DIRECT PHOTOLYSIS OF FENPYROXIMATE IN A BUFFERED AQUEOUS SOLUTION UNDER A XENON LAMP

摘要

Exposed to light from a xenon lamp of spectral intensity and wavelength distribution comparable to that of sunlight, fenpyroximate (I), a miticide manufactured by Nihon Nohyaku (Tokyo), degrades in neutral aqueous solution with a half-life of 1.5 h to form primarily its cis geometric isomer (II). The degradation of II was also measured and yielded a half-life of 10.5 h. The quantum yield of the phototransformation, 7.5%, was calculated directly from the absorption spectrum of I, the wavelength distribution of the light source, and the rate at which degradation occurred. This approach was selected rather than actinometry because it measures all parameters directly, does not depend on the additional assumptions inherent in actinometry, and requires only the parameters already requested in U.S. Environmental Protection Agency (EPA) guidelines. The rapid degradation of fenpyroximate and of its geometric isomer indicates that, when exposed to sunlight, they would not accumulate in an aqueous environment.