Adsorption and desorption of imazosulfuron by soil

Understanding and quantifying the adsorption and desorption of herbicides by soil is important for predicting their fate and transport in the environment. Here we report a study concerning the adsorption and desorption, by four different soils, of imazosulfuron, 1-(2-chloroimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4, 6-dimethoxypyrimidin-2-yl)urea, a new sulfonylurea herbicide. Both phenomena are well-described by the Freundlich equation, which shows this herbicide to be little adsorbed by each of the four soils investigated. The Freundlich adsorption constants, K(f-ads), ranged from 1.46 to 3.02. Distribution coefficients between soil and water, Kd, measured on soils of different organic matter contents and pH values showed an important effect of these two parameters on imazosulfuron retention. The Freundlich desorption data indicated that a significant amount of the imazosulfuron sorbed is not easily desorbed. The desorption process showed an evident hysteresis phenomenon, which may contribute to the persistence of imazosulfuron in soil.