Matrix Effects in the Heterogeneous Photochemistry of Neonicotinoid Pesticides

Abstract:

Neonicotinoids (NNs) and their environmental fates are of great interest because they are widely used on a global basis and become distributed throughout the environment. Their use has been increasingly associated with deleterious effects particularly on pollinators, including bee colony collapse disorder. A number of studies have been carried out on the chemistry and photochemistry of pure NNs. However, neonicotinoids are applied as dilute mixtures in commercial formulations. It is therefore important to understand if/how the matrix in which they are found impacts their chemistry and hence environmental fates and impacts.

Studies aimed at identifying differences in the photochemistry of pure versus formulated versions of selected commonly used NN pesticides (the nitroguanidine dinotefuran and the nitromethylene nitenpyram) will be presented. The loss of NN and formation of products during the photolysis of thin solid films of pure NN are followed using attenuated total reflectance (ATR)-FTIR as well as Direct Analysis in Real Time mass spectrometry (DART-MS), UPLC-MS, and high-resolution mass spectrometry. Due to experimental challenges, ATR-FTIR could not be applied to the formulations, so analogous studies are carried out by embedding the NN in a KBr matrix. The gas phase is interrogated using transmission FTIR. Kinetics and degradation products for the pure compared to formulated NNs will be compared, providing fundamental scientific understanding of the degradation processes involved and how these are sensitive to matrix effects will be discussed.