Enantioselective behavior of malathion enantiomers in toxicity to beneficial organisms and their dissipation in vegetables and crops

A ratiometric fluorescence imprinted sensor based on N-CDs and metal-organic frameworks for visual smart detection of malathion

Sensitive and rapid detection of pesticide residues in food is essential for human safety. A ratiometric imprinted fluorescence sensor N-CDs@Eu-MOF@MIP (BR@MIP) was constructed to sensitively detect malathion (Mal). Europium-based metal organic frameworks (Eu-MOF) were used as supporters to improve the sensitivity of the BR@MIP. N-doped carbon dots (N-CDs) were used as fluorescent source to produce fluorescent signal. A linear relationship between the concentration of Mal and the fluorescence response of the sensor was found in the Mal concentration range of 1-10 μM with a limit of detection (LOD) of 0.05 μM. Furthermore, the sensor was successfully applied for the detection of Mal in lettuce, tap water, and soil samples, with recoveries in the range of 93.0 % - 99.3 %. Additionally, smartphone-based sensors were used to detect Mal in simulated real samples. Thus, the construction of ratiometric imprinted fluorescence sensor has provided a good strategy for the detection of Mal.

Stereoselective study on chiral fungicide metconazole in four kinds of fruits: Absolute configuration, SFC-MS/MS enantioseparation, degradation and risk assessment

Metconazole is a novel chiral fungicide with two chiral carbon atoms, but the research on its stereoselective behavior is limited. Therefore, the stereoselective behaviors of metconazole in four fruits, including grape, peach, pear and jujube, were summarized in this study. After determining the absolute configuration of metconazole stereoisomers, a chiral separation method through supercritical fluid chromatography/tandem triple quadrupole mass spectrometry was first developed, which combined an improved QuEChERS method obtained the recoveries of 71.6-113 % with RSD ≤ 19.8 %. The LOD and LOQ were 4.30-95.9 and 10.5-143.2 ng/kg, respectively. Different stereoselective and diastereoselective behaviors were observed in four fruits. Dietary risk assessments of rac-metconazole were performed in populations with different ages and genders. Both acute (RQa, 0.0124-0.140 %) and chronic (HQ, 0.0234-0.0794 %) intake risks were acceptable. The results of this study would contribute to more complete risk assessments of metconazole and provide data for chiral studies.

Biodegradation strategies of veterinary medicines in the environment: Enzymatic degradation

One Health closely integrates healthy farming, human medicine, and environmental ecology. Due to the ecotoxicity and risk of transmission of drug resistance, veterinary medicines (VMs) are regarded as emerging environmental pollutants. To reduce or mitigate the environmental risk of VMs, developing friendly, safe, and effective removal technologies is an important means of environmental remediation for VMs. Many previous studies have proved that biodegradation has significant advantages in removing VMs, and biodegradation based on enzyme catalysis presents higher operability and specificity. This review focused on biodegradation strategies of environmental pollutants and reviewed the enzymatic degradation of VMs including antimicrobial drugs, insecticides, and disinfectants. We reviewed the sources and catalytic mechanisms of peroxidase, laccase, and organophosphorus hydrolases, and summarized the latest research status of immobilization methods and bioengineering techniques in improving the performance of degrading enzymes. The mechanism of enzymatic degradation for VMs was elucidated in the current research. Suggestions and prospects for researching and developing enzymatic degradation of VMs were also put forward. This review will offer new ideas for the biodegradation of VMs and have a guide significance for the risk mitigation and detoxification of VMs in the environment.

Bifunctional TiO2 Nanoflower-Induced H4TCBPE Aggregation Enhanced Electrochemiluminescence for an Ultrasensitive Assay of Organophosphorus

In this work, the aggregation-induced emission ligand 1,1,2,2-tetra(4-carboxylbiphenyl)ethylene (H4TCBPE) was rigidified in the Ti-O network to form novel electrochemiluminescence (ECL) emitter H4TCBPE-TiO2 nanospheres, which acted as an effective ECL emitter to construct an "on-off" ECL biosensor for ultrasensitive detection of malathion (Mal). H4TCBPE-TiO2 exhibited excellent ECL responses due to the Ti-O network that can restrict the intramolecular free motions within H4TCBPE and then reduce the nonradiative relaxation. Moreover, TiO2 can act as an ECL co-reaction accelerator to promote the generation of sulfate radical anion (SO4•-), which interacts with H4TCBPE in the Ti-O network to produce enhanced ECL response. In the presence of Mal, numerous ligated probes (probe 1 to probe 2, P1-P2) were formed and released by copper-free click nucleic acid ligation reaction, which then hybridized with hairpin probe 1 (H1)-modified H4TCBPE-TiO2-based electrode surface. The P1-P2 probes can initiate the target-assisted terminal deoxynucleoside transferase (TdTase) extended reaction to produce long tails of deoxyadenine with abundant biotin, which can load numerous streptavidin-functionalized ferrocenedicarboxylic acid polymer (SA-PFc), causing quenching of the ECL signal. Thus, the ultrasensitive ECL biosensor based on H4TCBPE-TiO2 ECL emitter and click chemistry-actuated TdTase amplification strategy presents a desirable range from 0.001 to 100 ng/mL and a detection limit low to 9.9 fg/mL. Overall, this work has paved an avenue for the development of novel ECL emitters, which has opened up new prospects for ECL biosensing.

Enantioselective activity and toxicity of chiral acaricide cyflumetofen toward target and non-target organisms

Cyflumetofen (CYF), a novel chiral acaricide, exert enantiomer-specific effects on target organisms by binding to glutathione S-transferase. However, there is limited knowledge regarding the response of non-target organisms to CYF, including enantioselective toxicity. In this study, we investigated the effects of racemic CYF (rac-CYF) and its two enantiomers (+)-CYF and (-)-CYF on MCF-7 cells and non-target (honeybees) and target (bee mites and red spider mites) organisms. The results showed that similar to estradiol, 1 μM (+)-CYF promoted the proliferation and disturbed the redox homeostasis of MCF-7 cells, whereas at high concentrations (≥100 μM) it exerted a negative effect on cell viability that was substantially stronger than that of (-)-CYF or rac-CYF. (-)-CYF and rac-CYF at 1 μM concentration did not significantly affect cell proliferation, but caused cell damage at high concentrations (≥100 μM). Analysis of acute CYF toxicity against non-target and target organisms revealed that for honeybees, all CYF samples had high lethal dose (LD₅₀) values, indicating low toxicity. In contrast, for bee mites and red spider mites, LD₅₀ values were low, whereas those of (+)-CYF were the lowest, suggesting higher toxicity of (+)-CYF than that of the other CYF samples. Proteomics profiling revealed potential CYF-targeted proteins in honeybees related to energy metabolism, stress responses, and protein synthesis. Upregulation of estrogen-induced FAM102A protein analog indicated that CYF might exert estrogenic effects by dysregulating estradiol production and altering estrogen-dependent protein expression in bees. Our findings suggest that CYF functions as an endocrine disruptor in non-target organisms in an enantiomer-specific manner, indicating the necessity for general ecological risk assessment for chiral pesticides.

Bioaccumulation, metabolism and toxicological effects of chiral insecticide malathion and its metabolites in zebrafish (Danio rerio)

The bioaccumulation, metabolism, tissue-specific distribution and toxicity of the widely used organophosphorous pesticide malathion to zebrafish were investigated on an enantiomeric level for evaluating the environmental risks. The metabolites were also monitored and evaluated. Malathion was metabolized by zebrafish very fast with the half-life of 0.12 d and showed a middle accumulation capacity in zebrafish with bioaccumulation factor (BCF) of 12.9 after a 15-d exposure. Brain could enrich higher concentration of malathion than other tissues. The metabolites malaoxon, malathion/malaoxon monocarboxylic acid (DMA), malathion/malaoxon dicarboxylic acid (DCA), dimethylthiophosphate (DMTP) and dimethyldithiophosphate (DMDTP) were found, in which DMTP and DCA were in higher level, indicating the metabolism was mainly induced by carboxylesterase degradation. The accumulation of malathion and malaoxon was stereoselective in zebrafish tissues, exhibiting S-enantiomer preferentially enriched. The acute toxicity test showed rac-malathion was low toxic to zebrafish, which was 1.2 and 1.6 folds more toxic than S-malathion and R-malathion respectively. Malaoxon was highly toxic to zebrafish and approximately 32 times more toxic than malathion. The toxicity of other metabolites was lower than malathion. Malathion could cause an apparent developmental toxicity to zebrafish embryo, including bradycardia, hatchability reduction and deformity, and abnormal movement patterns in zebrafish larva. Chronic toxicity indicated that malathion and malaoxon induced oxidative damage and neurotoxicity in the liver, brain and gill of zebrafish, and malaoxon exhibited a relatively high injury to the zebrafish brain. The results can provide information for the comprehensive assessment of the potential risk of malathion to aquatic organisms and highlight the necessity of consideration of stereoselectivity and metabolites when systemically evaluating pesticides.

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.

The profiles of chiral pesticides in peri-urban areas near Yangtze River: Enantioselective distribution characteristics and correlations with surface sediments

Chiral pesticides account for 30% of pesticides. Pesticides are inevitably leached into the groundwater by runoff. At the watershed level, the distribution characteristics of enantiomers in sediments collected from the river network of an agricultural area near the middle and lower reaches of the Yangtze River were tested, and their potential correlations with the physicochemical properties and microbial communities of the sediments were analyzed. The sediment pollution was serious at sites 8 and 9, with their pollution source possibly being agricultural or industrial sewage. Moreover, there were higher cumulative contents of pesticide residues at sites 4, 8, and 9. Specifically, Cycloxaprid was the most detected chiral pesticide in the study area, followed by Dinotefuran and Diclofop-methyl. Additionally, Ethiprole and Difenoconazole had strong enantioselectivity in the study area. Interestingly, the enantiomers of some chiral pesticides, such as Tebuconazole, had completely different distributions at different sites. Pearson correlation analysis showed that sediment catalase and microbial biomass carbon were important factors for enantioselectivity of chiral pesticides. The effect of sediment physicochemical properties on enantioselective distribution was achieved by influencing the microorganisms in the sediment. Furthermore, the enantioselective distribution of Tebuconazole was closely related to the genus Arenimonas. Overall, the enantioselective distribution of most of the chiral pesticides was positively correlated with the prokaryotic microbial community. This study provides empirical support for agricultural non-point source pollution caused by chiral pesticides, and also lays a research foundation for exploring the factors that affect the fate of chiral pesticides in the environment.

Systemic assessment of the chiral insecticide pyriproxyfen in a citrus nectar source system: Stereoselective degradation, biological effect and exposure risk

BACKGROUND

Balancing the safety and efficiency of chiral pesticides can help protect pollinators. We evaluated the stereoselective behavior, bioactivity, toxicity and exposure risk of the chiral insecticide pyriproxyfen in a citrus nectar system.

RESULTS

Density functional theory (DFT) and ultra-performance liquid chromatography tandem mass spectroscopy (UPLC-MS/MS) were applied for absolute configuration appraisal and chiral analysis validation, respectively. The recoveries ranged from 72.3% to 100.5% with an relative standard deviation (RSD) ranging from 1.2% to 9.7%. In a field trial, we determined insecticide half-lives in citrus leaves and flowers, which were 7.0 and 8.6 days for R-(+)-pyriproxyfen, and 11.7 and 14.7 days for S-(-)-pyriproxyfen, respectively. We found that the bioactivity of R-(+)-pyriproxyfen was 3.39 and 2.37 times higher than S-(-)-pyriproxyfen against Unaspis yanonensis and Diaphorina citri nymphs, respectively. S-(-)-pyriproxyfen had 3.8 times higher acute toxicity than R-(+)-pyriproxyfen on Apis mellifera L., and its exposure risk was moderate based on the hazard quotient.

CONCLUSION

The phenomenon of stereoselective degradation and biological effect demonstrated that the high-risk stereoisomer of S-(-)-pyriproxyfen degraded more slowly than R-(+)-pyriproxyfen, but R-(+)-pyriproxyfen with better efficiency for target. Therefore, an increased duration of R-(+)-pyriproxyfen activity on citrus was beneficial for efficacy. Our results could guide the scientific application and evaluation of chiral pesticides on nectar plants. © 2022 Society of Chemical Industry.

Evaluation of chiral triticonazole in three kinds of fruits: enantioseparation, degradation, and dietary risk assessment

The enantioselective behaviors of chiral pesticides would affect the accuracy of risk assessment. This study evaluated the enantioselectivity of chiral triticonazole (a widely used fungicide) in three kinds of fruits. Firstly, the enantioseparation of triticonazole enantiomers was carried out within 1.2 min utilizing CHIRALPAK OJ-3 column with a mixture of CO₂ and methanol (93:7, v/v) using SFC-MS/MS. Secondly, field trials were conducted to clarify the enantioselective degradation and residue of S-( +)-triticonazole and R-(-)-triticonazole in fruits. The initial concentrations of rac-triticonazole were 25.1-93.1 ng/g, and enantioselective degradation was observed in pear, peach, and jujube after 2 h, 10 days, and 3 days, respectively. The degradation of S-( +)-triticonazole was fastest in pear (T_1/2, 2.01 days), while the T_1/2 of R-(-)-triticonazole was 5.02 days. The residue concentrations of rac-triticonazole were less than the MRL set by EU (10 ng/g) on the 3rd and 21st day in pear and peach, respectively, which were lower than 10 ng/g in jujube on the 30th day (no MRL). Finally, we found that the dietary intake risks of rac-triticonazole in fruits were low for 2-7 age, 20-50 age/female, and 20-50 age/male. The current study could provide complimentary references for the rational usage, MRL formulation, and risk assessment of chiral triticonazole.

Enantioselective monitoring chiral fungicide mefentrifluconazole in tomato, cucumber, pepper and its pickled products by supercritical fluid chromatography tandem mass spectrometry

A fast, effective, and environmental-friendly method was developed for enantioseparation and analysis of mefentrifluconazole in vegetables based on supercritical fluid chromatography tandem mass spectrometry. The enantioselective behaviors of mefentrifluconazole enantiomers in tomato, cucumber, and pepper in the greenhouse, and pickled cucumber and pepper during processing were investigated. Mefentrifluconazole enantiomers could obtain baseline separation within 2 min. The average recoveries of all matrices ranged from 78.4% to 119.0%, with relative standard deviations less than 16.8% for two enantiomers. S-(+)-mefentrifluconazole was preferentially degraded in pepper, while there was no enantioselectivity in tomato and cucumber under field conditions. During processing, S-(+)-mefentrifluconazole was reduced preferentially than R-(-)-mefentrifluconazole in pickled cucumber and cucumber brine. Inversely, R-(-)-mefentrifluconazole degraded faster than S-(+)-mefentrifluconazole in pepper brine. But, no obvious enantioselectivity was observed in pickled pepper. The result of this study could contribute to a more accurate dietary risk assessment of mefentrifluconazole in vegetables and processed products.

Determination of etoxazole in different parts of citrus fruit and its potential dietary exposure risk assessment

In this study, the profile of etoxazole in whole citrus, peel and pulp samples collected from Chongqing, Guangdong and Anhui provinces was monitored and their dietary risk to human had also been assessed. The final residual levels and distributions of etoxazole in citrus samples were detected by using an ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). The results showed that final concentrations of etoxazole in whole citrus, peel, and pulp were ranged at 0.012-0.174, 0.010-0.637, and 0.010-0.011 mg kg^-1, respectively. The assessment of dietary risk suggested that chronic dietary risk of etoxazole in whole fruit and peel were 0.010-0.197% and 0.035-0.951%, respectively. Our findings indicated that the chronic risk of daily consumption of citrus fruit is acceptable at recommended dosage.

Enantioseparation and stereoselective dissipation of the novel chiral fungicide pydiflumetofen by ultra-high-performance liquid chromatography tandem mass spectrometry

Pydiflumetofen is a novel and efficient broad-spectrum chiral fungicide consisting of a pair of enantiomers. A simple and sensitive chiral analytical method was established to determine the enantiomers of this chiral fungicide in food and environmental samples by ultra-high-performance liquid chromatography tandem triple quadrupole mass spectrometry (UHPLC-MS/MS) using QuEChERS method coupled with octadecylsilane-dispersive solid-phase extraction (C₁₈-dSPE) as extraction procedure. The specific optical rotation and the absolute configuration of the enantiomers were identified by polarimetry and electronic circular dichroism (ECD). The elution order of the pydiflumetofen enantiomers on Lux Cellulose-2 was S-(-)-pydiflumetofen and R-(+)-pydiflumetofen. The average recoveries of eleven matrices ranged from 71.3% to 107.4%. The intraday relative standard deviations (RSDs) were less than 11.8%, and the interday RSDs were less than 12.6% for the two enantiomers. Stereoselective dissipation in pakchoi and soil were observed: S-(-)-pydiflumetofen was degraded faster than R-(+)-pydiflumetofen in pakchoi, causing the enantiomer fraction (EF) of the enantiomers to change from 0.50 to 0.42 in 7 days. However, R-(+)-pydiflumetofen was degraded faster than S-(-)-pydiflumetofen in soil, causing the EF of the enantiomers to change from 0.49 to 0.52 in 21 days. This study provides a method for monitoring pydiflumetofen enantiomer residues, which is crucial for improving risk assessments and the development of chiral pesticides.

Simultaneous enantiomeric determination of multiple triazole fungicides in fruits and vegetables by chiral liquid chromatography/tandem mass spectrometry on a bridged bis(β-cyclodextrin)-bonded chiral stationary phase

A LC-MS/MS method for simultaneous determination of twelve triazole enantiomers (hexaconazole, tebuconazole, triticonazole, flutriafol, diniconazole, paclobutrazol) in six fruits and vegetables was established based on a stable and self-made bridged bis(β-cyclodextrin)-bonded chiral stationary phase. Simultaneous enantio-separation of multiple analytes was achieved with resolution ca. 1.67-2.14. Magnetically assisted QuECHERS was used to simplify and optimize sample pre-treatment. The new method was validated (accuracy, precision, matrix effect, etc.). Good linearity (0.5-20 μg/L, R² > 0.99) and high recoveries (76.1-103.4%) based on intra- and inter-day relative standard deviation (RSDs) (2.6-11.9%), were obtained. Furthermore, a total of 90 samples were analyzed using this method and enantiomeric fractions (EF) for tebuconazole in strawberry and cucumber (0.63 and 0.43, respectively) were determined as well as 0.57 for flutriafol in tomato. This high-throughput detection method supported a convenient enantiomeric monitoring for chiral pesticides in fruits and vegetables.

Fluorescence and colorimetric dual-mode sensor for visual detection of malathion in cabbage based on carbon quantum dots and gold nanoparticles

A dual-mode fluorescence/colorimetric sensor based on carbon quantum dots (CQDs) and gold nanoparticles (GNPs) was developed for visual detection of malathion in cabbage. The CQDs-GNPs nanocomposite exhibited emission wavelength at 527 nm and absorption wavelength at 524 nm. The fluorescence intensity increased and absorption decreased with addition of malathion. Fluorescence and colorimetric calibration curves were established based on fluorescence intensity (R² = 0.9914) and absorbance (R² = 0.9608) in the range of 1 × 10^-9-1 × 10^-2 M, respectively. Furthermore, fluorescence and colorimetric standard arrays were prepared for visual detection of malathion according to the change of fluorescence brightness and color. Finally, the approximate concentrations of malathion in cabbage samples were estimated by the standard arrays and naked eyes. The calibration curves were used for accurate detection in cabbage samples with recoveries of 89.9%-103.4% (fluorescence) and 88.7%-107.6% (colorimetric). The established sensor for visual malathion detection in cabbage was accurate with strong application potential, especially for rapid screening.

Stereoselective uptake and metabolism of prothioconazole caused oxidative stress in zebrafish (Danio rerio)

Prothioconazole (PTA) is a novel, broad-spectrum, chiral triazole fungicide that is mainly used to prevent and control the disease of cereal crops. However, the adverse effects of PTA and its major metabolite on nontarget organisms have aroused wide concern. In the present work, the acute toxic of the metabolite prothioconazole-desthio (PTA-desthio), with an LC₅₀ of 1.31 mg L^-1, was 3.5-fold more toxic than the parent compound, indicating that the metabolism of PTA in zebrafish was toxic. The stereoselective uptake and metabolism of PTA and PTA-desthio in zebrafish was firstly investigated using LC-MS/MS. Remarkable enantioselectivity was observed: S-PTA and S-PTA-desthio were preferentially uptake with the uptake rate constants of 8.22 and 8.15 d^-1 at exposure concentration of 0.5 mg L^-1, respectively, and the R-PTA-desthio were preferentially metabolized. PTA-desthio was rapidly formed during the uptake processes. The antioxidant enzyme activities in the zebrafish changed significantly, and these effects were reversible. A metabolic pathway including 13 phase I metabolites and 2 phase II metabolites was firstly proposed. A glucuronic acid conjugate and sulfate conjugate were observed in zebrafish. The results of this work provide information that highlights and can help mitigate the potential toxicity of PTA to the ecological environment and humans health.

Gold Nanorods as an Efficient Substrate for the Detection and Degradation of Pesticides

The rapid, ultralow detection, degradation, and complete removal of pesticides demand the design of potential substrates. Herein, we discussed gold nanorods (Au NRs) as the potential substrate for the naked eye detection and degradation of two common and broad-spectrum pesticides, chlorpyrifos (CPF) and malathion (MLT), up to 0.15 ppt concentration within 2 min. Under certain environmental conditions, both the pesticides degraded and adsorbed on the surface of Au NRs. The degraded moieties of CPF and MLT on the surface of Au NRs formed side-to-side and end-to-end interactions, respectively, leading to a long-range assembly. This shows that no external agent is required, and only CPF and MLT analytes are quite enough for the formation of assembly of Au NRs. Assembly of Au NRs is confirmed by transmission electron microscopy (TEM) analysis, and degradation is supported by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and gas chromatography-mass spectrometry (GC-MS) analyses. Au NRs were recovered and reused for four consecutive cycles. The fast and ultralow detection of pesticides demonstrates that Au NRs are a potential substrate for the detection and degradation of pesticides.

A magnetic multi-walled carbon nanotube preparative method for analyzing asymmetric carbon, phosphorus and sulfur atoms of chiral pesticide residues in Chinese herbals by chiral liquid chromatography-quadrupole/linear ion trap mass spectrometry determination

An analytical method for the determination of asymmetric carbon, phosphorus and sulfur atoms in chiral pesticide residues by magnetic multi-walled carbon nanotube sample pretreatment combined with chiral ultra-performance liquid chromatography/quadrupole/linear ion trap mass spectrometry (UPLC-MS/Qtrap) was developed and applied to chiral pesticide residues analysis in Chinese herbals. Eleven different chiral pesticides were found, and 36.4% were positive in Chinese herbals. Three plants containing detectable pesticide residues were observed in Dendrobium nobile, Panax notoginseng flowers and honeysuckle, in the order of decreasing detected concentration. High detection frequencies of 26.1% for (R/S)-(±)-difenoconazole and 14.5% for (R/S)-(±)-metalaxyl and (R/S)-(±)-propiconazole were observed, the residual amount for (R/S)-(±)-difenoconazole, (R/S)-(±)-metalaxyl and (R/S)-(±)-propiconazole were 0.32 ~ 2.5 mg/kg, 0.022 ~ 0.23 mg/kg, 0.62 ~ 3.21 mg/kg respectively. The EF value of (R/S)-(±)-difenoconazole was 0.506 ± 0.046. The EF value of (R/S)-(±)-metalaxyl was lower than 0.5 in Dendrobium nobile, Panax notoginseng flowers, Panax notoginseng roots and hawthorn. The EF of (R/S)-(±)-propiconazole was not significantly enantioselective in honeysuckle and Panax notoginseng flowers. The enantioselectivity of various pesticide residues in different plants cannot be predicted from our existing knowledge and may closely depend on plant growth, environmental conditions or molecular structure.

A comprehensive review on enzymatic degradation of the organophosphate pesticide malathion in the environment

A comprehensive review of available bioremediation technologies for the pesticide malathion is presented. This review article describes the usage and consequences of malathion in the environment, along with a critical discussion on modes of metabolism of malathion as a sole source of carbon, phosphorus, and sulfur for bacteria, and fungi along with the biochemical and molecular aspects involved in its biodegradation. Additionally, the recent approaches of genetic engineering are discussed for the manipulation of important enzymes and microorganisms for enhanced malathion degradation along with the challenges that lie ahead.

Enantioselective metabolism of four chiral triazole fungicides in rat liver microsomes

Triazole fungicides with one or two chiral centers are widely used worldwide. The liver microsomes plays a major role in the metabolism and systemic elimination of chiral pesticides after exposure. In this present work, enantioselective metabolism of four representative chiral triazole fungicides (prothioconazole, flutriafol, triticonazole, and epoxiconazole) in rat liver microsomes (RLM) was investigated using LC-MS/MS. Baseline separation of the four chiral fungicides and prothioconazole-desthio was achieved on Lux-cellulose-1. The results demonstrated that the R-enantiomers of flutriafol and triticonazole were preferentially metabolized with half-life ranged from 17.33 min to 99.00 min. The R,S-epoxiconazole accumulated with a half-life of 173.25 min. There was no stereoselectivity for prothioconazole. However, remarkable stereoselective metabolism was observed for prothioconazole-desthio. The results of enzyme kinetic revealed different affinities between the enantiomers and metabolic enzymes. In addition, homologous modeling and molecular docking results indicated that enantioselectivity were partially to enantiospecific binding affinities with CYP enzymes. This study highlights a new quantitative approach for stereoselective metabolism of chiral agrochemicals and provides more accurate data on risk assessment of triazole fungicides.

Application and enantioselective residue determination of chiral pesticide penconazole in grape, tea, aquatic vegetables and soil by ultra performance liquid chromatography-tandem mass spectrometry

Penconazole is a typical triazole fungicide with wide use on fruits, vegetables, and tea plants to control powdery mildew. In the present study, an efficient graphite carbon black solid phase extraction (GCB-SPE) purification combined with chiral ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed for determination of penconazole enantiomers in different complex matrices, including grape, tea, soil, lotus root, lotus leaf, lotus seed and hulls. The method was then applied to investigate the enantioselective dissipation of penconazole enantiomers in a real field experiment of grape and soil. As a result, a satisfactory separation of penconazole enantiomers on a chiral Lux Cellulose-2 column (150 mm × 2 mm i.d., 3 µm) was obtained with 0.1% formic acid in methanol and 10 mmol L^-1 ammonium acetate in water (75/25, v/v) as mobile phase at 0.25 mL min^-1. The enantiomer (+)-penconazole was firstly eluted, and (-)-penconazole was then eluted. The method showed reliable performances in linearity, recovery and precision, the recoveries of (+)-penconazole and (-)-penconazole in all of six matrices were between 70.5% and 121.0% with the relative standard deviations (RSDs) ranging from 0.8% to 23.6% at the low, medium and high spiked levels. The limits of quantitation (LOQs) of this method were lower than 0.0025 mg kg^-1 in grape, soil and lotus root, 0.005 mg kg^-1 in lotus leaf, lotus seed meat and lotus seed shell, and 0.0125 mg kg^-1 in tea. Results of field trials indicated that (-)-penconazole degraded faster than its (+)-isomer in grape. While only a moderate stereoselectivity was observed in soil, with (-)-penconazole preferential degraded. The proposed method could be used to investigate enantioselective environmental behavior of penconazole enantiomers in complex matrices. And results in this study could provide useful information on realistic risk assessment of penconazole in grape.

A novel spectral method for determination of trace malathion using EryB as light scattering probe by resonance Rayleigh scattering technique

A convenient and sensitive spectrophotometric methods was proposed for determination of Malathion (Mala) using Erythrosin B (EryB) as a probe through the Resonance Rayleigh scattering (RRS) technique. The interaction between EryB, Pd²⁺and malathion in the system was investigated by fluorescence, RRS and UV-Vis spectroscopy. Under the optimum conditions, the RRS intensity of EryB, Pd²⁺ and malathion was weak when exist in alone or any two kinds, however, the RRS intensity of the EryB-Pd²⁺-Mala system had an obvious enhancement due to Pd²⁺ could interact with the hydrolysis products of Mala and EryB each other form a new complexes. At the same time, the fluorescence intensity of EryB was decreased significantly in the presence of Pd²⁺, and the fluorescence intensity of EryB-Pd²⁺ system further decreased when Mala added, interestingly. So it was further proved that there was a forming complex in EryB-Pd²⁺-Mala system. Under the optimal conditions, the RRS enhanced intensity of the system was linearly proportional to the Mala's concentration in the range of 0.012-0.8 μg/mL, and the LOD was 1.7 ng/mL, with the correlation coefficient was R² = 0.9960. So, a new method for determination of Mala was established and this method has been demonstrated in real sample with satisfactory results.

Different Toxic Effects of Racemate, Enantiomers, and Metabolite of Malathion on HepG2 Cells Using High-Performance Liquid Chromatography-Quadrupole-Time-of-Flight-Based Metabolomics

Commercial malathion is a racemic mixture that contains two enantiomers, and malathion has adverse effects on mammals. However, whether these two enantiomers have different effects on animals remains unclear. In this study, we tested the effect of racemate, enantiomers, and metabolite of malathion on the metabolomics profile of HepG2 cells. HepG2 cells showed distinct metabolic profiles when treated with rac-malathion, malaoxon, R-(+)-malathion, and S-(-)-malathion, and these differences were attributed to pathways in amino acid metabolism, oxidative stress, and inflammatory response. In addition, malathion treatment caused changes in amino acid levels, antioxidant activity, and expression of inflammatory genes in HepG2 cells. S-(-)-Malathion exhibited stronger metabolic perturbation than its enantiomer and racemate, consistent with the high level of cytotoxicity of S-(-)malathion. R-(+)-Malathion treatment caused significant oxidative stress in HepG2 cells but induced a weaker disturbance in the amino acid metabolism and a pro-inflammatory response compared to S-(-)-malathion and rac-malathion. Malaoxon caused more significant perturbation on antioxidase and a stronger antiapoptosis effect than its parent malathion. Our results provide insight into the risk assessment of malathion enantiomers and metabolites. We also demonstrate that a metabolomics approach can identify the discrepancy of the toxic effects and underlying mechanisms for enantiomers and metabolites of chiral pesticides.

Stereoselective Analysis and Dissipation of Propiconazole in Wheat, Grapes, and Soil by Supercritical Fluid Chromatography-Tandem Mass Spectrometry

An efficient and sensitive chiral analytical method was established for the determination of propiconazole stereoisomers by supercritical fluid chromatography-tandem mass spectrometry (SFC-MS/MS). Stereoisomeric separation was performed on a Chiralpak AD-3 column with CO₂/ethanol (93:7) as the mobile phase. The four propiconazole stereoisomers were well separated in 4.7 min with resolutions above 2.0. The specificity, linearity, matrix effects, accuracy, precision, and stability of the developed method were evaluated. The stereoselective dissipation of propiconazole in wheat straw, grape, and soil samples was investigated according to the proposed method. The results indicated that significant stereoselective degradation occurred in wheat straw and grapes, with preferential degradation of (-)-propiconazole A and (+)-propiconazole B in wheat straw and the opposite case in grapes. No enantioselectivity was observed in soil, although diastereoisomer A degraded more rapidly than diastereoisomer B. These results could contribute to a more accurate assessment of the environmental risk and food safety of propiconazole.

Stereoselective toxicity of etoxazole to MCF-7 cells and its dissipation behavior in citrus and soil

The stereoselective cytotoxicity of new chiral acaricide etoxazole and its dissipation in citrus and soil were investigated for the first time. Enantioselective toxicity and oxidative stress of etoxazole toward MCF-7 cells was conducted. The phenomenon of dose- and form-dependent cytotoxicity was demonstrated by MTT and LDH assays, ROS generation, and SOD and CAT activity alternation. Cytotoxicity ranks were found to be consistent with oxidative damage as (R)- > Rac- > (S)-etoxazole. Moreover, the results of enantioselective degradation showed that (S)-etoxazole degraded faster than its antipode (R)-etoxazole. The gradual raise of EF values indicated the achievement of enantioselective degradation in citrus and soil, leaving the enrichment of (R)-etoxazole isomer. Significant differences of environmental behavior and cytotoxicity of etoxazole enantiomers were found in this study which provided valuable insight into the mechanism of potential toxicity and warranted more careful assessment of this pesticide before its agricultural application.

Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications

Mechanisms governing the enantioselectivity of the processes that determine the behavior of chiral pollutants in the environment need to be better understood. Understanding these mechanisms should help improve predictions of the hazards and risks chiral compounds can pose to people and the environment. We report the results of batch sorption experiments indicating that the sorption of the chiral fungicide metalaxyl on soil from non-racemic initial solutions was enantioselective. While from a racemic initial solution the two enantiomers of metalaxyl were sorbed on the soil to the same extent, increasing the fraction of R-enantiomer in the initial solution led to enhanced sorption of this enantiomer and to reduced sorption of the S-enantiomer. Considering the shape of the sorption isotherms (S-type) and the sorption behavior of model sorbents, we attributed this effect to molecular interactions between metalaxyl enantiomer species at the sorbed state, where R-R metalaxyl interactions appeared to be more favorable than R-S metalaxyl interactions. We discuss important environmental implications of the proposed mechanism, such as those related to the fact that the biological degradation of metalaxyl is known to be an enantioselective process that can yield non-racemic residues in soils shortly after application of the fungicide as a racemic mixture.

Chemoenzymatic Kinetic resolution of (R)-malathion in aqueous media

BACKGROUND

Malathion (R,S)-diethyl-2-[(dimethoxyphosphorothioyl)sulfanyl]butanedioate is a chiral organophosphorus compound used widely as pesticide for suppression of harmful insects such as mosquitoes. It is well known that in biological systems (R)-malathion is the active enantiomer, therefore a sustainable approach could be the use of only the biologically active enantiomer. The resolution of the commercial racemic mixture to obtain the pure active enantiomer combined with a recycling of the undesired enantiomer through a racemization process could be an attractive alternative to reduce the environmental impact of this pesticide. Thus, this work evaluates the use of four commercially available lipases for enantioselective hydrolysis and separation of malathion enantiomers from the commercial racemic mixture.

RESULTS

Several lipases were methodologically assessed, considering parameters such as enzyme concentration, temperature and reaction rates. Among them, Candida rugosa lipase exhibited the best performance, in terms of enantioselectivity, E = 185 (selective to the (S)-enantiomer). In this way, the desired unreacted (R)-enantiomer was recovered in a 49.42 % yield with an enantiomeric excess of 87 %. The monohydrolized (S)-enantiomer was recovered and racemized in basic media, followed by esterification to obtain the racemic malathion, which was recycled. In this way, an enantioenriched mixture of (R)-malathion was obtained with a conversion of 65.80 % considering the recycled (S)-enantiomer.

CONCLUSION

This work demonstrated the feasibility of exploiting Candida rugosa lipase to kinetically resolve racemic malathion through an environmentally friendly recycling of the undesired (S)-enantiomer. Graphical AbstractLipase catalyzed enantioselective resolution of (R)-malathion in aqueous solvent.

Study on the stereoselective degradation of three triazole fungicides in sediment

The stereoselective degradation behaviors of chiral triazole fungicides (hexaconazole, flutriafol and tebuconazole) in sediment were investigated under laboratory conditions. The enantiomers were completely separated by high-performance liquid chromatography on a cellulose tris(3-chloro-4-methylphenylcarbamate) (Lux Cellulose-2) column. The mean recoveries of hexaconazole, flutriafol and tebuconazole in sediment ranged from 86.7% to 105.9%. The methods were successfully applied for the enantioselective degradation analysis of fungicides in sediment. The results showed that the dissipation of hexaconazole, flutriafol and tebuconazole stereoisomers in sediment followed first-order kinetics (R(2)>0.95). The degradation rate of the enantiomers was different in sediment, and the (-)-enantiomer (t(1/2) was 86 days for hexaconazole, 139 for flutriafol and 136 for tebuconazole) degraded faster than the (+)-enantiomer (t(1/2) was 94 days for hexaconazole, 144 for flutriafol and 151 for tebuconazole) in native condition. The fungicides were degraded slowly, and no significant enantioselective degradation were observed under sterilized conditions. The results may hold promising implications for the environmental and ecological risk assessment of three important chiral triazole fungicides.

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.

Enantiomeric separation of indoxacarb on an amylose-based chiral stationary phase and its application in study of indoxacarb degradation in water

Direct semipreparative enantioseparation of indoxacarb was performed on a semipreparative Chiralpak IA column using normal-phase high-performance liquid chromatography (HPLC) with n-hexane-isopropanol-ethyl acetate (70:20:10) mixture as mobile phase. Degradation of indoxacarb (2.33S + 1R) and its two enantiopure isoforms in three aqueous buffer solutions and four water samples collected from natural water sources was then elucidated by HPLC analysis on Chiralpak IA column. Degradation of all three indoxacarbs complied with first-order kinetics and demonstrated linearity with regression coefficients R(2) > n0.88. Indoxacarb (2.33S + 1R) underwent enantioselective degradation in river water, rain water, and buffer solution of pH 7.0. Enantiopure S-(+)-indoxacarb and R-(-)-indoxacarb were both found to be configurationally stable in water.

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 degradation of metalaxyl in cucumber, cabbage, spinach and pakchoi

The enantioselective degradation behaviors of the acylamino acid fungicide metalaxyl in vegetables (cucumber, cabbage, spinach and pakchoi) under field and greenhouse conditions were elucidated by reversed-phase high-performance liquid chromatography (HPLC). A cellulose tris (3-chloro-4-methyl phenyl carbamate) chiral column (Lux Cellulose-2) was used for the chiral separation of the enantiomers using acetonitrile-0.1% formic acid solution (40:60, v/v) as mobile phase at a flow rate of 1.0 mL min(-1). The two enantiomers could be completely separated with a resolution (Rs) of 5.2. The linearity range, matrix effect, precision and recovery were evaluated. The method was successfully applied for the enantioselective analysis of metalaxyl in cucumber, cabbage, spinach and pakchoi under different conditions. The results showed that R-enantiomer dissipated faster than S-enantiomer in cucumber of greenhouse. Inversely, a preferential degradation of S-form was found in spinach and pakchoi under field and greenhouse conditions. No stereoselective degradation in cabbage was observed. These results can be applied for evaluating the environmental risk and food safety.

Bioactivity, toxicity and dissipation of hexaconazole enantiomers

In this study, the bioactivity, acute toxicity and dissipation in vegetables of the individual enantiomers of the fungicide hexaconazole had been investigated. The optical pure single enantiomers were prepared and the bioactivity of (+)-, (-)- and rac-hexaconazole was tested using four target fungi including Colletotrichum gloeosporioides Penz, Alternaria solani, Alternaria mali Roberts and Monilinia fructicola. The results showed (-)-hexaconazole was always more active than (+)-hexaconazole with the fungicidal activity 11–13-fold higher to A. solani, A. mali Roberts and Monilinia fructicola, and 1.26-fold higher to C. gloeosporioides Penz. (-)-Hexaconazole also showed 1.3-fold higher acute toxicity to aquatic species Daphnia magna based on the 48 h EC50 values. There was obvious enantioselectivity in the dissipation in tomato with (-)-hexaconazole degraded faster resulting an enrichment of (+)-form, and the half-lives of (-)-hexaconazole and (+)-hexaconazole in tomato were 2.96 d and 3.38 d respectively, while it was not enantioselective in green pepper, in which the both enantiomers had the half-lives about 4.36 d. The findings are helpful for better environmental and ecological risk assessment of hexaconazole on an enantiomeric level.