin, and cypermethrin. The half-lives for individual enantiomers were calculated to be 277-770 days for cis-bifenthrin enantiomers, 99-141 days for cis-permethrin enantiomers, and 52-135 days for cypermethrin enantiomers, respectively. The direction and degree of enantioselectivity in degradation were found to closely depend on the specific compound as well as experimental conditions. Because no significant difference in degradation was observed after samples were sterilized, the observed enantioselectivity may be attributed to preferential biological transformations.

Separation and aquatic toxicity of enantiomers of the organophosphorus insecticide trichloronate.

Many of the organophosphorus pesticides (OPs) currently used are chiral and therefore consist of mixture of enantiomers. Despite the fact that the biological processes of chiral pesticides are enantioselective, the acute aquatic toxicity of chiral OPs with respect to enantioselectivity has so far received limited research. In this study, the enantiomeric separation and acute aquatic toxicity of trichloronate were investigated. Baseline enantioseparation of trichloronate was successfully achieved using high-performance liquid chromatography on a Chiralcel OJ column, with a mobile phase of n-hexane/n-heptane/ethanol (90/5/5, v/v/v) at the flow rate of 1.0 ml min(-1) and room temperature. The resolved enantiomers were characterized for their optical rotation and by gas chromatography coupled with mass spectrometry. Significant differences were found between the enantiomers in acute aquatic toxicity to Ceriodaphnia dubia and Daphnia magna. The (-)-trichloronate was 8-11 times more toxic to the test organisms than its (+)-form, while the racemate showed intermediate toxicity. These results suggest that assessment of the environmental safety of chiral OPs should take stereospecificity into consideration.

Inhibition of aquatic toxicity of pyrethroid insecticides by suspended sediment.

The use of pyrethroid insecticides is increasing in both agricultural and urban environments. Although pyrethroids display very high acute toxicities to water column organisms in laboratory tests, environmental water samples typically contain suspended sediment (SS) that can reduce the freely dissolved concentration of pyrethroids, hence their bioavailability. Consequently, phase distribution could play an important role in pyrethroid aquatic toxicology. In this study, we evaluated the effect of SS on the acute toxicity of four widely used pyrethroid insecticides to Ceriodaphnia dubia. In all assays, median lethal concentrations (LC50s) consistently increased with increasing SS, demonstrating the pronounced inhibitory effects of SS on pyrethroid toxicity. The LC50s in the 200 mg/L SS solutions were 2.5 to 13 times greater than those measured in sediment-free controls. Solid-phase microextraction (SPME) was used to determine the apparent distribution coefficient Kd for the pyrethroids in the water samples. Under the assumption that only the freely dissolved fraction is bioavailable, the measured Kd was used to predict C. dubia LC50s in the water samples. The predicted LC50s were within a factor of two of the measured values for 95% of the treatments. Results from this study suggest that the inhibitory effect of SS can be highly significant and must be considered in estimating exposures to pyrethroids in aquatic systems. The SPME methodology could be used effectively to measure bioavailable concentration and to predict the actual ecotoxicologic effects of pyrethroids.

Effect of suspended solids on bioavailability of pyrethroid insecticides.

Runoff and surface-water effluents commonly contain suspended solids. Adsorption to suspended particles and the associated dissolved organic matter (DOM) may significantly decrease the freely dissolved concentration of a hydrophobic compound and, hence, its availability to aquatic organisms. In the present study, we evaluated phase distribution and bioaccumulation of two synthetic pyrethroids, bifenthrin and permethrin, in water samples containing suspended solids from different source sediments. Uptake of [14C]bifenthrin or [14C] permethrin by Daphnia magna after 24 h consistently decreased with increasing levels of suspended solids in the range of 0 to 200 mg/L. The trend of decrease was closely mimicked by pesticide accumulation on polydimethylsiloxane (PDMS) fibers exposed under the same conditions, and the ratio of body residues in D. magna to the concentration detected in the PDMS fiber was consistently around 2.4. Regression analysis showed that the pesticide adsorbed on particles or DOM was completely unavailable to D. magna for uptake during the 24-h exposure. The relative contribution of particles and DOM to the reduced bioavailability depended on the organic matter content and the texture of the source sediment. The influence from particles was predominant for sandy sediments, but contribution from DOM became comparable to or even greater than particles when the organic matter content of the source sediment was 1% or greater. The inhibitory effects of suspended solids on bioavailability should be considered when monitoring runoff and surface-water effluents for synthetic pyrethroids. The proposed PDMS method is simple and inexpensive, and it may serve as an effective option for obtaining ecotoxicologically relevant concentrations.

Effects of dissolved organic matter on permethrin bioavailability to Daphnia species.

Synthetic pyrethroids are widely used insecticides in both agricultural and urban environments. Recent studies show frequent appearances of pyrethroid residues in runoff effluents and sediments, which stimulated concerns over the potential ecotoxicological implications. Pyrethroids are known to have two contrasting characteristics, high aquatic toxicity and strong affinity for the solid phase, that may negate the actual toxicity in a multiphased system. This study evaluated the effect of dissolved organic matter (DOM) on the pyrethroid uptake by and acute toxicity to water-column invertebrates using permethrin as a model compound. During the bioassays, the freely dissolved permethrin concentration was simultaneously measured using poly(dimethylsiloxane) (PDMS) fibers as a biomimetic surrogate. The presence of DOM consistently decreased permethrin uptake and increased its LC(50). For instance, compared to the DOM-free treatment, the LC(50) of permethrin to Ceriodaphnia dubia in a pond water containing DOM at 10 mg L(-)(1) increased from 0.56 to 1.03 microg L(-)(1), whereas the bioaccumulation factor by Daphnia magna decreased by 56%. Permethrin accumulation on the PDMS fiber closely mimicked permethrin uptake by D. magna. Statistical analyses suggest that permethrin associated with DOM was completely unavailable to D. magna or C. dubia. The effect of DOM on permethrin bioavailability appeared to depend also on the source of the DOM. These results indicate that the inhibitory role of DOM should be considered in the development of toxicologically relevant water quality limits and in monitoring protocols for permethrin and other pyrethroids in runoff effluents and surface streams that ubiquitously contain DOM.

Dechlorination of chloropicrin and 1,3-dichloropropene by hydrogen sulfide species: redox and nucleophilic substitution reactions.

The chlorinated fumigants chloropicrin (trichloronitromethane) and 1,3-dichloropropene (1,3-D) are extensively used in agricultural production for the control of soilborne pests. The reaction of these two fumigants with hydrogen sulfide species (H2S and HS-) was examined in well-defined anoxic aqueous solutions. Chloropicrin underwent an extremely rapid redox reaction in the hydrogen sulfide solution. Transformation products indicated reductive dechlorination of chloropicrin by hydrogen sulfide species to produce dichloro- and chloronitromethane. The transformation of chloropicrin in hydrogen sulfide solution significantly increased with increasing pH, indicating that H2S is less reactive toward chloropicrin than HS- is. For both 1,3-D isomers, kinetics and transformation products analysis revealed that the reaction between 1,3-D and hydrogen sulfide species is an S(N)2 nucleophilic substitution process, in which the chlorine at C3 of 1,3-D is substituted by the sulfur nucleophile to form corresponding mercaptans. The 50% disappearance time (DT50) of 1,3-D decreased with increasing hydrogen sulfide species concentration at a constant pH. Transformation of 1,3-D was more rapid at high pH, suggesting that the reactivity of hydrogen sulfide species in the experimental system stems primarily from HS-. Because of the relatively low smell threshold values and potential environmental persistence of organic sulfur products yielded by the reaction of 1,3-D and HS-, the effects of reduced sulfide species should be considered in the development of alternative fumigation practices, especially in the integrated application of sulfur-containing fertilizers.

Degradation of pesticides in nursery recycling pond waters.

Recycling or collection ponds are often used in outdoor container nursery production to capture and recycle runoff water and fertilizers. Waters in recycling ponds generally have high concentrations of nutrients, pesticides, and dissolved organic matter, as well as elevated salinity and turbidity. Little is known about pesticide degradation behavior in the unique environment of nursery recycling ponds. In this study, degradation of four commonly used pesticides diazinon, chlorpyrifos, chlorothalonil, and pendimethalin in waters from two nursery recycling ponds was investigated at an initial pesticide concentration of 50 microg/L. Results showed that the persistence of diazinon and chlorpyrifos appeared to be prolonged in recycling pond waters as compared to surface streamwaters, possibly due to decreased contribution from biotic transformation, while degradation of chlorothalonil and pendimethalin was enhanced. Activation energies of biotic degradation of all four pesticides were lower than abiotic degradation, indicating that microbial transformation was less affected by temperature than chemical transformation. Overall, the pesticide degradation capacity of recycling ponds was better buffered against temperature changes than that of surface streamwaters.

Time dependence of phase distribution of pyrethroid insecticides in sediment.

Synthetic pyrethroids are strongly hydrophobic compounds, and their toxicity in sediment is regulated by phase distribution among the sediment, dissolved organic matter, and water phases. In the present study, we spiked and equilibrated four pyrethroids in two sediments, and we characterized their phase distribution as a function of contact time. The freely dissolved concentration measured by solid-phase microextraction was only a small fraction (<16.3%) of the total pore-water concentration as determined by liquid-liquid extraction. The fraction of the freely dissolved concentration was significantly greater in the freshwater sediment (1.7-16.3%) than in the marine sediment (1.1-4.2%) following 9 d of equilibration, and it decreased substantially with contact time to less than 5% at 30 d after sediment dosing. Consequently, the apparent organic carbon partition coefficient (Koc) and dissolved organic carbon partition coefficient (Kdoc) values increased significantly over the contact time, especially in the freshwater sediment, suggesting that phase distribution was not at equilibrium after 9 d of equilibration. If only the freely dissolved concentration is bioavailable, these observations suggest that contact time after sediment dosing may greatly affect the bioavailability and, hence, the toxicity of pyrethroids. Therefore, a long contact time (> or = 30 d) is recommended for sediment toxicity testing of this class of compounds. The dependence of bioavailability on contact time also implies that test conditions must be standardized to allow comparison between laboratory-dosed samples and field samples.

Isomer selectivity in aquatic toxicity and biodegradation of bifenthrin and permethrin.

Synthetic pyrethroids are widely used insecticides, and contamination of surface aquatic ecosystems by pyrethroid residues from runoff is of particular concern because of potential aquatic toxicity. Pyrethroids also are chiral compounds consisting of multiple stereoisomers. In the present study, we evaluated the diastereomer and enantiomer selectivity of cis-bifenthrin (cis-BF) and permethrin (PM) in their aquatic toxicity and biodegradation. The 1R-cis enantiomer was the only enantiomer in cis-BF showing toxicity against Ceriodaphnia dubia. Incubation with pesticide-degrading bacteria showed that the trans diastereomer of PM was selectively degraded over the cis diastereomer, whereas the 1S-cis enantiomer in cis-BF or cis-PM was preferentially degraded over the corresponding 1R-cis enantiomer. The enantioselectivity was significantly greater for cis-PM than for cis-BF and also varied among different strains of bacteria. Isomer selectivity may be a common phenomenon in both aquatic toxicity and biodegradation of pyrethroids, and this should be considered when assessing ecotoxicological risks of these compounds in sensitive ecosystems.

Chiral stability of synthetic pyrethroid insecticides.

Synthetic pyrethroids are chiral compounds consisting of multiple stereoisomers. Evaluation of enantioselectivity in environmental fate and ecotoxicity requires analytical methods that preserve stereoisomer integrity during analysis. In this study, we characterized the stability of stereoisomers from four commonly used pyrethroids, cis-bifenthrin (cis-BF), permethrin (PM), cypermethrin (CP), and cyfluthrin (CF), during gas chromatography (GC) analysis and sample preparation. Stereoisomers of cis-BF and PM were found to be stable, but those of CP and CF were unstable, under heat or in water. Isomer conversion occurred only at the alphaC in CP or CF, causing the analyte stereoisomer to convert to an epimer. At a GC inlet temperature of 260 degrees C, about 9% conversion occurred for CP and CF. In organic solvents and sterile water, stereoisomers of cis-BF and PM were stable, but slow isomer conversion was observed for CP and CF in water at ambient temperature. However, isomer conversion for CP and CF was relatively insignificant (2-3%) when the GC inlet temperature was kept at < or = 180 degrees C or when on-column injection was used. Isomer conversion at the alphaC in water suggests that abiotic processes may also contribute to enantioselectivity observed in the environment for pyrethroids with the asymmetric alphaC.

Enantioselectivity in environmental safety of current chiral insecticides.

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 cis-permethrin 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.

Persistence of selected organophosphate and carbamate insecticides in waters from a coastal watershed.

Organophosphate and carbamate compounds are among the most widely used pesticides. Contamination of surface water by these compounds is of concern because of potential toxicity to aquatic organisms, especially those at lower trophic levels. In this study we evaluated the persistence of diazinon, chlorpyrifos, malathion, and carbaryl in waters from various sites in the Newport Bay-San Diego Creek watershed in southern California (USA). The persistence of diazinon and chlorpyrifos was much longer than that of malathion or carbaryl and was further prolonged in seawater. Microbial degradation contributed significantly to the dissipation of diazinon and chlorpyrifos in freshwater, but was inhibited in seawater, leading to increased persistence. In contrast, degradation of malathion and carbaryl was rapid and primarily abiotic. A greater temperature dependence was observed for carbaryl degradation in all waters and for diazinon degradation in freshwater. The interactions of pesticide persistence with water location, temperature, and type of pesticides suggest that site- and compound-specific information is needed when evaluating the overall ecotoxicological risks of pesticide pollution in a watershed. Because the persistence of diazinon and chlorpyrifos may increase significantly in seawater, mitigation should occur before the pesticides reach seawater. The relatively short persistence of these compounds in freshwater suggests that practices aimed at extending residence time (e.g., diversion to wetlands) may effectively reduce pesticide output to downstream water bodies.