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The direct photodegradation quantum yields ( Φ ) of five representative aromatic carbamate pesticides - carbaryl, carbofuran, propoxur, isoprocarb, and metolcarb - were examined in both aqueous and non-aqueous solutions, the latter mimicking hydrophobic environments such as leaf surfaces. For carbaryl, carbofuran, isoprocarb, and metolcarb, the Φ values generally followed the order Φ water -CH 3 > -OH. For propoxur, the ether group also contributes to the formation of S-O • , which further reacts with H 2 O and enhances degradation in aqueous environments. Solvent polarity had a minimal effect on photodegradation. This comparative study of degradation in aqueous and nonaqueous phases provides insights for designing and selecting pesticides that are effective during use in nonaqueous environments, such as on leaf surfaces, yet degrade rapidly in aqueous environments in the post-application phase. • Photodegradation is dominated by S*, while polycyclic compounds further produce T * . • The degradation of MCAEs involves the generation of S •+ and S-O • . • Polarity has minimal impact, structure and hydrogen-donating ability of solvents are key. • The hydrogen-donating ability of solvents significantly affects photodegradation. • MCAE structures with heteroatoms may have different reaction sites.
Yuan et al. (Sat,) studied this question.