Stereoselective Environmental Behavior And Toxicological Effects Of Pyriproxyfen And Its Metabolites

Pyriproxyfen is a juvenile hormone insecticide,which not only can be used as a field insecticide,can also be used as a health insecticide.It can produce more than a dozen metabolites in the environment.In our research,the stereoselective metabolism and toxicological effects of pyriproxyfen and its metabolites in soil and animal were studied,which provided the basis for assessing the potential risk of pyriproxyfen and its metabolites.Eleven kinds of metabolites for pyriproxyfen were firstly synthesized and identified by nuclear magnetic and mass spectrometry in our research.Then the quantitative analysis was carried out by high performance liquid chromatography.The purities of all metabolites were found to be greater than 94.0%.As the metabolites of pyriproxyfen are mostly chiral,in order to explore the stereoselective behavior and toxicity of pyriproxyfen and its metabolites in the environment,high performance liquid chromatography was used on different chiral stationary phases.The results showed that Chiralcel OJ-H exhibited the best separation ability in all the chiral columns used under normal phase conditions,while Lux Cellulose-3 had the best separation ability under reverse phase conditions.The proportion,type and temperature of the mobile phase would have a certain degree of influence on the ablity of separation.In most cases,the reduction use of isopropanol and acetonitrile content in the mobile phase would result in better separation,and enantiomeric separation was mostly driven by enthalpy.The elution order was determined by the stationary phase and the mobile phase.Soil is an important bearing medium for pesticides.By investigating the stereoselective metabolism of pyriproxyfen in soil,metabolite B was detected only in two soils and found to have both generation and degradation process.Metabolite K was not detected within 120 days of full monitoring and metabolite A was the most important metabolite.The degradation rate of pyriproxyfen was affected by soil organic matter content and soil particle size.The higher the content of organic matter,the smaller the soil particle size was,the faster the degradation rate was.The degradation of(+)-pyriproxyfen takes precedence over(-)-pyriproxyfen,and its degradation half-life was 2.11 d-9.69 d.In the Beijing soil,Heilongjiang soil and Hunan paddy soil,the formation and degradation of metabolite A were selective and are preferentially generated in Beijing soil and Hunan paddy soil.(+)-A generated preferentially in the soil of Heilongjiang than(-)-A.The degradation rate of metabolite A in the red soil of Hunan was slower and the degradation half-life was between 2.80 d and 13.30 d.Pyriproxyfen had a complex effect on the activity of soil enzymes,in which dehydrogenase and catalase were more sensitive to pyriproxyfen,and pyriproxyfen could inhibit the activity of dehydrogenase and promote the activity of catalase.Most soil enzymes can be restored to activity with difficulty to restore the original active state after 120 d.The effect of pyriproxyfen on the activities of different soil enzymes was different in different soils.Metabolite C and metabolite D had strong irritations to earthworm skin,and the toxicity of pyriproxyfen was minor to earthworms.It was found that the toxicity of metabolites was much greater than that of pyriproxyfen.It was concluded that environmental factors,the mode of application and the use of fertilizers could affect the degradation of pyriproxyfen.Water content of 25%made pyriproxyfen show the fastest degradation,while water content of 10%and 50%could slow down the degradation rate accordingly.After the second application,the degradation rate of pyriproxyfen was slowed down and the soil capacity decreased.At the same time,the addition of imidacloprid could accelerate the degradation of pyriproxyfen.On the contrary,amino-avermectin benzoate could slow down its degradation and decrease its selectivity.Fertilization will change the nature of soil,and then affect the degradation of pesticides in the soil.The effect of adding different fertilizers on the degradation rate of pyriproxyfen was complex,in which the compound fertilizer could promote the degradation of pyriproxyfen in the soil,while the organic fertilizer,potassium dihydrogen phosphate and urea slowed down the degradation of pyriproxyfen.The degradation showed no obvious selectivity.Among them,the addition of urea made pyriproxyfen no degradation appear after 42 d.In order to evaluate the health risks of pyriproxyfen and its metabolites,we investigated the metabolism in rat liver microsomes and cytotoxic effects of pyriproxyfen with its metabolites.The half-life of(+)-pyriproxyfen was 77.26 min,and the half-life of(-)-pyriproxyfen was 39.24 min,which degraded faster than(+)-pyriproxyfen.Metabolites A and B were all detected and the concentration increased first and then decreased in the analysis time.The 48 h acute toxicity test on rat hepatocytes showed that the IC50 of the parent pyriproxyfen was more than 196.00 μg/mL,and the IC50 values of the metabolites B,D and K were 9.82,35.78 and 5.23 μg/mL respectively,in which most metabolites showed greater toxicity than pyriproxyfen.The metabolites B,D and K of the saturation concentration,concentration of IC50,smaller concentration of environmental analysis showed a certain apoptosis effect on rat hepatocytes,and produced 2 or 3 level damage to the cells.Thus,the toxicity of metabolites can not be ignored with greater risk than pyriproxyfen.