Study On The Movement And Degradation Of Isoproturon In Soil Environment

As irrigation or rainwater causes pesticides in the soil to enter groundwater through leaching and surface runoff,pesticides results in water pollution.The main dominance factor of pesticide in soil-water environment is considered as the adsorption-desorption behavior of pesticide.Therefore,the adsorption and desorption of pesticides in the soil plays a key role in the environmental behavior of pesticides such as migration and degradation.Isoproturon(IPU)is a selective inhalation-type herbicide.The solubility of IPU in water affects its adsorption in the soil and it is easily lost from the soil.Studies have shown that isoproturon in the environment is very risky for aquatic ecosystems.Therefore,it is particularly important to study the behavior and fate of isoproturon in the environment.Surfactant is a class of the material containing both polar groups(hydrophilic)and non-polar groups(lipophilic)and has a certain structure and special adsorption properties.At low concentrations it can significantly reduce the water surface tension.It is a chemically synthesized substance that is inherently toxic.A large amount of emissions in the environment will have a negative impact on the reproduction and survival of ecosystems,especially aquatic organisms,thereby undermining the ecosystem balance.It is very important to study the effect of surfactants on the migration and transformation of pesticides in soil environment.The adsorption-desorption characteristics of isoproturon in soil were studied by oscillatory equilibrium method.The results showed that the Freundlich model can better describe the adsorption-desorption process of isoproturon in the soil,and the R2 value in the Freundlich model is in the range of 0.9981-0.9988.The adsorption free energy AG of isoproturon in soil is-12.62 kJ mol-1 and the absolute value is less than 40 kJ mol-1,suggesting that the adsorption of isoproturon in the soil is dominated by the distribution and mainly by physical adsorption.The mechanism of adsorption of isoproturon may be the action of hydrogen bonding,hydrophobic interaction,van der Waals force and dipole force.The effects of different initial concentrations,temperature,soil-water ratio,ionic strength and exogenous surfactants on the adsorption-desorption behavior of herbicidal isoproturon were investigated.The adsorption and desorption in soil increased with the increase of isoproturon concentration.The adsorption-desorption weakened with the increase of temperature.The adsorption capacity of isoproturon was positive correlation with the ratio of the soil and water and the CaCl2 concentration.Cationic surfactant CTAB promoted adsorption and inhibits desorption;nonionic surfactant Triton X-100 inhibited adsorption and promoted desorption.Herbicidal isoproturon leaching migration characteristics in soil and the effects of different surfactants on the leaching and migration of isoproturon in soil were studied by thin layer chromatography and simulated soil column experiment in door.The results showed that the nonionic surfactant Triton X-100 promoted the leaching migration of isoproturon in the soil compared with the control without surfactant.And the Rf values increased with the increase of Triton X-100 concentration.Based Rf values between 0.406?0.477,it is part of the medium mobility of pesticides according to the level of pesticide mobility.Cationic surfactant CTAB delayed the leaching of isopropenone in soil.The photodegradation of isoproturon in soil under different environments was studied by high performance liquid chromatography(HPLC)under 100 W UV lamp.The results showed that the photodegradation rate of isoproturon was affected by soil moisture,which accorded with the first order kinetics(R2>0.937)under different humidity conditions.When the water capacity of soil holding between 40%to 80%,the degradation rate of isoproturon is accelerated with the increase in soil moisture,and the degradation half-life is shortened.At 15?35 ?,the degradation rate of isoproturon increased with the increase of temperature.When the initial concentration is 10 mg kg-1,the degradation rate constant k is the largest,the half-life T1/2 is the shortest;the initial concentration is 5 mg kg-1 or 20 mg kg-1,the photodegradation rate decreases.The addition of catalyst TiO2 can greatly promote the degradation,and the photodegradation rate of isoproturon increases sharply.