Studies On The Degradation Of Pyrethroid Pesticides

Pyrethroid pesticides are widely used as broad-spectrum,high-efficiency,low-toxicity insecticides.Extensive use can lead to environmental pollution,ecological damage,endanger human health and other problems.How to effectively remove these pesticides from the environment has become a widespread concern.In this paper,the photodegradation and microbial degradation of pyrethroid pesticides were studied.The main results are as follows:1.The degradation of X,-cyhalothrin and deltamethrin in aqueous solution under different light sources was studied.The results showed that the degradation rate under ultraviolet light(UV)radiation was much faster than that under simulated sunlight radiation.The degradation rates were accelerated 50.97 and 54.51 times,respectively.At the same time,the photodegradation process under the irradiation of two light sources conformed to the first order kinetics.2.The photocatalytic degradation of ?-cyhalothrin and deltamethrin in aqueous solution was studied by using nano titania(nTiO2)as photocatalyst under simulated sunlight radiation.The results showed that nTiO2 played a catalytic role in the degradation process.The degradation rates were 12.22 and 8.48 times higher than those without nTiO2,respectively.And the degradation behavior accorded with the first order kinetics.3.We also optimized the dosage of photocatalyst under simulated sunlight radiation.The results showed that the degradation rate firstly increased and then decreased with the increase of catalyst amount,and the optimal dosage was 2.0 mg/L nTiO2 to ?-cyhalothrin and 0.8 mg/L to deltamethrin in aqueous solution,respectively.4.The photodegradation products were indentified by ultra performance liquid chromatography-mass/mass spectrometry(UPLC-MS/MS)and gas chromatograph-mass spectrometry(GC-MS).On the basis of the structurally identified photoproducts,possible degradation pathway was proposed for the photolysis of ?-cyhalothrin and deltamethrin in aqueous solution.The photodegradation process of ?-cyhalothrin mainly involves ester bond breakage,C-C bond breakage,C-O bond breakage,photooxidation,photoisomerization,decyanation,and dehydroxylation.The degradation products are mainly phenoxybenzaldehyde,m-phenoxybenzene acetonitrile,?-cyano-3-phenoxybenzyl alcohol.The photodegradation process of deltamethrin in aqueous solution mainly involves ester bond breakage,C-C bond breakage,C-O bond breakage,photooxidation,decyanation,dehydroxylation,and rearrangement.The degradation products are mainly phenoxybenzaldehyde,m-phenoxybenzene acetonitrile,m-phenoxybenzoic acid methyl ester.5.Two strains of A4 and G3,which had higher degradation ability to ?-cyhalothrin,were screened from the activated sludge in the biochemical treatment tank about the pyrethroid pesticides,and strains A4 and G3 can be survived with?-cyhalothrin as sole carbon source or nitrogen source,respectively.The selected strains were tested for their colony morphology,ITS sequences,and phylogenetic tree.Strains A4 and G3 were ultimately identified as Aspergillus aculeatus and Penicillium oxalicum.6.The degradation characteristics of strains A4 and G3 by varying inoculation,pH,temperature and initial concentration were studied by high pressure liquid chromatograph(HPLC).The results showed that the degradation behavior of strains A4 and G3 at different initial concentrations was consistent with the first order kinetics.The strain A4 had the best degradation effeciency under the condition of inoculation 0.015 g/L,pH 7.0,and temperature 28 ?.The strain G3 had the best degradation effeciency under the condition of inoculation 0.010 g/L,pH 7.0,and temperature 28 ?.