Enantioselectivity of indoxacarb during the growing, processing, and brewing of tea: Degradation, metabolites, and toxicities.

Chiral pesticides are unique hazardous materials. Here, we systematically studied the potentially harmful products of enantioselective indoxacarb degradation throughout tea growth, processing, and brewing and tested their toxicity to tea geometrid larvae and honeybees. The half-lives of S-indoxacarb and R-indoxacarb during tea growth were 2.6 d and 3.3 d, respectively. There was a trend toward the production of S-indoxacarb from R-indoxacarb. The degradation products IN-JT333, IN-MK638, IN-MF014, and IN-KG433 were also characterized in tea growth and processing and detected. IN-JT333, previously known as a direct insecticidal compound produced by the enzymatic transformation of indoxacarb in insects, was first found in plant samples. The fixation and rolling of green tea and the rolling of black tea were the most important steps that affected indoxacarb and its degradation products. The leaching rates of R-indoxacarb and S-indoxacarb were slightly higher in green tea than in black tea. The maximum leaching rates of IN-MK638 and IN-MF014 during the brewing process reached 89.9% and 94.1%, respectively. Contact toxicity tests with honeybees and tea geometrid larvae in the lab showed that the relative toxicities of the compounds could be ranked as follows: S-indoxacarb > indoxacarb (3S + 1R) ≫ R-indoxacarb. TEST toxicity predictions showed that relative toxicities were ranked IN-KG433 > indoxacarb > IN-JT333 > IN-MK638 > IN-MF014. The toxicity of the degradation product IN-KG433 is higher than that of indoxacarb itself, and its maximum leaching rate is as high as 88.2%. It therefore transfers readily from processed tea to the tea infusion during the brewing process. These findings indicate the need to pay attention to the risk of metabolites and enantiomeric differences and provide new, comprehensive insight into the risk factors for indoxacarb in tea and are relevant to the study of other chiral pesticides.

Positive effects of an oil adjuvant on efficacy, dissipation and safety of pyrimethanil and boscalid on greenhouse strawberry.

Methylated vegetable oil adjuvants can enhance initial deposition and decrease the required dosages of pesticides sprayed on plants, so an oil adjuvant mixed with fungicides were used to prevent and control gray mold in greenhouse strawberry. As the persistence and dietary exposure risks from fungicides on strawberries after using adjuvants have not been assessed, the efficacy, dissipation and safety of pyrimethanil and boscalid in the presence and absence of a methylated vegetable oil adjuvant were evaluated. To better describe the actual use of fungicides in greenhouse strawberry, twice repeated application of fungicides were conducted follower by an optimized QuEChERS pre-treatment method. When applied at 60% of their recommended dosages with the adjuvant, the efficacy of pyrimethanil and boscalid for gray mold was similar to that shown by the treatment of 100% fungicides in absence of the adjuvant based on Duncan's Multiple-Range test, and their average residues increased to 89.0% and 89.3%, respectively. The adjuvant enhanced the accumulation effect of pyrimethanil residue by 31.7% after repeated applications, and the half-lives were similar (5.2 and 4.2 d). The adjuvant had comparable accumulation effects (1.75 and 1.83) and similar half-lives (5.4 and 5.5 d) for boscalid. In absence of adjuvant, the risk quotients (RQs) of pyrimethanil (0.41 and 0.33) and boscalid (0.49 and 0.63) after twice applications at pre-harvest interval were lower than 1. Adding the methylated vegetable oil adjuvant to fungicides would result in unprolonging half-life and acceptably low dietary exposure risk on strawberries, but lower dosage of fungicides were used.

Residue behavior and risk assessment of imidacloprid applied on greenhouse-cultivated strawberries under different application conditions.

A risk assessment for imidacloprid applied on strawberries under different conditions was performed after residue determination using the quick, cheap, effective, rugged, and safe (QuEChERS) method. The application conditions were varied according to the applied dosage, addition of a plant oil or organosilicon surfactant, water volume, and sprayer type. The degradation dynamics of imidacloprid on strawberries followed first-order kinetics. At applied doses of 30-60 g a.i. ha-1, the half-lives of imidacloprid were 2.89-3.46, 1.98-3.65, and 2.57-2.77 days after application without a surfactant or with a plant oil or organosilicon surfactant, respectively. For water volumes of 112.5, 225, 450, 675, and 900 L ha-1, the half-lives of imidacloprid applied in the presence of the plant oil surfactant were 3.30, 7.70, 5.33, 7.70, and 6.30 days, respectively. The half-lives after application with a knapsack mist duster, electric sprayer, and manual sprayer were 2.16, 5.77, and 7.70 days, respectively. The health risk assessment revealed risk quotients less than 1 in all cases, indicating that the application of imidacloprid poses a low health risk to humans after a pre-harvest interval of 10 days under our application conditions. The risk assessment results can provide reference data for setting a reasonable maximum residue limit for imidacloprid on strawberries in China.