Neonicotionids are a relatively recent class of pesticides that were introduced in the 1990's, largely replacing carbamates as seed dressings. They have been proposed to be at least partially responsible for the phenomenon of bee colony collapse, and as a result, restrictions are in place in Europe on several compounds in this class. While there is some understanding of their chemistry and photochemistry in solutions, relatively little is known about their reactions on solid substrates such as seeds. Neonicotinoids fall into three classes: nitroguanidines (imidacloprid, thiamethoxam, clothianidin, dinotefuran), cyanamidines (thiacloprid, acetamiprid) and nitromethylenes (nitenpyram). Laboratory studies have been carried out on the photochemistry of these compounds on solid substrates using attenuated total reflectance-FTIR and DART-MS. The nitroguanidines and nitromethylenes absorb light in the actinic region, l &gt; 290 nm. Quantum yields for were measured using o-nitrobenzaldehyde as an actinometer, and are found to be in the range ~ 10-2 - 10-3. This results in lifetimes of the order of hours to days at a solar zenith angle of 0°. Products are identified using DART-MS and ATR-FTIR, and in some cases, include compounds that have been previously identified as having greater mammalian toxicity than the parent neonicotinoid. Theoretical studies provide insight into the fundamental photochemistry of these compounds.

Chemistry and photochemistry of surface-bound neonicotinoids

251st National Meeting (2016)

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