Benzoylphenylurea residues in peppers and zucchinis grown in greenhouses: determination of decline times and pre-harvest intervals by modelling

Dissipation patterns, residue analysis, and risk evaluation of hexaflumuron in turnip and cauliflower under Chinese growth conditions

Hexaflumuron has been globally registered over 2 decades to control the pests in brassicaceous vegetables, while data on its dissipation and residues in turnip and cauliflower is scarce. Herein, field trials were carried out at six representative experimental sites to study the dissipation behaviors and terminal residues of hexaflumuron in turnip and cauliflower. The residual amounts of hexaflumuron were extracted using a modified QuEChERS and analyzed with liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), the chronic dietary risk to Chinese populations was evaluated, and the maximum residue limit (MRL) in cauliflower, turnip tubers, and turnip leaves was calculated by the OECD MRL calculator. The single first-order kinetics model was the best-fitted kinetics model for hexaflumuron dissipation in cauliflower. The indeterminate order rate equation and first-order multi-compartment kinetic model were the best formulae for hexaflumuron dissipation in turnip leaves. The half-lives of hexaflumuron ranged from 0.686 to 1.35 and 2.41 to 6.71 days in cauliflower and turnip leaves, respectively. The terminal residues of hexaflumuron in turnip leaves of 0.321-9.59 mg/kg were much higher than in turnip tubers of < 0.01-0.708 mg/kg and cauliflower of < 0.01-1.49 mg/kg at sampling intervals of 0, 5, 7, and 10 days. The chronic dietary risk of hexaflumuron in the preharvest interval of 7 days was lower than 100% and much higher than 0.01%, indicating acceptable but nonnegligible health hazards for Chinese consumers. Therefore, MRL values of hexaflumuron were proposed as 2, 0.8, and 10 mg/kg in cauliflower, turnip tubers, and turnip leaves, respectively.

Safety assessment of a new benzoylphenylurea TXH09 and its efficacy against two borers Ostrinia furnacalis and Grapholitha molesta in field

Benzoylphenylureas as an important type of insect growth regulators, acting on the moulting stage in immature insects, are highly effective and low toxic. The new benzoylphenylurea TXH09 [N-((2,6-dimethyl-4-(heptafluoropropyl-2-yl)phenyl)carbamoyl)-2,6-difluorobenzamide] has high efficacy against chewing insect pests harming vegetables and rice. In this paper, the efficacy of TXH09 against two intractable borers Ostrinia furnacalis and Grapholitha molesta were evaluated in field, and safety assessment by exploring the characteristics of photodegradation, cytotoxicity, micronucleus generation and chromosome aberration was performed. The results showed that TXH09 had good capability in preventing infested corn and reducing the population of O. furnacalis larvae, and maintained high efficacy on shoot protection and peach conservation against G. molesta larvae. There were no significant differences between the control effects of TXH09 and that of hexaflumuron or diflubenzuron at the same active dose. TXH09 photolysis in solvents N,N-dimethylformamide, toluene and methanol yielded two major products, and the photodegradation of TXH09 was more prone to occur in N,N-dimethylformamide. TXH09 and the mixture of its photoproducts showed higher cytotoxicity on insect Sf-9 cells than on human Hek293 cells. Moreover, TXH09 didn't show significant effects in inducing micronucleated cells in both male and female mice and chromosomal aberrations in mouse spermatocytes by its own. In conclusion, TXH09, as an effective insecticide, has good environmental safety performance against O. furnacalis and G. molesta in field.

Foliar persistence and residual activity of four insecticides of different mode of action on the predator Engytatus varians (Hemiptera: Miridae)

A greenhouse study was conducted to investigate the degradation kinetics of spinosad, flufenoxuron, dimethoate and imidacloprid in tomato (Solanum lycopersicum L.) foliage and their residual toxicity on Engytatus varians (Distant) (Hemiptera: Miridae), a predator of the tomato psyllid Bactericera cockerelli (Sulcer) (Hemiptera: Triozidae). Insecticides were sprayed at 100% and 50% of their maximum field-registered concentrations (MFRC). Starting 6 h after spraying, leaf samples were taken every 10 d for 40 d and analyzed while E. varians adults were exposed to treated leaves to evaluate residual toxicity. Immediately after application at 100% MFRC, the residue concentrations were 73.34 μg g^-1 spinosyn A and 59.2 μg g^-1 spinosyn D, 9.21 μg g^-1 flufenoxuron, 71.49 μg g^-1 dimethoate and 31.74 μg g^-1 imidacloprid. At 50% MFRC, initial residue concentrations were between 75% and 90% those at 100% MFRC. The estimated half-life (DT₅₀) of spinosyns A and D, flufenoxuron, and dimethoate was between 34 and 40 d, while that of imidacloprid was 112 d. Flufenoxuron caused no mortality, while mortality due to spinosad was less than 10%, and only during the first 10 d. Mortality caused by either imidacloprid or dimethoate was around 100% up to 10 d after application, then decreased to around 30% after 40 d. Dimethoate toxicity was approximately proportional to residue concentration, while for imidacloprid there was an apparent threshold around 15 μg g^-1. These results can be used to establish periods harmless for release of E. varians in the control of B. cockerelli on tomato crops under greenhouse conditions.

Variability of pesticide dissipation half-lives in plants

Information on dissipation kinetics of pesticides in food crops and other plants is a key aspect in current risk and impact assessment practice. This is because human exposure to pesticides is predominantly caused by residues in agricultural crops grown for human and animal consumption. However, modeling dissipation of pesticides in plants is highly uncertain and therefore strongly relies on experimental data. Unfortunately, available information on pesticide dissipation in plants from experimental studies only covers a small fraction of possible combinations of substances authorized for use on food and fodder crops. Additionally, aspects and processes influencing dissipation kinetics are still not fully understood. Therefore, we systematically reviewed 811 scientific literature sources providing 4513 dissipation half-lives of 346 pesticides measured in 183 plant species. We focused on the variability across substances, plant species and harvested plant components and finally discuss different substance, plant and environmental aspects influencing pesticide dissipation. Measured half-lives in harvested plant materials range from around 1 hour for pyrethrins in leaves of tomato and pepper fruit to 918 days for pyriproxyfen in pepper fruits under cold storage conditions. Ninety-five percent of all half-lives fall within the range between 0.6 and 29 days. Our results emphasize that future experiments are required to analyze pesticide-plant species combinations that have so far not been covered and that are relevant for human exposure. In addition, prediction models would help to assess all possible pesticide-plant species combinations in the context of comparative studies. The combination of both would finally reduce uncertainty and improve assumptions in current risk and impact assessment practice.

Application of QuEchERS Method in Determining Imidaclothiz Residue in Soil and Citrus by Ultra-Performance Liquid Chromatography Tandem Mass Spectrometry

A simple method for the determination of imidaclothiz residue in soil and citrus samples was established by ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) under the multiple reaction monitoring (MRM) mode. Imidaclothiz was extracted from soil and citrus samples using a procedure known as the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method. Experiments on 3 fortification concentrations were carried out, and the limit of determination is 1.0×10-10g. The recoveries ranging from 80.7% to 118.9% with high correlation coefficient (r>0.99) were obtained within the linear range (0.01-1.0mg/kg). Based on the above method, we also carried out field trials. Results showed that the degradation of imidaclothiz coincided with the fitted equations Ct=0.1028e-0.0266t, Ct=0.1778e-0.0311tin soil and Ct=1.3612e-0.0632t, Ct=0.7162e-0.0968tin citrus, respectively, with the average half-lives of 24.2 d in soil and 9.1 d in citrus, respectively. The results indicate that the developed method is fast, accurate, and easy to operate. It also demonstrates that the method can meet the requirements of determination of imidaclothiz in soil and citrus.

Dissipation and evaluation of hexaflumuron residues in chinese cabbage grown in open fields

The dissipation and residue behavior of hexaflumuron in Chinese cabbage ( Brassica pekinensis ) under different treatments were investigated at two main cabbage-growing areas in China. The dissipation rates of hexaflumuron in cabbages and soils fit a first-order decay process very well. The dissipation times for 50% of the hexaflumuron in cabbage and soil were 3.37 and 3.01 days from Hunan province and 5.58 and 3.68 days in Tianjin, respectively, when Chinese cabbage was treated with 180 g of active ingredient (ai)/ha. Hexaflumuron residual times in cabbage and soil were influenced strongly by the application rate and frequency. The application regimen of hexaflumuron in the cabbage field, a rate of 120 g of ai/ha with two applications at a 7 day interval and a 21 day preharvest interval, was recommended from the point of view of ensuring food safety. The residual levels of hexaflumuron in cabbages were lower than the standards of the "Positive List System for Agricultural Chemical Residues in Foods" based on the recommended application regimen.