A Study On Environmental Behaviors Of Pyridaphenthione

A study to environmental behaviors of pyridaphenthione was aimed at elucidating pyridaphenthione fate and potential hazards, and providing a scientific basis for reasonable using, and evaluating environmental safety. A method for residue determination of pyridaphenthione was developed and the environmental behavior of pyridaphenthione was investigated, including hydrolysis, photolysis, soil degradation, absorption and leaching.An analytical method for determining pyridaphenthione residues in water and soil using GC were developed. Pyridaphenthione were extracted from samples with organic solvent and determined with GC-FPD. The recoveries of pyridaphenthione spiked in water and soil samples ranged from100.99%～102.39%and87.29%～89.98%, respectively. And the relative standard deviation was1.36%～3.03%and1.53%～3.16%. The LOD in water and soil samples were0.02mg/L and0.05mg/L, respectively. An analytical method for determining pyridaphenthione residues in water using HPLC was also developed. The water samples can be detected directly after being filtrated through membrane and the LOD was0.2mg/L. The method did not need sample preparation and the operation was simpleThe hydrolytic rate of pyridaphenthione in different pH value buffed solutions showed the following sequence:pH9>pH7>pH5, and hydrolysis half lives (25℃) were10.52,30.00and73.72d, respectively. The hydrolysis of pyridaphenthione was base-catalyzed hydrolysis, which indicated that the pH was a crucial influencing factor. Temperature also had a significant effect on pyridaphenthione hydrolysis, which was increased with temperature increasing. The hydrolytic rate increased by2.98times for each temperature increased by10℃. We also found that SDS could restrain the hydrolysis rates of pyridaphenthione and the restraining degree was enhanced with the increasing concentration of SDS. The hydrolytic rate of pyridaphenthione under simulating field environment was faster than in laboratory, which indicated that photolysis and biodegradation may had some positive effects on the degradation of pyridaphenthione in water.The photochemical degradation of pyridaphenthione in various solvents and the relevant effect factors were investigated by the irradiation of high-pressure mercury lamp. The results showed that the half-life of pyridaphenthione in distilled water was9.82hours at the concentration of5mg/L. The photolytic rates of pyridaphenthione in different organic solvent showed the following sequence: n-h.exane>ethyl acetate> methanol> acetonitrile. The photolytic rate of pyridaphenthione in alkaline buffer solution was much faster than in acid or neutral buffer solution. The photolytic rate was negatively correlated with the increasing concentration of pyridaphenthione in aqueous solution and methanol at ranged from2mg/L to20mg/L. In aqueous solutions, nitrate showed photosensitizing effect on the photodegradation of pyridaphenthione, but surfactant (SDS) obviously quenched its photodegradation and the quenching effect showed the direct proportion with the dosage ratio. We also found that Fe3+and Fe2+could have an intense photosensitizing effect on photolysis of pyridaphenthione, and as the increasing concentration of the ions, the photosensitive efficiency display first increased and then decreased. Detecting the photoproducts by HPLC-MS indicated that two mainly photolytic pathways of pyridaphenthione in aqueous solutions were photo-oxidation and photo-isomerization.The half lives of pyridaphenthione in three kinds of soils, black soil of Northeast China, red soil of Jiangxi and yellow-brown soil of Nanjing were10.27,78.75and105.00days, respectively. All in aerobic, anaerobic and sterilized conditions, the degradation rate in three soils showed the following sequence:yellow-brown soil of Nanjing> black soil of northeast> red soil of Jiangxi. The degradation rate was positively correlated with the pH values of soils. Pyridaphenthione was degraded mainly by biodegradation in soils, and anaerobic microorganisms in anaerobic condition were conducive to the degradation. The degradation rate of pyridaphenthione in soils under simulating field environment was faster than in laboratory under dark condition, which indicated that photolysis may had some positive effects on the degradation of pyridaphenthione in soils.The adsorption of pyridaphenthione in three kinds of soils was studied. The result showed that adsorption isotherms of pyridaphenthione on the soils could be described well by Freundlich equation, and the adsorption isotherms exhibited L-type isotherm. The adsorption ability of soils to pyridaphenthione showed the following sequence:black soil of northeast>yellow-brown soil of Nanjing>red soil of Jiangxi. The Koc value of pyridaphenthione ranged from1043.64-1656.62. The average adsorption free energy(△G) was-17.62kJ/mol, which indicated that the adsorption of pyridaphenthione was dominated by physical adsorption, the soil adsorption capacities of pyridaphenthione were positively related with the contents of soil organic matter. The desorption capacities of soils to pyridaphenthione showed the following sequence:red soil of Jiangxi> yellow-brown soil of Nanjing> black soil of northeast, complying with the regularity that desorption capacities was negatively correlated with the adsorption capacities.Soil thin layer chromatography and Soil column leaching method were used to study the leaching of pyridaphenthione in soils. The results showed that pyridaphenthione in the tested three kinds of soils display non-mobile and non-leaching, which indicted that under normal use, pyridaphenthione was not easy to cause pollution of groundwater. The leaching capacities of pyridaphenthione in three soils showed the following sequence:red soil of Jiangxi> yellow-brown soil of Nanjing> black soil of northeast, the leaching capacities weakened with the increasing of soil organic matter content.