Adsorption And Desorption Of Fenpropathrin In Five Soils

Fenpropathrin is one of phenoxy cyclopropane ester, belongs to the third-generation pyrethroid insecticide. Fenpropathrin is stronger than other pyrethroid pesticides in toxicity and water solublility. Thus rearch on its migration laws in soil is particularly important.In this paper five soils [phaeozem, albic soil, solonetz, solonchak, paddy soil(phaeozem type)] as test materials,by using batch equilibrium method it was studied that adsorption and desorption of fenpropathrin in five soils and with surfactants in phaeozem. The test results were as follows:(1) The most suitable description for fenpropathrin adsorption behavior in soils was Freundlich equation. In the Freundlich isotherm, the Kf value was proportional to adsorption strength. The order of fenpropathrin adsorption capacity in five types of soils was described as follows: phaeozem > solonchak > paddy soil> albic soil > solonetz. The mobility of fenpropathrin in soils was weak. Adsorption in five types of soils was mainly physical adsorption.(2) The correlation analysis of the soil organic matter content, soil p H, clay content and cation exchange capacity with fenpropathrin adsorption constant of Kf showed that the soil OM content, which was the most important factor on affecting fenpropathrin adsorption in soils, had high correlation with fenpropathrin adsorption constant of Kf. The equilibrium adsorption capacity in five types of soils removed organic matter was about 60% of the original soils.(3) On desorption hysteresis, the research found that the higher initial concentration of fenpropathrin was, the smaller hysteresis constant was; phaeozem, at initial fenpropathrin desorption concentration of 15 mg/L in phaeozem, solonchak, paddy soil had no hysteresis; the remaining cases had negative hysteresis; and that at various concentrations in albic soil, solonetz had negative hysteresis.(4) The result of fenpropathrin adsorption-desorption kinetics tests in the five types of soils showed the dynamics at the double initial concentration: 0~8 h for quick adsorption/desorption stage, 8~24 h for a slow adsorption/desorption stage, after 24 h basically reached the adsorption / desorption equilibrium. Whether the initial concentration of fenpropathrin was relatively high(12.5 mg/L) or low(7.5 mg/L), the order of the adsorption and desorption equilibrium amount was phaeozem > solonchak > paddy soil> albic soil > solonetz. Fenpropathrin adsorption-desorption kinetics equations in soils were in line with double constant equation(ln St = a + blnt), kinetics of fenpropathrin was mainly influenced by the non-homogeneous diffusion process.(5) Adsorption/desorption behavior of fenpropathrin treated with 3 different types of surfactants respectively was suitable described by Freundlich isotherm in phaeozem. With the increase of anionic surfactant SDBS concentration, the adsorption constant Kf value was first decreased and then increased trend, and the cationic surfactant CTAB and non-ionic surfactant Tween-80 was first increased and then decreased trend. When the surfactant concentrations were close to the CMC(SDBS is 418 mg/L, CTAB is 335 mg/L, Tween-80 is 10.48 mg/L), the effect of the surfactant on fenpropathrin adsorption in phaeozem was significant. Meanwhile, Tween-80 and CTAB could significant promote the fenpropathrin adsorption, and the inhibition of SDBS on fenpropathrin adsorption was slight.As shown in the results of fenpropathrin desorption, when the Tween-80 and SDBS were added to fenpropathrin, desorption hysteresis coefficient and the negative hysteresis effect were all increased. However, with addition of CTAB, the desorption hysteresis coefficient was decreased and the negative hysteresis effect was disappeared. It indicated that Tween-80 and SDBS had a promotion effect on the fenpropathrin desorption in phaeozem, while the effect of CTAB was inhibited. In addition, the effect of Tween-80 was better than SDBS. In summary, the conclusion was that surfactant could affect the fenpropathrin desorption in phaeozem.