Study On The Environmental Behavior And Residual Dynamics In Paddy Field Envionment Of Chlorfenapyr

Chlorfenapyr is aryl pyrrole compound, reformed by natural antibiotics, developed by American Cyanamid Company, mainly for the prevention of drill decayed sucking and chewing pest, especially the tetranychus mites. In order to evaluate the residues in environmental media, the residues of chlorfenapyr in paddy field and hydrolysis, photodegradation, soil degradation, absorption and leaching were researched. The main results were as follows:1. An analytical method for determining chlorfenapyr residues was established. Paddy samples were determined with gas chromatography (ECD) after extracted with organic solvent. The average recoveries of chlorfenapyr in different paddy samples ranged from80.45%to116.83%at0.005～0.5mg/L or0.01-0.5mg/kg spiked, the maximum relative standard deviations (RSD) was12.48%. The limit of detection (LOD) was0.005mg/L in water, and0.01mg/kg in soil, paddy straw, rice and rice husk. These results indicated that the developed method could be applied for residue determination of chlorfenapyr.2. The results of residues degradation dynamics of chlorfenapyr at four paddy fields in two years showed that the degradation dynamics accord with the kinetic equation. The half-lives of chlorfenapyr was2.14～4.91d in paddy water,3.80～8.37d in soil,6.86～15.40d in straw.240g/L chlorfenapyr suspension concentrate was sprayed for2times and3times, each time intervals for7days. with the dose of100.8g.ai/ha and151.2g.ai/ha in the emergence period of Cnaphalocrocis medinalis, the residues were detected after28days on the last use. The residues of chlorfenapyr in rice and soil were less than maximum residue limit (MRL)(0.05mg/kg).3. The result of hydrolysis test showed that chlorfenapyr is belongs to medium hydrolysis of pesticide. In buffer solutions, the hydrolysis rates order was as follows: pH7>pH5>pH9. Temperature also had a significant effect on hydrolysis, which was increased with temperature increasing. The average of temperature coefficient (Q10) was1.30.4. Under high pressure mercury lamp, the photochemical degradation of chlorfenapyr in solvents and aqueous was studied. The main results were summarized as follows:The half-life of chlorfenapyr in distilled water was25.86min at the concentration of2mg/L, the photolytic rate negatively correlated with the increasing concentration of chlorfenapyr in pure water at ranged from1mg/L to10mg/L. The photolytic rates of chlorfenapyr in buffer solutions showed the following sequence:pH7>pH9>pH5. The photolytic rates of chlorfenapyr in different organic solvent showed the following sequence:n-hexane>methyl alcohol>ethyl acetate>acetone. The existence of NO2, NO3-, NH4+in water solution inhibited photochemical degradation of chlorfenapyr.5. The research of soil degradation showed:In aerobic conditions, the half-lives of chlorfenapyr in yellow-brown soil of Nanjing, red soil of Jiangxi, and black soil of northeast were25.48d,40.30d and46.83d, respectively. In anaerobic conditions the half-lives were31.80d,45.01d and63.01d, respectively. In sterilized conditions the half-lives were58.74d,86.64d and96.27d, respectively. It indicated that soil microorganisms, especially the aerobic microorganisms, had significant effect on the degradation of chlorfenapyr in soils.6. The adsorption and desorption of chlorfenapyr was studied. The result showed that adsorption and desorption isotherms of chlorfenapyr in three kinds of soils was in accord with Freundlich equation, the adsorption coefficient (Kf) were469.87,550.94and607.16, respectively. The adsorption isotherms of chlorfenapyr were S-type. The average adsorption free energy(⊿G) was-37.93kJ/mol. The adsorptions of chlorfenapyr were physical adsorption.7. Soil thin layer chromatography and Soil column leaching method were used to study the mobility of chlorfenapyr. The results showed that chlorfenapyr in the tested three kinds of soils displayed non-mobile and non-leaching, which indicated that chlorfenapyr has no pollution of groundwater under normal use. The mobility of chlorfenapyr in three soils showed the following sequence:red soil of Jiangxi> yellow-brown soil of Nanjing> black soil of northeast, the mobility weakened with the increasing of soil organic matter content.