Studies On The Enantioselective Degradation Of Chiral Pesticides Lambda-cyhalothrin

Because of the stereoselective between the chiral pesticide and acceptor, degradation behavior for the enantiomers of a chiral pesticide in the environment exhibit significant differences. Therefore, research on chiral pesticide separation methods and environmental fate as well as metabolization mechanism, is very important to security application and environmental risk assessment on chiral pesticides.In this thesis, the chiral pesticides separations and the environmental behavior were carried out by HPLC on the cellulose CSPs under normal phase conditions. The research work could be divided into four parts:Firstly, the chiral resolution of three chiral pesticides indoxacarb, lambda-cyhalothrin(LCT), simeconazole were studied on cellulose tris-(3,5-dimethylphenylcarbamate)-coated chiral stationary phase (CDMPC-CSP) using normal phase high-performance liquid chromatography (NP-HPLC). The effects of the mobile phase composition including the concentration and type of the alcohol modifiers in hexane, flow rate and column temperature on enantiomers separation were determined. The thermodynamical mechanism of enantioseparation and chiral recognition mechanism had also been discussed. The results showed that the best separation were achieved using20%n-propanol for indoxacarb,2%iso-butanol for lambda-cyhalothrin, and20%iso-propanol for simenconazole as modifiers in hexane at25℃with the selectivity factor (a) of1.69,1.82and1.70. The resolution factors (Rs) decreased with the flow rates increased over a range from0.4to1.1mL·min-1. The retention factors (k1) and selectivity factors (a) for the enantiomers of analytes decreased upon increasing the temperature. The lna-1/T plots for racemic chiral pesticides were linear at the range of15-35℃, the chiral separations were controled by enthalpy. The different hydrogen bonding, π-π, and dipole-dipole interactions between the enantiomers and the CDMPC-CSP played an important role in chiral discrimination.Secondly, the dissipation dynamic and the enantioselective degradation of lambda-cyhalothrin (LCT) in soils were studied by incubation with racemate LCT in four agricultural soils. The dissipation of LCT enantiomers in soils was followed pseudo-first-order kinetic’s law. The dissipation rate was greatly influenced by pH and organic matter of each soil. The results showed that the degradation of LCT in soils was associated with organic matter of each soils, and the dissipation rate in the descending order was4#>1#>3#>2#. The results indicated that LCT was dissipated faster in lower organic matter of soil, and high pH value was perfered for degradation. The stereoselective degradation in the soils led to significant difference between two enantiomers. The EF value was decreased with the increase of incubation time in1#soil, the first enantiomer was dissipated faster than the second one.Thirdly, the dissipation dynamic and the enantioselective degradation of indoxacarb in soils were studied by incubation with racemate indoxacarb in four agricultural soils. The dissipation of indoxacarb enantiomers in soils were followed pseudo-first-order kinetic’s law. The dissipation rate was greatly influenced by pH and organic matter of each soil. The results showed that the degradation rate of indoxacarb was different in four soils, and the dissipation rate in the descending order was3#>4#>1#>2#. The results indicated that a faster dissipation rate for indoxacarb in alkaline soil than acidic soil, and there was a bigger difference of half-time period in high organic matter of soil. The stereoselective degradation in the soils led to significant difference between two enantiomers in test soils except1#. The EF value was inceased with the increase of incubation time in3#soil, the second enantiomer was dissipated faster than the first one.Fourthly, the leaching of lambda-cyhalothrin and indoxacarb enantiomer in four agricultural soils were studied by soil thin layer chromatography. The Rf value of lambda-cyhalothrin in the descending order was4#>1#>3#>2#, the results concluded that the higher the organic matter of soil, the worse leaching. The Rf value of indoxacarb in the descending order was4#>3#>2#>1#, it indicated that the transferability of indoxacarb was associated with the pH, and the mobility of indoxacarb was increased with the cation exchange capacity decrease.