Kinetics of the riboflavin-sensitized degradation of pyrethroid insecticides

[Display omitted] •Photochemical reaction of Riboflavin and pyrethroid insecticides was studied.•Bioallethrin and Ethyl Chrysanthemate are reactive toward singlet oxygen.•Bioallethrin and Ethyl Chrysanthemate quench the riboflavin triplet state.•Photosensitized degradation of pyrethroids depends on the structure of the pyrethroids. The Riboflavin (Rf) photosensitized degradation of pyrethroid insecticides was studied under visible-light conditions. The pyrethroid insecticides studied (Pyrs) were Bioallethrin (Bio), Ethyl chrysanthemate (EC), Permethrin (Per), and Cypermethrin (Cyp). Riboflavin, one of the natural photosensitizers widely distributed in nature, was used as a photosensitizer in order to mimic the natural environment. Pyrs degradation would occur due to the reaction of the insecticide with the excited electronic states of the Rf and/or the reactive oxygen species (ROS) generated mainly from the triplet excited state of the Rf (3Rf*). Singlet oxygen (1O2) and superoxide anion (O2•−) are the main ROS photogenerated from 3Rf*. Only EC and Bio react towards 1O2 with reactive rate constants of 3.1 × 106 and 2.4 × 106 M−1s−1, respectively. Rf-sensitized photolysis of Pyrs in the presence and absence of superoxide dismutase indicates that O2•− does not participate in Pyrs degradation. Per and Cyp are poor quenchers of 3Rf* (3kq