Separation of Chiral Pyrethroid Pesticides and Application in Pharmacokinetics Research and Human Exposure Assessment

Abstract

The pesticides are originally used to kill insects, fungi and other organisms hazarding crops to improve agricultural production. With the development of technology, people have been gradually aware of the impact of pesticides to the environment and food safety. More than 25% of over 650 existing commercial pesticides are characterized by chirality (Zheng, 2001; Williams, 1996). Of the commercial pesticides, the pyrethroid insecticides account for 25% of the sales of pesticides in the world, and most of them have chiral isomers(You et al., 2001). The chiral enantiomers of pesticides were usually not distinguished in previous studies, and as a result, the risk assessment of pyrethroid pesticides was incomplete. With the development of stereochemistry, the chirality of compounds has aroused wide concern. The researches on medicine and pesticides have penetrated into the field of molecular stereochemistry. Especially in the field of medicine, there have been more researches on and application of the single enantiomers of chiral drugs, and the natures of the enantiomers have been well studied. However, the researches on chiral pesticides relatively lag behind. The researches of various natures of pyrethroid pesticides are usually carried out by using racemic mixture, so there are few detailed data and related researches of single chiral enantiomers. Despite the same chemical and physical properties of the enantiomers of chiral pesticides, they may have entirely different biological activities, toxicities, toxicologies and metabolic pathways in the biological systems. For instance, usually only one out of the four chiral monomers of permethrin is provided with high insecticide efficiency, and the remaining three are low efficient or even ineffective in terms of insecticidal effect. And of the eight chiral enantiomers of cypermethrin, only two monomers of ciscypermethrin and two monomers of transcypermethrin have high insecticidal effect. And as a result, not only the cypermethrin with 8 chiral monomers but the beta-cypermethrin with 4 highly effective monomers has been commericially producted. The overwhelming number of widely used pyrethroid pesticides are almost sold and used in the form of racemic mixtures. The use of low efficient or ineffective isomers of the racemic mixtures not only cannot effectively control insect pests, resulting in the waste of manpower