A thorough understanding of absorption, distribution, metabolism, and excretion (ADME) of insecticide candidates is essential in insecticide development and structural optimization. Here, ADME of pyraquinil, a novel insecticidal GABA receptor antagonist, in Plutella xylostella larvae during the accumulation phase and depuration phase was investigated separately using a combination of UHPLC-Q-Orbitrap, HPLC-MS/MS, and MALDI-MSI. Five new metabolites of pyraquinil were identified, and a metabolic pathway was proposed. The oxidative metabolite (pyraquinil-sulfone) was identified as the main metabolite and confirmed by its standard. Quantitative results showed that pyraquinil was taken up by the larvae rapidly and then undergone a cytochrome P450s-mediated oxidative transformation into pyraquinil-sulfone. Both fecal excretion and oxidative metabolism were demonstrated to be predominant ways to eliminate pyraquinil in P. xylostella larvae during accumulation, while oxidative metabolism followed by fecal excretion was probably the major pathway during depuration. MALDI-MSI revealed that pyraquinil was homogeneously distributed in the larvae, while pyraquinil-sulfone presented a continuous enrichment in the midgut during accumulation. Conversely, pyraquinil-sulfone located in hemolymph can be preferentially eliminated during depuration, suggesting its tissue tropism. It improves the understanding of the fate of pyraquinil in P. xylostella and provides useful information for insecticidal mechanism elucidation and structural optimization of pyraquinil.

ＤＯＩ： １０．３７２４ ／ ＳＰ．Ｊ．１１２３．２０２２．０１０１１ * 收稿日期：２０２２•０１•１７ * 通讯联系人．Ｔｅｌ：(０２０)８５１６１４３０，Ｅ•ｍａｉｌ：ｔａｎｇｘｕｅｍｅｉ＠ ｇｄａａｓ．ｃｎ． 基金项目：国家重点研发计划(２０１９ＹＦＣ１６０５６００) ；广东省自然科学基金(２０２０Ａ１５１５０１０６２０) ；广东省农业科学院科技创新战略专项 资金( 高水平农科院建设) ；广东省农产品质量安全风险评估重点实验室项目(２０１９Ｂ１２１２０３００９) ． Ｆｏｕｎｄａｔｉｏｎ ｉｔｅｍ： Ｎａｔｉｏｎａｌ Ｋｅｙ Ｒ＆Ｄ Ｐｒｏｇｒａｍ ｏｆ Ｃｈｉｎａ ( Ｎｏ． ２０１９ＹＦＣ１６０５６００) ； Ｎａｔｕｒａｌ Ｓｃｉｅｎｃｅ Ｆｏｕｎｄａｔｉｏｎ ｏｆ Ｇｕａｎｇｄｏｎｇ Ｐｒｏｖｉｎｃｅ ( Ｎｏ． ２０２０Ａ１５１５０１０６２０) ； Ｓｐｅｃｉａｌ Ｆｕｎｄ ｆｏｒ Ｓｃｉｅｎｃｅ ａｎｄ Ｔｅｃｈｎｏｌｏｇｙ Ｉｎｎｏｖａｔｉｏｎ Ｓｔｒａｔｅｇｙ ( Ｃｏｎ• ｓｔｒｕｃｔｉｏｎ ｏｆ Ｈｉｇｈ•Ｌｅｖｅｌ Ａｃａｄｅｍｙ ｏｆ Ａｇｒｉｃｕｌｔｕｒａｌ Ｓｃｉｅｎｃｅｓ ｏｆ Ｇｕａｎｇｄｏｎｇ Ｐｒｏｖｉｎｃｅ) ； Ｇｕａｎｇｄｏｎｇ Ｐｒｏｖｉｎｃｉａｌ Ｋｅｙ Ｌａｂｏｒａｔｏｒｙ ｏｆ Ｑｕａｌｉｔｙ ａｎｄ Ｓａｆｅｔｙ Ｒｉｓｋ Ａｓｓｅｓｓｍｅｎｔ ｏｆ Ａｇｒｉｃｕｌｔｕｒａｌ Ｐｒｏｄｕｃｔｓ ( Ｎｏ． ２０１９Ｂ１２１２０３００９) ．

As new pesticides are continuously introduced into agricultural systems, it is essential to investigate their environmental behavior and toxicity effects to better evaluate their potential risks. In this study, the degradation kinetics, pathways, and aquatic toxicity of the new fused heterocyclic insecticide pyraquinil in water under different conditions were investigated for the first time. Pyraquinil was classified as an easily degradable pesticide in natural water, and hydrolyzes faster in alkaline conditions and at higher temperatures. The formation trends of the main transformation products (TPs) of pyraquinil were also quantified. Fifteen TPs were identified in water using ultrahigh-performance liquid chromatography coupled to quadrupole Orbitrap high-resolution mass spectrometry (UHPLC-Orbitrap-HRMS) and Compound Discoverer software, which adopted suspect and nontarget screening strategies. Among them, twelve TPs were reported for the first time and 11 TPs were confirmed by synthesis of their standards. The proposed degradation pathways have demonstrated that the 4,5-dihydropyrazolo­[1,5-a]­quinazoline skeleton of pyraquinil is stable enough to retain in its TPs. ECOSAR prediction and laboratory tests showed that pyraquinil was “very toxic” or “toxic” to aquatic organisms, while the toxicities of all of the TPs are substantially lower than that of pyraquinil except for TP484, which was predicted to pose a higher toxicity. The results are important for elucidating the fate and assessing the environmental risks of pyraquinil, and provide guidance for scientific and reasonable use.

Background Cowpea (Vigna unguiculata L. Walp.) is an economically important crop. It is nutritious and popular with consumers. However, it has been listed as one of the agricultural products of critical concern about safety in China and cyromazine is the major risk factor. Objectives This study analyzed the dissipation and permeation kinetics of cyromazine residue in cowpea, to offer a scientific basis for the rational use of pesticide and ensuring the safety of agricultural products. Materials and methods Investigated the dissipation and residue level of the systemic insecticide cyromazine on cowpea under field and stored conditions. Subsequently, studied the spatial distribution of cyromazine using MSI to visualize the dynamic processes of permeation and migration in the tissues post pesticide application. Results The dissipation processing of cyromazine in cowpea was shown to follow the first-order kinetics and half-life was 7.76 days in the field. In cowpea, the permeation and migration rate of cyromazine was quite faster than that in the kidney beans and accumulation mainly in the pulp. It is not safe to apply cyromazine to cowpeas with reference to the application method on kidney beans. Conclusions These findings present vital data for the determination of risks linked with cowpea consumption and pesticide intake.