Optimizing the QuEChERS method for efficient monitoring of fipronil, thiobencarb, and cartap residues in paddy soils with varying properties.

This study aims to optimize the QuEChERS methodology for extracting three pesticides (fipronil, thiobencarb, and cartap) from two paddy soils with distinct characteristics. Various modifications were explored to enhance extraction efficiency, employing acetonitrile (MeCN) or ethyl acetate (EtOAc) for extraction and primary-secondary amine (PSA) and graphitized carbon black (GCB) for the clean-up. Assessment criteria included accuracy, precision, linearity, detection limits, uncertainty, and matrix effects. Results revealed that the clayey soil with lower organic carbon (OC) content (1.26%) and 100% moisture yielded the highest pesticide recoveries (113.72%, 115.73%, and 116.41% for FIP, THIO, and CART, respectively). In contrast, the silty clayey soil with higher OC content (2.91%) and 20% water content exhibited poor recoveries (< 60%). FIP and CART demonstrated better recoveries with MeCN, while THIO performed better with EtOAc under specific moisture conditions. Clean-up sorbents significantly reduced FIP and CART recoveries, with THIO recoveries less affected. Acidifying with HCl substantially improved CART recovery. EtOAc introduced a moderate to strong matrix effect for FIP and THIO, while MeCN in soils with 100% moisture resulted in a strong matrix effect for CART. The study highlighted the substantial impact of extraction conditions, pesticide properties, and soil conditions on the outcomes of the QuEChERS method. A comprehensive understanding of these interplays was deemed crucial for accurately quantifying pesticide residues in agricultural soils.

Physiological responses of plants and mites to salicylic acid improve the efficacy of spirodiclofen for controlling Tetranychus urticae (Acari: Tetranychidae) on greenhouse tomatoes.

Salicylic acid (SA) is a signaling molecule that can induce plant resistance to certain herbivores. Although the role of jasmonic acid in mediating mite-tomato plant interactions has been well studied, the role of salicylic acid has not. This study examined how the application of exogenous SA, via its effects on tomato plant physiology, alters the activity of mite digestive enzymes, mite energy reserves, and mite susceptibility to spirodiclofen. Enzymatic activity-including superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase-along with contents of total phenolic, hydrogen peroxide, and total chlorophyll significantly increased in plants 24 h after treatment with 2 mM of SA. In contrast, catalase activity significantly decreased in treated plants, and malondialdehyde content was unaffected. Mites fed on tomato plants treated with SA had significantly lower glutathione S-transferase, esterase, α-amylase, and aminopeptidase activities than those fed on control plants. Energy reserve analyses demonstrated a significant decrease in contents of lipid, protein, and glycogen in mites fed on SA-treated plants, whereas carbohydrate content significantly increased. The LC50 of spirodiclofen was decreased 1.8-fold for Tetranychus urticae fed on SA-treated tomato plants compared to controls. Treatment of adult mites with 2 mM SA on leaf discs did not cause any direct mortality after 24 h. Finally, a greenhouse bioassay confirmed that spider mite mortality following exposure to spirodiclofen was significantly higher on SA plants than on control plants. Mortality of mites exposed to half of the recommended rate of spirodiclofen was similar to those exposed to the recommended rate when they were held on treated plants. These results have valuable implications for T. urticae management programs in tomato production.

Dissipation of S-metolachlor and butachlor in agricultural soils and responses of bacterial communities: Insights from compound-specific isotope and biomolecular analyses.

The soil dissipation of the widely used herbicides S-metolachlor (SM) and butachlor (BUT) was evaluated in laboratory microcosms at two environmentally relevant doses (15 and 150 µg/g) and for two agricultural soils (crop and paddy). Over 80% of SM and BUT were dissipated within 60 and 30 days, respectively, except in experiments with crop soil at 150 µg/g. Based on compound-specific isotope analysis (CSIA) and observed dissipation, biodegradation was the main process responsible for the observed decrease of SM and BUT in the paddy soil. For SM, biodegradation dominated over other dissipation processes, with changes of carbon isotope ratios (Δδ13C) of up to 6.5‰ after 60 days, and concomitant production of ethane sulfonic acid (ESA) and oxanilic acid (OXA) transformation products. In crop soil experiments, biodegradation of SM occurred to a lesser extent than in paddy soil, and sorption was the main driver of apparent BUT dissipation. Sequencing of the 16S rRNA gene showed that soil type and duration of herbicide exposure were the main determinants of bacterial community variation. In contrast, herbicide identity and spiking dose had no significant effect. In paddy soil experiments, a high (4:1, V/V) ESA to OXA ratio for SM was observed, and phylotypes assigned to anaerobic Clostridiales and sulfur reducers such as Desulfuromonadales and Syntrophobacterales were dominant for both herbicides. Crop soil microcosms, in contrast, were associated with a reverse, low (1:3, V/V) ratio of ESA to OXA for SM, and Alphaproteobacteria, Actinobacteria, and Bacillales dominated regardless of the herbicide. Our results emphasize the variability in the extent and modes of SM and BUT dissipation in agricultural soils, and in associated changes in bacterial communities.

The dissipation kinetics of malathion in aqueous extracts of different fruits and vegetables.

The dissipation of malathion in 5% aqueous extracts of some fruits and vegetables including bell pepper, tomato, cucumber, cantaloupe, carrot, and also buffer (control) was investigated at 37 °C for 4 h. The dissipation trend of malathion in the fruit/vegetable samples and buffer followed first-order double-exponential decay (FODED) and simple first-order kinetic (SFOK) models, respectively. The initial dissipation rate of malathion in tomato (DT10=0.05 h), bell pepper (DT10=0.06 h), and carrot (DT10=0.07 h) was faster compared to the other samples. The slowest rate of pesticide decline belonged to cantaloupe (DT50=1.92 h) with a significant difference from the other samples (p≤0.01), whereas tomato (DT50=0.43 h) and carrot (DT50=0.53 h) showed the fastest dissipation rate. DT90 values derived from the models revealed no significant difference between the samples except for cantaloupe which had the slowest rate of dissipation (DT90=8.27 h) with a significant difference compared to others (p≤0.01). A direct correlation was observed between protein content of the samples and the rate of malathion decline which indicates the role of plant enzymes in degrading malathion residues.

Efficacy of novel bacterial consortia in degrading fipronil and thiobencarb in paddy soil: a survey for community structure and metabolic pathways.

Introduction: Fipronil (FIP) and thiobencarb (THIO) represent widely utilized pesticides in paddy fields, presenting environmental challenges that necessitate effective remediation approaches. Despite the recognized need, exploring bacterial consortia efficiently degrading FIP and THIO remains limited. Methods: This study isolated three unique bacterial consortia-FD, TD, and MD-demonstrating the capability to degrade FIP, THIO, and an FIP + THIO mixture within a 10-day timeframe. Furthermore, the bioaugmentation abilities of the selected consortia were evaluated in paddy soils under various conditions. Results: Sequencing results shed light on the consortia's composition, revealing a diverse bacterial population prominently featuring Azospirillum, Ochrobactrum, Sphingobium, and Sphingomonas genera. All consortia efficiently degraded pesticides at 800 µg/mL concentrations, primarily through oxidative and hydrolytic processes. This metabolic activity yields more hydrophilic metabolites, including 4-(Trifluoromethyl)-phenol and 1,4-Benzenediol, 2-methyl-, for FIP, and carbamothioic acid, diethyl-, S-ethyl ester, and Benzenecarbothioic acid, S-methyl ester for THIO. Soil bioaugmentation tests highlight the consortia's effectiveness, showcasing accelerated degradation of FIP and THIO-individually or in a mixture-by 1.3 to 13-fold. These assessments encompass diverse soil moisture levels (20 and 100% v/v), pesticide concentrations (15 and 150 µg/g), and sterile conditions (sterile and non-sterile soils). Discussion: This study offers an understanding of bacterial communities adept at degrading FIP and THIO, introducing FD, TD, and MD consortia as promising contenders for bioremediation endeavors.

Diazinon residues and degradation kinetics for grapes under field conditions.

The dissipation of diazinon (O,O-diethyl O-2-isopropyl-6-methylpyrimidin-4-yl phosphorothioate) in grapes was investigated to determine its pre-harvest interval (PHI). Diazinon was applied to grapes at the recommended dosage (0.9 g a.i. L(-1)) and twice the recommended dosage (1.8 g a.i. L(-1)) three times, at the fruit formation stage, the sour stage, and the ripening stage, in a field trial with three replications. Samples were taken at 0, 1, 2, 4, 7, 11, 15, 20, 26 and 32 days after spraying. The residue was extracted using a water/methanol/acetonitrile (1:1:1, v/v/v) solvent and solid phase extraction was employed for cleanup. Quantitative analysis was performed using a gas chromatograph equipped with a nitrogen-phosphorus detector. The dissipation trend for the recommended dosage and twice the recommend dosage followed the simple first-order kinetic model (SFOK) (DT(50) = 3.29 days, DT(90) = 11 days, PHI = 13.5 days) and first-order double-exponential decay (FODED) model (DT(50) = 1.08 days, DT(90) = 5.82 days, PHI = 15.29 days), respectively. The average initial deposit of diazinon at the recommended dosage was 9.04 mg kg(-1)and for twice the recommended dosage was 27.38 mg kg(-1)and it dissipated rapidly within days of spraying.

Residue kinetics of neonicotinoids and abamectin in pistachio nuts under field conditions: model selection, effects of multiple sprayings, and risk assessment.

Pistachio is an economically valuable crop, and Iran is among the biggest producers, exporters, and consumers of this product in the world. During the growing season, pistachios are subjected to multiple sprayings with various pesticides, which result in the accumulation of their residues in nuts. These residues have raised concerns regarding consumers' health. In this research, uptake and dissipation kinetics of insecticides imidacloprid (IMI), thiacloprid (THI), thiamethoxam (THX), and abamectin (ABA) were investigated in pistachio nuts. Field experiments were conducted in a pistachio orchard. Pistachio trees were sprayed with the recommended dose of each insecticide formulation and water as the control. Samplings were performed for up to 49 days. Based on the results, pesticides uptake and dissipation kinetics were best fitted to first-order exponential growth (FOEG) and single first-order kinetic (SFOK) models, respectively. Variations in pesticides uptake/dissipation rates were mostly related to their water solubility, pKa, and log Kow. THX showed a higher uptake rate (0.16 ± 0.04) compared to IMI (0.10 ± 0.01) and THI (0.06 ± 0.01). The fastest dissipation rates were observed for IMI (0.04 ± 0.002 day-1) and THX (0.03 ± 0.001 day-1), while the slowest belonged to THI (0.02 ± 0.003 day-1). ABA residues were below the quantification limit (LOQ) throughout the experiment. Based on FOEG and SFOK model predictions, multiple sprayings with THI and THX resulted in final concentrations exceeding the maximum residue limit (MRL). Hazard quotients for all pesticides were <1, indicating no risk to humans via consumption of the pistachio nut.

Diazinon dissipation in pesticide-contaminated paddy soil: kinetic modeling and isolation of a degrading mixed bacterial culture.

Dissipation kinetics of diazinon was investigated in soils culled from a paddy field with a long history of the pesticide application. Goodness of fit statistical indices derived from several fitted mono- and bi-exponential kinetic models revealed a bi-phasic pattern of the diazinon dissipation curve at 15 and 150 mg kg-1 spiking levels, which could be described best by the first-order double exponential decay (FODED) model. Parameters obtained from this model were able to describe the enhanced dissipation of diazinon as the result of repeated soil applications, where a larger fraction of the pesticide readily available in the solution phase was dissipated with a fast rate. Cluster and principal component analysis (PCA) of denaturing gradient gel electrophoresis (DGGE) obtained from soil bacterial populations revealed that they were only affected at the 150 mg kg-1 diazinon concentration. This was also supported by the phylogenetic tree obtained from sequences of the main gel bands. Accordingly, bacterial populations belonging to Proteobacteria were enriched in the soil following three treatments with diazinon at 150 mg kg-1. The Shannon's index revealed a nonsignificant increase (P ≤ 0.05) in overall diversity of soil bacteria following diazinon application. Diazinon-degrading bacteria were isolated from the paddy soils in a mineral salt medium. Results showed that the isolated mixed culture was able to remove 90% of the pesticide at two concentrations of 50 and 100 mg L-1 by 16.81 and 19.60 days, respectively. Sequencing the DGGE bands confirmed the role of Betaproteobacteria as the main components of the isolated mixed culture in the degradation of diazinon.