Enantioselective degradation and ecotoxicity of the chiral herbicide diclofop in three freshwater alga cultures

Characterization of two novel hydrolases from Sphingopyxis sp. DBS4 for enantioselective degradation of chiral herbicide diclofop-methyl

Diclofop-methyl, an aryloxyphenoxypropionate (AOPP) herbicide, is a chiral compound with two enantiomers. Microbial detoxification and degradation of various enantiomers is garnering immense research attention. However, enantioselective catabolism of diclofop-methyl has been rarely explored, especially at the molecular level. This study cloned two novel hydrolase genes (dcmA and dcmH) in Sphingopyxis sp. DBS4, and characterized them for diclofop-methyl degradation. DcmA, a member of the amidase superfamily, exhibits 26.1-45.9% identity with functional amidases. Conversely, DcmH corresponded to the DUF3089 domain-containing protein family (a family with unknown function), sharing no significant similarity with other biochemically characterized proteins. DcmA exhibited a broad spectrum of substrates, with preferential hydrolyzation of (R)-(+)-diclofop-methyl, (R)-(+)-quizalofop-ethyl, and (R)-(+)-haloxyfop-methyl. DcmH also preferred (R)-(+)-quizalofop-ethyl and (R)-(+)-haloxyfop-methyl degradation while displaying no apparent enantioselective activity towards diclofop-methyl. Using site-directed mutagenesis and molecular docking, it was determined that Ser175 was the fundamental residue influencing DcmA's activity against the two enantiomers of diclofop-methyl. For the degradation of AOPP herbicides, DcmA is an enantioselective amidase that has never been reported in research. This study provided novel hydrolyzing enzyme resources for the remediation of diclofop-methyl in the environment and deepened the understanding of enantioselective degradation of chiral AOPP herbicides mediated by microbes.

Enantiomerization and enantioselective bioaccumulation of diclofop-methyl in tubifex worms

In this study, the hydrolysis of diclofop-methyl (DM) in aqueous system and the bioaccumulation of its main metabolite, Diclofop (DA), in the tubifex worms were investigated using enantioselective high-performance liquid chromatography. With the addition of tubifex, rapid hydrolysis was observed for DM. It is revealed that the hydrolysis of DM in the water and the accumulation of DA in the worms were both enantioselective. Meanwhile, either the hydrolysis amount or the levels of enantioselectivity were influenced by the tubifex. After incubated for 24 h, about 94.6% of the DM was hydrolyzed and the enantiomer fraction of metabolite (DA) deviated from 0.5 with R-DA significantly higher than S-DA. The enantiopure S-DM and R-DM and S-DA and R-DA were incubated, and enantiomerizations were detected between the two DM enantiomers with S-form inversing into R-form and vice versa. It was found that the S-DM exhibited a higher tendency to invert than the R-DM.

An enantioselective high-performance liquid chromatography-mass spectrometry method to study the fate of quizalofop-P-ethyl in soil and selected agricultural products

In this study, the attention was focused on quizalofop-ethyl, a chiral herbicide whose formulation has recently been marketed as quizalofop-P-ethyl, i.e. the (+)-enantiomer exhibiting herbicidal activity. To verify the real enantiomeric purity of this product as well as to study its environmental fate, the enantioselective separation of the P- and M- enantiomers of quizalofop-ethyl was achieved on Lux Cellulose-2 column (3‑chloro,4-methylphenilcarbamate cellulose) under isocratic conditions in polar organic mode. Once established that the commercial formulation contains ˜ 0.6% (enantiomeric fraction) of M as an impurity, an HPLC-MS/MS method was developed, validated and applied to the analysis of soil, carrots and turnips treated with the herbicide. A simple solid-liquid extraction allowed recoveries greater than 70%; limits of detections of P and M enantiomers were below 5 ng g-1. The analyses of the real samples showed a modification of the enantiomeric fraction of quizalofop-M-ethyl between the commercial formulation (EFM = 0.63 ± 0.03%) and the analysed matrices (EFM = 7.6 ± 0.1% for carrots; EFM = 0% for the other matrices). This outcome highlighted the occurrence of an enantioselective biotic dissipation, responsible for a greater persistency of the distomer in carrots. On the other hand, since screening analyses revealed the occurrence of residues of the metabolite quizalofop-acid with the same EFs as the ester precursor, it was concluded that the hydrolytic conversion was an abiotic process.

Chiral pesticides levels in peri-urban area near Yangtze River and their correlations with water quality and microbial communities

Pesticides are considered to be the second-largest non-point source pollution in water. Our research assayed the river network of typical agricultural areas in the middle and lower Yangtze River as the study area. Pesticides residues in aquatic environment were determined by QuEChERS, combined with high-performance liquid chromatography tandem mass spectrometry, or gas chromatograph-mass spectrometer. At chiral pesticides' levels, we detected pesticides contents in water, classified and counted the types of pesticides, and analyzed their environmental risk assessment. Furthermore, potential correlations between chiral pesticides concentrations and water quality indicators were assayed. Additionally, we explored their relations with microbial communities at species levels. Enantiomers of Diclofop-methyl, Ethiprole, Difenoconazole and Epoxiconazole were enantioselectively distributed. More interestingly, due to various chiral environment of the sampling site, the enantiomers of Tebuconazole Acetochlor, Glufosinate ammonium and Bifenthrin had completely different distributions at different sites. Based on that, the chiral pesticides Diclofop-methyl, Bifenthrin, Ethiprole, Tebuconazole and Difenoconazole are enantioselective to the risk of aquatic environment. Generally, enantiomeric selectivity had high positive correlations with total nitrogen and phosphorus. Then we found that chiral fate behavior of Tebuconazole and Paichongding in water might be affected by prokaryotes. In addition, the chiral behavior of Diclofop-methyl, Propiconazole, Difenoconazole, and Tebuconazole isomers in water might be negatively affected by eukaryotes. That research helped us to comprehensively understand the impact of non-point source pollution of chiral pesticides in aquatic environment and provided basic data support for developing biological and water quality indicators for monitoring pollution in aquatic environment.

Development of reliable quantitative structure-toxicity relationship models for toxicity prediction of benzene derivatives using semiempirical descriptors

The Health and environmental hazards of benzene and nitrobenzene (NB) derivatives have remained a topic of interest of researchers. In silico methods for prediction of toxicity of chemicals have proved their worth in accurate forecast of environmental as well as health toxicity and are strongly recommended by regulatory authorities. Two quantitative structure-toxicity relationship (QSTR) models explaining Scenedesmus obliquus toxicity trends among 39 benzene derivatives and Tetrahymena pyriformis toxicity of 103 NB and 392 benzene derivatives are developed using semiempirical quantum chemical parameters. The best constructed QSTR models have good fitting ability (R² = 0.8053, 0.7591, and 0.8283) and robustness (Q²_LOO = 0.7507, 0.7227, and 0.8194; Q²_LMO = 0.7338, 0.7153, and 0.8172). The external predictivity of all the models are quite good (R²_EXT = 0.8256, 0.9349, and 0.8698). Electronegativity, Cosmo volume, total energy, and molecular weight are responsible for the increase and decrease of toxicity of benzene derivatives against S. obliquus while electronegativity, electrophilicity index, the heat of formation, total energy, hydrophobicity, and cosmo volume are responsible for modulation of toxicity of NB and benzene derivatives toward T. pyriformis. These models fulfill the requirements of all the five OECD principles.

Toxicity of Tetracycline and Metronidazole in Chlorella pyrenoidosa

Antibiotics have become a new kind of organic pollutant as they are widely used in the water environment of China. Tetracycline (TC) is a class of broad-spectrum antibiotics produced or semi-synthesized by actinomycetes. Metronidazole (MTZ) is the first generation of typical nitroimidazoles. The content of nitroimidazoles is relatively high in medical wastewater, and their ecotoxicity is worthy of attention because they are difficult to completely eliminate. In this paper, the effects of TC and MTZ on the growth, cell morphology, extracellular polymer and oxidative stress of Chlorella pyrenoidosa (C. pyrenoidosa) were studied, and the toxic interactions between TC and MTZ mixture components were analyzed. The results showed that the 96h-EC50 of TC and MTZ was 8.72 mg/L and 45.125 mg/L, respectively. The toxicity of TC to C. pyrenoidosa was higher than that of MTZ, and the combined toxicity effect of TC and MTZ was synergistic after the combined action of a 1:1 toxicity ratio. In addition, the algal cells of C. pyrenoidosa died to varying degrees, the membrane permeability of algal cells was increased, the membrane was damaged, the surface of algal cells exposed to higher concentration of pollutants was wrinkled, and their morphology was changed. The extracellular polymer of C. pyrenoidosa was affected by a change in concentration. The effect of pollutants on the reactive oxygen species (ROS) level and malondialdehyde (MDA) content of C. pyrenoidosa also had an obvious dose-effect relationship. This study contributes to the assessment of the possible ecological risks to green algae due to the presence of TC and MTZ in aquatic environments.

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.

Natural colloids at environmentally relevant concentrations affect the absorption and removal of benzophenone-3 in zebrafish

Aquatic natural colloids are closely related to the environmental behavior of pollutants, which may affect their bioavailability in aquatic organisms. This study explored the potential mechanisms of the natural colloids at environmentally relevant concentrations affecting the bioaccumulation process of benzophenone-3 (BP3) in zebrafish (Danio rerio). The results of kinetic model fitting showed that the natural colloids decreased the uptake and loss rate of BP3 by zebrafish but prolonged the time to reach the cumulative equilibrium, eventually resulting in a higher cumulative concentration in zebrafish. According to the tissue concentration at equilibrium and the results of toxicokinetic analysis, the presence of high molecular colloids could enhance the bioaccumulation of freely dissolved BP3 due to its high desorption rate with BP3 in the intestines of fish, increasing the freely dissolved BP3 concentrations to which zebrafish were exposed. Both natural colloids and BP3 could enhance the cell permeability of zebrafish, which allowed colloid-bound BP3 to directly enter the fish and accumulate in its muscle. Besides, although both natural colloids and BP3 could cause the metabolic disorders in adult zebrafish, they affected the physiological and biochemical activities of zebrafish through different pathways. The disturbance of glutathione metabolism in zebrafish induced by natural colloids may be the reason for the diminished ability of zebrafish to clear and transform BP3 in the mixture system. The carrier effect of natural colloids and reduced clearance ability of zebrafish eventually increased the bioaccumulation of BP3 in zebrafish. This study highlights the significance of natural colloids at environmentally relevant concentrations on the biological effects of emerging contaminants in actual waters, however, natural colloids are always ignored in most field investigation of pollutants, which would ultimately lead to an underestimation of the true ecological risk of pollutants.

Different degradation patterns and mechanisms of chiral contaminant enantiomers: beta-cypermethrin as a case study

Studies often neglect the differences between enantiomers in soil chiral contaminants, and the molecular ecological mechanisms involved in enantiomer selective degradation behaviors remain elusive. In the present study, we used the stepwise regression analysis to establish the quantitative relationships between degradation rates and genes that determine different degradation patterns and mechanisms among enantiomers; and beta-cypermethrin (BCYM) was chosen as the target analyte. Stepwise regression analysis demonstrated the relationships established for different enantiomers varied even under the same conditions, and results from path analysis showed the same functional gene exhibited different direct and indirect contributions to different enantiomer degradation rates. The genome and primary microbial communities during different enantiomer degradation rates were also analyzed based on Illumina MiSeq next-generation sequencing technology, and the results indicated the soil microbial community structure and abundance varied during different enantiomer degradation rates. Results from this study served to enhance our understanding of the molecular biological mechanisms of chiral contaminant selective degradation behaviors under the context of functional genes and degrading microorganisms.

Enantioselective degradation of prothioconazole in soil and the impacts on the enzymes and microbial community

In this work, the stereoselective degradation of prothioconazole in five soils was investigated and the metabolite prothioconazole-desthio was determined. The effects of prothioconazole on soil enzymes activities and microbial community were also studied. The dissipation of prothioconazole fitted with a first-order kinetic equation with half-lives ranging from 3.45 to 9.90 days. In addition, R-prothioconazole degraded preferentially than S-prothioconazole in all soils with EF values >0.5. Prothioconazole-desthio formed rapidly with preference in R-enantiomer, and the concentration kept at a considerable level even at the end of the incubation, indicating it was relatively persistent in soil. Prothioconazole and its metabolite inhibited the activity of dehydrogenase, catalase and urease in soils, and could affect the diversity of the soil microbiota as well. Redundancy analysis (RDA) and Spearman analysis showed the abundance of Proteobacteria, Fusobacteria, Firmicutes, Thaumarchaeota, Saccharibacteria, Chloroflexi, Chlorobi, Actinobacteria and Nitrospirae might be related to the enantioselective degradation. The work was helpful for understanding the environmental behavior of the fungicide prothioconazole and its primary metabolite on an enantiomeric level.

Toxic effects and molecular mechanisms of sulfamethoxazole on Scenedesmus obliquus

The antibiotic sulfamethoxazole (SMX) is a pollutant that is widely distributed in the global water environment.This substance has toxic effects on various aquatic organisms. Previous studies on SMX have focused on its acute toxicity towards algae and the changes induced at biological and cellular levels, rather than its biotoxicity and mechanisms at the molecular level. In this study, we investigated the effects of SMX on Scenedesmus obliquus as the model organism by performing transmission electron microscopy and transcriptome sequencing analyses. Exposure to SMX promoted gene expression, resulting in changes to algal cell ultrastructure. The cell walls became blurred, the chloroplast structure was seriously damaged, and the number and volume of mitochondria per cell increased. These changes were related to the inhibition of cell growth, decrease in chlorophyll content, increase in cell membrane permeability, and increased production of reactive oxygen species, which led to increased amounts of the lipid peroxidation product malondialdehyde, and higher activities of antioxidant enzymes. Our results suggest that SMX affects gene expression by influencing non-coding RNA metabolic processes, leading to changes in nuclear structures. Abnormally expressed long non-coding RNAs extensively regulate downstream gene expression through various mechanisms, such as chromatin recombination, thereby promoting tumor occurrence, invasion, and metastasis. This abnormal expression may be an important mechanism underlying the carcinogenic effects of SMX.

Absolute Configuration Sensing of Chiral Aryl- and Aryloxy-Propionic Acids by Biphenyl Chiroptical Probes

The absolute configuration of chiral 2-aryl and 2-aryloxy propionic acids, which are among the most common chiral environmental pollutants, has been readily and reliably established by either electronic circular dichroism spectroscopy or optical rotation measurements employing suitably designed 4,4′-disubstituted biphenyl probes. In fact, the 4,4′-biphenyl substitution gives rise to a red shift of the diagnostic electronic circular dichroism signal of the biphenyl A band employed for the configuration assignment, removing its overlap with other interfering dichroic bands and allowing its clear sign identification. The largest A band red shift, and thus the most reliable results, are obtained by employing as a probe the 4,4′-dinitro substituted biphenylazepine 3c. The method was applied to the absolute configuration assignment of 2-arylpropionic acids ibuprofen (1a), naproxen (1b), ketoprofen (1c) and flurbiprofen (1d), as well as to the 2-aryloxypropionic acids 2-phenoxypropionic acid (2a) and 2-naphthoxypropionic acid (2b). This approach, allowing us to reveal the sample’s absolute configuration by simple optical rotation measurements, is potentially applicable to online analyses of both the enantiomeric composition and absolute configuration of these chiral pollutants.

Four cypermethrin isomers induced stereoselective metabolism in H295R cells

Cypermethrin (CP) is widely used for controlling agricultural and indoor vermin. Previous studies have reported the stereoselective difference of CP in biological activities. However, little is known about their potential mechanisms between metabolic phenotypes and endocrine-disrupting effects. Herein, nuclear magnetic resonance (NMR)-based metabolomics combining metabolite identification and pathway analysis were applied to evaluate the stereoselective metabolic cdisorders induced by CP isomers in human adrenocortical carcinoma cells (H295R) culture medium. Then, gene expression levels related to disturbed metabolic pathways were assessed to verify according to metabolic phenotypes. Metabolomics profiles showed that [(S)-cyano(3-phenoxyphenyl)methyl](1R,3R)-3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane-1-carboxylate [(1R,3R,αS)-CP] induced the most significant changes in metabolic phenotypes than did the other stereoisomers. There are 10 differential metabolites (isoleucine, valine, leucine, ethanol, alanine, acetate, aspartate, arginine, lactate, and glucose) as well as two significantly disturbed pathways, including "pyruvate metabolism" and "alanine, aspartate, and glutamate metabolism," that were confirmed in H295R cells culture medium of (1R,3R,αS)-CP compared with other stereoisomers. Polymerase chain reaction (PCR) array also confirmed the results of metabolomics. Our results can help to understand the potential mechanisms between the isomer selectivity in metabolic phenotypes and endocrine-disrupting effects. Data provided here not only lend authenticity to the cautions issued by the scientists and researchers but also offer a solution for the balance between environment and political regulations.

Nanometer Titanium Dioxide Mediated High Efficiency Photodegradation of Fluazifop-p-Butyl

The widespread use of fluazifop-p-butyl (FPB) contributes to its presence in the environment. Considering the ecological risks of FPB residues in the environment, the anatase nanometer titanium dioxide (nano-TiO₂) mediated photocatalytic degradation of FPB was studied by smearing FPB and nano-TiO₂ together on a glass plane; illumination, trimethylsilane derivatization of photolysis products, high performance liquid chromatography (HPLC) quantitative analysis and gas chromatograph-mass spectrometer (GC-MS) identification were used. Results showed that the first order dynamic model could describe the photodegradation of FPB by nano-TiO₂ mediated, and the photodegradation and photosensitization rates were found to be positively correlated with the dose of nano-TiO₂ at lower dose ranges. It is noticeable that a strong photosensitization effect was exhibited on degradation of FPB, not only under high-pressure mercury lamps, but also simulated sunlight (xenon lamp light). Ultimately, twelve main photolytic products were reasonably speculated, whilst five photolysis pathways were proposed. These results together suggest that nano-TiO₂ can be used as an effective photosensitizer to accelerate FPB photolysis.

In vitro assessment of corticosteroid effects of eight chiral herbicides

Information regarding the enantioselective endocrine disruption of chiral herbicides is scarce. This study assessed the disrupting effects of eight typical chiral herbicides on corticosteroids (including glucocorticoids and mineralocorticoids). Enantioselectivity of eight chiral herbicides were evaluated for their agonistic/antagonistic effects on glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) with CHOK1 cell line using reporter gene assay. Their influence on the production of corticosteroids were further investigated in H295R cell line using enzyme-linked immunosorbent assay (ELISA). None of the racemates or enantiomers of eight chiral herbicides exhibited GR or MR agonistic activity at non-cytotoxic concentrations. However, rac-propisochlor and S-imazamox antagonized cortisol-induced transactivation of GR by 21.79% and 38.73% at the concentration of 1.0 × 10^-7 M and 1.0 × 10^-6 M, respectively, and R-napropamide remarkably attenuated aldosterone-induced MR transactivation by 68.78% at 1.0 × 10^-6 M. The secretion of cortisol was significantly restrained after treated with 1.0 × 10^-6 M rac-propisochlor and rac-/R-napropamide at the concentration of 1.0 × 10^-6 M by 26.49%, 30.10% and 35.27%, respectively, while this glucocorticoid was remarkably induced by 1.0 × 10^-5 M rac-diclofop-methyl and its two enantiomers at the concentration of 1.0 × 10^-5 M by 75.60%, 100.1% and 68.78%, respectively. Exposure to rac-propisochlor (1.0 × 10^-6 M), S-diclofop-methyl (1.0 × 10^-5 M) or rac-/S-/R- acetochlor (1.0 × 10^-6 M) and rac-/S-/R-lactofen (1.0 × 10^-6 M) inhibited the secretion of aldosterone by approximately 40%. Our findings suggested that chiral herbicides disrupted corticosteroid homeostasis in an enantioselective way. Therefore, more comprehensive screening is required to better understand the ecological and health risks of chiral pesticides.

Toxicity and Metabolic Fate of the Fungicide Carbendazim in the Typical Freshwater Diatom Navicula Species

Fungicides are frequently detected in natural water and have gained increasing attention as a result of their potential toxicity to non-target aquatic organisms. Carbendazim (CAR), a commonly used fungicide, was selected to explore its toxicity and biodegradation in a typical freshwater diatom Navicula sp. Results showed that the growth of Navicula sp. was inhibited by CAR, with a 24 h EC₅₀ value of 2.18 mg L^-1. Although the algal growth rate was recovered after 72 h of exposure, the chlorophyll a content remained significantly decreased when the concentration of CAR was above 0.5 mg L^-1. Moreover, Navicula sp. had a negative effect on the removal of CAR, and the acute toxicity by CAR was likely due to its rapid accumulation in algal cells. Mass spectrometric data revealed the transformation products of CAR from hydroxylation, methylation, decarboxylation, demethylation, and deamination in algal cultures. These results provide a better understanding of the environmental risks of CAR in water and point to the need for additional studies on the potential adverse biological effects of its intermediates.

Size-dependent toxicity of ThO2 nanoparticles to green algae Chlorella pyrenoidosa

Thorium (Th) is a natural radioactive element present in the environment and has the potential to be used as a clean nuclear fuel. Relatively little is known about the aquatic toxicity of Th, especially in nanoparticulate form, which may be the main chemical species of Th in the natural waters. In this study, impacts of ThO₂ nanoparticles (NPs) with two different sizes (52 ± 5 nm, s-ThO₂vs. 141 ± 6 nm, b-ThO₂) on a green alga Chlorella pyrenoidosa (C. pyrenoidosa) were evaluated. Results indicated that C. pyrenoidosa was more sensitive to s-ThO₂ (96-h EC₃₀ = 64.1 μM) than b-ThO₂ (96-h EC₃₀ = 100.2 μM). Exposure to 200 μM of ThO₂ NPs reduced the chlorophyll-a and chlorophyll-b contents of the algal cells. At 96 h, SEM and TEM showed that more agglomerates of s-ThO₂ than those of b-ThO₂ were attached onto the surface of algal cells. Reactive oxygen species (ROS) generation and membrane damage were induced after the attachment of high concentrations of ThO₂ NPs. The heteroagglomeration between ThO₂ NPs and algal cells and increased oxidative stress might play important roles in the toxicity of ThO₂ NPs. To the best of our knowledge, this is the first report on aquatic toxicity of ThO₂ NPs.

Enantioselective Toxicity of Chiral Herbicide Metolachlor to Microcystis aeruginosa

The enantioselective effects of chiral herbicides on aquatic organisms have received increasing attention. As one kind of freshwater algae responsible for most algal blooms, Microcystis aeruginosa can produce hepatotoxic microcystin and cause serious health concerns for drinking water. Thus, the effects of chiral herbicides on M. aeruginosa are of vital significance but poorly understood, especially as the structures of chiral herbicides become more complex. In this study, the enantioselective effects of four metolachlor enantiomers based on carbon center and axis chirality on M. aeruginosa were investigated for the first time at an enantiomeric level. The results of the investigation into algal growth inhibition, chlorophyll a content, and cell integrity indicated that ( S)-metolachlor [( S)-Met] was significantly more toxic than any other isomer. The toxicity ranking of different enantiomers at the highest concentration (15 mg/L) against M. aeruginosa was ( S)-Met > (α R,1' S)-Met > (α S,1' S)-Met > (α S,1' R)-Met > (α R,1' R)-Met, with (α S,1' S)-Met and (α R,1' S)-Met displaying a synergistic effect. Additionally, the Fe distribution in M. aeruginosa presented distinct enantioselectivity, which may contribute to the enantioselective toxicity of metolachlor. Furthermore, metolachlor upregulated the expression of genes mcyD and mcyH in an enantioselective manner, indicating that this herbicide can potentially promote the synthesis and efflux of microcystin, thus aggravating agricultural water contamination to different extents. Overall, this study will help to understand the ecotoxicity of metolachlor at a deeper level and provide theoretical insights into the enantioselective behaviors of metolachlor.

Dichlorprop induced structural changes of LHCⅡ chiral macroaggregates associated with enantioselective toxicity to Scnedesmus obliquus

The enantioselective toxic mechanisms of chiral herbicides in photosynthetic organisms are closely related to the production of reactive oxygen species (ROS) production, however, there are few reports on how the enantioselective production of ROS can be triggered. In suboptimal conditions, photosynthesis is one of the most important processes in the production of ROS, especially in the process of light utilization and electron transfer. In this study, we investigated the interactions between chiral herbicide dichlorprop (DCPP) enantiomers and the chiral macroaggregates of the photosynthetic light-harvesting chlorophyll a/b pigment-protein complexes (LHCII) in Scenedesmus obliquus, which is of great significance in capturing and utilizing sun light, and also in dissipating the excess excitation energy. The results of the circular dichroism indicated that DCPP induced the structural changes of the LHCII chiral macroaggregates in an enantioselective manner and that the (R)-DCPP treated-group showed a bigger change accompanied by a changed enantioselective dissipation of the excitation energy. The excitation energy was excessed in DCPP treated-groups and the degree of excess was enantioselective and the detrimental non-chemical energy triggered the enantioselective production of ROS, that induced the enantioselective toxicity to green algae S. obliquus. Overall, this study has identified that how the enantioselective production of ROS can be triggered in chloroplasts; this can help to reveal the enantioselective mechanisms of chiral herbicides to photosynthetic organisms.

Enantioselective bioaccumulation and metabolism of lactofen in zebrafish Danio rerio and combined effects with its metabolites

Pesticide residue in agricultural land might led to contamination of fresh waters, creating potential risks to organisms. The environmental behavior of herbicide lactofen may be enantioselective and the metabolites may have high toxic effects in individual or in combination. In this work, the enantioselective bioaccumulation, metabolism and toxic effects of lactofen and three metabolites (desethyl lactofen, acifluorfene, and amino acifluorfene) in zebrafish were investigated. The antioxidase activity (superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase), lipid peroxidation content were measured after exposure, and genetic toxicity was evaluated by a micronucleus test. The integrated biomarker response (IBR) method was used to determine the effects of the lactofen and its metabolites as well as their combinations. The metabolites were found to have higher toxic effects, and enantioselective toxic effects of lactofen and desethyl lactofen were observed, with the S-enantiomer more toxic. Based on IBR values, synergistic effects existed in combination of lactofen and desethyl lactofen, while antagonistic effects of lactofen with acifluorfene or amino acifluorfene were observed. Zebrafish were exposed to 0.5 mg L^-1 lactofen and the bioaccumulation were measured during a 15 d period followed by a 7 d elimination. The half-lives of the metabolites varied between 0.66 and 5.21 d, with bioconcentration factors (BCFs) in the range of 39-120. The metabolic pathways of R- and S-lactofen were found to be significantly different. The results supported our hypothesis. Therefore, the assessment of enantiomers and metabolites in individual or in combination should be taken into consideration in evaluating chiral pesticide risks.

Enantioselective toxic effects and digestion of furalaxyl enantiomers in Scenedesmus obliquus

Research on the enantioselective environmental behavior of chiral pesticides has been a hot spot of environmental chemistry recently. In this study, the acute toxicity and digestion of furalaxyl enantiomers were determined on the aquatic algae Scendesmus obliquus. After exposure for 96 hours, the EC₅₀ values for (S)-furalaxyl and (R)-furalaxyl were 13.59 and 15.26 mg/L, respectively. In addition, enantioselectivity was observed from the determined chlorophyll contents and antioxidant enzyme (CAT and SOD) activities of algae cells after exposure to furalaxyl enantiomers for 96 hours. The digestion rate of (S)-furalaxyl and (R)-furalaxyl were almost the same in S. obliquus. On the basis of these data, the inactive enantiomers (S)- furalaxyl is more toxic than the active one on the non-target species S. obliquus, indicating that such enantiomeric differences should be taken into consideration in the study of pesticide risk assessment.

Enantioseparation and determination of dufulin enantiomers in cucumber and soil by chiral liquid chromatography-tandem mass spectrometry

A simple and rapid method for enantioselective determination of dufulin in cucumber and soil was developed by liquid chromatography with tandem mass spectrometry. The enantiomers were separated on a Superchiral S-OD chiral cellulose tris(3,5-dimethylphenylcarbamate) column at 20°C, with a mixture of acetonitrile and water (0.1% formic acid; 52:48, v/v) as mobile phase at a flow rate of 0.65 mL/min. The pretreatment conditions were optimized using an orthogonal test, and the optimized method showed good linearity and sensitivity. The limits of detection and limits of quantification of two dufulin enantiomers were 0.006 and 0.02 mg/kg, respectively. The average recoveries of S-enantiomer and R-enantiomer in cucumber and soil were 80.61-99.83% and 80.97-102.96%, respectively, with relative standard deviations of 1.30-9.72%. The method was successfully applied to determine dufulin in real cucumber and soil samples. The results demonstrate that the method could facilitate further research on the differences between individual dufulin enantiomers with respect to metabolites and environmental fate and finally help reveal the complex interactions that exist between dufulin, humans and the environment.

Enantiomeric characterization of herbicide lactofen: Enantioseparation, absolute configuration assignment and enantioselective activity and toxicity

Chiral herbicides consist of two or more enantiomers, which usually differ in their biological properties and behave enantioselectively in biochemical process. Scant studies have been published in the past decades to characterize the enantiomers of herbicide lactofen. In this study, a laboratory method was developed to prepare the lactofen enantiomers using normal phase high performance liquid chromatography with an AD-H column, and μg level production yield was achieved in a single run. The two separated enantiomers had purity of ≫99%, with their absolute configurations assigned by experimental and calculated electronic and vibrational circular dichroism. Spectral analyses including semi-empirical rules as well as comparisons with the results of quantum chemical calculations confirmed the molecular configurations of R-lactofen and S-lactofen, in this elution order. The enantioselective bioactivity toward weed (Echinochloa crusgalli) and toxicity toward aquatic algae (Microcystis aeruginosa) was assessed by measuring their growth rates after the treatments with lactofen enantiomers and racemate. The results showed that R-lactofen affected E. crusgalli more severely, while S-lactofen was more toxic to algae. Using active enantiomer instead of racemate may be more efficient and safe. Therefore, a more comprehensive understanding of the behaviors of chiral enantiomers is a need to improve activity and risk assessment and regulations of chiral compounds. Our work will be helpful to easily prepare single enantiomers from racemic mixtures and to establish effective absolute configurations of the enantiomers.

Metabolite identification of ursolic acid in mouse plasma and urine after oral administration by ultra-high performance liquid chromatography/quadrupole time-of-flight mass spectrometry

Ursolic acid (UA), a pentacyclic terpenoid carboxylic acid widely existing in various medicinal plants, has been reported to have multifarious biological activities such as anti-inflammatory, anticancer and antioxidant activities. In this paper, we analyzed the metabolic profile of UA in mice (including plasma and urine) by using ultra-high performance liquid chromatography (UPLC) coupled with a quadrupole time-of-flight (Q/TOF) method. Principal component analysis (PCA) was applied to differentiate the control and experimental groups. Potential biomarkers were filtered by using loading plots followed by further analysis with UPLC-Q/TOF-MS data. The results showed that 3 metabolites in plasma were identified as markers, one of which was UA and the others were UA epoxides, which belonged to phase I metabolites. Additionally, 5 phase II metabolites were tentatively identified in urine through an accurate mass and characteristic fragment ions. These data suggested that the biotransformation of UA undergoes the major metabolic reactions of the phase I metabolic route of olefin oxidation and phase II metabolic routes of glycine conjugation, glutathione conjugation and glucuronidation. This is the first report of analysis and characterization of the metabolites after the oral administration of UA in mice. The proposed metabolic pathways of UA in mice is also raised for the first time. It might provide further understanding of the potential biological mechanism of UA.

First report on metabolism study of ursolic acid (UA) in vivo of mice.

Microbial catabolism of chemical herbicides: Microbial resources, metabolic pathways and catabolic genes

Chemical herbicides are widely used to control weeds and are frequently detected as contaminants in the environment. Due to their toxicity, the environmental fate of herbicides is of great concern. Microbial catabolism is considered the major pathway for the dissipation of herbicides in the environment. In recent decades, there have been an increasing number of reports on the catabolism of various herbicides by microorganisms. This review presents an overview of the recent advances in the microbial catabolism of various herbicides, including phenoxyacetic acid, chlorinated benzoic acid, diphenyl ether, tetra-substituted benzene, sulfonamide, imidazolinone, aryloxyphenoxypropionate, phenylurea, dinitroaniline, s-triazine, chloroacetanilide, organophosphorus, thiocarbamate, trazinone, triketone, pyrimidinylthiobenzoate, benzonitrile, isoxazole and bipyridinium herbicides. This review highlights the microbial resources that are capable of catabolizing these herbicides and the mechanisms involved in the catabolism. Furthermore, the application of herbicide-degrading strains to clean up herbicide-contaminated sites and the construction of genetically modified herbicide-resistant crops are discussed.

Enantioselective metabolism of triadimefon and its chiral metabolite triadimenol in lizards

Chinese lizards (Eremias argus) were exposed to separated R-(-)-triadimefon, S-(+)-triadimefon and racemic triadimefon to evaluate enantioselective accumulation of triadimefon. After single oral administration of R-(-)-triadimefon, S-(+)-triadimefon and racemic triadimefon, the time-concentration curves in different tissues were found to be different. Triadimefon enantiomers crossed the blood-brain barrier and brain is a main target organ. The residues of triadimefon enantiomers in fat were highest after 24h indicating that fat was the main tissue of accumulation. In racemic triadimefon exposure group, the enantiomer fractions of R-(-)-triadimefon in different tissues showed that the differences between R-(-)-triadimefon and S-(+)-triadimefon were significant in absorption and metabolism, but the differences became smaller in exclusion and accumulation. From the results of mathematical models, S-(+)-triadimefon was absorbed and eliminated faster than R-(-)-triadimefon, and R-(-)-triadimefon was easily distributed in the tissues and more easily converted into its metabolites. Furthermore, among the four enantiomers of triadimenol, SR-(-)-triadimenol produced by S-(+)-triadimefon may have the highest fungicidal activity and the strongest biological toxicity, RR-(+)-triadimenol produced by R-(-)-triadimefon was most likely to bioaccumulate in lizard. Identifying toxicological effects and dose-response relationship of SR-(-)-triadimenol and RR-(+)-triadimenol will help fully assess the risk of TF enantiomers use in the future. The results enrich and supplement the knowledge of the environmental fate of triadimefon enantiomers.

Enantioselective Bioaccumulation, Tissue Distribution, and Toxic Effects of Myclobutanil Enantiomers in Pelophylax nigromaculatus Tadpole

Research on the enantioselective behavior of chiral pesticides on amphibians has received growing attention, because amphibians are experiencing a population decline and amphibian metamorphosis shares many similarities with human fetal development. In this study, the enantioselective behavior of myclobutanil on Pelophylax nigromaculatus tadpole was studied. The antioxidant enzyme (SOD, GST) activities and malondialdehyde (MDA) content were investigated to assess the different toxic effects when tadpoles were exposed to myclobutanil enantiomers for 96 h. In the chronic exposure experiment, the bioaccumulation concentration of (-)-myclobutanil in tadpoles is significantly higher than that of (+)-myclobutanil, and the concentration of myclobutanil in tadpole intestine and liver was higher compared with other tissues. During the elimination experiment, about 95% of myclobutanil in tadpoles was eliminated within only 24 h. On the basis of these data, the enantiomeric differences should be taken into consideration in the risk assessment of myclobutanil.

Enantioselective oxidative stress and oxidative damage caused by Rac- and S-metolachlor to Scenedesmus obliquus

The rational use and environmental security of chiral pesticides has gained the interest of many researchers. The enantioselective effects of Rac- and S-metolachlor on oxidative stress in Scenedesmus obliquus were determined in this study. Stronger green fluorescence was observed in response to S-metolachlor treatment than to Rac-metolachlor treatment, suggesting that more reactive oxygen species (ROS) were stimulated by S-metolachlor. ROS levels following S-metolachlor treatment were 1.92-, 8.31-, and 1.08-times higher than those observed following Rac-metolachlor treatment at 0.1, 0.2, and 0.3 mg/L, respectively. Superoxide dismutase (SOD) and catalase (CAT) were stimulated with increasing herbicide concentrations, with S-metolachlor exhibiting a greater effect. Oxidative damage in terms of chlorophyll (Chl) content, cellular membrane permeability, and cellular ultrastructures of S. obliquus were investigated. Chla and Chlb contents in algae treated with Rac-metolachlor were 2-6-fold higher than those in algae treated with S-metolachlor at 0.1, 0.2, and 0.3 mg/L. The cellular membrane permeability of algae exposed to 0.3 mg/L Rac- and S-metolachlor was 6.19- and 42.5-times that of the control. Correlation analysis implied that ROS are the major factor responsible for the oxidative damage caused by Rac- and S-metolachlor. Damage to the chloroplasts and cell membrane of S. obliquus, low production of starch granules, and an increased number of vacuoles were observed upon ultrastructural morphology analysis by transmission electron microscope. These results indicate that S-metolachlor has a greater effect on S. obliquus than Rac-metolachlor.

Interaction of chiral herbicides with soil microorganisms, algae and vascular plants

Chiral herbicides are often used in agriculture as racemic mixtures, although studies have shown that the fate and toxicity of herbicide enantiomers to target and non-target plants can be enantioselective and that herbicide toxicity can be mediated by only one enantiomer. If one enantiomer is active against the target plant, the use of enantiomer-rich herbicide mixtures instead of racemic herbicides could decrease the amount of herbicide applied to a crop and the cost of herbicide application, as well as unintended toxic herbicide effects in the environment. Such a change in the management of herbicide applications requires in-depth knowledge and a critical analysis of the fate and effects of herbicide enantiomers in the environment. This review article first synthesizes the current state of knowledge on soil and plant biodegradation of herbicide enantiomers. Second, we discuss our understanding of the biochemical toxicity mechanisms associated with both enantiomers in target and non-target plants gained from state-of-the-art genomic, proteomic and metabolomic tools. Third, we present the emerging view on the "side effects" of herbicides in the root microbiome and their repercussions on target or non-target plant metabolism. Although our review of the literature indicates that the toxicity of herbicide enantiomers is highly variable depending on plant species and herbicides, we found general trends in the enantioselective toxic effects of different herbicides in vascular plants and algae. The present study will be helpful for pesticide risk assessments as well as for the management of applying enriched-enantiomer herbicides.

Oxidative Damage and Cytotoxicity of Perfluorooctane Sulfonate on Chlorella vulgaris

We studied the effects of perfluorooctane sulfonate (PFOS) on the chlorophyll content, cell permeability, and antioxidant defense systems of the green alga Chlorella vulgaris. The results showed that the production of reactive oxygen species increased in a concentration-dependent manner after exposure to PFOS for 96 h. Superoxide dismutase and catalase activity was elevated after exposure to the lower concentrations and then decreased with higher concentrations. Malondialdehyde content was significantly higher than that of controls at the higher PFOS concentrations. Cell membrane permeability increased. These results indicate that PFOS exposure leads to oxidative damage in C. vulgaris. At these concentrations, chlorophyll and the structure of chloroplasts were destroyed.

Reduced graphene oxide induces cytotoxicity and inhibits photosynthetic performance of the green alga Scenedesmus obliquus

Increased use of graphene materials might ultimately lead to their release into the environment. However, only a few studies have investigated the impact of graphene-based materials on green plants. In this study, the impact of reduced graphene oxide (RGO) on the microalgae Scenedesmus obliquus was evaluated to determine its phytotoxicity. Treatment with RGO suppressed the growth of the microalgae. The 72-h IC₅₀ values of RGO evaluated using the logistic and Gompertz models were 148 and 151 mg L^-1, respectively. RGO significantly inhibited Chl a and Chl a/b levels in the algal cells. Chlorophyll a fluorescence analysis showed that RGO significantly down-regulated photosystem II activity. The mechanism of how RGO inhibited algal growth and photosynthetic performance was determined by analyzing the alterations in ultrastructural morphology. RGO adhered to the algal cell surface as a semitranslucent coating. Cell wall damage and membrane integrity loss occurred in the treated cells. Moreover, nuclear chromatin clumping and starch grain number increase were noted. These changes might be attributed to the increase in malondialdehyde and reactive oxygen species levels, which might have exceeded the scavenging ability of antioxidant enzymes (including peroxidase and superoxide dismutase). RGO impaired the extra- and intra-cellular morphology and increased oxidative stress and thus inhibited algal growth and photosynthesis.

Effect of fluoride on the cell viability, cell organelle potential, and photosynthetic capacity of freshwater and soil algae

Although fluoride occurs naturally in the environment, excessive amounts of fluoride in freshwater and terrestrial ecosystems can be harmful. We evaluated the toxicity of fluoride compounds on the growth, viability, and photosynthetic capacity of freshwater (Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata) and terrestrial (Chlorococcum infusionum) algae. To measure algal growth inhibition, a flow cytometric method was adopted (i.e., cell size, granularity, and auto-fluorescence measurements), and algal yield was calculated to assess cell viability. Rhodamine123 and fluorescein diacetate were used to evaluate mitochondrial membrane potential (MMA, ΔΨ_m) and cell permeability. Nine parameters related to the photosynthetic capacity of algae were also evaluated. The results indicated that high concentrations of fluoride compounds affected cell viability, cell organelle potential, and photosynthetic functions. The cell viability measurements of the three algal species decreased, but apoptosis was only observed in C. infusionum. The MMA (ΔΨ_m) of cells exposed to fluoride varied among species, and the cell permeability of the three species generally decreased. The decrease in the photosynthetic activity of algae may be attributable to the combination of fluoride ions (F^-) with magnesium ions (Mg²⁺) in chlorophyll. Our results therefore provide strong evidence for the potential risks of fluoride compounds to microflora and microfauna in freshwater and terrestrial ecosystems.

Stomatal behaviors reflect enantioselective phytotoxicity of chiral herbicide dichlorprop in Arabidopsis thaliana

Stomata in plants play vital roles in water transpiration and gas exchange necessary for photosynthesis, which are critical for the plants growth. Until now, however, the effect of chiral herbicides on the response of stomata was poorly understood. To unveil this puzzle, the enantioselective effect of chiral herbicide dichloroprop (DCPP) on stomata in Arabidopsis thaliana was investigated. It was found that (R)-DCPP preferentially promoted the extent of stomatal opening in Arabidopsis leaves, resulting in 59.84% enhancement at 0.3μmol·L(-1) comparing to the control, where (S)- and (Rac)-DCPP exhibited no significant differences. Enantioselectivity was also observed in the response of stomata to DCPP. To better understand the mechanism involved, the reactive oxygen species (ROS) production and antioxidant system defense were measured. Interestingly, the ROS production in Arabidopsis leaves was also enantioselective. The (R)-DCPP treatments resulted in 6.08-fold enhancement compared with the control, whereas 1.35- and 2.51-fold increases occurred in (S)-DCPP and (Rac)-DCPP treatments, respectively. The promoting of stomatal opening was positively correlated with ROS production. In addition, the antioxidant system response provided evidence of oxidative stress and damage caused by DCPP. This study confirmed that the ROS produced by DCPP promoted stomatal opening and suggested a potential sight to elucidate the phytotoxicity of chiral herbicides.

Chiral quizalofop-ethyl and its metabolite quizalofop-acid in soils: Enantioselective degradation, enzymes interaction and toxicity to Eisenia foetida

An enantioselective chromatographic method to analyze enantiomers of quizalofop-ethyl and its metabolite quizalofop-acid was established using a high-performance liquid chromatography (HPLC) on (R, R) Whelk-O 1 column. The enantioselective degradation kinetics of quizalofop-ethyl and quizalofop-acid in three soils were investigated. Moreover, the interaction with urease and catalase in the soils and the acute toxicity to Eisenia foetida of quizalofop-ethyl were also determined in order to assess their metabolism mechanism and environmental risk. From the results, quizalofop-ethyl was configurationally stable and was hydrolyzed rapidly to quizalofop-acid, which also degraded enantioselectively but slowly, and the inversion of the S-(-)-quizalofop-acid into the R-(+)-quizalofop-acid was observed in Xinxiang soil. In addition, quizalofop-ethyl and quizalofop-acid enantioselectively affected urease activity but not catalase. The acute toxicity assays to earthworm indicated that the racemic quizalofop-ethyl and quizalofop-acid were more toxic than quizalofop-p-ethyl and quizalofop-p-acid respectively, dramatically, the toxicity of the metabolite was much higher than the parent compound. These results revealed the enantioselective degradation of quizalofop-ethyl and quizalofop-acid, and the differences of toxicity among the enantiomers of the parent compound and the metabolite, which should be considered in future environmental risk evaluation.

Enantioselective Separation of 4,8-DHT and Phytotoxicity of the Enantiomers on Various Plant Species

As a candidate for bioherbicide, 4,8-dihydroxy-1-tetralone (4,8-DHT) was isolated from Caryospora callicarpa epicarp and its two enantiomers, S-(+)-isosclerone and R-(-)-regiolone, were separated by chiral high-performance liquid chromatography (HPLC) on a Chiralcel OD column with chiral stationary phase (CSP)-coated cellulose-tris(3,5-dimethylphenylcarbamate). Then, the phytotoxicity of 4,8-DHT and its enantiomers toward the seeds germination and seedling growth of the five tested plant species, including lettuce (Latuca sativa), radish (Raphanus sativus), cucumber (Cucumis sativus), onion (Allium cepa), and wheat (Triticum aestivum), were investigated and the results indicated a hormesis at low concentration of 4,8-DHT and its enantiomers, but a retardant effect at high concentration. Between the two enantiomers of 4,8-DHT, the S-(+)-isosclerone was more toxic to seeds germination and seedling growth of the five tested plant species than the R-(-)-regiolone, and also the phytotoxicity of S-(+)-isosclerone varied with different plants. For example, S-(+)-isosclerone was the most active to seedling growth of lettuce, indicating that S-(+)-isosclerone had specific effects on different organisms. Thus, all of the chirality and concentration of 4,8-DHT, as well as the affected plant species, need to be taken into consideration in the development and utilization of 4,8-DHT.

Are Nutrient Stresses Associated with Enantioselectivity of the Chiral Herbicide Imazethapyr in Arabidopsis thaliana?

Plant growth can be inhibited by herbicides and is strongly limited by the availability of nutrients, which can influence human health through the food chain. Until now, however, cross talk between the enantioselectivity of herbicides and nutrient stresses has been poorly understood. We analyzed trace element and macroelement contents in shoots of Arabidopsis thaliana treated by the chiral herbicide imazethapyr (IM) and observed that multiple-nutrient stress (trace elements Mn, Cu, and Fe and macroelements P, K, Ca, and Mg) was enantioselective. The (R)-IM treatments resulted in Mn 23.37%, Cu 63.53%, P 30.61%, K 63.70%, Ca 34.32%, and Mg 36.14% decreases compared with the control. Interestingly, it was also found that herbicidally active (R)-IM induced notable aggregation of nutrient elements in leaves and roots compared with the control and (S)-IM. Through gene expression analyses, it was found that herbicidally active (R)-IM induced the up- or down-regulation of genes involved in the transport of nutrient elements. We propose that (R)-IM affected the uptake and translocation of nutrient elements in A. thaliana, which destroyed the balance of nutrient elements in the plant. This finding reminds us to reconsider the effect of nutrient stresses in risk assessment of herbicides.

Enantioselective and Synergetic Toxicity of Axial Chiral Herbicide Propisochlor to SP2/0 Myeloma Cells

The axial chiral herbicide propisochlor is used to control weeds. Different enantiomers of a compound usually have different biological activities. It is unclear how the toxicities of the propisochlor enantiomers differ. Propisochlor enantiomers, separated by high-performance liquid chromatography, were tested on SP2/0 myeloma cells. Cytotoxicity and apoptosis were measured, and interactions between the enantiomers were evaluated. The rac-propisochlor, pure R-(+) isomer, and pure S-(-) isomer inhibited cell proliferation and induced apoptosis. The rac-propisochlor, R-(+) isomer, and S-(-) isomer half maximal effective concentration values after 24 h of incubation were 111 ± 0.15, 68 ± 0.09, and 99 ± 0.21 μM, respectively. R-(+) isomer induced the most apoptosis. R-(+) isomer was ∼1.63 times more cytotoxic than rac-propisochlor and ∼1.46 times more cytotoxic than S-(-) isomer. Antagonistic cytotoxic interactions were found between R-(+) and S-(-) isomers. This is the first time the toxicities of these enantiomers and antagonism between the enantiomers have been reported. The antagonism indicates that the ecotoxicological effects of the enantiomers should be investigated.

Environmental behavior of the chiral herbicide haloxyfop. 2. Unchanged enantiomer composition in blackgrass (Alopecurus myosuroides) and garden cress (Lepidium sativum)

Haloxyfop-methyl is a chiral herbicide against grasses in dicotyledonous crops. In plants and soil, haloxyfop-methyl is rapidly hydrolyzed to haloxyfop-acid, whose R-enantiomer carries the actual herbicidal activity. In soil, S-haloxyfop-acid is converted within less than 1 day and almost completely into R-haloxyfop-acid. In this study, we investigated the possible interconversion of the enantiomers of haloxyfop-methyl and haloxyfop-acid in blackgrass and garden cress. Racemic or enantiopure haloxyfop-methyl was applied to the leaves of plants grown in agar. The metabolism was followed during 4 days using enantioselective GC-MS. In contrast to soils, no interconversion was observed in plants, and metabolism was nonenantioselective. These findings are consistent with the fact that after pre-emergence application to soil and uptake by roots, the observed herbicidal effect is basically independent of the enantiomer composition of the applied substance, whereas after postemergence application, the efficacy clearly is different for the two enantiomers.

Enantioselective developmental toxicity and immunotoxicity of pyraclofos toward zebrafish (Danio rerio)

Pyraclofos, a relatively new organophosphorus pesticide, has shown potential ecotoxicities, however, its aquatic toxicity, especially enantioselective aquatic toxicity, remains largely unknown. Using zebrafish (Danio rerio) as a preeminent vertebrate aquatic model, the enantioselective differences in the developmental toxicity and immunotoxicity of pyraclofos were evaluated. Following 96-h exposure, pyraclofos enantiomers exhibited acute toxicity and showed lethal concentration 50 of 2.23 and 3.99 mg/L for (R)-Pyraclofos and (S)-Pyraclofos, respectively. Exposure to pyraclofos caused time- and concentration-dependent malformations such as pericardial edema, yolk sac edema, crooked bodies and hatching during the embryonic development, with markedly higher percentages of malformation at higher concentrations. The concentration-dependent immunotoxicity to zebrafish embryo exposed to low level pyraclofos was induced with significant up-regulation of mRNA levels of immune-related interleukin-1β (IL-1β) gene. (R)-Pyraclofos was consistently more toxic than (S)-Pyraclofos for the acute toxicity, developmental toxicity and immunotoxicity to zebrafish. Molecular dynamics simulations revealed that at the atomic level, (R)-Pyraclofos binds more potently to IL-1β protein than (S)-Pyraclofos. This enantioselective binding is mainly contributed by the distinct binding mode of pyraclofos enantiomers and their electrostatic interactions with IL-1β, which potentially affects IL-1β-dependent proinflammatory signal transduction. Our in vitro and in silico studies provided a better insight into the molecular basis for aquatic toxicity and thus improved the risk assessment for pyraclofos and other chiral organophosphorus pesticides.