Degradation kinetics and pathways of spirotetramat in different parts of spinach plant and in the soil

Residual estimation of spirotetramat and its metabolites in chilli and soil by LC-MS/MS

Two applications of spirotetramat were done to study the dissipation and persistence of spirotetramat and its four different metabolites in chilli and soil at 10 days interval. Total spirotetramat residues were estimated by LC-MS/MS instrument. The mean initial deposits of total spirotetramat after application of spirotetramat 15.31 OD @ 60 (X dose), 75 (1.25 × dose) and 120 (2 × dose) g a.i. ha-1 on green chilli were found to vary from 0.38 to 0.83 mg kg-1 during the initial year. Spirotetramat and its metabolite residues in green chilli were found to be below limit of quantification (0.01 mg kg-1) after 15 days of application. The spirotetramat cis enol (the major metabolite) was formed in both the soil and the plant. The residues of spirotetramat-monohydroxy were below LOQ irrespective of any substrate during the estimation. In soil, the total initial spirotetramat deposits for the 1st year were found 0.09 for X dose, 0.12 for 1.25 × dose and 0.20 mg kg-1 for 2 × dose. After 3 days for both X and 1.25 × doses and 5 days for 2 × dose, the total spirotetramat residues were below LOQ. The spirotetramat's half-life values have been determined to be between 3.19 and 3.93 days and 1.00 and 1.59 days, respectively, in soil and green chilli fruits. One day waiting period is proposed for the safe consumption of green chilli when the spirotetramat was applied irrespective of the dose.

Dissipation, residues, and evaluation of processing factor for spirotetramat and its formed metabolites during kiwifruit growing, storing, and processing

Spirotetramat is widely used around the world to control sucking pests and may form in agricultural products. In the current study, the dissipation, residues, and evaluation of processing factor (PF) for spirotetramat and its formed metabolites were investigated during kiwifruit growing, storing, and processing. The residue analysis method was established based on high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) combined with a QuEChERS method to detect the residues of spirotetramat and its metabolites in kiwifruit and its processed products. The method provided recoveries of 74.7-108.7%, and the relative standard deviations (RSDs) were 0.6-13.1%. The LOQs of spirotetramat and its four metabolites were 1 μg kg-1. The degradation of spirotetramat was best fitted for the first-order kinetics model with a half-life of 9.90-10.34 days in the field and 24.75-30.13 days during storage. Residues of spirotetramat and its formed metabolites in kiwifruit would not pose dietary risk to consumers. Moreover, the peeling and fermentation were the highest removal efficiency for the spirotetramat and its formed metabolite residues during processing. The PF values calculated after each individual process were < 1, indicating a significant reduction of residues in different processing processes of kiwifruit. The spirotetramat was degraded during kiwifruit wine-making process with half-lives of 3.36-4.91 days. B-enol and B-keto were the main metabolites detected in kiwifruit and its processed products. This study revealed the residues of spirotetramat and its formed metabolites in kiwifruit growing, storing, and processing, which helps provide reasonable data for studying the dietary risk factors of kiwifruits and products.

Uptake and Biotransformation of Spirotetramat and Pymetrozine in Lettuce (Lactuca sativa L. var. ramosa Hort.)

Here, we investigated the uptake, transport, and subcellular distribution of the pesticides pymetrozine and spirotetramat, and spirotetramat metabolites B-enol, B-glu, B-mono, and B-keto, under hydroponic conditions. Spirotetramat and pymetrozine exhibited high bioconcentrations in lettuce roots, with both having root concentration factor (RCF) values >1 after exposure for 24 h. The translocation of pymetrozine from roots to shoots was higher than that of spirotetramat. Pymetrozine is absorbed in roots mainly via the symplastic pathway and is primarily stored in the soluble fraction of lettuce root and shoot cells. The cell wall and soluble fractions were the major enrichment sites of spirotetramat and its metabolites in root cells. Spirotetramat and B-enol were mainly enriched in the soluble fractions of lettuce shoot cells, whereas B-keto and B-glu accumulated in cell walls and organelles, respectively. Both symplastic and apoplastic pathways were involved in spirotetramat absorption. Pymetrozine and spirotetramat uptake by lettuce roots was passive, with no aquaporin-mediated dissimilation or diffusion. The findings of this study enhance our understanding of the transfer of pymetrozine, spirotetramat, and spirotetramat metabolites from the environment to lettuce, and their subsequent bioaccumulation. This study describes a novel approach for the efficient management of lettuce pest control using spirotetramat and pymetrozine. At the same time, it is of great significance to evaluate the food safety and environmental risks of spirotetramat and its metabolites.

Dissipation kinetics and exposure of spirotetramat and pymetrozine in open fields, a prelude to risk assessment of green bean consumption

Determination and dissipation kinetics of pymetrozine and spirotetramat in green bean were studied using a QuEChERS method coupled to high-performance liquid chromatography-tandem mass spectrometry. Pymetrozine recoveries ranged between 88.4-93.7%, with relative standard deviation (RSD) of 5.5-14.4%. For spirotetramat the recoveries ranged between 91.7-103.4%, and the RSD were in the range of 3.2 to 12.4%. The limits of quantification (LOQs) were 0.01 mg/kg and 0.005 mg/kg for pymetrozine and spirotetramat, respectively.The developed analytical method was used to study the degradation rates of pymetrozine and spirotetramat in green bean grown in open field. Results showed that pymetrozine and spirotetramat followed the first-order kinetics model with half-lives of 3.3 days and 4.2 days, respectively. Furthermore, risk assessment was carried out which showed that, the chronic risk quotient (RQc) values for pymetrozine and spirotetramat were much lower than 100%. The present results indicated that the health risks posed for consumers by the pymetrozine and spirotetramat residues were negligible at the recommended dosages.

Uptake, translocation, and degradation of spirotetramat in tomato (Lycopersicon esculentum Miller): Impact of the mixed-application with pymetrozine

In this study, we investigated the impact of the mixed-application with pymetrozine on the behavior (i.e., uptake, translocation, and degradation) of spirotetramat in tomatoes under laboratory conditions. Results showed that pymetrozine promoted the uptake of spirotetramat from the nutrition solution after root application. The root concentration factor was 0.290 and 1.566 after spirotetramat single application and mixed-application with pymetrozine, respectively. It had little effect on the degradation of spirotetramat, with the metabolites of M-keto, M-enol, and M-glu in tomato issue (root, stems, and leaves). After foliar treatments, pymetrozine accelerated the translocation of spirotetramat from leaves to stems, with the translocation factor of 0.145 and 0.402 after spirotetramat single application and mixtures with pymetrozine, respectively. Pymetrozine also promoted the degradation of spirotetramat to M-kto and M-enol in leaves. Besides, a partition-limited model was used to describe the distribution processes of spirotetramat in the tomato-water system after root application. It showed that pymetrozine accelerated the distribution balance of spirotetramat in the whole system. Our result indicates that the interaction among pesticides should be considered when studied for the uptake, translocation, and degradation of pesticides in crops.

Multi-residue analysis, dissipation behavior, and final residues of four insecticides in supervised eggplant field

In this study, the residues of four insecticides, spirotetramat, flonicamid, thiamethoxam, and tolfenpyrad, and their metabolites, including spirotetramat-enol, spirotetramat-mono-hydroxy, spirotetramat-keto-hydroxy, spirotetramat-enol-glucoside, 4-trifluoromethylnicotinamide, 4-trifluoromethylnicotinic acid, N-(4-trifluoromethylnicotinoyl) glycine, and clothianidin, were assessed using a single analysis method. The samples were extracted by acetonitrile, then purified by dispersive solid phase extraction and quantified using high performance liquid chromatography tandem mass spectrometry. The average recovery rate of 12 target compounds was 73.5-103.7%, the relative standard deviation was 1.1-18.3%, and the limit of quantification was 0.01-0.05 mg/kg. The results showed good linearity (R² >0.99), meeting the requirements of the pesticide residue analysis. The dissipation half-lives of the four insecticides in eggplant were 3.4-14.5 days. After the last applications at 7 and 10 days, the final residues of the four insecticides in eggplant were <0.01-0.21, 0.085-0.26, <0.05-0.078, and <0.01-0.21 mg/kg, respectively. The dissipation and final residue results could provide a theoretical basis for the rational application of four insecticides in eggplant fields.HighlightsHPLC-MS/MS for simultaneous determination of four insecticides and their metabolites in eggplant fields.The dissipation dynamics and final residue of the target compounds in field eggplant were studied.Guidance for the safe use of four insecticides on eggplant.

Dissipation characteristics of spirotetramat and its metabolites in two phenotypically different Korean vegetables under greenhouse conditions

This study involved analysis and method validation of spirotetramat applied to two phenotypically different Korean vegetables (e.g. Korean cabbage and shallots) to determine the safe pre-harvest residue limit (PHRL) and comparative dissipation patterns. Two steps of the investigation involved greenhouse monitoring during crop cultivation followed by LC-MS/MS analysis. Commercial spirotetramat was sprayed twice with seven-day intervals according to the spray schedule (0, 3, 7, 10, 14, and 21 days before harvest) at the dose recommended by the Ministry of Food and Drug Safety (MFDS), Korea. During the validation of the analytical method, good linearity, specificity, and acceptable recoveries (82%-114% for Korean cabbage and 82%-111% for shallot) were established for spirotetramat and its four metabolites. The calculated biological half-life derived from the first-order reaction (t_1/2) of spirotetramat was 4.8 days for Korean cabbage and 4.0 days for shallot, respectively. The safe PHRL for Korean cabbage was suggested at 7 days, due to permissible spirotetramat concentration in terms of an acceptable MRL. The findings of the study will be used as the analytical reference point for developing spirotetramat safety guidelines for use in the vegetables investigated.

Insecticide-contaminated honeydew: risks for beneficial insects

Honeydew is the sugar-rich excretion of phloem-feeding hemipteran insects such as aphids, mealybugs, whiteflies, and psyllids, and can be a main carbohydrate source for beneficial insects in some ecosystems. Recent research has revealed that water-soluble, systemic insecticides contaminate honeydew excreted by hemipterans that feed on plants treated with these insecticides. This contaminated honeydew can be toxic to beneficial insects, such as pollinators, parasitic wasps and generalist predators that feed on it. This route of exposure has now been demonstrated in three plant species, for five systemic insecticides and four hemipteran species; therefore, we expect this route to be widely available in some ecosystems. In this perspective paper, we highlight the importance of this route of exposure by exploring: (i) potential pathways through which honeydew might be contaminated with insecticides; (ii) hemipteran families that are more likely to excrete contaminated honeydew; and (iii) systemic insecticides with different modes of action that might contaminate honeydew through the plant. Furthermore, we analyse several model scenarios in Europe and/or the USA where contaminated honeydew could be problematic for beneficial organisms that feed on this ubiquitous carbohydrate source. Finally, we explain why this route of exposure might be important when exotic, invasive, honeydew-producing species are treated with systemic insecticides. Overall, this review opens a new area of research in the field of ecotoxicology to understand how insecticides can reach non-target beneficial insects. In addition, we aim to shed light on potential undescribed causes of insect declines in ecosystems where honeydew is an important carbohydrate source for insects, and advocate for this route of exposure to be included in future environmental risk assessments.

Investigation of the dissipation behaviour and exposure of spitotetramat, flonicamid, imidacloprid and pymetrozine in open field strawberries in Egypt

The dissipation behaviour and the consumer risk assessment of spitotetramat, flonicamid, imidacloprid and pymetrozine in open field strawberries were studied. Insecticides were applied at the authorised levels and the more critical good agricultural practice regimes (GAP). The initial concentrations varied from 0.069 to 1.75 mg kg^-1 depending on the compound, while the dissipation half-lives and terminal residues, 14 days from the last applications, were similar. After application according to the authorised pattern the half-lives were 2.8 days for flonicamid and 3.2 days for spitotetramat, imidacloprid and pymetrozine. The dietary risk assessment, performed using the hazard quotient and the EFSA PRIMo model showed no concern to consumer health with exposure values <2% of the acceptable daily intake (ADI) and <32% of the acute reference dose (ARfD) of each compound.

Dissipation kinetics and risk assessments of tricyclazole during Oryza sativa L. growing, processing and storage

Because of the increase of people's attention to food safety, monitoring the residue of pesticide in rice is becoming more and more important. Commercial and home processing techniques have been used to transform paddy rice into rice products for human or animal consumption, which may reduce the pesticide content in rice. The degradation of tricyclazole during different stages of commercial and home processing and storage was assessed in this paper. Many researches studying the occurrence and distribution of pesticide residues during rice cropping and processing have been reported. Rice samples were extracted with acetonitrile, the extracts were enriched, and then residues were analyzed by liquid chromatography/tandem mass spectrometry method. The dissipation dynamics of tricyclazole in rice plant, soil, and paddy water fitted the first-order kinetic equations. The dissipation half-lives of tricyclazole in the rice plant, water, and soil at dosage of 300~450 g a.i. hm ^-2 were 4.84~5.16, 4.64~4.85, and 3.57~3.82 days, respectively. The residue levels of tricyclazole gradually reduced with different processing procedures. What is more, decladding process could effectively remove the residues of tricyclazole in raw rice, and washing process could further remove the residues of tricyclazole in polished rice. Degradation dynamic equations of tricyclazole in the raw rice and polished rice were based on the first-order reaction dynamic equations, and the half-lives of the degradation of tricyclazole was 43.32~58.24 days and 46.83~56.35 days in raw rice and polished rice. These results provide information regarding the fate of tricyclazole in the rice food chain, while it provides a theoretical basis for systematic evaluation of the potential residual risk of tricyclazole.

Adsorption and Desorption Behaviors of Spirotetramat in Various Soils and Its Interaction Mechanism

Spirotetramat is a pesticide with bidirectional systemicity and can effectively control pests by inhibiting the biosynthesis of fatty acids. In this study, adsorption and desorption behaviors of spirotetramat in six soils and its interaction mechanism were studied using the batch equilibrium method and infrared radiation. The results showed that the adsorption and desorption behaviors of spirotetramat conformed to the Freundlich isotherm model. The values of adsorption capacities K_F-ads ranged from 2.11 to 12.40, and the values of desorption capacities K_F-des varied from 2.97 to 32.90. From the hysteresis coefficient, spirotetramat was easily desorbed from the test soils. The adsorption capacity of the soil to spirotetramat enhanced with an increasing temperature. Moreover, the changes in pH values and exogenous addition of humic acid and surfactant could also affect soil adsorption capacity, but for desorption, there was no correlation.

Behavior of quizalofop-p and its commercial products in water by liquid chromatography coupled to high resolution mass spectrometry

A degradation study of quizalofop-p and its commercial products (quizalofop-p-ethyl, quizalofop-p-tefuryl and propaquizafop) in water samples has been performed using ultra high-performance liquid chromatography coupled to Orbitrap mass spectrometry (UHPLC-Orbitrap-MS). CHHQ (dihydroxychloroquinoxalin), CHQ (6-chloroquinoxalin-2-ol) and PPA ((R)-2-(4-hydroxyphenoxy)propionicacid) were the main metabolites of this active substance (quizalofop-p) in water. The degradation of the parent compound has been monitored in distilled water. Several commercial products (Panarex®, Master-D® and Dixon®) were used to evaluate the degradation of the target compounds into their metabolites. The concentration of the main active substances (quizalofop-p-tefuryl, quizalofop-p-ethyl and propaquizafop) decreased during the degradation studies, whereas the concentration of quizalofop-p increased. DT₅₀ of the main active substances ranged from 10 days to 70 days for most of the analytes, so it can be concluded that compounds are medium-high persistent in this matrix. Metabolites, such as PPA, CHHQ and CHQ, were detected in water samples after 7 days of the application of the commercial products at concentrations higher than their limits of quantification (> 0.1 µg/L). CHQ was detected at 1400 µg/L after 75 days of the application of quizalofop-p-ethyl commercial product. CHHQ and CHQ were found at the highest concentrations at 7-45 days after the application of quizalofop-p-tefuryl, whereas PPA was detected at higher concentrations (up to 5.37 µg/L) in propaquizafop samples.

Environmental behaviors of spirotetramat in water

Spirotetramat is a pesticide with bidirectional systemicity in both xylem and phloem. Currently, researches show that spirotetramat has definite toxicity to aquatic organism. This paper aims to study the environmental behaviors of spirotetramat in water, in the hope of providing guidance for security evaluation of spirotetramat. The researches in this paper showed that under lighting condition, the half-life period of spirotetramat in water was 13.59 days. In water, spirotetramat could be degraded into B-enol and B-keto. As seen from the residual concentrations of two products, B-enol was the dominant degradation product. Under different temperatures, the hydrolysis products of spirotetramat remain B-enol and B-keto. The temperature has little effect on the residual concentration of spirotetramat in water. The residual concentration of B-enol in water gradually increased with the extension of time but B-keto had no significant change. In the buffer solution of different pH values, the degradation rate of spirotetramat was significantly enhanced with the increase of solution pH value. The hydrolysis products of spirotetramat in buffer solution of different pH values were still B-enol and B-keto, and pH exerted certain influence on the residual concentration of B-enol in water. The hydrolysis conversion of spirotetramat has theoretical and practical significance for the safe and reasonable usage of it, as well as for the further evaluation of spirotetramat's ecological risk in water.

The fate of spirotetramat and dissipation metabolites in Apiaceae and Brassicaceae leaf-root and soil system under greenhouse conditions estimated by modified QuEChERS/LC-MS/MS

The aim of this study was to investigate the dissipation of spirotetramat and its four metabolites (B-enol, B-keto, B-mono and B-glu) in different parts of vegetables belong to the minor crops (Appiacea and Brassicaceae) and soil from cultivation. The challenge of this study was to apply an optimized clean up step in QuEChERS to obtain one universal sorbent for different complex matrices like leaves with high levels of pigments, roots containing acids, sugars, polyphenolls and pigments and soil with organic ingredients. Eight commercial (Florisil, neutral alumina, GCB, PSA, C18, diatomaceous earth, VERDE and ChloroFiltr) and one organic (Chitosan) sorbents were tested. A modified clean up step in QuEChERS methodology was used for analysis. The dissipation of spirotetramat and its metabolites was described according to a first-order (FO) kinetics equation with R² between 0.9055 and 0.9838. The results showed that the time after 50% (DT₅₀) of the substance degraded was different for soil, roots and leaves, and amounted to 0.2day, 2.8-2.9days and 2.1-2.4days, respectively. The terminal residues of spiroteramat (expressed as the sum of spirotetramat, B-enol, B-glu, B-keto and B-mono) were much lower than the MRLs.

Nicosulfuron Biodegradation by a Novel Cold-Adapted Strain Oceanisphaera psychrotolerans LAM-WHM-ZC

Nicosulfuron is a common environmental pollutant, posing a great threat to aquatic systems and causing significant damage to crops. This study reported a cold-adapted strain Oceanisphaera psychrotolerans LAM-WHM-ZC, which efficiently degrades nicosulfuron over a wide range of temperatures (5 to 40 °C). The Box-Behnken design method was used to optimize the degradation conditions. O. psychrotolerans LAM-WHM-ZC can degrade 92.4% and 74.6% of initially supplemented 100 mg/L nicosulfuron under the optimum and low temperature of 18.1 and 5 °C, respectively, within 7 days. O. psychrotolerans LAM-WHM-ZC was found to be highly efficient in degrading cinosulfuron, chlorsulfuron, rimsulfuron, bensulfuron methyl, and ethametsulfuron methyl. Metabolites from nicosulfuron degradation were identified by UPLC-MS, and a possible degradation pathway was proposed. Furthermore, O. psychrotolerans LAM-WHM-ZC can also degrade nicosulfuron in soil; 78.6% and 67.4% of the initial nicosulfuron supplemented at 50 mg/kg were removed at 18.1 and 5 °C, respectively, within 15 days.