Environmental and laboratory studies of the photodegradation of the pesticide fenarimol

Abstract

The photophysics and photochemistry of the pesticide fenarimol were studied. From the absorption and fluorescence spectra, quantum yields and lifetimes, it is suggested that the lowest excited singlet state has predominatly n,π * character, and is localized on the pyrimidine ring. Phosphorescence measurements suggest a small singlet—triplet splitting. Halide ions are found to quench fenarimol flourescence. Photodecomposition of fenarimol in a variety of solvents was studied by gas chromatography—mass spectrometry. Although the products have not yet been characterized, degradation of this compound appears to involve cleavage of bonds to the quaternary carbon without significant dechlorination. Preliminary studies of the kinetics and relative quantum yields of photodegration show that the reaction proceeds via a first-order process, which is independent of pH, but which involves a photoactive intermediate. Chloride and bromide ions inhibit the photolysis,whereas the triplet quencher sorbic acid has no effect.