UC Irvine

The environmental fate of neonicotinoids (NNs) is a key regulatory issue due to their widespread distribution, mobility, and role in honeybee colony collapse disorder. Here, we explore the potential matrix effects of the commercial formulations on the photochemistry of two NNs, dinotefuran (DNF) and nitenpyram (NPM). The commercial formulations and the pure reagents, both embedded in KBr pellets, were irradiated at wavelengths from 254 to 350 nm. Loss of the NN and product formation were followed using Fourier transform infrared spectroscopy and direct analysis in real time mass spectrometry. Quantum yields for loss of NN in commercial formulations were within experimental error of the pure NN. However, quantum yields for loss in KBr were consistently smaller than those previously measured for thin films of pure compounds, suggesting increased quenching of excited intermediates in the dense solid KBr matrix. At 350 nm where NPM absorbs, the quantum yield for loss in the formulation was about half that of the pure compound, which was attributed to a reduction in the NPM absorption cross section due to the presence of water taken up by additional formulation ingredients. Major products of DNF and NPM photolysis were the same in the formulation and in the pure compound. However, in contrast to previous thin film measurements, unexpected infrared peaks at 2222 and 2136 cm-1 during photolysis of DNF in KBr were identified as N2O trapped in the KBr matrix and NO+, respectively. Overall, the presence of other compounds in the formulations did not significantly alter the photochemistry compared to the pure compounds.