Residues and Dietary Risk Assessments of 2,4-D Isooctyl Ester, Metribuzin, Acetochlor, and 2-Ethyl-6-methylaniline in Corn or Soybean Fields

Enhanced Dechlorination of the Herbicide Acetochlor by an Anaerobic Consortium via Sulfate Acclimation

Acetochlor residues can contaminate anoxic habitats where anaerobic microbial transformation dominates. Herein, a highly efficient anaerobic acetochlor-degrading consortium ACT6 was enriched using sulfate and acetochlor as selection pressures. The acclimated consortium ACT6 showed an 8.7-fold increase in its ability to degrade acetochlor compared with the initial consortium ACT1. Two degradation pathways of acetochlor were found: reductive dechlorination and thiol-substitution dechlorination in the chloroacetyl group, in which the latter dominated. Acclimation enhanced the abundances of Desulfovibrio, Proteiniclasticum, and Lacrimispora from 0.7 to 28.0% (40-fold), 4.7 to 18.1% (4-fold), and 2.3 to 12.3% (5-fold), respectively, which were positively correlated with sulfate concentrations and acetochlor degradation ability. Three acetochlor-degrading anaerobes were isolated from the acclimated consortium ACT6, namely Cupidesulfovibrio sp. SRB-5, Proteiniclasticum sp. BAD-10, and Lacrimispora sp. BAD-7. This study provides new insights into the anaerobic catabolism of acetochlor and the anaerobic treatment of acetochlor in wastewater.

Determination of acetochlor by UPLC-MS3 in cells and its application to a cellular pharmacokinetic study

The aim of this work was to develop a fast, simple, and reliable UPLC-MS3 method for the sensitive detection of acetochlor in biological samples. In MS3 mode, the ion transition m/z 270.1 → 224.1→148.1 was chosen for quantification with butachlor as the internal standard. In the UPLC system, separation was performed on a UPLC column (2.1 × 50 mm ID, 1.7 μm) with 0.1 % FA in water and acetonitrile as mobile phases. After simple protein precipitation via acetonitrile, the method was well validated with good linearity (0.5-20 ng/mL, r > 0.995), accuracy (-3.70 %-2.98 %), and precision (<15 %). The selectivity and sensitivity were improved obviously in MS3 mode than that in MRM mode. The developed UPLC-MS3 method was successfully applied to the cellular pharmacokinetics study of acetochlor in MCF-7 cells.

Insights into the metabolic pathways and biodegradation mechanisms of chloroacetamide herbicides

Chloroacetamide herbicides are widely used around the world due to their high efficiency, resulting in increasing levels of their residues in the environment. Residual chloroacetamides and their metabolites have been frequently detected in soil, water and organisms and shown to have toxic effects on non-target organisms, posing a serious threat to the ecosystem. As such, rapid and efficient techniques that eliminate chloroacetamide residues from the ecosystem are urgently needed. Degradation of these herbicides in the environment mainly occurs through microbial metabolism. Microbial strains such as Acinetobacter baumannii DT, Bacillus altitudinis A16, Pseudomonas aeruginosa JD115, Sphingobium baderi DE-13, Catellibacterium caeni DCA-1, Stenotrophomonas acidaminiphila JS-1, Klebsiella variicola B2, and Paecilomyces marquandii can effectively degrade chloroacetamide herbicides. The degradation pathway of chloroacetamide herbicides in aerobic bacteria is mainly initiated by an N/C-dealkylation reaction, followed by aromatic ring hydroxylation and cleavage processes, whereas dechlorination is the initial reaction in anaerobic bacteria. The molecular mechanisms associated with bacterial degradation of chloroacetamide herbicides have been explored, with amidase, hydrolase, reductase, ferredoxin and cytochrome P450 oxygenase currently known to play a pivotal role in the catabolic pathways of chloroacetamides. The fungal pathway for the degradation of these herbicides is more complex with more diversified products, and the degradation enzymes and genes involved remain to be discovered. However, there are few reviews specifically summarizing the microbial degrading species and biochemical mechanisms of chloroacetamide herbicides. Here, we briefly summarize the latest progress resulting from research on microbial strain resources and enzymes involved in degradation of these herbicides and their corresponding genes. Furthermore, we explore the biochemical pathways and molecular mechanisms for biodegradation of chloroacetamide herbicides in depth, thereby providing a reference for further research on the bioremediation of such herbicides.

Residue analysis, dissipation patterns of chlorfenapyr, diafenthiuron and their corresponding metabolites in tea trees, and dietary intake risk assessment

BACKGROUND

Recently, chlorfenapyr and diafenthiuron have been widely used to prevent and control diseases and pests in tea production. However, rare studies have investigated the dissipation patterns of chlorfenapyr, diafenthiuron and their metabolites simultaneously in tea matrices. Here, we established an analytical method to investigate the degradation patterns of five target compounds in tea shoots and made tea samples. Moreover, the dietary intake risk assessment of chlorfenapyr-diafenthiuron mixture among Chinese populations was evaluated based on the supervised field experiment.

RESULTS

The mean recoveries of the primary analytes at five spiking levels were between 95.6% and 112.6% in tea shoots and made tea, respectively, and the values of RSD (relative standard deviation) were lower than 9.7% for all the target analytes. The field trial results showed that the half-lives of chlorfenapyr and diafenthiuron based on the residue definition were 10.0-12.4 days and 4.3-5.9 days, respectively, in tea shoots. For the dietary intake risk assessment, the risk quotient (RQ) values in made tea ranged from 30.4% to 73.9% at the pre-harvest interval of 14 days, which were significantly less than 100%.

CONCLUSION

The accuracy and precision of the developed method were satisfied by the measurement requirements according to the validation results. The dynamic dissipation experiments suggested that diafenthiuron was much easier to dissipate than chlorfenapyr. Moreover, the existence of tralopyril made the half-life of chlorfenapyr significantly increase, indicating that practical application of chlorfenapyr should take careful consideration of its metabolite. Finally, the potential chronic dietary risks of the chlorfenapyr-diafenthiuron mixture to human communities were within the acceptable range. © 2022 Society of Chemical Industry.

Dissipation, Residue, and Dietary Risk Assessment of Bifenthrin, Bifenazate, and Its Metabolite Bifenazate-Diazene in Apples Based on Deterministic and Probabilistic Methods

A rapid, sensitive, and effective multiresidue analytical method was established to investigate the degradation rate and final residues of bifenthrin, bifenazate, and its metabolite bifenazate-diazene in apples, and the dietary risk of consumers was evaluated. The residues of bifenthrin, bifenazate, and bifenazate-diazene in apple samples from 12 different apple-producing areas of China were determined by high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS). The average recoveries of the three compounds in apples were 88.4-104.6%, and the relative standard deviations (RSDs) were 1.3-10.5%. The limit of quantification (LOQ) for each compound was 0.01 mg/kg. Although the degradation half-lives of bifenthrin, bifenazate, and bifenazate-diazene were 17.8-28.9, 4.3-7.8, and 5.0-5.8 days, under good agricultural practice (GAP) conditions, the final residues of bifenthrin, bifenazate, and the sum of bifenazate and its metabolite bifenazate-diazene in apples were <0.01-0.049, < 0.01-0.027, and <0.02-0.056 mg/kg, respectively, which were lower than the maximum residue limit (MRL) in China. By comparing the deterministic model with the probabilistic model, the results of the probabilistic model at the P95 level (12.91-48.9% for bifenthrin, 17.48-52.01% for bifenazate including its metabolite) were selected as reasonable assessment criteria for chronic dietary risk, and the acute risk was at the P99.9 level (3.00-15.59% for bifenthrin). Although the exposure risk calculated by both the deterministic model and the probabilistic model was less than 100%, the risk to children is significantly higher than that of the general population. This suggests that in future research and policy making, we should pay more attention to the risk of vulnerable groups such as children.

Residual levels and dietary risk assessment of bifenthrin and dinotefuran and its major metabolites in open wheat field conditions

To evaluate the residual levels of bifenthrin and dinotefuran, a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS) and high-performance liquid chromatography-tandem mass spectrometry method for simultaneous detection of bifenthrin and dinotefuran and its major metabolites in wheat was developed and validated. Dietary risk assessments were further performed based on the relevant residual data from 12 wheat fields, toxicology data and dietary patterns. In wheat grain and straw, the recoveries of all analytes ranged from 77 to 102% with the relative standard deviation <9.7% and the limit of quantitation 0.05 mg kg^-1 . The highest terminal residue of bifenthrin in wheat grain was 0.069 mg kg^-1 and dinotefuran was 0.34 mg kg^-1 . Residual concentrations of bifenthrin and dinotefuran decreased to <0.05 and 0.15 mg kg^-1 at 21 days (pre-harvest interval), respectively. The chronic risk quotient ranged from 6.4 to 62.7% and the acute risk quotient varied from 0.38 to 17.73%. The chronic and acute dietary risks caused by the terminal residues of the two insecticides were negligible for Chinese populations. The recommended pre-harvest interval was proposed to ensure safe wheat consumption. These data could provide a scientific reference to establish the Chinese maximum residue limit of dinotefuran in wheat.

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.

Dynamics and risk assessment of pesticides in cucumber through field experiments and model simulation

Pesticides are often applied multiple times during cucumber cultivation in China. In order to obtain the residue concentrations and subsequently human health risk assessment after pesticide multiple applications, plenty of field trials have been conducted, consuming a lot of labor force and funds. The application of kinetic models can address this problem to some extent by predicting the residue values of pesticides in cucumber. In this study, a dynamic model (dynamiCROP) was applied in combination with field experiments to investigate the distribution, translocation, and dissipation after the one-time application of seven pesticides in a cucumber-soil environment. Moreover, the residue concentrations after the second and third applications of the seven pesticides were estimated through a "simple superposition method", i.e., superimposing the output results of dynamiCROP after each single pesticide application. The estimated residue concentrations show good agreement with that measured through field experiments with R² = 0.865 and relative root mean squared error (RRMSE) = 13.2%. Meanwhile, the short- and long-term risks of each pesticide were assessed according to the concentrations estimated by the "simple superposition method" with the dynamiCROP model. It shows that the seven pesticides, applied multiple times during cucumber cultivation, pose a very low dietary risk to human health through cucumber intake. Our study presents a cost- and time-efficient way to investigate the dissipation of pesticides in the cucumber-soil environment, predicate the residue concentrations of pesticides after multiple applications and assess the dietary risk of pesticides to human health through cucumber intake.