| Studies have shown that 80%-90%of pesticides flow into the soil after being used,which will cause soil pollution.Meanwhile,about 30%of existing pesticides are chiral and the small structural differences of enantiomers can lead to the difference in degradation,enrichment,toxicity and toxicology in the environment.This paper chooses ?-cypermethrin,one of the pyrethroid Insecticides,for study of the selective degradation of ?-cypermethrin in soil spiked with heavy metal and fertilizer,and also select three environmental biology,plant(cabbage,rape,chili,cucumber and tomatoes),earthworms,frogs,studied selective metabolism of the compound.Two biochars were studied for the repair effect of?-cypermethrin in soils.Meanwhile,the two metabolites of ?-cypermethrin of cis-chrysanthemic acid(cis-DCCA)and 3-phenoxybenzoic acid(3-PBA)were also detected in the experiment.In terms of toxicity,the individual and joint toxicity of ?-cypermethrin and its metabolites to earthworms were determined,and the three compounds with cadmium and lead ion on the activity of soil toxicity were also conducted.Five soils were chosen for the study of degradation of ?-cypermethrin and its metabolites in soils.Results show that the degradation of ?-cypermethrin in five soil fits first-order kinetics,with half-time period ranging 13.3 to 47.08.There are differences in the degradation rate of ?-cypermethrin in the five soils and a-cypermethrin had the slowest degradation rate in high content of organic matter soil.Meanwhile,a-cypermethrin showed difference in selective degradation in the five soils.The degradation rate of(+)-(1R,cis,aS)is faster than(-)-(1S,cis,?R).Both of the two metabolites of a-cypermethrin,cis-DCCA and 3-PBA,can be detected in the process of cultivation and they are not easy to degrade in acid soil.Based on the experiment of enantioselective degradation of ?-cypermethrin in soil,the article also chooses the Heilong iang soil for study the influence of two species of heavy metals and four fertilizers on the metabolism of ?-cypermethrin and its metabolites for considering that conbined pollution from heavy metals and fertilizers may affect the environmental behaviour of pesticide.Results show that half-life of ?-cypermethrin in treatment groups is significantly lower than the control group.Meanwhile,the concentrations of cis-DCCA and 3-PBA in treatment group are significantly less than the control group and this may be explained by the evidence that addition of heavy metals lead to the reduction of?-cypermethrin degradation rate.Meanwhile,?-cypermethrin showed more selective degradation in treatment group than in the control group.Single and joint toxicity of ?-cypermethrin and heavy metals to soil enzyme was studied and the activity of soil enzyme of urease,catalase and sucrose in the treatment group was lower than in the control group.In addition,experiment of the influence of the addtion of fertilizers on the environmental behavior of ?-cypermethrin and its metolites was conducted and the result shows that the addition of fertilizer can affect the degradation half-life of ?-cypermethrin.Urea and chicken manure can accelerate the degradation of ?-cypermethrin,while microorganisms and SSP can inhibit the degradation of a-cypermethrin.Meanwhile,the concentrations of cis-DCCA and 3-PBA in treatment groups have a great difference with the control group.In the group added by urea,the concentration is higher than the control group,while in the group added by microorganism,the concentration is less than the control group.This may be explained by the evidence that change of the degration rate of parent compound effect the generation of its metabolites,?-cypermethrin showed more marked selective degradation in the group added by Urea and chicken than in the control group.In addition,a-cypermethrin showed less marked selective degradation in the group added by than microorganisms and SSP in the control group.The result of selective degradation of a-cypermethrin indicates that(+)-(1R,cis,aS)degradated preferentially and there was difference in selective degradation in treatment group.Selective degradation of a-cypermethrin would be enhanced by the addition of chicken manure and urea and the group added by chicken manure had a lowest EF value of 0.38.Selective degradation of a-cypermethrin would be enhanced by the addition of superphosphate and microbial fertilizer and the group added by microbial fertilizer had a highest EF value of 0.50.Five plants(cabbage,rape,chili,cucumber and tomato)were chosen for the study of the enantioselective degradation of a-cypermethrin.There are differences in the degradation rate of a-cypermethrin in the five plants and a-cypermethrin owned the fastest degradation rate in the cabbage.Meanwhile,a-cypermethrin in five plants shows a different selective degradation and the degradation rate of(+)-(1R,cis,aS)is faster than(-)-(1S,cis,aR).Pepper had the highest stereoselectivity according to the ES value test,which may due to different microorganisms or different enzyme systems.The article studies the metabolic behaviors ofa-cypermethrin and its metabolites in bullfrog and earthworm for evaluating stereoselectivity degradation and metabolic behaviorsof ?-cypermethrin in organism.Firstly,this study examined the ?-cypermethrin and its metabolites of cis-DCCA and 3-PBA in bullfrog organs in the experiment of oral administration and water exposure.Experimental results show that in water exposure experiments,Bullfrog skin can absorb the ?-cypermethrin and this compound and its two metabolites can be detected in large part of bullfrog organs.Concentration of these three compounds metabolism increased and reached equilibrium in various organs of the bullfrog.In the oral test,?-cypermethrin and its two metabolites degradated fastly in the various organs of the Bullfrog,reaching peak concentration at 8-12h,and degradating rapidly.Selective degradation of?-cypermethrin in the was detected and(-)-(1S-cis-aR)are more likely to gather in liver in the two experimental conditions.Bioaccumulaiton of ?-cypermethrin in earthworm were studied and the result showed that bioaccumulation curve of ?-cypermethrin in earthworm demonstrated in peak pattern.The main metabolites of ?-cypermethrin in earthworm were cis-DCCA and 3-PBA and the metabolic curve of cis-DCCA and 3-PBA were similar to their parent compound.Meanwhile,the concentration of 3-PBA was much higher than cis-DCCA.a-Cypennethrin degradated fast in soil and its metabolites of cis-DCCA and 3-PBA could be both detected in soil.The concentration of cis-DCCA increased during the experiments and topped at the 35th day and the concentration of 3-PBA increased and topped at the 11th day and then decreased with time and reached a equilibrium concentration at 14th day.The use of a-cypermethrin will lead to soil pollution and it is very important to develop a method to repair the contaminated soil by a-cypermethrin and its metabolites.Two kinds of biochar(Bamboo and straw)were add into Beijing soil to study the influence of bioaccumulation of a-cypermethrin in earthworms,with the two biocarbon adding at the percentage of 1%and 3%respectively.Results show that the 3%concentration of bamboo and straw will cause the decrease in the concentration of a-cypermethrin and its two metabolites in earthworm.Meanwhile,the half-life of a-cypermethrin in soils in the groups of 3%bamboo and straw group is significantly higher than in the control group,which showed tihat high levels of carbon addition will inhibit the soil degradation of a-cypermethrin. |
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