Research On Photoloysis Of Pyrethroid Pesticide And The Chiral Stability Of Degradation In Soil

At present,25%of commercialed pesticides are chiral. Among the chiral pesticides,pyrethroids are a group of chiral agricultural and hygiene insecticides. It has broadspectrum of pesticides, with quick high-efficiency low residue for crop safety etc. But ithas one or several chiral center and consists of several enantiomers. Different enantiomersof pyrethroids often exhibit different bioactivity, toxicity as well as metabolism behaviorin the environment. Research on enantioselective environmental behavior of pyrethroids isa hot spot in environmental chemistry.In this paper, cypermethrin was investigated in this study related to their photolysischaracteristics by using mercury lamp source and sun light. And fenpropathrin wasinvestigated in details related to their chiral separation and enantioselective degradation insoil. Following experimental results were obtained:(1) Elution order of cypermethrin enantiomers was concludedEnantiomers of cypermethrin were successfully separated by using chiral HPLC, andelution order of cypermethrin enantiomers was further concluded on Chiralcel OD-Hcolumn.(2) The photolysis of enantiomer4and enantiomer8in high-pressure mercury lampThe enantiomer4and enantiomer8of cypermethrin were prepared by chiral HPLC.Using this method, this paper studied two enantiomers of the chiral pesticides inhigh-pressure mercury lamp irradiation in the degradation trend. The result showed thatthe degradation of the two enantiomers in the trend is slow down after the last tends tobalance; the degradation half-life of enantiomer4was7.11d, the degradation half-life ofenantiomer8was7.21d. In addition, light stimulation of two enantiomers of the chiralpesticides in the conversion occurred, and study their transformation law of enantiomers.Cypermethrin obtained while in the degradation of enantiomer4, were transformed toenantiomer6, enantiomer2, enantiomer3. Cypermethrin obtained while in the degradationof enantiomer8, were transformed to enantiomer1, enantiomer7, enantiomer5.(3) The photolysis of enantiomer2under different light conditionsThe enantiomer2of cypermethrin was prepared by chiral HPLC. Using this method,this paper studied degradation trend of enantiomer2under different lights. The resultsshowed that between the two light sources, the photolysis rate of enantiomer2undermercury lamp was higher than that under sun light. The degradation half-life of enantiomer2was7.29d under mercury lamp, the degradation half-life of enantiomer2was11.38d under sun light. In addition, light stimulation of monomer of the chiralpesticides in the conversion occurred. And the two experiments exhibifed sameenantiomerization, were transformed to enantiomer6, enantiomer3, enantiomer4.(4) Study on enantioselective degradation of fenpropathrin in soilEnantioselective determinantion of fenpropathrin in soils was accomplished by MatrixSolid-phase Dispersion (MSPD) extraction in combination with chiral and achiral HPLC.On this basis, enantioselective degradation of S-(+)-fenpropathrin and fenpropathrin wereinvestigaed in details. The degradation of fenpropathrin in Shijiazhuang soil showed thehalf-lives was13.15d, and S-(+)-fenpropathrin was11.79d. Obvious enantioselectivitywas observed in Shijiazhuang soil with S-(+)-fenpropathrin faster degraded thanfenpropathrin. Moreover, S-(+)-fenpropathrin in the Shijiazhuang soils showed certainenantiomerization during the degradation process. But the enantiomerization rate was lowand the bioactivity of total fenpropathrin was not influence significantly by thisenantiomerization.