Dissipation and sorption-desorption of benzisothiazolinone in agricultural soils and identification of its metabolites.

Benzisothiazolinone has been widely used to control bacterial and fungal diseases in various agricultural crops by destroying the nuclear structure and interfering with the metabolism of microbial cells. In this study, the dissipation, transformation and sorption-desorption of benzisothiazolinone (BIT) in five soils were investigated to evaluate its environmental fate. Results showed that the degradation of BIT in all the tested soils fitted the first order kinetics and increased with soil organic matter (OM) content. Degradation differences between unsterilized natural and sterilized soils (t 1/2 = 0.09-26.66 and 6.80-86.64 d) suggested that BIT degradation is primarily driven by biological processes and assisted by abiotic degradation. Additionally, BIT dissipated fastest in flooded soils (t 1/2 = 0.20-4.53 d), indicating that anaerobic microorganisms are more likely to degrade BIT compared to aerobic microbes. Also, during the soil degradation process, two metabolites were monitored and identified for the first time. BIT sorption was a spontaneous physical process with no desorption hysteresis effect, which fit the Freundlich model. BIT causes relatively strong sorption (log K OC = 3.76-4.19) and low persistence in soils, thus exhibiting a low potential risk for groundwater contamination.

Dissipation, Processing, Leaching, and Safety Evaluation of Flonicamid and Its Metabolites in Tea.

BACKGROUND: Tea is a popular traditional non-alcoholic beverage worldwide. Flonicamid is a selective systemic pyridine carboxamide insecticide that is widely used for controlling tea leafhopper in tea. OBJECTIVE: The leaching rates, dissipation dynamics, and residue levels of flonicamid and its metabolites in tea leaves during processing and transferring were investigated to validate the safe risk in tea and transfer behavior using high performance liquid chromatography-tandem mass spectrometry with a convenient pretreatment method. METHOD: The extracting method and immersion rate experiments were optimized by single factor analysis and orthogonal tests. The acetonitrile extracting solvent with 0.5% formic acid was used and optimal leaching conditions were obtained with a regime of 15 min immersion time, 100°C temperature, three immersions and a tea-to-water ratio of 1:50. RESULTS: Average recoveries in processed green tea and infusions were 80.85-98.75% with relative standard deviations <5.87%. LODs and LOQs of flonicamid, 4-trifluoromethylnicotinic acid (TFNA), N-(4-trifluoromethylnicotinoyl) glycine (TFNG), and 4-trifluoromethylnicotinamide (TFNA-AM) were 0.0013-0.350 and 0.004-1 µg/g, respectively. The processing factor of flonicamid was 0.36-5.52 during green tea manufacture. The leaching rates were 22.9-97.4% from processed tea to infusion. CONCLUSIONS: The risk of long-term and short-term dietary intake of flonicamid was safe in tea infusions with the risk quotient (RQ) values <1 for the Chinese consumer. This work may provide guidance for safe and reasonable consumption of flonicamid in tea in China. HIGHLIGHTS: The suitable leaching factors of flonicamid and its metabolites in tea infusions were optimized by orthogonal experimentation for the first time.

Dissipation, residues and risk assessment of oxine-copper and pyraclostrobin in citrus.

An efficient, sensitive, simple and fast method for the simultaneous determination of oxine-copper and pyraclostrobin in citrus fruit was developed and validated. The method uses ethylene diamine tetra-acetic acid as a competitive ligand to convert oxine-copper to soluble 8-hydroxyquinoline for analysis by QuEChERS and LC-MS/MS. Linear relationships were determined with correlation coefficients ranging from 0.9904 to 0.9998. The limits of detection for the analytes were 0.012-0.8 µg kg-1, and the limits of quantitation were 0.04-2.6 µg kg-1 in citrus. The average recoveries were 79.1-114.9% with relative standard deviations of less than 7.4%. The analyses of dissipation indicated that the half-lives of oxine-copper and pyraclostrobin were 1.94-3.67 and 1.79-2.48 days and the terminal residues were <0.08-8.99 and <0.02-1.90 mg kg-1, respectively. The risk quotients of oxine-copper and pyraclostrobin were 0.026-0.199 and 0.003-0.022, respectively. This risk assessment provides a reference for the safe and reasonable use of oxine-copper and pyraclostrobin and may help to establish maximum residue limits for these pesticides in China.

Dissipation, residues, and risk assessment of imidacloprid in Zizania latifolia and purple sweet potato under field conditions using LC-MS/MS.

A shortened version of Quick, Easy, Cheap, Effective, Rugged, and Safe method (QuEChERS) for determining the dissipation and residue of imidacloprid present in Zizania latifolia and purple sweet potato was established by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The average recoveries of imidacloprid in the two crops ranged from 82.12 to 113.79%, with relative standard deviation (RSD) of <7.32%. The dissipation dynamics of imidacloprid in Z. latifolia plants and purple sweet potato plants followed first-order kinetics, with half-lives of 3.2-5.5 days in each of sampling locations. The terminal imidacloprid residues in Z. latifolia and purple sweet potato at each of location were <0.005-0.120 mg kg-1. According to the risk assessment results, both the acute dietary risk quotient and chronic dietary risk quotient values were <1, indicating that imidacloprid is unlikely to pose health risks to humans with normal recommended use. The present study may serve as a valuable reference for the safe and reasonable use of imidacloprid in Z. latifolia and purple sweet potato fields.