Toxicity and environmental fate of the less toxic chiral neonicotinoid pesticides: a review

Neonicotinoids represent 25% of the insecticidal market and are essential for crop production, yet traditional neonicotinoids are toxic to most pollinators, which are also essential for food production. This issue may be addressed by the use of some chiral neonicotinoid isomers, which are much less toxic. Here, we review the chiral neonicotinoids dinotefuran, sulfoxaflor, cycloxaprid, and paichongding, with focus on their chiral characteristics, configuration stability, biological activity, ecological toxicology, and environmental fate. Isomeric separation of chiral neonicotinoids can be achieved by chromatography. The dinotefuran R isomer is less toxic than the S isomer to honeybees and earthworms by a factor of 2.7–145.9, with similar control efficiency of common agricultural pests. The insecticidal activity of (5R,7S)-paichongding are up to 20.1 times higher than that of other isomers, and it is absorbed fastest by crop roots and tends to be preferentially degraded and mineralized in soils. Therefore, formulations containing R-dinotefuran or (5R,7S)-paichongding could decrease ecological damage without compromising food production. On the other hand, it has not been possible to synthesize chiral isomers of sulfoxaflor and cycloxaprid, owing to the instability of their monomers in polar solvents.