Competitive Adsorption And Mobility Of Carbendazim,Atrazine, Imidacloprid In Soil

In agricultural practices, different classes of pesticides, such as, insecticides, fungicides, and herbicides are often applied simultaneously or one after another for the purpose of crop protection and these chemicals may interact with each other within the soil systems. The environmental behaviors of a single pesticide might be altered through its interaction with other pesticide(s) coexisting in soil. Competitive adsorption/desorption and leaching of carbendazim, atrazine, imidacloprid alone and their combination in soil were investigated in the present study.The data obtained in this study indicates that all adsorption isotherms of carbendazim, atrazine, imidacloprid in the tested soil were well fitted with Freundlich, equation with adsorption coefficient (Kfads) of19.04,2.07,1.33, and the determination coefficient (R2) of0.997,0.995,0.999, respectively. The adsorption capacity of the soil for the tested pesticides varied in an order of carbendazim>atrazine>imidacloprid. The desorption isotherms of carbendazim, atrazine and imidacloprid were also found to be well fitted with Freundlich equation with desorption coefficient (Kfdes) values of24.74,6.34,2.43, respectively. The desorption rates of carbendazim, atrazine and imidacloprid depended upon their concentrations adsorbed and varied in the ranges of14.77～38.17%,48.29～67.37%,7.41-78.49%, respectively.The combination of two pesticides in soil induced their competitive adsorption. Influenced by, the Kfads values of carbendazim in soil were decreased from23.47to16.01and from23.85to19.53in the presence of atrazine (0～268.19μmol/L) and imidacloprid (0～312.87μmol/L), respectively. Similarly, the Kfads values of atrazine in soil were decreased from2.19to0.86and from2.59to1.49in the presence of carbendazim (0～312.87μmol/L) and imidacloprid (0～312.87μmol/L), respectively. The Kfads values of imidacloprid in soil were decreased from1.73to0.83and from2.14to1.20in the presence of carbendazim (0～312.87μmol/L) and atrazine (0～268.19μmol/L), respectively.The migration rate (Rf) of carbendazim, atrazine, imidacloprid was determined to be0.058,0.29,0.37, respectively. The mobility of carbendazim, atrazine, imidacloprid is regarded as immobile, less mobile, medium mobile, respectively. The value of Rf of a single pesticide was altered by the presence of other pesticides duo to the competitive adsorption among them. The value of Rf of carbendazim was increased significantly by31.0%and29.3%with the presence of atrazine and imidacloprid both at level of16ug, respectively. The data suggested that the mobility of carbendazim in soil is enhanced by the decreased adsorption of carbendazim caused by the combination with atrazine and imidacloprid. Similar trends were also observed in mobility of atrazine and imidacloprid. The Rf value of atrazine in soil was increased by17.2%and10.3%with the addition of carbendazim and imidacloprid of16μg, respectively. The Rf value of imidacloprid in soil was increased by8.1%and5.4%with the addition of carbendazim and atrazine of16μg, respectively.