Uptake, translocation, and metabolism of thiamethoxam in soil by leek plants

Translocation, subcellular distribution, and safety assessment of chlorfenapyr (CFP) and its metabolite tralopyril (TLP) in soil-cultivated cherry radish

Chlorfenapyr is a frequently used insecticide in vegetables, and understanding its translocation and distribution are important for determining the residues and dietary safety in these crops. In this paper, we studied the translocation, subcellular distribution, and dissipation of chlorfenapyr and tralopyril in soil-cultivated cherry radish. Both upward and downward translocations were observed for the analytes, although the extent was limited, as indicated by the bioconcentration and translocation factors (both <1). The analytes were primarily accumulated in the cell walls. Chlorfenapyr dissipated rapidly with half-lives of 5.90-7.10 d. Tralopyril can prolonged the dissipation rate of chlorfenapyr due to the total chlorfenapyr's half-lives of 7.20-9.46 d. The dietary risk for consumers can be neglected, when the sampling interval was 10 d. This study provided additional information on the translocation, distribution, and application method of chlorfenapyr in cherry radish and assessed the potential threats of chlorfenapyr to human health.

Pesticide Residue Detection Using Grating Spectroscope and GWO-CNN-BiLSTM Method

Pesticide residues represent a globally significant issue due to their high toxicity and broad dissemination. Thiamethoxam (TMX), commonly applied during the cultivation of vegetables like spinach, has its principal metabolite, clothianidin, which can accumulate in crops, posing significant long-term dietary risks. To accurately detect TMX residues in spinach, this study developed a portable detection device integrating a grating spectrometer (GS) with a smartphone and introduced image processing techniques alongside deep learning detection methods. This method employs a ResNet50 model enhanced by Squeeze-and-Excitation Networks (SE) attention mechanism to extract key features, which are subsequently input into a hybrid model combining a convolutional neural network (CNN) and a bidirectional long short-term memory (BiLSTM) network, optimized using the gray wolf optimization (GWO) algorithm. The results demonstrate that the method achieves a root mean square error (RMSE) of approximately 0.220, a mean absolute error (MAE) of about 0.060, a mean bias error (MBE) of about 0.002, and a coefficient of determination (R2) of approximately 0.960. The R2 increased by 0.049 compared to pre-optimization values and by 0.060 relative to the top traditional machine learning models, thereby enhancing the precision of detection. This technology promises to be a vital tool in the field of pesticide residue detection, offering robust support for ensuring food safety and public health.

Metabolic mechanism, responses, and functions of genes HDH1, HDH3, and GST1 of tea (Camellia sinensis L.) to the insecticide thiamethoxam

Misuse of insecticides such as thiamethoxam (TMX) not only affects the quality of tea but also leaves residues in tea. Therefore, exploring the metabolic mechanisms of TMX in tea plants can evaluate effects of pesticides on the environment and human health. Here, effects of TMX on tea plants were studied. Malondialdehyde (MDA) content reached a maximum of 12.59 nmol/g fresh weight (FW) on 1st d under X (the recommended dose: 0.015 kg a.i./ha) of TMX. Under 2 X (0.03 kg a.i./ha), the catalase, glutathione S-transferase and superoxide dismutase activity were increased by 45.0 %, 55.5 %, and 49.7 % at 7 d respectively. Metabolomic and transcriptomic analyses revealed that TMX significantly affected amino acid metabolism, flavonoid biosynthesis and glutathione metabolism, and induced the expression of 3-hydroxyisobutyric acid dehydrogenase genes (CsHDH1 and CsHDH3) and glutathione S-transferase gene (CsGST1). The three genes were transiently expressed in Nicotiana benthamiana for the first time to verify the function of TMX degradation, with the degradation rate of 59.2 %-85.3 % at X. This study elucidated the response of tea plants to abiotic stress on the molecular-scale perspective, and the molecular approaches could serve as a model for the study on pesticide metabolism in plants. SYNOPSIS: Degradation ability of CsHDH1, CsHDH3 and CsGST1 genes to thiamethoxam was verified for the first time, providing genetic resources for phytoremediation of pollutants.

Efficacy of salicylic acid (SA) in modulating the dynamics of pesticide-thiamethoxam-induced stress responses in Brassica juncea L. insights from biochemical and molecular dissection

The present study uncovers the impacts of pesticide-thiamethoxam (TMX- 750 mg L-1) and salicylic acid (SA- 0.01, 0.1 and 1 mM) in Brassica juncea L. TMX poisoning exacerbates the nuclear and membrane damage, whereas an increment in the oxidative stress markers like hydrogen peroxide (H2O2), superoxide anions (O2-) and malondialdehyde (MDA) contents has been observed. The significance of phytohormone SA in mitigating TMX toxicity by enhancing the growth, and antioxidant capacities of B. juncea seedlings is not well documented. Salicylic acid priming to these TMX-exposed seedlings maximizes the germination potential by 34%, and root, shoot length by 86.9% and 41.5%, whereas, minimizing the levels of oxidative stress indicators such as H2O2 by 34.8%, O2- by 26.9% and amounts of MDA by 45.6% and EL (electrolyte leakage) contents by 22.7% under 1 mM of SA. Also, an increment in the activity of enzymatic antioxidants like superoxide dismutase (SOD), ascorbate peroxidase (APOX), glutathione peroxidase (GPOX), dehydroascorbate reductase (DHAR), glutathione reductase (GR), peroxidase (POD), and catalase (CAT) by 122.1%, 186%, 39%, 82.61%, 40.02%, 75.6% and 59.5% was observed when TMX exposed seeds were supplemented with the highest SA (1 mM) concentration. Whereas, an upregulation in the gene expressions of enzymatic antioxidants was assessed as well as a swift decrease in the RBOH1 (respiratory burst oxidase1) gene expression was observed under the subsequent SA supplementation. Thus, the results effectively address the ameliorative potentials of exogenously applied SA in order to maximize the growth and development, by mediating osmotic adjustments, and antioxidant potentials in B. juncea L.

Uptake kinetics and distribution of flupyrimin by rice (Oryza sativa L.): Effects of subcellular fractionation and soil factors

Flupyrimin is an emerging neonicotinoid insecticide primarily used to control rice planthoppers. However, knowledge gaps exist regarding its uptake and transport in rice planting systems. Elucidating the absorption and distribution properties of flupyrimin in rice will help assess the potential risks of human exposure to flupyrimin via the food chain. Here, we studied the uptake kinetics and transport mechanisms of flupyrimin in rice plants grown under hydroponic and soil conditions. The hydroponic experiment indicated that flupyrimin was easily taken up by rice roots via a symplastic passive diffusion process and was mainly distributed in the cell soluble fractions (50.6 %－88.0 %). Compared with transportation from the roots to the stems, flupyrimin was ultimately transported from the stems to the leaves with a greater translocation factor (TF) (TFLeave/Stem = 27.8 > TFStem/Root = 3.1). In rice-soil systems, the accumulation of flupyrimin by rice plants is influenced primarily by the soil organic matter content, which leads to increased adsorption of flupyrimin onto soils (R2 > 0.897, P < 0.014). Interestingly, the concentration of flupyrimin in rice was significantly positively correlated with its amount in the soil pore water (CIPW) (R2 > 0.967, P < 0.003), indicating that the uptake and accumulation of flupyrimin in rice planting systems can be estimated by CIPW. These findings enhance our knowledge of flupyrimin absorption and distribution in rice plants from treated soils and are important for guiding its field application and conducting environmental risk assessments.

Accumulation, translocation, metabolism and subcellular distribution of mandipropamid in cherry radish: A comparative study under hydroponic and soil-cultivated conditions

The accumulation and transportation of pesticides in plants can provide valuable insights to assess potential risks and ensure food safety. The uptake and downward translocation of mandipropamid were examined in hydroponic and soil-cultivated cherry radishes. The uptake of mandipropamid in cherry radish was rapid (bioconcentration factors of 1.1-10.7), whereas the downward translocation was limited (translocation factors of 0.1-0.9). The subcellular distribution results indicated a predominant accumulation in solid fractions of cherry radish (proportions of 52.9-98.7%), potentially because of the hydrophobicity (log Kow of 3.2) of mandipropamid. Owing to the decrease in half-life (>10%), the cultivation of cherry radish enhanced the dissipation of mandipropamid in both nutrient solutions (without stereoselectivity) and soils (with stereoselectivity). In addition, eleven metabolites and three pathways are proposed. This study provides valuable insights for the varying extent of translocation and proper utilization and safety evaluation of mandipropamid in crops.

Comparative uptake, translocation and metabolism of phenamacril in crops under hydroponic and soil cultivation conditions

Many studies investigate the plant uptake and metabolism of xenobiotics by hydroponic experiments, however, plants grown in different conditions (hydroponic vs. soil) may result in different behaviors. To explore the potential differences, a comparative study on the uptake, translocation and metabolism of the fungicide phenamacril in crops (wheat/rice) under hydroponic and soil cultivation conditions was conducted. During 7-14 days of exposure, the translocation factors (TFs) of phenamacril were greatly overestimated in hydroponic-wheat (3.6-5.2) than those in soil-wheat systems (1.1-2.0), with up to 3.3 times of difference between the two cultivation systems, implying it should be cautious to extrapolate the results obtained from hydroponic to field conditions. M-144 was formed in soil pore water (19.1-29.9 μg/L) in soil-wheat systems but not in the hydroponic solution in hydroponics; M-232 was only formed in wheat shoots (89.7-103.0 μg/kg) under soil cultivation conditions, however, it was detected in hydroponic solution (20.1-21.2 μg/L), wheat roots (146.8-166.0 μg/kg), and shoots (239.2-348.1 μg/kg) under hydroponic conditions. The root concentration factors (RCFs) and TFs of phenamacril in rice were up to 2.4 and 3.6 times higher than that in wheat for 28 days of the hydroponic exposure, respectively. These results highlighted that cultivation conditions and plant species could influence the fate of pesticides in crops, which should be considered to better assess the potential accumulation and transformation of pesticides in crops.

Insight into the uptake, translocation, metabolism, dissipation and risk assessment of tolfenpyrad in romaine and edible amaranth grown in hydroponic conditions

Tolfenpyrad is an alternative to highly water-soluble and ecotoxic insecticides that is widely used in China. It is absorbed and accumulates in vegetables, leading to potential public-health hazards. A systematic study of the fate of tolfenpyrad is necessary for proper application and food safety. Herein, we report on the uptake, translocation, metabolism, dissipation, and dietary risks of tolfenpyrad in hydroponic romaine and amaranth plants. Roots easily absorbed and accumulated tolfenpyrad, although transport was moderate in both vegetables. Basipetal translocation of tolfenpyrad occurred in romaine but not in edible amaranth, owing to differences in specific transport behaviour in each case. Six metabolites and three pathways were proposed. Tolfenpyrad affected antioxidant enzyme activities in different parts of the two vegetables. Tolfenpyrad dissipation proceeded swiftly, entailing an acceptable risk to humans. Our results provide information on the distribution and transport of tolfenpyrad, as well as on the safety in using it on vegetables.

Comprehensive metabolome and growth effects of thiamethoxam uptake and accumulation from soil on pak choi

Extensive use of the neonicotinoid thiamethoxam (TMX) results in its deposition in soil, which can then be absorbed and translocated in vegetables. Here we analyzed the comprehensive effects of TMX on pak choi. The TMX translocation factor (TF) was 0.37-11.65 and 0.46-39.75 for low and high treatments over 28 d, respectively, indicating its ready ability to move from the roots to the leaves of these plants. This uptake was associated with significant decrease in the fresh weight, and increase in vitamin C (VC), soluble sugars and soluble solid of pak choi. A metabolomic analysis revealed that fatty acids and purine nucleosides significantly decreased, and flavonoids and carbohydrates increased in the presence of TMX. TMX exposure thus influenced plant growth and disrupted the carbohydrate and lipid metabolism pathways. Our study raises concerns for food safety risk associated with TMX-contaminated soil.

Efficacy of drip irrigation with thiamethoxam on control of Monolepta hieroglyphica, and uptake, translocation and dietary risk of thiamethoxam in maize

BACKGROUND

Monolepta hieroglyphica (Motschulsky) is an important agricultural pest that causes significant economic losses in terms of crop production. Conventional pesticide spraying treatments can result in pesticide drift, endanger nontarget organisms and cause pests to fly away, resulting in unsatisfactory prevention and control effects. To study the effect of thiamethoxam on the control of maize M. hieroglyphica, a field experiment was conducted to determine the optimal thiamethoxam application dose, its spatial and temporal distribution dynamics, and its dietary risk based on its control effect when applied by spray and drip irrigation.

RESULTS

The results of the field trials showed that compared with spray irrigation, drip irrigation resulted in greater control starting from Day 5. This result was a consequence of the hysteresis effect of thiamethoxam being first absorbed by the roots and then continuously transferred upward, where it accumulates. After 30 days of drip irrigation with 75 and 150 g a.i. ha-1 thiamethoxam, the control effect on M. hieroglyphica was 32.41-49.44% and 69.77-80.57%, respectively. The results of the dietary risk assessment showed that the risk of thiamethoxam ingestion through maize kernels was acceptable regarding its effect on human health.

CONCLUSIONS

Drip irrigation with thiamethoxam can improve the effective utilization rate of pesticides, achieve precise control of maize M. hieroglyphica, and provide a new method for sustainable agricultural production. © 2023 Society of Chemical Industry.

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.

Potential Toxic Mechanisms of Neonicotinoid Insecticides in Rice: Inhibiting Auxin-Mediated Signal Transduction

Inappropriate application of pesticides not only causes sub-lethal effects on ecosystem service providers but also reduces crop yield and quality. As a xenobiotic signal molecule, pesticides may interact with signal transduction receptors in crops, resulting in oxidative damage and even metabolic perturbations. We discovered that three neonicotinoid insecticides (NIs), namely, imidacloprid, thiamethoxam, and clothianidin, at 0.06-0.12 kg ai/ha significantly inhibited the auxin signal pathway in rice leaves, thereby reducing the intracellular auxin (IAA) content. Molecular simulation further confirmed that NIs occupied the binding site where auxin transporter-like proteins 1 (LAX11) and 2 (LAX12), in which Thr253 and Asn66 of LAX11, as well as Thr244 and Asn57 of LAX12, were bound to the nitroguanidine of NIs via H-bonds. Meanwhile, Asn66 of LAX11 and Asn57 of LAX12 interacted with nitroguanidine via aromatic H-bonds. Moreover, phenylpropanoid biosynthesis was significantly disturbed because of the inhibited auxin signal pathway. Notably, peroxidase-coding genes were downregulated with a maximum value greater than 10-fold, resulting in decreased antioxidant metabolites flavone (37.82%) and lignin content (20.15%). Ultimately, rice biomass was reduced by up to 25.41% due to the decline in IAA content and antioxidant capacity. This study deeply explored the molecular mechanism of metabolic perturbations in crops stressed by pesticides, thus providing a scientific basis for pesticide environmental risk assessment and agricultural product safety.

Photocatalytic Removal of Thiamethoxam and Flonicamid Pesticides Present in Agro-Industrial Water Effluents

Pesticide residues, when present in agricultural wastewater, constitute a potential risk for the environment and human health. Hence, focused actions for their abatement are of high priority for both the industrial sectors and national authorities. This work evaluates the effectiveness of the photocatalytic process to decompose two frequently detected pesticides in the water effluents of the fruit industry: thiamethoxam-a neonicotinoid compound and flonicamid-a pyridine derivative. Their photocatalytic degradation and mineralization were evaluated in a lab-scale photocatalytic batch reactor under UV-A illumination with the commercial photocatalyst Evonik P25 TiO2 by employing different experimental conditions. The complete degradation of thiamethoxam was achieved after 90 min, when the medium was adjusted to natural or alkaline pH. Flonicamid was proven to be a more recalcitrant substance and the removal efficiency reached ~50% at the same conditions, although the degradation overpassed 75% in the acidic pH medium. Overall, the pesticides’ degradation follows the photocatalytic reduction pathways, where positive charged holes and hydroxyl radicals dominate as reactive species, with complete mineralization taking place after 4 h, regardless of the pH medium. Moreover, it was deduced that the pesticides’ degradation kinetics followed the Langmuir-Hinshelwood (L-H) model, and the apparent rate constant, the initial degradation rate, as well as the L-H model parameters, were determined for both pesticides.

Enhanced biodegradation of thiamethoxam with a novel polyvinyl alcohol (PVA)/sodium alginate (SA)/biochar immobilized Chryseobacterium sp H5

Long-term and extensive usage of thiamethoxam, the second-generation neonicotinoid insecticide, has caused a serious threat to non-target organisms and ecological security. Efficient immobilized microorganism techniques are a sustainable solution for bioremediation of thiamethoxam contamination. A Gram-negative aerobic bacterium Chryseobacterium sp H5 with high thiamethoxam-degrading efficiencies was isolated from activated sludge. Then we developed a novel polyvinyl alcohol (PVA)/sodium alginate (SA)/biochar bead with this functional microbe immobilization to enhance the biodegradation and removal of thiamethoxam. Results indicated that the total removal and biodegradation rate of thiamethoxam with PVA/SA/biochar (0.7 %) beads with Chryseobacterium sp H5 immobilization at 30 °C and pH of 7.0 within 7 d reached about 90.47 % and 68.03 %, respectively, much higher than that using PVA/SA immobilized microbes (75.06 %, 56.05 %) and free microbes (61.72 %). Moreover, the PVA/SA/biochar (0.7 %) immobilized microbes showed increased tolerance to extreme conditions. Biodegradation metabolites of thiamethoxam were identified and two intermediates were first reported. Based on the identified biodegradation intermediates, cleavage of C-N between the 2-chlorothiazole ring and oxadiazine, dichlorination, nitrate reduction and condensation reaction would be the major biodegradation routes of thiamethoxam. Results of this work suggested the novel PVA/SA/biochar beads with Chryseobacterium sp H5 immobilization would be helpful for the effective bioremediation of thiamethoxam contamination.

Environmental occurrence, toxicity concerns, and biodegradation of neonicotinoid insecticides

Neonicotinoids (NEOs) are fourth generation pesticides, which emerged after organophosphates, pyrethroids, and carbamates and they are widely used in vegetables, fruits, cotton, rice, and other industrial crops to control insect pests. NEOs are considered ideal substitutes for highly toxic pesticides. Multiple studies have reported NEOs have harmful impacts on non-target biological targets, such as bees, aquatic animals, birds, and mammals. Thus, the remediation of neonicotinoid-sullied environments has gradually become a concern. Microbial degradation is a key natural method for eliminating neonicotinoid insecticides, as biodegradation is an effective, practical, and environmentally friendly strategy for the removal of pesticide residues. To date, several neonicotinoid-degrading strains have been isolated from the environment, including Stenotrophomonas maltophilia, Bacillus thuringiensis, Ensifer meliloti, Pseudomonas stutzeri, Variovorax boronicumulans, and Fusarium sp., and their degradation properties have been investigated. Furthermore, the metabolism and degradation pathways of neonicotinoids have been broadly detailed. Imidacloprid can form 6-chloronicotinic acid via the oxidative cleavage of guanidine residues, and it is then finally converted to non-toxic carbon dioxide. Acetamiprid can also be demethylated to remove cyanoimine (=N-CN) to form a less toxic intermediate metabolite. A few studies have discussed the neonicotinoid toxicity and microbial degradation in contaminated environments. This review is focused on providing an in-depth understanding of neonicotinoid toxicity, microbial degradation, catabolic pathways, and information related to the remediation process of NEOs. Future research directions are also proposed to provide a scientific basis for the risk assessment and removal of these pesticides.

Differential effects of thiamethoxam and clothianidin exposure on their tissue distribution and chronic toxicity in mice

The frequent application of second-generation neonicotinoids thiamethoxam (TMX) and clothianidin (CLO) has led to a high detectable rate in environment samples and poses threats to nontarget organisms and human beings, however, the information on the influences of long-term exposure at low doses was limited. In this study, the tissue distribution of TMX and CLO in mice at acceptable daily intake (ADI) level and 5 × ADI was determined and the health effects were assessed. TMX and CLO were detected in the liver, serum, lung, heart and kidney in the TMX exposure groups, which indicated that TMX degraded to CLO in mice. Residue levels of TMX in tissues increased with the increasing of doses. The concentrations of CLO in different tissues in the CLO exposure groups were in the order C_kidney > C_lung > C_heart > C_liver. Measurement of biochemical indicators, combined with metabolomic analysis of liver, kidney, and cecal contents, examination of changes in the gut microbiota, and histopathological assessment indicated that both TMX and CLO affected energy absorption and lipid metabolism in mice and destroyed tissue structures. Furthermore, we found that CLO had a stronger effect on metabolism in mice, despite its lower acute toxicity. These results have prompted us to consider the chronic toxicity and potential hazards of chemicals in future risk assessments.