Study of the Photodegradation Kinetics and Pathways of Hexaflumuron in Liquid Media

Hexaflumuron, one of the benzoylphenylurea insect growth regulators, can be leached into surface water and thus having a potential impact on aquatic organisms. In this study, the photodegradation processes of hexaflumuron under high-pressure mercury lamp irradiation were assessed. The photodegradation kinetics were studied, as were the effects of pH, different light sources, organic solvents and environmental substances, including nitrate ions (NO3-), nitrite ions (NO2-), ferrous ions (Fe2+), ferric ions (Fe3+), humic acid, sodium dodecyl sulfate (SDS) and hydrogen peroxide (H2O2). Three photodegradation products in methanol were identified by gas chromatography-mass spectrometry (GC-MS). In general, the degradation of hexaflumuron followed first-order kinetics. In the four media studied, the photodegradation rate order was n-hexane>methanol>ultrapure water>acetone. Faster degradation was observed under high-pressure mercury lamp irradiation than under xenon lamp irradiation. The pH had a considerable effect, with the most rapid degradation occurring at pH 5.0. The photodegradation rate of hexaflumuron was promoted in the presence of NO3-, NO2-, Fe2+, humic acid, SDS and H2O2, but inhibited by Fe3+. Moreover, the presumed photodegradation pathway was proposed to be the cleavage of the urea linkage.