title: Determination of enantiomeric fractions of cypermethrin and cis-bifenthrin in Chinese teas by GC/ECD.
abstract: BACKGROUND
  The pyrethroids cypermethrin and cis-bifenthrin are the major pesticides used in tea plantations in China. Potential neurotoxic, genotoxic and immunotoxic effects of chronic exposure to pyrethroids have been reported. All synthetic pyrethroids are chiral compounds. There is a need to investigate the chiral transformation among isomers after tea processing in order to obtain an accurate risk assessment of these compounds.
  
  
  RESULTS
  The enantiomeric fraction (EF) of cis-bifenthrin residues was close to 0.5 in all tea samples tested, showing that the levels of (+)-isomer and (-)-isomer were equivalent and there was no preferential degradation. However, the patterns of EFs of cypermethrin residues varied depending on the type of tea. The EF of isomer 1R-3R-alphaS increased in black and dark tea samples (EF = 0.200-0.343) compared with the reference cypermethrin commercial mixture (EF = 0.116). In one oolong tea sample it was found that the relative abundance of some isomers was preferentially enhanced: 1R-3R-alphaS (EF = 0.260), 1S-3S-alphaR (EF = 0.263) and 1R-3S-alphaS/1S-3R-alphaR (the last elution peak, EF = 0.275). The relationship between EF and compound concentration was also analysed, showing that the variation in EFs of cypermethrin was concentration-dependent.
  
  
  CONCLUSIONS
  These findings appear to be useful for assessing the species-specific risk of exposure to cypermethrin and cis-bifenthrin.
authors.affiliation: School of Food Science and Technology, Jiangnan University, Wuxi, JiangSu, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Kuang
authors.forename: Hong
authors.initials: H
authors.lastname: Miao
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Hou
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Zhao
authors.forename: Jianzhong
authors.initials: J
authors.lastname: Shen
authors.forename: Yongning
authors.initials: Y
authors.lastname: Wu
mesh_terms: D028241:Camellia sinensis / Q000737:chemistry*; D004781:Environmental Exposure / Q000009:adverse effects; D005506:Food Contamination / Q000032:analysis*; D015394:Molecular Structure; D010575:Pesticides / Q000032:analysis*; D011722:Pyrethrins / Q000032:analysis*; D012307:Risk Factors; D013237:Stereoisomerism; D013662:Tea / Q000737:chemistry* / Q000145:classification
chemical_list: D010575:Pesticides; D011722:Pyrethrins; D013662:Tea