Neonicotinoids (NNs) are widely used since they were first introduced in 1991 due to their low mammalian toxicity. However, there are increasing concerns regarding their effects on non-target species, especially bees, and hence it is important to understand their fates once they are applied in the environment. Photolysis is considered to be one of the major environmental fates for NNs that absorb in the actinic region above 290 nm. Photolysis studies were performed using a broad band emission lamp centered at 313 nm and a 254 nm low pressure mercury lamp for investigating the wavelength dependence. Photolysis quantum yields of the NNs imidacloprid, clothianidin, thiamethoxam, dinotefuran, acetamiprid, thiacloprid, and nitenpyram were studied using attenuated total reflectance FTIR (ATR-FTIR). Thin films of NN were formed on a Ge crystal and ATR-FTIR spectra were taken before and during UV irradiation. Quantum yields were measured for the 313 nm irradiation to be of the order of 10-3 for the NNs that absorb above 300 nm. After irradiation, the cell was repositioned to scan above the crystal for gas phase products by transmission FTIR. Gas phase products were also studied using a transmission FTIR through solid films of the NN deposited on the surface of an IR window, where both the solid and the gas-phase could be probed at the same time. The sole gas phase product observed was N2O, generated in approximately 100% yield from the nitroguanidine NNs. The implications for photodegradation of the NNs on surfaces in the environment such as seeds, soil and dust particles, and for atmospheric N2O will be discussed.

Quantum yields and product studies for photolysis of neonicotinoids solid films

2019 Fall National Meeting

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