Adsorption of non-systemic pesticide chlorothalonil on grape cuticles and dewaxed grape cuticles: elucidating the role of wax

BACKGROUND Cuticular wax is vital for preventing pesticide migration into fruit tissue, yet interactions between pesticides and wax components remain unclear. This study investigated the adsorption of non-systemic pesticide chlorothalonil on grape cuticles and dewaxed grape cuticles to quantify wax contributions and elucidate the interaction between chlorothalonil and wax components. RESULTS The wax was distributed on the surface of the grape cuticles with higher lipophilicity. The distinct chlorothalonil adsorption behaviors on grape cuticles (featuring heterogeneous and multilayer chemical adsorption) and dewaxed grape cuticles (featuring homogeneous and monolayer physical adsorption) were attributed to the presence of wax. Wax accounted for 40.36% of the total grape cuticle content and contributed 67.47% to the chlorothalonil adsorption capacity, indicating that wax was the main site for chlorothalonil adsorption. Through wax analysis and molecular docking, hexadecanoic acid and octadecanoic acid were considered as the major contributors, primarily engaging in hydrophobic interactions with chlorothalonil. Furthermore, gradual fluorescence quenching of chlorothalonil was observed with increasing concentrations of these acids (both below saturation concentrations, r = 0.99), confirming the intermolecular interaction between chlorothalonil and these acids. CONCLUSION The study clarified the residue behavior in fruit cuticles and the interaction between pesticides and cuticular wax. The findings provide important insights for optimizing pesticide application strategies to reduce pesticide residues in fruits and improve pest management efficiency. © 2025 Society of Chemical Industry.