Photodegradation of nitenpyram under UV and solar radiation: Kinetics, transformation products identification and toxicity prediction.

The photodegradation of the neonicotinoid insecticide nitenpyram (NPY) under UV and solar irradiation has been investigated in water solutions in order to assess its persistence in the environment and its transformation into other potentially more toxic species. Time-courses were followed by ultra-high performance liquid chromatography-tandem mass spectrometry. Transformation products (TPs) were identified by their accurate product ion spectra, obtained with a quadrupole time-of-flight mass spectrometer after their liquid chromatographic separation. NPY was rapidly photodegraded under all the investigated conditions, following a first-order model and with half-lives varying from seconds to <10 min. Quantum yields were between 0.0385 and 0.0534 mol einstein. The identified TPs, some of them reported for the first time in this study, were formed through different reactions involving the nitro-ethylene moiety of the parent insecticide. Conversely to the lability of NPY, its TPs were more photo-stable in both ultrapure and river water. Moreover, in-silico toxicity assessment showed that most of them display a higher acute toxicity than NPY.