Photodegradation of the Novel Herbicide Pyraquinate in Aqueous Solution: Kinetics, Photoproducts, Mechanisms, and Toxicity Assessment

Abstract

Pyraquinate, a newly developed 4-hydroxyphenylpyruvate dioxygenase class herbicide, has shown excellent control of resistant weeds in paddy fields. However, its environmental degradation products and corresponding ecotoxicological risks after field application remain ambiguous. In this study, we systematically investigate the photolytic behaviors of pyraquinate in aqueous solutions and in response to xenon lamp irradiation. The degradation follows first-order kinetics, and its rate depends on pH and the amount of organic matter. No vulnerability to light radiation is indicated. Ultrahigh-performance liquid chromatography with quadrupole-time-of-flight mass spectrometry and UNIFI software analysis reveals six photoproducts generated by methyl oxidation, demethylation, oxidative dechlorination, and ester hydrolysis. Gaussian calculation suggests that activities due to hydroxyl radicals or aquatic oxygen atoms caused these reactions on the premise of obeying thermodynamic criteria. Practical toxicity test results show that the toxicity of pyraquinate to zebrafish embryos is low but increases when the compound is combined with its photoproducts.

Comparison of Biological and Genetic Characteristics between Two Most Common Broad-Leaved Weeds in Paddy Fields: Ammannia arenaria and A. multiflora (Lythraceae)

“…We selected three populations for each species to avoid the impact of herbicide use history on the study of sensitivity differences between A. arenaria and A. multiflora. The synthetic auxin herbicides, florpyrauxifen-benzyl [44] and MCPA-Na [45], had the best control effect on the two Ammannia species; however, the traditional acetolactate synthase inhibitor, pyrazosulfuron-ethyl [46], and the new 4-hydroxyphenylpyruvate dioxygenase inhibitor, pyraquinate [47], were ineffective in managing them. This study can serve as a basis for herbicide selection.…”

Complete chloroplast genome and comparison of herbicides toxicity on Aeschynomene indica (Leguminosae) in upland direct-seeding paddy field

“…The experiment included three to four biological replicates and the entire experiment was repeated twice. The effective rate of each herbicide causing 50% reduction in plant growth (GR 50 ) was determined using the four-parameter logistic function with the “drc” add-on package [ 38 ] in the R 3.1.3 Language and Environment for Statistical Computing [ 39 ]. This model is defined as follows: …”

Design, One-Step Highly Selective Synthesis and Enhancing Insecticidal Activity and Photo-Self-Degradation of Phenylpyrazole Esterified Derivatives as GABA and nACh Receptor Inhibitors

“…Jiao et al systematically investigated the photolytic behavior of pyrethroids under aqueous solution and xenon lamp irradiation. 17 The degradation rate depended on pH and the amount of organic matter. The analysis revealed six photoproducts generated by methyl oxidation, demethylation, oxidative dechlorination, and ester hydrolysis.…”

“…The results show that pyrethroids can degrade into small molecules of different structures under natural light, and the degradation process follows first-order kinetics. Jiao et al systematically investigated the photolytic behavior of pyrethroids under aqueous solution and xenon lamp irradiation . The degradation rate depended on pH and the amount of organic matter.…”