Photolysis of the novel meta-diamide insecticide broflanilide in solutions: Kinetics, degradation pathway, DFT calculation and ecotoxicity assessment

Risk assessment of broflanilide for human and non-target terrestrial organisms in cauliflower production

Broflanilide is a newly-developed meta-diamide insecticide, proposed for the control of a wide variety of chewing pests on many crops. In view of the proposed use of broflanilide and its environmental fate, it may be exposed to consumers and non-target organisms, which adversely affect human and the environment. In this paper, a rapid, sensitive and valid UPLC-MS/MS method was established for simultaneous analysis of broflanilide and its two major metabolites, DM-8007 and S (PFP-OH)-8007, in cauliflower. Then, the dissipation behaviors and final residues of broflanilide and its two major metabolites in cauliflower from eight sites with different climatic conditions in China were studied via the described analytical method. In addition, the acute toxicity test of 9.5 % suspension concentrate of broflanilide, broflanilide standard, DM-8007 and S (PFP-OH)-8007 were conducted to non-target terrestrial organisms. Risk assessment for human and non-target terrestrial organisms in cauliflower production was evaluated based on the maximum annual application rates and intervals. The results showed that the highest residue of broflanilide detected in cauliflower samples was all lower than the corresponding MRLs (2 mg/kg) in Japan. Chronic food dietary risk estimates for broflanilide do not exceed 50 % for all the Chinese population groups. Moreover, broflanilide is of low acute toxicity to birds and earthworm, while broflanilide and its metabolites is classified as highly toxic to adult honeybees. Acute risks of broflanilide to birds and earthworms were deemed to be acceptable in a realistic worst-case scenario, while its risk to adult honeybees and ladybug was unacceptable. A protection statement for honeybees and ladybug is required to recognize the high toxicity of broflanilide on related product labels. The study will be conducive to provide guidance for the rational application of broflanilide in cauliflower production.

Photochemical Degradation of the New Nicotine Pesticide Acetamiprid in Water

Acetamiprid is a novel nicotinic pesticide widely used in modern agriculture because of its low toxicity and specific biological target properties. The objective of this study was to understand the photolysis pattern of acetamiprid in the water column and elucidate its degradation products and mechanism. It was observed that acetamiprid exhibited different photolysis rates under different light source conditions in pure water, with ultraviolet > fluorescence > sunlight; furthermore, its photolysis half-life ranged from 17.3 to 28.6 h. In addition, alkaline conditions (pH 9.0) accelerated its photolysis rate, which increased with pH. Using gas chromatography-mass spectrometry, five direct photolysis products generated during the exposure of acetamiprid to pure water were successfully separated and identified. The molecular structure of acetamiprid was further analyzed using density functional theory, and the active photodegradation sites of acetamiprid were predicted. The mechanism of the photolytic transformation of acetamiprid in water was mainly related to hydroxyl substitution and oxidation. Based on these findings, a comprehensive transformation pathway for acetamiprid was proposed.

Hydrolytic Behavior of Novel Pesticide Broflanilide and Its Dissipative Properties in Different Types of Soils

All pesticides are toxic by nature and pose short- or long-term safety risks to human or the environment, especially when they were used extensively and absence of safety measures. As a new insecticidal active compound with a novel mechanism of action, there is a serious inadequate of information on the hydrolytic behavior of broflanilide in the aqueous environment, as well as its degradation pattern in agricultural soils. In particular, the effects of temperature and pH of the aqueous environment on its hydrolytic behaviors and the dissipation pattern in different types of agricultural soils were still in a dark box. And the further understanding and insights into this insecticidal active ingredient were being deeply conditioned by these doubts. The hydrolysis behavior of broflanilide and the dissipation pattern in soil were systematically investigated by constructing hydrolysis systems with different temperatures and pH values, and conducting spiking experiments in different types of agricultural soil in the laboratory. The obtained results showed that the longest hydrolysis half-life of 10 mg/L broflanilide at 25 °C was 43.32 h (in pH 4.0 buffer), while it was only 12.84 h in pH 9.0 buffer. In pH 7.0 buffer, the hydrolysis rate of broflanilide exhibited a significant temperature dependence, as shown by the fact that for every 10 °C increase in the system temperature, the corresponding hydrolysis rate will increase about 1.5 times. The dissipation experiments in soils showed that broflanilide was most rapidly dissipated in fluvo-aquic soil (half-life of 1.94 days), followed by lime concretion black soil (half-life of 2.53 days) and cinnamon soil (half-life of 3.11 days), and slower in paddy soil (half-life of 4.03 days). It was indicated that broflanilide was a readily degradable pesticide in both aqueous environment and agricultural soil, and it was significantly affected by the temperature and pH of the system.

Photolysis mechanism of eleven insecticides under simulated sunlight irradiation: Kinetics, pathway and QSAR

Insecticides are widely used in crop protection against insects and frequently detected in aquatic environment. Photolysis kinetics are directly related with exposure assessment and risk assessment. However, the photolysis mechanism of neonicotinoid insecticides with different structures has not been studied and compared systematically in the literature. In this paper, the photolysis rate constants in water were determined for eleven insecticides under irradiation of simulated sunlight. At the same time, the photolysis mechanism and effect of dissolved organic matter (DOM) on their photolysis were studied. The results showed that photolysis rates of eleven insecticides vary in a large range. The photolysis rates of nitro-substituted neonicotinoids and butenolide insecticide are much faster than that of cyanoimino-substituted neonicotinoids and sulfoximine insecticide. The ROS scavenging activity assays reveal that direct photolysis dominates the degradation of seven insecticides and, on the other hand, self-sensitized photolysis dominates four insecticides. The shading-effect from DOM can reduce the direct photolysis rates, on the other hand, ROSs generated by triplet-state DOM (³DOM*) can also accelerate photolysis of insecticides. According to the photolytic products identified from HPLC-MS, these eleven insecticides have different photolysis pathways. Six insecticides are degraded from the removal of nitro group from their parent compounds and four insecticides are degraded through ·OH reaction or singlet oxygen (¹O₂) reaction. QSAR (quantitative structure-activity relationship) analysis showed that photolysis rate was directly related to the energy gap between the highest occupied molecular orbital to the lowest unfilled molecular orbital (E_gap = E_LUMO-E_HOMO) and dipole moment (δ). These two descriptors reflect the chemical stability and reactivity of insecticides. The pathways developed from identified products and the molecular descriptors of QSAR models can well verify the photolysis mechanisms of eleven insecticides.