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

Quantitative assessment of selective degradation behavior of etoxazole in different classes of organisms by compound-specific isotope analysis

In this paper, the stereoselective degradation and quantitative identification of chiral pesticide etoxazole in organisms with different classes of organisms (soil, chlorella algal fluid and mice) were carried out by compound-specific isotope analysis (CSIA). The degradation behavior and stable isotope fractionation effect of etoxazole in soil, chlorella and mice were investigated. The R-etoxazole degraded faster than S-etoxazole in different classes of organisms. The metabolites M1, M2 and M3 were detected in all three substrates. Biodegradation is the main factor for the change of stable isotope ratio of chiral pesticide etoxazole. Furthermore, the relationship between fractionation value of carbon isotope and residual concentration of etoxazole is established by Rayleigh equation, and the biodegradation rate of etoxazole could be calculated by using CSIA without measuring the concentration of etoxazole. Therefore, the use of CSIA can accurately assess the degradation behavior of pesticide pollution in the environment and provide a certain scientific evidence and technical support in the process of environmental remediation.

Stereoselective behavior and residues of the imazalil during strawberry growth and strawberry wine production

Imazalil is a chiral fungicide widely used to protect strawberries against gray mold, which may pose threats to food safety. This study aims to investigate the stereoselective behavior of imazalil during strawberry growth and strawberry wine production. A method was proposed and validated for the extraction and quantitative analysis of imazalil residues in strawberry, strawberry pomace, and strawberry wine by using ultra-high performance liquid chromatography-tandem mass spectrometry. The method exhibited mean recoveries ranging from 86.2% to 119.7% with relative standard deviations of 0.1-11.3%. The dissipation curve of imazalil during strawberry growth followed the first-order kinetic model with a half-life ranging from 6.5 to 7.1 days. Significant enantioselectivity of imazalil was observed in strawberry grown under field conditions and strawberry wine production process, with enantiomeric fraction values ranging from 0.51 (2 h) to 0.42 (27d) and from 0.48 (0d) to 0.52 (10d), respectively. (+)-imazalil was preferentially degraded in strawberry under field conditions, while (-)-imazalil was preferentially degraded during the fermentation process. The processing factor was lower than 1 for each procedure, indicating that the wine-making process can reduce imazalil residue in strawberry. These findings may facilitate a more accurate risk assessment of imazalil and provide important guidance for the safe and efficacious use of imazalil in agriculture.

Risk assessment of oxidative stress and multiple toxicity induced by Etoxazole

Etoxazole is among the systemic pesticides with acaricidal and insecticidal characteristics. This paper reports the first evaluation of the toxic effects of Etoxazole on Allium cepa L. Etoxazole solutions were applied to three groups formed from A. cepa bulbs at 0.125 mL/L, 0.25 mL/L and 0.5 mL/L doses, respectively. The control group was treated with tap water throughout the experimental period. The toxic effects of Etoxazole became more apparent as the dose of Etoxazole was increased. The growth-limiting effect was most pronounced in the highest dose group with approximately 29%, 70% and 58.5% reductions in germination percentage, root elongation and weight gain, respectively. The genotoxic effect of Etoxazole was most severe in the 0.5 mL/L dose group. In this group, the mitotic index decreased by 30% compared to the control group, while the micronucleus frequency increased to 45.3 ± 3.74. The most observed aberrations were fragment, vagrant chromosome, sticky chromosome, unequal distribution of chromatin, bridge, reverse polarization and nucleus with vacuoles. The malondialdehyde level showed a gradual increase with increasing Etoxazole doses and reached 2.7 times that of the control group in the 0.5 mL/L Etoxazole applied group. Catalase and Superoxide dismutase activities increased in the groups exposed to 0.125 mL/L and 0.25 mL/L Etoxazole with dose dependence and decreased abruptly in the group treated with 0.5 mL/L Etoxazole. Etoxazole triggered meristematic cell damages, such as epidermis cell damage, thickening of cortex cell walls, flattened cell nucleus and indistinct transmission tissue. Considering the versatile toxicity induced by Etoxazole, we announce that this chemical has the potential to cause serious damage to non-target organisms. It should be noted that the higher the dose of exposure, the more severe the level of damage. This study will be an important reminder to limit the indiscriminate use of this highly risky agrochemical.

Determination of five pesticides in kumquat: Dissipation behaviors, residues and their health risk assessment under field conditions

The present study was carried out to profile the dissipation patterns and residues of five pesticides (triazophos, profenofos, chlorpyrifos, etoxazole and bifenthrin) on kumquat using QuEChERS method coupled with HPLC-MS/MS. The corresponding dietary health risks were also estimated. In the method validation, satisfactory results of good linearity (r2 ≥ 0.9956), sensitivity (limits of quantification ≤0.01 mg/kg), recoveries (71.0-95.7%) with relative standard deviations (0.70-9.4%) were obtained. The half-lives of the five pesticides in kumquat were 13.6-38.5 d under field conditions according to first-order kinetics. Based on the final residue experiment, dietary exposure risks of profenofos, chlorpyrifos, etoxazole and bifenthrin were all acceptably low, with RQc and RQa values of 0.00199-0.122 and 0.00145-0.200, respectively. However, exposure intake of triazophos posed unacceptable acute and chronic health risks for Chinese residents, especially for children with RQa and RQc up to 4.25 and 2.19. Forbidden use suggestion of triazophos and recommended MRLs of profenofos and bifenthrin were put forward in kumquat for safe production and consumption. This work was significant in providing guidance on appropriate application and MRL establishment of pesticides in kumquat.

Residues and Safety Evaluation of Etoxazole, Bifenazate and Its Metabolite Bifenazate-diazene in Citrus Under Open-Field Conditions

The residues of bifenazate (sum of bifenazate and bifenazate-diazene) and etoxazole in whole citrus and pulp collected from twelve regions of China were monitored and their chronic dietary risk to consumer were also evaluated. The citrus samples were extracted by a QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, and analyzed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The average recoveries of target compounds were ranged from 83 to 100% with relative standard deviations (RSDs) of 0.59-11.8%. The limits of quantification (LOQs) for three analytes were 0.01 mg/kg. At the interval to harvest of 20 and 30 days, the residues of total bifenazate and etoxazole were from below 0.02 to 0.26 mg/kg and from below 0.01 to 0.30 mg/kg in citrus samples. The chronic risk quotients (RQs) were below 100%, indicating no unacceptable risk to consumers.

Evaluation of exploitive potential for higher bioactivity and lower residue risk enantiomer of chiral fungicide pydiflumetofen

BACKGROUND

Pydiflumetofen, as a new succinate dehydrogenase inhibitor (SDHI) chiral fungicide, has been used in crop production because of its broad-spectrum and high-efficiency antifungal activity. However, little is known about pydiflumetofen at the chiral level. The stereoselective bioactivity and degradation of pydiflumetofen enantiomers were therefore investigated.

RESULTS

Pydiflumetofen presented effective bioactivity against the eight tested phytopathogens, and its enantiomers showed significant differences in activity. The bioactivity of R-pydiflumetofen was 9.0-958.8 times higher than that of the S enantiomer. Treatment with R-pydiflumetofen increased the cell membrane permeability of Sclerotinia sclerotiorum and decreased exopolysaccharide and oxalic acid production more than treatment with S-pydiflumetofen. Furthermore, R-pydflumetofen exhibited better inhibitory activity against the succinate dehydrogenase enzyme of S. sclerotiorum than S-pydiflumetofen by 584-fold. According to homology modeling and molecular docking studies, the binding affinities of the R and S enantiomers were -7.0 and -5.3 kcal mol^-1 , respectively. Additionally, the degradation half-lives of S- and R-pydiflumetofen in three vegetables (cucumber, eggplant, and cowpea) under field conditions were 2.56-3.12 days and 2.48-2.76 days, respectively, which reveals that R-pydiflumetofen degrades faster than S-pydiflumetofen.

CONCLUSION

Based on the results obtained, R-pydiflumetofen not only exhibited a higher bactericidal activity, but also posed fewer residual risks in the environment. The mechanism of the stereoselective bioactivity was correlated with the stereoselective inhibition activity of the target enzyme and affected the cell membrane permeability and the production of exopolysaccharide and oxalic acid. This research could provide a foundation for the systematic evaluation of pydiflumetofen from an enantiomeric view. © 2021 Society of Chemical Industry.

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.

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

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

Etoxazole stereoselective determination, bioaccumulation, and resulting oxidative stress in Danio rerio (zebrafish)

An environmentally-friendly and fast analytical method for the stereoselective determination of etoxazole was developed and then applied to estimate stereoselective bioaccumulation and elimination in zebrafish using SFC-MS/MS. Optimal enantioseparation conditions were determined using a Chiralpak IG-3 column and CO₂/MeOH mobile phase (80/20, v/v), at 3.0 mL/min within 1 min, 30°Me and 18 MPa. A modified QuEChERS method was developed for zebrafish sample pretreatment, and mean recoveries were 88.43-110.12% with relative standard deviations ranging from 0.32 to 5.34%. The enantioselectives of etoxazole enantiomers in zebrafish during uptake and depuration phases were evaluated. Significant enantioselective bioaccumulation was observed, with preferential accumulation of (-)-R-etoxazole compared to its antipode, during uptake at both low and high exposure concentrations. The toxic effects of etoxazole on zebrafish were further explored, and activities of antioxidant enzymes were determined in liver of zebrafish. Significant changes were observed in the SOD and GST activities and in the MDA levels, which indicated the occurrence of oxidative stress in liver of zebrafish. The toxic effects exhibited time- and dose-dependent properties. These results can facilitate the accurate risk evaluation of etoxazole and provide basic knowledge for further study of biotoxicity mechanisms.

The bioactivity of new chitin oligosaccharide dithiocarbamate derivatives evaluated against nematode disease (Meloidogyne incognita)

Plant-parasitic nematodes cause substantial crop losses annually; however, current nematicides are environmentally unfriendly and highly toxic to nontarget organisms. The development of green efficient nematicides from multifunctional natural bioactive substances such as chitin oligosaccharide (COS) is promising. In this paper, COS dithiocarbamate derivatives (COSDTC, COSDTA, COSDTB) were synthesized to increase nematicidal activity (against Meloidogyne incognita), and their structures were characterized by FTIR, NMR, TGA/DTG and elemental analysis. Furthermore, the nematicidal activities, egg hatching inhibitory activities, plant growth adjustment abilities, cytotoxicity and phytotoxicity of the derivatives were evaluated. The primary mechanism was assessed by heavy metal ion absorption and GSH-binding assays. The results showed COS dithiocarbamate derivatives could possess multiple efficacies, including high nematicidal activities and egg hatching inhibitory activities, plant growth regulating effects, low cell toxicities and phytotoxicities. Additionally, it was inferred that nematicidal activity may be correlated with GSH-binding activity but not heavy metal ion complexation. COS modification has immense potential for controlling plant-parasitic nematodes.

Residue, dissipation, and safety evaluation of etoxazole and pyridaben in Goji berry under open-field conditions in the China's Qinghai-Tibet Plateau

The dissipation and residual levels of etoxazole and pyridaben in Goji berry under open field conditions were determined by using GC-NPD (gas chromatography with nitrogen and phosphorus detector) with modified QuEChERS method. At fortification levels of 0.01, 1, and 5 mg/kg in Goji berry, it was shown that recoveries were ranged from 80.40 to 100.9% with relative standard deviation of the method (RSD) for repeatability ranged from 2.20 to 4.25%. The limit of quantification (LOQ) of the method was 0.01 mg/kg. The dissipation rates of etoxazole and pyridaben were described by using first-order kinetics and its half-life, as they are 7.13 days, 5.77 days, and 5.99 days (etoxazole) and 1.02 day, 0.67 day, 1.02 day (pyridaben). The terminal residues of etoxazole and pyridaben were below the European maximum residue limit (MRL, 0.1 mg/kg) in Goji berry when measured 7 days after the final application, which suggested that the use of these insecticides was safe for humans. This study would help in providing the basic information for developing regulation to guard a safe use of etoxazole and pyridaben in Goji berry and prevent health problem from consumers.

Investigation of etoxazole metabolites in citrus, soil and earthworms by ultra-performance liquid chromatography with time-of-flight mass spectrometry

Etoxazole is a newly registered and widely used acaricide. However, its metabolites were not fully understood and might exhibit similar or even higher toxicity than parent compound. Therefore, in this study, the metabolites of etoxazole in citrus, soil and earthworms were firstly identified by an ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QTOF/MS). Four potential metabolites in citrus, 11 in soil, and 8 in earthworms were determined. These metabolites were then further structural elucidated based on the fragment pathways, and accurate mass measurement. The distributions of etoxazole and its main metabolites (M1, M2, M3, M4 and M5) which were identified as the dehydrogenation, hydrolysis, oxidation products of etoxazole (M0) were also monitored in citrus, soil and earthworms at different exposure periods. The 45 days exposure experiment showed that M0 gradually decreased in citrus and soil samples by 80% and 28% of the initial amounts, respectively. In earthworm samples, M0 accumulated in the bodies of the worms during 24 days exposure and then decreased with time. The dissipation rate of etoxazole were citrus > earthworms > soil. Concentrations of M1 and M3 in soil were found continuously increased with time during the experimental period. Moreover, the persistence of M1 in earthworm samples was also observed. Great attention should be paid to these two compounds due to their potential risks to both environmental and human health.

Systemic Stereoselectivity Study of Etoxazole: Stereoselective Bioactivity, Acute Toxicity, and Environmental Behavior in Fruits and Soils

This is the first systemic assessment of the stereoselectivity of etoxazole enantiomers. Etoxazole's stereoselective bioactivity was assessed against target organisms ( Tetranychus urticae eggs and Tetranychus cinnabarinus eggs), and its acute toxicity was assessed toward nontarget aquatic organisms ( Daphnia magna and Danio rerio). Additionally, stereoselective elimination was investigated in three species of fruits (grape and strawberry grown in a greenhouse and apple grown in an open field) and in field soil. The ovicidal activity of (+)-( S)-etoxazole against Tetranychus urticae and Tetranychus cinnabarinus eggs was about 16 and 24 times higher, respectively, than that of (-)-( R)-etoxazole. Inconsistent order of etoxazole isomer toxicity was found toward different aquatic organisms: (+)-( S)-etoxazole showed nearly 8.7 times higher acute toxicity than (-)-( R)-etoxazole toward Daphnia magna, whereas (-)-( R)-etoxazole was ∼4.5 times more toxic to Danio rerio than (+)-( S)-etoxazole. Stereoselective degradation of etoxazole enantiomers showed significant variation in various fruits and field soil. The (+)-( S)-etoxazole was preferentially dissipated in grape and strawberry fruits grown under greenhouse condition, whereas (-)-( R)-etoxazole degraded faster than its antipode in apple fruits and soils under open-field condition. Overall, the stereoselectivity of etoxazole enantiomers should be fully considered in comprehensive environmental health risk in future work.