Single and joint acute toxicity of isocarbophos enantiomers to Daphnia magna

A review on the enantioselective distribution and toxicity of chiral pesticides in aquatic environment

Chiral pesticides account for about 40% of the total pesticides. In the process of using pesticides, it will inevitably flow into the surface water and even penetrate into the groundwater through surface runoff and other means, as a consequence, it affects the water environment. Although the enantiomers of chiral pesticides have the same physical and chemical properties, their distribution, ratio, metabolism, toxicity, etc. in the organism are often different, and sometimes even show completely opposite biological activities. In this article, the selective fate of different types of chiral pesticides such as organochlorine, organophosphorus, triazole, pyrethroid and other chiral pesticides in natural water bodies and sediments, acute toxicity to aquatic organisms, chronic toxicity and other aspects are summarized to further reflect the risks between the enantiomers of chiral pesticides to non-target organisms in the water environment. In this review, we hope to further explore its harm to human society through the study of the toxicity of chiral pesticide enantiomers, so as to provide data support and theoretical basis for the development and production of biochemical pesticides.

Comprehensive evaluation of chiral sedaxane with four stereoisomers for risk reduction: Bioactivity, toxicity, and stereoselective dissipation in crop planting systems

A comprehensive evaluation of chiral pesticide at the stereoisomeric level is an effective strategy to improve efficiency and reduce risk on foods. For chiral sedaxane with four stereoisomers, there were 517-1013 fold differences in bioactivity for three kinds of phytopathogens and 3.73 fold differences in toxicity against model organism (Danio rerio) between the best (trans-1R2S-sedaxane) and worst stereoisomer (cis-1S2S-sedaxane). Trans-1R2S-sedaxane had the strongest affinity with the active site than other stereoisomers, which might contribute to the highest bioactivity. Trans-sedaxane was 28.2-331 fold more effective than cis-sedaxane. The dissipation half-lives of sedaxane stereoisomers ranged from 3.28 to 30.7 d in the test crops and soils. Trans-1S2R-sedaxane and cis-1S2S-sedaxane were preferentially dissipated in corn plants, while the preferential dissipation of trans-1R2S-sedaxane was found in wheat plants, potato plants and corn soil. The preferential dissipation of trans-sedaxane in corn plants, wheat plants, potato plants and corn soil would be environmentally friendly.

Application and Progress of Machine Learning in Pesticide Hazard and Risk Assessment

Long-term exposure to pesticides is associated with the incidence of cancer. With the exponential increase in the number of new pesticides being synthesized, it becomes more and more important to evaluate the toxicity of pesticides by means of simulated calculations. Based on existing data, machine learning methods can train and model the predictions of the effects of novel pesticides, which have limited available data. Combined with other technologies, this can aid the synthesis of new pesticides with specific active structures, detect pesticide residues, and identify their tolerable exposure levels. This article mainly discusses support vector machines, linear discriminant analysis, decision trees, partial least squares, and algorithms based on feedforward neural networks in machine learning. It is envisaged that this article will provide scientists and users with a better understanding of machine learning and its application prospects in pesticide toxicity assessment.

Development of S-penthiopyrad for bioactivity improvement and risk reduction from the systemic evaluation at the enantiomeric level

For the purpose of screening high-efficiency and low-risk green pesticides, a systematic study on fungicide penthiopyrad was conducted at the enantiomeric level. The bioactivity of S-(+)-penthiopyrad (median effective concentration (EC50), 0.035 mg/L) against Rhizoctonia solani was 988 times higher than R-(-)-penthiopyrad (EC50, 34.6 mg/L), which would reduce 75% usage of rac-penthiopyrad under the same efficacy. Furthermore, their antagonistic interaction (toxic unit (TUrac), 2.07) indicated the existence of R-(-)-penthiopyrad would reduce the fungicidal activity of S-(+)-penthiopyrad. AlphaFold2 modeling and molecular docking illustrated that S-(+)-penthiopyrad had the higher binding ability with the target protein than R-(-)-penthiopyrad, showing higher bioactivity. For model organism Danio rerio, S-(+)-penthiopyrad (median lethal concentrations (LC50), 3.02 mg/L) and R-(-)-penthiopyrad (LC50, 4.89 mg/L) were both less toxic than rac-penthiopyrad (LC50, 2.73 mg/L), and the existence of R-(-)-penthiopyrad could synergistically enhance the toxicity of S-(+)-penthiopyrad (TUrac, 0.73), using S-(+)-penthiopyrad would reduce at least 23% toxicity to fish. The enantioselective dissipation and residues of rac-penthiopyrad were tested in three kinds of fruits, and their dissipation half-lives ranged from 1.91 to 23.7 d. S-(+)-penthiopyrad was dissipated preferentially in grapes, which was R-(-)-penthiopyrad in pears. On the 60th d, the residue concentrations of rac-penthiopyrad in grapes were still higher than its maximum residue limit (MRL), but the initial concentrations were lower than their MRL values in watermelons and pears. Thus, more tests in different cultivars of grapes and planting environments should be encouraged. Based on the acute and chronic dietary intake risk assessments, the risks in the three fruits were all acceptable. In conclusion, S-(+)-penthiopyrad is a high-efficiency and low-risk alternative to rac-penthiopyrad.

Systemic enantioselectivity study of penthiopyrad: enantioselective bioactivity, acute toxicity, degradation and influence on tomato

BACKGROUND

In order to promote the green development of agriculture, it is important to study the enantioselective effect of chiral pesticides. The bioactivity of the chiral fungicide penthiopyrad (PEN) racemate and enantiomers against phytopathogens, toxicity to non-target organisms, effect on tomato fruit growth and maturation, and environmental fate in tomato cultivation were evaluated at an enantioselective level in this study.

RESULTS

The results indicated that at the same efficacy, the optically pure S-(+)-PEN could lower the dosage of racemate by 20-96%. The S-enantiomer had low toxicity to earthworms. Besides, the S-(+)-PEN did not cause significant abiotic stress to the tomato and increased fruit fresh weight and size via modulating the contents of plant hormones. However, the content of hydrogen peroxide (H₂ O₂ ), superoxide (O₂ ^- ) and malondialdehyde in the R-enantiomer treatment group was significantly higher than the control group. The effect of the racemate on tomato fruit was between the enantiomers. Furthermore, compared to R-(-)-PEN and racemate, the S-enantiomer degraded more quickly in tomato fruit, leaves, and soil, reducing the danger of human exposure.

CONCLUSION

The S-enantiomer is highly effective and less toxic. The development of enantiomer pure S-(+)-PEN products might be an efficient and low-risk strategy. The results lay the foundation for comprehensive evaluation and proper application of PEN. © 2023 Society of Chemical Industry.

A chiral fluorescent COF prepared by post-synthesis modification for optosensing of imazamox enantiomers

We report a post-synthesis modification for the preparation of a novel chiral fluorescent covalent organic framework (COF) for selective recognization of imazamox enantiomers. In this study, chiral COF was firstly synthesized via a Schiff-base reaction between 2,5-dihydroxyterephthalaldehyde (Dha) and 1,3,5-tris(4-aminophenyl)benzene (Tab) followed by a nucleophilic substitution using (1S)-(+)-10-camphorsulfonyl chloride as chiral modifier. The resulting regular spherical chiral COF Dha Tab not only presented the high optical efficiency, strong covalent bond structure, good crystallinity, large specific surface area but also showed the specific enantioselectivity and quick identification for imazamox enantiomers among five pesticide enantiomers (S/R-imazamox, acephate, acetochlor, propisochlor and metalaxyl). The detection limits for S- and R-imazamox were 4.20 μmol/L and 3.03 μmol/L, respectively. Meanwhile, the enantiomeric excess value (5.30 %) manifested that the chiral COF Dha Tab had the strong adsorption ability to imazamox enantiomers and more higher affinity for R-imazamox. This chiral fluorescent COF opened up a new way for the recognition of enantiomers.

Dissecting the Enantioselective Neurotoxicity of Isocarbophos: Chiral Insight from Cellular, Molecular, and Computational Investigations

Chiral organophosphorus pollutants are found abundantly in the environment, but the neurotoxicity risks of these asymmetric chemicals to human health have not been fully assessed. Using cellular, molecular, and computational toxicology methods, this story is to explore the static and dynamic toxic actions and its stereoselective differences of chiral isocarbophos toward SH-SY5Y nerve cells mediated by acetylcholinesterase (AChE) and further dissect the microscopic basis of enantioselective neurotoxicity. Cell-based assays indicate that chiral isocarbophos exhibits strong enantioselectivity in the inhibition of the survival rates of SH-SY5Y cells and the intracellular AChE activity, and the cytotoxicity of (S)-isocarbophos is significantly greater than that of (R)-isocarbophos. The inhibitory effects of isocarbophos enantiomers on the intracellular AChE activity are dose-dependent, and the half-maximal inhibitory concentrations (IC₅₀) of (R)-/(S)-isocarbophos are 6.179/1.753 μM, respectively. Molecular experiments explain the results of cellular assays, namely, the stereoselective toxic actions of isocarbophos enantiomers on SH-SY5Y cells are stemmed from the differences in bioaffinities between isocarbophos enantiomers and neuronal AChE. In the meantime, the modes of neurotoxic actions display that the key amino acid residues formed strong noncovalent interactions are obviously different, which are related closely to the molecular structural rigidity of chiral isocarbophos and the conformational dynamics and flexibility of the substrate binding domain in neuronal AChE. Still, we observed that the stable "sandwich-type π-π stacking" fashioned between isocarbophos enantiomers and aromatic Trp-86 and Tyr-337 residues is crucial, which notably reduces the van der Waals' contribution (ΔG_vdW) in the AChE-(S)-isocarbophos complexes and induces the disparities in free energies during the enantioselective neurotoxic conjugations and thus elucidating that (S)-isocarbophos mediated by synaptic AChE has a strong toxic effect on SH-SY5Y neuronal cells. Clearly, this effort can provide experimental insights for evaluating the neurotoxicity risks of human exposure to chiral organophosphates from macroscopic to microscopic levels.

Comprehensive evaluation of novel fungicide benzovindiflupyr at the enantiomeric level: Bioactivity, toxicity, mechanism, and dissipation behavior

Racemates in the environment can lead to inaccurate risk assessment. To obtain the enantiomeric level information of benzovindiflupyr for accurate risk assessment, the absolute configuration of benzovindiflupyr was first confirmed, and the enantioseparation method was developed by supercritical fluid chromatography tandem mass spectrometry. The enantioselectivity for bioactivity and toxicity was investigated, and the mechanism was explored by molecular docking and detecting succinate dehydrogenase (SDH) activity and content of succinate acid. 1S,4R-(-)-benzovindiflupyr was identified as the most active against the six targeted phytopathogens, which showed higher 1.7-54.5 times than 1R,4S-(+)-benzovindiflupyr. Additionally, 1S,4R-(-)-benzovindiflupyr (LD₅₀: 21.54 μg L^-1) was 103.7 times more toxic than 1R,4S-(+)-benzovindiflupyr against Daphnia magna. 1S,4R-(-)-benzovindiflupyr had a stronger affinity for SDH and significantly inhibited SDH activity, resulting in an increase in succinate acid in the tricarboxylic acid cycle, while its downstream products, fumaric and L-malic acid were significantly reduced. Moreover, the dissipation behavior of benzovindiflupyr on three vegetables was evaluated. 1S,4R-(-)-benzovindiflupyr was preferentially degraded in tomato, but opposite in leaves. The enantioselectivity in pepper and cucumber leaves was the same as in tomato, while there was no enantioselectivity in pepper and cucumber. The study provides a basis for accurate risk assessment and the development of high-effective and low-risk fungicides.

Enantioselectivity in the toxicological effects of chiral pesticides: A review

As a special category of pesticides, chiral pesticides have increased the difficulty in investigating pesticide toxicity. Based on their usage, chiral pesticides can be divided into insecticides, herbicides, and fungicides. Over the past decades, great efforts have been made on elucidating their toxicological effects. However, no literature has reviewed the enantioselective toxicity of chiral pesticides since 2014. In recent years, more chiral pesticides have been registered for application. As such, huge research progresses have been achieved in enantioselective toxicity of chiral pesticides. Generally, more researches have remedied the knowledge gap in toxicological effects of old and new chiral pesticides. And the toxicological endpoints being evaluated have become more specific rather than centering on basic toxicity and target organisms. Besides, the underlying mechanisms accounting for the enantioselectivity in toxicological effects of chiral pesticides have been discussed as well. All in all, this review provides the critical knowledge for risk assessments, and help to drive the green-technology of single- or enriched-enantiomer pesticides and formulation of relevant laws and regulations.

Systematic evaluation of chiral pesticides at the enantiomeric level: A new strategy for the development of highly effective and less harmful pesticides

Over the past few decades, pesticides have been used in large quantities, and they pose potential risks to organisms across various environments. Reducing the use of pesticides and their environmental risks has been an active research focus and difficult issue worldwide. As a class of pesticides with special structures, chiral pesticides generally exhibit enantioselectivity differences in biological activity, ecotoxicity, and environmental behavior. At present, replacing the racemates of chiral pesticides by identifying and developing their individual enantiomers with high efficiency and environmentally friendly characteristics is an effective strategy to reduce the use of pesticides and their environmental risks. In this study, we review the stereoselective behaviors of chiral pesticide, including their environmental behavior, stereoselective biological activity, and ecotoxicity. In addition, we emphasize that the systematic evaluation of chiral pesticides at the enantiomeric level is a promising novel strategy for developing highly effective and less harmful pesticides, which will provide important data support and an empirical basis for reducing pesticide application.

A comprehensive review on electrochemical and optical aptasensors for organophosphorus pesticides

There has been a rise in pesticide use as a result of the growing industrialization of agriculture. Organophosphorus pesticides have been widely applied as agricultural and domestic pest control agents for nearly five decades, and they remain as health and environmental hazards in water supplies, vegetables, fruits, and processed foods causing serious foodborne illness. Thus, the rapid and reliable detection of these harmful organophosphorus toxins with excellent sensitivity and selectivity is of utmost importance. Aptasensors are biosensors based on aptamers, which exhibit exceptional recognition capability for a variety of targets. Aptasensors offer numerous advantages over conventional approaches, including increased sensitivity, selectivity, design flexibility, and cost-effectiveness. As a result, interest in developing aptasensors continues to expand. This paper discusses the historical and modern advancements of aptasensors through the use of nanotechnology to enhance the signal, resulting in high sensitivity and detection accuracy. More importantly, this review summarizes the principles and strategies underlying different organophosphorus aptasensors, including electrochemical, electrochemiluminescent, fluorescent, and colorimetric ones.

Chiral perspective evaluations: Enantioselective hydrolysis of 6PPD and 6PPD-quinone in water and enantioselective toxicity to Gobiocypris rarus and Oncorhynchus mykiss

As a ubiquitous tire antidegradant, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is persistently released into the environment. It is highly toxic to aquatic organisms, and its transformation product 6PPD-quinone (6PPD-Q), is "very highly toxic" to Oncorhynchus kisutch at a median lethal concentration (LC50) of < 0.1 ng/mL. Notably, 6PPD and 6PPD-Q are chiral compounds. Here, enantioselective evaluations, including hydrolysis and acute toxicity were conducted after preparing the enantiomer, confirming the enantiomer absolute configuration and establishing enantioseparation methods. In the 6PPD hydrolysis experiments, the products 6PPD-Q, phenol, 4-[(1,3-dimethylbutyl)amino]- (4-DBAP) and 4-hydroxydiphenylamine (4-HDPA) were detected. In different water solutions, the hydrolysis of 4-DBAP and 4-HDPA was very fast (0.87-107 h), while the 6PPD-Q hydrolysis half-lives (12.8-16.3 d) were significantly longer than 6PPD (4.83-64.1 h). At the enantiomeric level, no enantioselective hydrolysis and conversion occurred. R-6PPD generated R-6PPD-Q, and S-6PPD generated S-6PPD-Q, and the formation rate of S-6PPD-Q was 1.77 times faster than R-6PPD-Q. In terms of the enantioselective toxicity, the 6PPD enantiomer was highly toxic to China-specific Gobiocypris rarus (LC50, 162-201 ng/mL), and it had no enantioselective difference. 6PPD-Q was "very highly toxic" (LC50, 1.66-4.31 ng/mL) to Oncorhynchus mykiss, which is of commercial importance, and the toxicities of rac-6PPD-Q and S-6PPD-Q were 1.9 and 2.6 times higher than R-6PPD-Q. Furthermore, the formation concentrations of S-6PPD-Q and R-6PPD-Q in 6PPD water solutions were higher than the LC50 values of O. kisutch and O. mykiss, and the toxicity of 6PPD-Q was highly species-specific, which should raise concern. These results provide important information for environmental risk assessments of 6PPD and 6PPD-Q, especially from the perspective of enantiomers.

Toxicity, bioactivity of triazole fungicide metconazole and its effect on mycotoxin production by Fusarium verticillioides: New perspective from an enantiomeric level

The chiral triazole fungicide metconazole has four stereoisomers, is a broad-spectrum fungicide and is widely used for controlling Fusarium head blight caused by Fusarium species. In this study, systemic assessments of metconazole stereoisomers were performed, including stereoselective toxicity toward the aquatic organism Daphnia magna, fungicidal activity and effects on fumonisin production by the pathogen Fusarium verticillioides (F. verticillioides) in relation to different conditions. The toxicity of metconazole was enantioselective, and there was a 2.1-2.9-fold difference. The activities of superoxide dismutase (SOD) and catalase (CAT) increased and decreased, respectively, after treatment with metconazole stereoisomers, and the differences were observed among the stereoisomers. Among the four stereoisomers, (1S,5R)-metconazole showed the highest fungicidal activity under all assayed conditions, and the differences ranged from 4.4 to 45.2 times. Moreover, metconazole stereoisomers can stereoselectively affect on fumonisin B₁ production by F. verticillioides and abiotic factors, such as water activity and temperature, play an important role. Our study provides new insight into metconazole at the stereoisomeric level, including its toxicity, bioactivity, and effect on Fusarium species producing mycotoxins.

Comprehensive evaluation of chiral pydiflumetofen from the perspective of reducing environmental risks

The spatial structures of chiral pesticide enantiomers can affect their activity, toxicity and behavior, thereby altering exposure risk. Identifying enantiomer differences and developing high-efficiency green enantiopure pesticide is an important strategy for reducing the negative effects of pesticides. In this study, after confirming the absolute configuration of pydiflumetofen enantiomers, fungicidal activity evaluation indicated that the activity of S-(+)-pydiflumetofen was 81.3-421 times higher than R-(-)-pydiflumetofen on three kinds of phytopathogens that control Fusarium wilt (Fusarium spp.), Alternaria rot (Alternaria alternata) and Southern blight (Sclerotinia rolfsii), which might be caused by the stronger binding ability of S-(+)-pydiflumetofen with the active site of the target protein. The coexistence of R-(-)-pydiflumetofen would enhance the toxicity of S-(+)-pydiflumetofen on zebrafish through synergistic effect. Low-activity R-(-)-pydiflumetofen was preferentially dissipated in soybean, soybean plants, cabbage and celery, which was opposite in soil. The persistence of S-(+)-pydiflumetofen in crops and degradability in soil were advantageous for pesticide effects and environmental protection. Based on the maximum residue limit (MRL) and hazard quotient (HQ), the dietary risks were determined to be acceptable for all crops. Thus, developing enantiopure S-(+)-pydiflumetofen products might be a high-efficiency and low-risk strategy, and more studies should be conducted in this aspect.

Preparation and evaluation of a perylenediimide bridged bis(β-cyclodextrin) chiral stationary phase for HPLC

A large π-conjugated perylenediimide bridged bis(β-cyclodextrin)-bonded stationary phase (PBCDP) was first prepared and characterized. The chiral HPLC performance was systematically evaluated using a series of chiral probes. The results showed that PBCDP could resolve 36 kinds of chiral compounds in reversed-phase and polar organic modes with high resolutions (Rs) 1.48-3.28 for profens, 1.25-2.85 for triazoles, 1.34-5.29 for flavanones, 1.66-4.58 for amino acids and 1.22-1.97 for β-blockers. Especially, PBCDP could completely resolve acidic non-steroidal chiral drugs (profens) and simultaneously resolve basic five triazole pesticides, which were difficult to separate by ordinary CDCSP. Compared with CDCSP (15 kinds), the new stationary phase has a wider resolution range (36 kinds). Obviously, the synergistic inclusion of the two cavities of bridged cyclodextrin, as well as the large π-π stacking, hydrogen bond, dipole-dipole and basic primary amine site (-NH-) provided by the perylenediimide bridging group contributed together to the improvement of the above chiral separations. PBCDP was a new type of versatile chiral separation material without port derivatization.

Old pesticide, new use: Smart and safe enantiomer of isocarbophos in locust control

Locust plagues are still worldwide problems. Selecting active enantiomers from current chiral insecticides is necessary for controlling locusts and mitigating the pesticide pollution in agricultural lands. Herein, two enantiomers of isocarbophos (ICP) were separated and the enantioselectivity in insecticidal activity against the pest Locusta migratoria manilensis (L. migratoria) and mechanisms were investigated. The significant difference of LD₅₀ between (+)-ICP (0.609 mg/kg bw) and (-)-ICP (79.412 mg/kg bw) demonstrated that (+)-ICP was a more effective enantiomer. The enantioselectivity in insecticidal activity of ICP enantiomers could be attributed to the selective affinity to acetylcholinesterase (AChE). Results of in vivo and in vitro assays suggested that AChE was more sensitive to (+)-ICP. In addition, molecular docking showed that the -CDOKER energies of (+)-ICP and (-)-ICP were 25.6652 and 24.4169, respectively, which suggested a stronger affinity between (+)-ICP and AChE. Significant selectivity also occurred in detoxifying enzymes activities (carboxylesterases (CarEs) and glutathione S-transferases (GSTs)) and related gene expressions. Suppression of detoxifying enzymes activities with (+)-ICP treatment suggested that (-)-ICP may induce the detoxifying enzyme-mediated ICP resistance. A more comprehensive understanding of the enantioselectivity of ICP is necessary for improving regulation and risk assessment of ICP.

Enantioselective Bioactivity, Toxicity, and Degradation in Vegetables and Soil of Chiral Fungicide Mandipropamid

Mandipropamid (MDP) is a widely used chiral fungicide to control oomycete pathogens with two enantiomers. In this study, the enantioselective bioactivity, toxicity, and degradation of MDP were investigated for the first time. The bioactivity of S-MDP was 118-592 times higher than that of R-MDP and 1.14-1.67 times higher than that of Rac-MDP against six phytopathogens. Molecular docking found that S-MDP formed a strong halogen bond with HIS 693 of cellulose synthase and possessed a lower binding energy, which validated the results of the bioactivity assay. S-MDP showed lower toxicity toward Spirodela polyrhiza, while it exhibited higher toxicity in Danio rerio embryo and larva. S-MDP preferentially degraded in cowpea and pepper, while R-MDP preferentially degraded in soil. There is no significant difference between the two enantiomers in the toxicity of adult D. rerio and in cucumber degradation. Therefore, the development of the S-enantiomer was considered as a better option to exhibit high efficiency, which could reduce the residual risk of the pesticide and ensure environmental safety.

Enantioselective Fungicidal Activity and Toxicity to Early Wheat Growth of the Chiral Pesticide Triticonazole

In this study, the enantioselective activity of the chiral fungicide triticonazole (TRZ) against target pathogens of seed-borne diseases and the effect on the early phenotypic indexes and physiological and biochemical indexes of wheat following the soaking of seeds were studied. S-TRZ had low fungicidal activity and significantly inhibited the germination of wheat seeds. Seedlings in the S-TRZ treatment group suffered severe oxidative damage; the contents of glutathione (GSH) and malondialdehyde (MDA) were significantly increased. S-TRZ significantly inhibited the synthesis of gibberellin (GA) and ethylene (ETH), while it significantly increased that of jasmonic acid (JA). R-TRZ showed the highest activity against two smut fungi; the treatment of seeds with 5 g (ai)/100 kg R-TRZ had little influence on early wheat growth. The plant hormones were synthesized normally; seedlings grew well, and the fresh weight increased significantly following this treatment. Based on these data, we propose to develop and apply R-TRZ using the national recommended doses to control seed-borne diseases of wheat.

Stereoselective degradation behavior of the novel chiral antifungal agrochemical penthiopyrad in soil

Penthiopyrad is a chiral carboxamide fungicide with a broad spectrum of fungicidal activity. However, there is no report on the analysis of the enantiomers of penthiopyrad and their environmental behavior. Soil is an important carrier for pesticides to affect the environment. Therefore, this study aimed to investigate the absolute configuration, stereoselective degradation, configuration stability and potential metabolites of this agrochemical in soil under different laboratory conditions. R-(-)-penthiopyrad and S-(+)-penthiopyrad were identified by the electronic circular dichroism method. Regarding the racemic analyte, the degradation half-lives of the stereoisomers ranged from 38.9 to 97.6 days, the S-(+)-stereoisomer degraded preferentially in four types of Chinese soil. However, enantiopure R-(-)-penthiopyrad degraded faster than its antipode, a finding that might be related to the microbial activity in soil. The organic matter (OM) content influenced the stereoselective degradation of rac-penthiopyrad. No configuration conversion was observed in both enantiopure analyte degradation processes. One possible metabolite, 753-A-OH, was detected in the treated soil samples, and the degradation pathway might be a hydroxylation reaction. This is the first report of the absolute configuration of penthiopyrad stereoisomers and the first comprehensive evaluation of the stereoselective degradation of penthiopyrad in Chinese soil. Stereoselective degradation of rac-penthiopyrad was observed in the four types of soil. And the stereoselectivity might be inhibited by OM. This study provides more accurate data to investigate the environmental behavior of penthiopyrad at the stereoisomer level.

Chiral Separation and Determination of Etoxazole Enantiomers in Vegetables by Normal-Phase and Reverse-Phase High Performance Liquid Chromatography

The chiral separation of etoxazole enantiomers on Lux Cellulose-1, Lux Cellulose-3, Chiralpak IC, and Chiralpak AD chiral columns was carefully investigated by normal-phase high performance liquid chromatography and reverse-phase high performance liquid chromatography (HPLC). Hexane/isopropanol, hexane/n-butanol, methanol/water, and acetonitrile/water were used as mobile phase at a flow rate of 0.8 mL/min. The effects of chiral stationary phase, mobile phase component, mobile phase ratio, and temperature on etoxazole separation were also studied. Etoxazole enantiomers were baseline separated on Lux Cellulose-1, Chiralpak IC, and Chiralpak AD chiral columns, and partially separated on Lux Cellulose-3 chiral column under normal-phase HPLC. However, the complete separation on Lux Cellulose-1, Chiralpak IC, and partial separation on Chiralpak AD were obtained under reverse-phase HPLC. Normal-phase HPLC presented better resolution for etoxazole enantiomers than reverse-phase HPLC. Thermodynamic parameters, including ΔH and ΔS, were also calculated based on column temperature changes from 10 °C to 40 °C, and the maximum resolutions (Rs) were not always acquired at the lowest temperature. Furthermore, the optimized method was successfully applied to determine etoxazole enantiomers in cucumber, cabbage, tomato, and soil. The results of chiral separation efficiency of etoxazole enantiomers under normal-phase and reverse-phase HPLC were compared, and contribute to the comprehensive environmental risk assessment of etoxazole at the enantiomer level.

Enantioselective bioactivity, toxicity, and degradation in different environmental mediums of chiral fungicide epoxiconazole

To clarify the environmental behaviour and bioactivity of epoxiconazole enantiomers, an integrated assessment has been done. The degradation in soil, water, and river-sediments were studied. The toxicity to Chlorella vulgaris and Daphnia magna was also examined. The bioactivity to plant-pathogens and molecular docking to CYP51 were investigated. The obtained results showed that the half-lives of R,S-(+)- and S,R-(-)-epoxiconazole were 38.8 and 21.2 days in Jiangsu soil, 43.2 and 22.7 days in Jiangxi soil, 29.1 and 21.3 days in Jilin soil, 43.5 and 32.7 days in anaerobic Jilin soil, 12.3 and 10.1 days in river sediments, and 33.2 and 9.3 days in river water, respectively. Maximum EF was 0.36 in Yangzi-river water. No enantioselective degradation was found in sterilized conditions. The EC₅₀ to C. vulgaris after 48 h was 27.78 mg L^-1, and 18.93 mg L^-1 for R,S-(+)-, and S,R-(-)-epoxiconazole, respectively. The LC₅₀ to D. magna was 4.16 mg L^-1, and 8.49 mg L^-1 for R,S-(+)-, and S,R-(-)-epoxiconazole, respectively. R,S-(+)-epoxiconazole bioactivity was 1.3-7.25 times higher than S,R-(-)-epoxiconazole. In conclusion, R,S-(+)- has higher bioactivity and higher environmental toxicity. In opposite, S,R-(-)- has lower environmental toxicity and lower bioactivity. R,S-(+)-epoxiconazole use is recommended with lower concentrations, which is appropriate for environment safety.

Resolution of alkaloid racemate: a novel microbial approach for the production of enantiopure lupanine via industrial wastewater valorization

BACKGROUND

Lupanine is a plant toxin contained in the wastewater of lupine bean processing industries, which could be used for semi-synthesis of various novel high added-value compounds. This paper introduces an environmental friendly process for microbial production of enantiopure lupanine.

RESULTS

Previously isolated P. putida LPK411, R. rhodochrous LPK211 and Rhodococcus sp. LPK311, holding the capacity to utilize lupanine as single carbon source, were employed as biocatalysts for resolution of racemic lupanine. All strains achieved high enantiomeric excess (ee) of L-(-)-lupanine (> 95%), while with the use of LPK411 53% of the initial racemate content was not removed. LPK411 fed with lupanine enantiomers as single substrates achieved 92% of D-(+)-lupanine biodegradation, whereas L-(-)-lupanine was not metabolized. Monitoring the transcriptional kinetics of the luh gene in cultures supplemented with the racemate as well as each of the enantiomers supported the enantioselectivity of LPK411 for D-(+)-lupanine biotransformation, while (trans)-6-oxooctahydro-1H-quinolizine-3-carboxylic acid was detected as final biodegradation product from D-(+)-lupanine use. Ecotoxicological assessment demonstrated that lupanine enantiomers were less toxic to A. fischeri compared to the racemate exhibiting synergistic interaction.

CONCLUSIONS

The biological chiral separation process of lupanine presented here constitutes an eco-friendly and low-cost alternative to widely used chemical methods for chiral separation.

New Insight Regarding the Relationship Between Enantioselective Toxicity Difference and Enantiomeric Toxicity Interaction from Chiral Ionic Liquids

Chirality is an important property of molecules. The study of biological activity and toxicity of chiral molecules has important theoretical and practical significance for toxicology, pharmacology, and environmental science. The toxicological significance of chiral ionic liquids (ILs) has not been well revealed. In the present study, the enantiomeric joint toxicities of four pairs of chiral ILs 1-alkyl-3-methylimidazolium lactate to Allivibrio fischeri were systematically investigated by using a comprehensive approach including the co-toxicity coefficient (CTC) integrated with confidence interval (CI) method (CTCICI), concentration-response curve (CRC), and isobole analysis. The direct equipartition ray (EquRay) design was used to design five binary mixtures of enantiomers according to molar ratios of 1:5, 2:4, 3:3, 4:2, and 5:1. The toxicities of chiral ILs and their mixtures were determined using the microplate toxicity analysis (MTA) method. Concentration addition (CA) and independent action (IA) were used as the additive reference models to construct the predicted CRC and isobole of mixtures. On the whole, there was an enantioselective toxicity difference between [BMIM]D-Lac and [BMIM]L-Lac, and [HMIM]D-Lac and [HMIM]L-Lac, while no enantioselective toxicity difference was observed for [EMIM]D-Lac and [EMIM]L-Lac, and [OMIM]D-Lac and [OMIM]L-Lac. Thereinto, the enantiomer mixtures of [BMIM]D-Lac and [BMIM]L-Lac, and [HMIM]D-Lac and [HMIM]L-Lac presented antagonistic action, and the enantiomer mixtures of [EMIM]D-Lac and [EMIM]L-Lac, and [OMIM]D-Lac and [OMIM]L-Lac overall presented additive action. Moreover, the greatest antagonistic toxicity interaction occurred at the equimolar ratio of enantiomers. Based on these results, we proposed two hypotheses, (1) chiral molecules with enantioselective toxicity difference tended to produce toxicity interactions, (2) the highest or lowest toxicity was usually at the equimolar ratio and its adjacent ratio for the enantiomer mixture. These hypotheses will need to be further validated by other enantiomer mixtures.

Comprehensive Study of Isocarbophos to Various Terrestrial Organisms: Enantioselective Bioactivity, Acute Toxicity, and Environmental Behaviors

The enantioselective bioactivity, toxicity, and environmental behaviors of isocarbophos (ICP) were investigated. The order of the bioactivity and toxicity was S-(+) ≥ rac > R-(-), and the difference of R-(-) and S-(+) was up to 232 times. The usage of S-(+)-ICP may efficiently reduce the usage amount of rac-ICP by 35% under the same effect, and the toxicity was not increased. Based on the toxic unit analysis, the additive effect and synergistic effect of ICP enantiomers were found in the four nontarget organisms, and R-(-)-ICP might cooperate the side-effects of S-(+)-ICP. The accumulation of rac-ICP in earthworms was enantioselective with an enantioenrichment of R-(-)-ICP, so the usage of racemic ICP might increase the exposure risk of R-(-)-ICP to earthworms. From the comprehensive results, the production of enantiomer enriched S-(+)-ICP might increase bioactivity and reduce environmental pollution, while the toxicity of S-(+)-ICP to other nontarget organisms needs to be further assessed.

A systemic study of enantioselectivity of isocarbophos in rice cultivation: Enantioselective bioactivity, toxicity, and environmental fate

The enantioselective bioactivity and acute toxicity to target and non-target model species, and environmental fate of isocarbophos (ICP) in rice cultivation were investigated systematically. Bioactivity and toxicity of S-(+)-ICP was significantly greater than R-(-)-ICP, and the difference was 2.9-101 times. Based on the toxic unit analysis, the toxic interaction of ICP enantiomers for target pests was synergistic effect, while for non-target fish was concentration addition or antagonistic effect. Rac-ICP displayed equivalent bioactivity to S-(+)-ICP under the equal dosage, but the toxicity of rac-ICP to the tested fishes reduced at least 2 times. Rac-ICP is more suitable than optically pure S-(+)-ICP for rice cultivation based on the toxicity and bioactivity results. In environmental behavior experiments, the main metabolite of ICP, isocarbophos oxon (ICPO) was detected in rice plants, water, rice and rice hull samples. S-(+)-ICP and S-(+)-ICPO were more persistent than the R-form in these matrices. The comprehensive data of ICP enantiomers in rice cultivation will improve environmental and ecological risk assessment, and using racemate may be more safe and reasonable in rice cultivation system.

A potential biomarker of isofenphos-methyl in humans: A chiral view

Isofenphos-methyl (IFP) is a very active and persistent chiral insecticide. However, IFP has lower activity against acetylcholinesterases (AChEs). Previously, it was confirmed that phosphorothioate organophosphorus pesticides with N-alkyl (POPN) require activation by oxidative desulfuration and N-dealkylation. In this work, we demonstrated that IFP could be metabolized in human liver microsomes to isofenphos-methyl oxon (IFPO, 52.7%), isocarbophos (ICP, 14.2%) and isocarbophos oxon (ICPO, 11.2%). It was found that (R)-IFP was preferentially degraded compared to the (S)-enantiomer, and the enantiomeric fraction (EF) value reached 0.61 at 60 min. However, (S)-enantiomers of the three metabolites, were degraded preferentially, and the EF values ranged from 0.34 to 0.45. Cytochrome P450 (CYP) isoforms CYP3A4, CYP2E1, and CYP1A2 and carboxylesterase enzyme have an essential role in the enantioselective metabolism of IFP; but, the enzymes that participate in the degradation of IFP metabolites are different. The AChE inhibition bioassay indicated that ICPO is the only effective inhibitor of AChE. The covalent molecular docking has proposed that the metabolites of IFP and its analogs after N-dealkylation and oxidative desulfuration will possess the highest inhibitory activity against AChE. This study is the first to demonstrate that ICPO can be regarded as a potential biomarker for the biomonitoring of IFP and ICP exposure in humans.

Insights into pesticide toxicity against aquatic organism: QSTR models on Daphnia Magna

The toxicities of agrochemicals to non-target aquatic organisms are key items in chemical ecological risk assessment. However, it is still an urgent need to develop new tools to assess the agrochemical aquatic toxicity efficiently and accurately. In this work, QSTR studies were performed on a data set containing 639 diverse pesticides with measured EC₅₀ toxicity against Daphnia magna, by using five machine learning methods combined with seven fingerprints and a set of molecular descriptors. The imbalance problem of the data set was successfully solved by clustering analysis. The top-10 QSTR models displayed greater predicative abilities than ECOSAR. The optimal model, Ext-SVM, showed the best performance in 10-fold cross validation (Q_high=0.807, Q_moderate=0.806, Q_low=0.755, Q_total=0.794), and also in the test set verification (Q_high=0.865, Q_moderate=0.783, Q_low=0.931, Q_total=0.848). The relevance of the key physical-chemical properties with the toxicity was also investigated, in which the MW, a_np, logP(o/w), GCUT_SLOGP_1, chilv and SMR_VSA7 values displayed positive correlation with Daphnia magna toxicity, whereas the logS and a_don showed negative correlation. The robust QSTR models provided efficient tools for assessing agrochemical aquatic toxicity, and the revealed different physical-chemical properties between the high and low toxic compounds might be useful in the discovery and design of low aquatic toxic pesticides.

Stereoselective toxicity of metconazole to the antioxidant defenses and the photosynthesis system of Chlorella pyrenoidosa

Metconazole (MEZ) is a broad-spectrum fungicide with four optical stereoisomers. Compared to traditional fungicides, it achieves better control effect at lower dosages. However, its toxicity to non-target organisms has rarely been investigated. This study investigated the stereoselective toxicity of metconazole to Chlorella pyrenoidosa (C. pyrenoidosa). The results indicate that the presence of the racemate and four stereoisomers of MEZ caused a sudden increase of reactive oxygen species (ROS). This in turn stimulated antioxidant defense, impaired photosynthesis and responses of subcellular structure, and eventually inhibited cell growth. The 96 h-EC₅₀ of the racemate, cis-1R,5S-MEZ, cis-1S,5R-MEZ, trans-1S,5S-MEZ, and trans-1R,5R-MEZ were 0.058, 0.182, 0.129, 0.032, and 0.038 mg/L, respectively. Furtheromre, the generation of ROS, antioxidant response, and the loss of photosynthetic function in C. pyrenoidosa were all preferentially trans-1S,5S-MEZ induced. These results aid the understanding of the stereoselective effects of chiral pesticides on C. pyrenoidosa. Such stereoselective differences must be considered when assessing the risk of metconazole to environment.

Enantiomeric separation of six chiral pesticides that contain chiral sulfur/phosphorus atoms by supercritical fluid chromatography

Six chiral pesticides containing chiral sulfur/phosphorus atoms were separated by supercritical fluid chromatography with supercritical CO₂ as the main mobile phase component. The effect of the chiral stationary phase, different type and concentration of modifiers, column temperature, and backpressure on the separation efficiency was investigated to obtain the appropriate separation condition. Five chiral pesticides (isofenphos-methyl, isocarbophos, flufiprole, fipronil, and ethiprole) were baseline separated under experimental conditions, while isofenphos only obtained partial separation. The Chiralpak AD-3 column showed a better chiral separation ability than others for chiral pesticides containing chiral sulfur/phosphorus atoms. When different modifiers at the same concentration were used, the retention factor of pesticides except flufiprole decreased in the order of isopropanol, ethanol, methanol; meanwhile, the retention factor of flufiprole increased in the order of isopropanol, ethanol, methanol. For a given modifier, the retention factor and resolution decreased on the whole with the increase of its concentration. The enantiomer separation of five chiral pesticides was an "enthalpy-driven" process, and the separation factor decreased as the temperature increased. The backpressure of the mobile phase had little effect on the separation factor and resolution.

The occurrence and risk assessment of five organophosphorus pesticides in river water from Shangyu, China

Organophosphorus pesticides (OPs), which are some of the most extensively used pesticides, have drawn much attention in recent years owing to their ubiquity as well as the potential ecological and health risks they pose to aquatic organisms and even to humans. In this study, we investigated the residue of five OPs in 49 river cross sections in Shangyu, Zhejiang province, China, a rainy region with relatively developed agriculture. Correlations analysis, principal component analysis, and cluster analysis were conducted. The results showed that dichlorvos exhibited the highest concentrations (0.01 to 5.63 μg/L) among the OPs in most monitoring sites. Weak positive correlations were found between methyl parathion and dichlorvos as well as malathion and dimethoate. The principal component analysis and cluster analysis indicated a correlation among these river cross sections. We then calculated the hazard index (HI) to estimate the potential adverse health effects. The mean HI presented no risk to adults but showed potential health risks to children, with values of 0.285, 0.228, and 0.166 for dichlorvos, methyl parathion, and dimethoate, respectively. Our study will help elucidate the potential risks of OPs and their residues in the rivers of Shangyu in the Zhejiang province in China and will be beneficial for managing water quality and will provide valuable suggestions to local policy makers. Graphical abstract Comparison of the ∑₅OPs concentrations among 49 river cross sections.

Etoxazole is Metabolized Enantioselectively in Liver Microsomes of Rat and Human in Vitro

Acaricide etoxazole belongs to the ovicides/miticides diphenyloxazole class, affecting adults to lay sterile eggs by inhibiting chitin biosynthesis possibly. The reverse-phase HPLC-MS/MS method was used to determine the etoxazole enantiomers. The enantioselective degradation behavior of rac-etoxazole in liver microsomes of rat and human in vitro with NADPH was dramatically different. The t1/2 of (R)-etoxazole was 15.23 min in rat liver microsomes and 30.54 min in human liver microsomes, while 21.73 and 23.50 min were obtained for (S)-etoxazole, respectively. The Vmax of (R)-etoxazole was almost 5-fold of (S)-etoxazole in liver microsomes of rat in vitro. However, the Vmax of (S)-etoxazole was almost 2-fold of (R)-etoxazole in liver microsomes of human in vitro. The CLint of etoxazole was also shown the enantioselectivity on the contrary in liver microsomes of rat and human. These results indicated that the metabolism of two etoxazole enantiomers was selective in liver microsomes of rat and human in vitro, and enantioselectivity in the two kinds of liver microsomes was in the difference in degradation performance. The reason might be related to the composition and content involved in the enzyme system.

Enantioselective Metabolism of Flufiprole in Rat and Human Liver Microsomes

The enantioselective metabolism of flufiprole in rat and human liver microsomes in vitro was investigated in this study. The separation and determination were performed using a liquid chromatography system equipped with a triple-quadrupole mass spectrometer and a Lux Cellulose-2 chiral column. The enantioselective metabolism of rac-flufiprole was dramatically different in rat and human liver microsomes in the presence of the β-nicotinamide adenine dinucleotide phosphate regenerating system. The half-lives (t1/2) of flufiprole in rat and human liver microsomes were 7.22 and 21.00 min, respectively, for R-(+)-flufiprole, whereas the values were 11.75 and 17.75 min, respectively, for S-(-)-flufiprole. In addition, the Vmax of R-(+)-flufiprole was about 3-fold that of S-(-)-flufiprole in rat liver microsomes, whereas its value in the case of S-(-)-flufiprole was about 2-fold that of R-(+)-flufiprole in human liver microsomes. The CLint of rac-flufiprole also showed opposite enantioselectivy in rat and human liver microsomes. The different compositions and contents of metabolizing enzyme in the two liver microsomes might be the reasons for the difference in the metabolic behavior of the two enantiomers.

Enantioselective phytotoxicity and bioacitivity of the enantiomers of the herbicide napropamide

Enantioselectivity of chiral pesticide enantiomers should be taken into consideration in pesticide application and environmental risk assessment. The phytotoxicity of the enantiomers of napropamide to cucumber, soybean, and the bioactivity to the target weeds Poa annua and Festuca arundinacea have been studied in this work. To the nontarget crops, the influences of napropamide on the root, shoot, fresh weight, chlorophyll, superoxide dismutase (SOD) and catalase (CAT) activities and membrane lipid peroxides have been studied. (-)-Napropamide was more toxic than the racemate and (+)-napropamide to soybean and cucumber in terms of root, shoot and fresh weight. The content of chlorophyll was not affected by napropamide. The impacts on the activities of SOD, CAT and membrane lipid peroxides showed that napropamide could induce the oxidative stress and rac-napropamide caused a stronger oxidative damage to cucumber and soybean than (-)-napropamide and (+)-napropamide. For the target weeds, the influences of napropamide on root, shoot and fresh weight have been studied. (-)-Napropamid was more active to P. annua, while rac-napropamide was more active to F. arundinacea. To reduce environmental pollution and improve the effectiveness of chiral pesticide, single enantiomer should be developed and produced. This work may provide evidence for developing optical pure product.

Bioaccumulation of isocarbophos enantiomers from laboratory-contaminated aquatic environment by tubificid worms

The benthic fauna is of great importance to assess the environmental fate of contaminations in aquatic ecosystem. In this study, tubificids were exposed to both laboratory-contaminated aqueous phases and spiked sediment to study the bioaccumulation of isocarbophos (ICP). Two types of spiked sediments were used in the spiked sediment experiment. During the exposure period, an enantioselective bioaccumulation was found in spiked water treatment, with concentrations of the (-)-ICP higher than that of the (+)-ICP, but no enantioselectivity was detected in the spiked sediment treatments. However, different bioaccumulation patterns were observed in the two spiked sediment treatments. Results showed that for spiked forest field sediment (FF sediment) incubation, bioaccumulation was governed by the concentrations in soil. Whereas ICP was bioaccumulated dominantly from overlying water in spiked Chagan Lake sediment (CG sediment) test. The dissipation rates were proved different in the two sediments and ICP dissipated much faster in CG sediment than that in FF sediment. Significant difference in ICP's half-life was also observed between worm-present and worm-free treatments in FF sediment. The detections of concentrations in overlying water indicated that much more ICP diffused to aquatic phase with the present of tubificids.

Enantioselectivity in tebuconazole and myclobutanil non-target toxicity and degradation in soils

Tebuconazole and myclobutanil are two widely used triazole fungicides, both comprising two enantiomers with different fungicidal activity. However, their non-target toxicity and environmental behavior with respect to enantioselectivity have received limited attention. In the present study, tebuconazole and myclobutanil enantiomers were isolated and used to evaluate the occurrence of enantioselectivity in their acute toxicity to three non-target organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio). Significant differences were found: R-(-)-tebuconazole was about 1.4-5.9 times more toxic than S-(+)-tebuconazole; rac-myclobutanil was about 1.3-6.1 and 1.4-7.3 more toxic than (-)-myclobutanil and (+)-myclobutanil, respectively. Enantioselectivity was further investigated in terms of fungicide degradation in seven soil samples, which were selected to cover a broad range of soil properties. In aerobic or anaerobic soils, the S-(+)-tebuconazole degraded faster than R-(-)-tebuconazole, and the enantioselectivity showed a correlation with soil organic carbon content. (+)-Myclobutanil was preferentially degraded than (-)-myclobutanil in aerobic soils, whereas both enantiomers degraded at similar rates in anaerobic soils. Apparent correlations of enantioselectivity with soil pH and soil texture were observed for myclobutanil under aerobic conditions. In addition, both fungicides were configurationally stable in soils, i.e., no enantiomerization was found. Enantioselectivity may be a common phenomenon in both aquatic toxicity and biodegradation of chiral triazole fungicides, and this should be considered when assessing ecotoxicological risks of these compounds in the environment.

Comparative toxicity of rac- and S-tebuconazole to Daphnia magna

Tebuconazole is a chiral triazole fungicide used as raceme in a variety of agricultural applications. Earlier studies showed that tebuconazole is toxic to many non-target aquatic organisms but relative data for tebuconazole enantiomers are lacking. Thus, goal of this study was to evaluate and compare the toxicity of rac- and S-tebuconazole with Daphnia magna at both acute and chronic levels according to Organization for Economic Cooperation and Development (OECD) guidelines 202 and 211 respectively, to provide some guidelines for optimizing chiral pesticides application and management. The exposure concentrations were 0.1, 0.5, 1, 2, 4, 8, 10 mg L(-1) for both rac- and S-tebuconazole and their 48-h EC(50) values to D. magna were 3.53 (3.32-3.78) and 2.74 (2.33-3.10) mg L(-1) respectively, indicating that these both are medium toxic to D. magna with no significant toxicity difference at acute level. In chronic test, <24-h old D. magna were exposed to 0.01, 0.05, 0.10, 0.20, and 0.40 mg L(-1) of rac- and S-tebuconazole with one blank and one solvent control for 21 days according to OECD guideline 211. Four developmental (molting rate, days to the 1st and 3rd brood, and body length) and five reproductive (size of the 1st and 3rd brood, number of broods, and number of neonates) parameters for each D. magna were determined. Results showed that both rac- and S-tebuconazole significantly reduced the reproduction and impacted the development of D. magna at concentrations of 0.05 mg L(-1) or higher. Furthermore, S-tebuconazole was more toxic than raceme, and the difference between effects on the same parameters induced by rac- and S-tebuconazole was statistically significant. These results demonstrated that the chronic toxicity of S-tebuconazole might be underestimated in general use, and further studies should focus more on the biological behaviors of enantiomers and not just the raceme of tebuconazole and other chiral pesticides in the environment.

Toxicity and bioaccumulation of ethofumesate enantiomers in earthworm Eisenia fetida

Earthworms represent an important food source for many vertebrates and as a result, predators may encounter toxic effects via the food chain from consumption of contaminated worms. Therefore, including an assessment of xenobiotic to worms in risk assessment procedures is advisable. Here we studied the acute toxicity, bioaccumulation and elimination of ethofumesate enantiomers in earthworm, Eisenia fetida, in a soil. A slight difference in toxicity to earthworm between two enantiomers was found, and the calculated LC50 values for (+)-, rac- and (-)-ethofumesate were 4.51, 5.93 and 7.98 μg/cm(2), respectively, indicating that the acute toxicity of ethofumesate enantiomers was enantioselective. Earthworm can uptake ethofumesate but the bioaccumulation curve did not reach the steady state. In the elimination experiment, the concentrations of ethofumesate in earthworm declined following a first-order decay model with a short half life of 1.8d. The bioaccumulation and elimination of ethofumesate in earthworm were both nonenantioselective. In combination with other studies, a linear relationship between Log BSAFs and Log Kow was observed, and the Log BSAFs increased with increasing Log Kow. But the elimination rate did not show any correlation with the Kow value.

Contribution of carboxylesterase and cytochrome P450 to the bioactivation and detoxification of isocarbophos and its enantiomers in human liver microsomes

Organophosphorus pesticides are the most widely used pesticides in modern agricultural systems to ensure good harvests. Isocarbophos (ICP), with a potent acetylcholinesterase inhibitory effect is widely utilized to control a variety of leaf-eating and soil insects. However, the characteristics of the bioactivation and detoxification of ICP in humans remain unclear. In this study, the oxidative metabolism, esterase hydrolysis, and chiral inversion of ICP in human liver microsomes (HLMs) were investigated with the aid of a stereoselective LC/MS/MS method. The depletion of ICP in HLMs was faster in the absence of carboxylesterase inhibitor (BNPP) than in the presence of NADPH and BNPP, with t1/2 of 5.2 and 90 min, respectively. Carboxylesterase was found to be responsible for the hydrolysis of ICP, the major metabolic pathway. CYP3A4, CYP1A2, CYP2D6, CYP2C9, and CYP2C19 were all involved in the secondary metabolism pathway of desulfuration of ICP. Flavin-containing monooxygenase (FMO) did not contribute to the clearance of ICP. The hydrolysis and desulfuration of (±)ICP, (+)ICP, and (-)ICP in HLMs follow Michaelis-Menten kinetics. Individual enantiomers of ICP and its oxidative desulfuration metabolite isocarbophos oxon (ICPO) were found to be inhibitors of acetylcholinesterases at different extents. For example, (±)ICPO is more potent than ICP (IC50 0.031μM vs. 192μM), whereas (+)ICPO is more potent than (-)ICPO (IC50 0.017μM vs. 1.55μM). Given the finding of rapid hydrolysis of ICP and low abundance of oxidative metabolites presence in human liver, the current study highlights that human liver has a greater capacity for detoxification of ICP.

Chiral fungicide triadimefon and triadimenol: Stereoselective transformation in greenhouse crops and soil, and toxicity to Daphnia magna

Various chiral pesticides are used in greenhouses to ensure high crop yields. However, detailed knowledge on the environmental behavior of such chiral contaminants with respect to enantioselectivity in the greenhouse has received little attention so far. Here, the widely used fungicide triadimefon was chosen as a "chiral probe" to investigate its enantioselective degradation and formation of triadimenol in greenhouse tomato, cucumber, and soil under different application modes. In addition, the stereoselectivity of individual isomers of triadimefon and triadimenol in aquatic toxicity were first studied. Significant differences in their acute toxicity to Daphnia magna were observed among the isomers. Under foliage application or soil irrigation application, S-(+)-triadimefon was preferentially degraded, resulting in relative enrichment of the more toxic R-(-)-enantiomer in tomato, cucumber, and soil. Further enantioselective analysis of converted triadimenol showed that the compositions of the four product stereoisomers were different and closely dependent on environmental conditions: the most toxic RS-(+)-triadimenol was the most preferentially produced isomer in tomato under foliage treatment, while the RR-(+)-triadimenol was proved to be the highest amount of metabolite isomer in cucumber and soil under both treatment modes and in tomato under soil treatment.

Enantioselective physiological effects of the herbicide diclofop on cyanobacterium Microcystis aeruginosa

Water blooms caused by cyanobacteria are currently major global environmental issues. The outbreaks induced by nutrient elements have attracted much attention; however, the effects of environmental pollutants on the cyanobacteria are themselves poorly understood, especially those due to chiral chemicals. To explore the enantioselective eco-effects of the chiral herbicide diclofop-methyl (DM) and its major metabolite diclofop acid (DA), the physiological characteristics of Microcystis aeruginosa were investigated. The results showed that using both biomass and protein content as growth parameters is necessary to access the impact of the herbicides, that stimulation biomass production by R-DA and S-DA was apparent (nonessential), and that the concentration of 5 mg/L is worth noting. Ultrastructure changes in gas vacuoles, thylakoids, glycogen, cyanophycin granules, poly beta-hydroxybutyrate, polyhedral body, and lipids indicated different toxicity modes among the four chemicals. The different effects between R-DA and S-DA demonstrated that R-DA probably acts as a proton ionophore shuttling protons across the plasmalemma, whereas S-DA did not demonstrate such action. The toxicity order in the present study is S-DA < R-DA < DM < DA. Stimulation of the growth of M. aeruginosa during the first 3 days by herbicidally inactive S-DA was greater than that due to R-DA, which is adverse to water quality in water bodies. Therefore, using the herbicidally active R-enantiomer is recommended. These results are helpful in understanding the enantioselective effects of chiral pesticides on cyanobacteria, which is important for environmental assessment and protection. It is also helpful for guiding the application of chiral pesticides in agricultural settings.

Development of a multi-residue enantiomeric analysis method for 9 pesticides in soil and water by chiral liquid chromatography/tandem mass spectrometry

A novel and sensitive chiral liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous measuring individual enantiomers of 9 pesticides including herbicides, insecticides, and fungicides in soil and water. The separation and determination were performed using reversed-phase chromatography on an amylose chiral stationary phase, a Chiralpak AD-RH column, under gradient elution using a mixture of ACN-2mM ammonium acetate in water as the mobile phase at 0.45 mL/min flow rate. The effects of three cellulose-based columns and three amylose-based columns on the separation were also investigated. The QuEChERS (acronym for Quick, Easy, Cheap, Effective, Rugged and Safe) method and solid-phase extraction (SPE) were used for the extraction and clean-up of the soil and water samples, respectively. Parameters including the matrix effect, linearity, precision, accuracy and stability were undertaken. Under optimal conditions, the mean recoveries for all enantiomers from the soil and water samples were ranged from 77.8% to 106.2% with the relative standard deviations (RSD) less than 14.2%. Good linearity (at least R(2) ≥ 0.9986) was obtained for all studied analytes in the soil and water matrix calibration curves over the range from 2.0 to 125 μg/L. The limits of detection (LOD) for all enantiomers in the soil and water were less than 1.8 μg/kg or μg/L, whereas the limit of quantification (LOQ) did not exceed 5.0 μg/kg or μg/L. The results of the method validation confirm that this proposed method is convenient and reliable for the enantioselective determination of the enantiomers of 9 chiral pesticides in soil and water.

Enantioselective analysis and degradation studies of isocarbophos in soils by chiral liquid chromatography-tandem mass spectrometry

An enantioselective method is presented for the determination of isocarbophos in soil by liquid chromatography coupled with tandem mass spectrometry. The pesticide residues in soil samples were extracted with acetonitrile, and complete enantioseparation was obtained on an amylose tris(3,5-dimethylphenylcarbamate) chiral column using acetonitrile/2 mM ammonium acetate solution containing 0.1% formic acid (60:40, v/v) as the mobile phase. The absolute configuration of isocarbophos enantiomers was determined by the combination of experimental and calculated electronic circular dichroism spectra. The method was utilized to investigate the degradation of isocarbophos in soils (Changchun, Hangzhou, and Zhengzhou) under sterilized or native conditions. Isocarbophos enantiomers were configurationally stable in the selected soils, and the pesticide degradation was not enantioselective in the sterilized condition. The degradation behavior of rac-isocarbophos was different under native conditions, with no enantioselectivity in the Changchun soil and with the S-(+)-isocarbophos enriched in the Hangzhou and Zhengzhou soils.