Photolysis of Fungicides on Simulated Leaf Surfaces vs. Aqueous Solutions: Pathways, Kinetics, and Environmental Detoxification Insights

The photochemical behaviors of fungicides under irradiation differ significantly between leaf surfaces and aqueous solutions. However, few studies have compared the photolysis of fungicides between these two environmental media. In this study, three typical fungicides—kresoxim-methyl (KM), pyraclostrobin (PAS), and cyprodinil (CRL)—were examined using carnauba wax to simulate leaf surfaces The photolysis kinetics, products, and pathways were systematically compared between aqueous solutions and wax films. On wax film, the photolysis rate constants of selected fungicides were observed to be significantly faster than in aqueous solution, with increases of 44, 5 and 36-fold for KM, PAS and CRL, respectively. The primary photolysis pathways on wax films involved photoisomerization and ether cleavage; while the hydroxylation process, commonly observed in aqueous systems, was absent. Toxicity assessments demonstrated that photolysis effectively reduced their ecotoxicities in both systems, with the photolysis on wax film documented as a more profound detoxification process. Moreover, wax film thickness and pesticide additives significantly influenced photodegradation kinetics of all the three fungicides. The present study highlighted the significant influence of environmental media on the photodegradation pathways of pesticides.