Dissipation Behavior and Acute Dietary Risk Assessment of Thiamethoxam and Its Metabolite Clothianidin on Spinach

Microbial degradation mechanism and pathway of the insecticide thiamethoxam by isolated Bacillus Cereus from activated sludge

The high water solubility and ecotoxicity of thiamethoxam (TMX) is a potential hazard to ecosystems and human health. Here, a strain of Bacillus cereus with high TMX degradation activity was isolated from the sediment of the A2O process in the wastewater treatment plant and was able to utilize TMX as its sole carbon source. Under different environmental conditions, the degradation efficiency of TMX by Bacillus cereus-S1 (strain S1) ranged from 41.0% to 68.9% after 216 h. The optimum degradation conditions were DO = 3.5 mg/L and pH 9.0. The addition of an appropriate carbon-to-nitrogen ratio could accelerate the degradation of TMX. A plausible biodegradation pathway has been proposed based on the identified metabolites and their corresponding degradation pathways. TMX can be directly converted into Clothianidin (CLO), TMX-dm-hydroxyl and TMX-Urea by a series of reactions such as demethylation, oxadiazine ring cleavage and C=N substitution by hydroxy group. The main products were TMX-dm-hydroxyl and TMX-Urea, the amount of CLO production is relatively small. This study aims to provide a new approach for efficient degradation of TMX; furthermore, strain S1 is a promising biological source for in situ remediation of TMX contamination.

Dissipation, Processing Factors and Dietary Exposure Assessment of Myclobutanil in Tomato

Myclobutanil residue poses a potential threat to consumers' health. This work aims to investigate the degradation behavior, residue levels, processing factors (PFs) and dietary risk of myclobutanil in tomato. Myclobutanil was analyzed using a modified quick, easy, cheap, effective, rugged, safe (QuEChERS) method combined with ultra-performance liquid chromatography-mass spectrometry (UPLC-MS/MS), and average recoveries ranged from 82% to 102% with relative standard deviations RSDs ≤ 9.1%. After spraying myclobutanil miscible oil under field conditions, the initial concentration of myclobutanil was 0.055 mg/kg, and its dissipation followed the first-order kinetics equation with a half-life of 2.88 days. Myclobutanil was mainly present in the tomato skin, and its concentration was about four times that in the whole tomato. The initial concentration of myclobutanil in raw tomato was 0.100 mg/kg. After washing, peeling, homogenization, simmering and canning, the residual level of myclobutanil decreased to 0.067 mg/kg, 0.023 mg/kg, 0.013 mg/kg, 0.044 mg/kg and 0.041 mg/kg, respectively. Although the procedure of simmering led to an increase in myclobutanil concentration, the PFs were all less than 1 in the whole process, showing that the processing procedure significantly decreased the residual level of myclobutanil canned tomato paste in comparison with the raw agricultural commodity. Washing, peeling, and homogenization played critical roles in reducing pesticide residues. The residues of myclobutanil during the processing of tomato pose low dietary exposure risks to consumers in China, which were acceptable. However, the acute and chronic risk quotient for children revealed that it was necessary to monitor the dietary exposure of pesticide residues for children closely.

Translocation and dissipation of thiamethoxam applied by root irrigation in tomato plant-soil system

Thiamethoxam (TMX) has been registered for use on a wide range of crops due to its versatile application methods, however, there is limited literature evaluating the residue behaviors of TMX applied through root irrigation. In this study, the uptake and translocation of TMX, its degradation to clothianidin (CLO), and dissipation in the tomato plant-soil system were conducted. TMX applied by root irrigation was transferable within the tomato plant, including stems, leaves, and fruits at different heights. TMX concentrations in the four sections of stems were ordered as Clower > Cmid > Cupper > Ctop, while in the leaves were ordered as Ctop > Cupper > Cmid > Clower. The degradation product CLO was detected in the tomato plant, and concentrations of CLO were even higher than those of TMX in the leaves. The translocation factor (TF) of TMX in the same section generally followed the order of TFleaf > TFstem > TFfruit. Residues of TMX and CLO in tomato on 7 days after application were below maximum residue limits (MRLs) in China and Codex Alimentarius Commission (CAC). This study promotes the evaluation of TMX applied through root irrigation for use in the tomato system from a dietary safety perspective.

Determination of thiamethoxam residues and dissipation kinetic in tomato plants and its efficacy against Bemisia tabaci under open field eco system

Whitefly, Bemisia tabaci cause important losses for many crops especially tomato, therefore farmers often use many chemical insecticides which had dangerous side effects on human beings and environment, thus there are need to determine the residues of these chemicals in plant . The dissipation of thiamethoxam in tomato leaves and fruits followed the first order kinetics; Half-lives were 2.91 and 3.15 days for fruits and leaves, respectively. The residues of thiamethoxam were determined using a QuEChERS method with HPLC-DAD and it was 0.14 mg/ kg in fruits after 7 days of treatment and less than the maximum residue limit (MRL 0.2 mg/kg. The residue in leaves was more than in fruits. Seedlings produced from treated seeds were more resistant to different stages of the whitefly population and protect tomato plants from whitefly infestation for 6-10 weeks after transplanting. The three sprays of thiamethoxam increased the reduction percentage of B. tabaci stages and the highest increase was recorded after the third spray in egg, nymph, and adult stages. It could be recommend that Thiamethoxam is considered an unconventional insecticide appropriate for B. tabaci control and safe for humans and the environment.

Dissipation and Residue of Metalaxyl-M and Azoxystrobin in Scallions and Cumulative Risk Assessment of Dietary Exposure to Hepatotoxicity

Metalaxyl-M and azoxystrobin have been used to control various fungal diseases on scallion and other crops. In view of the adverse toxic effects of both on the mammalian liver, it is necessary to conduct a cumulative risk assessment of their dietary exposure to consumers. The residues of metalaxyl-M and azoxystrobin on scallion were determined by a quick, easy, cheap, effective, rugged, and safe method (QuEChERS) combined with high-performance liquid chromatography tandem mass spectrometry (LC-MS/MS). The half-lives were about 1.15 and 3.89 days, respectively, and the final residues after a seven-day harvest interval were <0.001−0.088 mg/kg and 0.190−4.687 mg/kg, respectively. The cumulative dietary risk quotient of the two fungicides to Chinese consumers calculated by the probability model is 13.94%~41.25%. According to the results of the contribution analysis, the risk posed by azoxystrobin is much greater than that of metalaxyl-M. Although metalaxyl-M and azoxystrobin do not pose a cumulative risk to Chinese consumers, the risk to children and adolescents is significantly higher than that to adults. This suggests that in future research, more consideration should be given to the cumulative risk of compounds to vulnerable groups.