Sorption of Tribenuron-methyl, Chlorsulfuron, and Imazamethabenz-methyl by Soils

The sorption at 25 °C of the acidic herbicides tribenuron-methyl, chlorsulfuron, and imazamethabenz-methyl on three soils (clay content percentages ranging from 7.2 to 54.6, pH values ranging from 6.5 to 7.6, and organic matter percentages <1.5) was studied. Only imazamethabenz-methyl presented significant sorption in these soils. Sorption isotherms of imazamethabenz-methyl were well correlated to the Freundlich model, although linearity can be reasonably assumed. Desorption studies of this herbicide presented remarkable hysteresis and nonlinearity. Chlorsulfuron sorption was low, and tribenuron-methyl presented negligible or negative adsorption. The effect of the soil/solution ratio employed in batch experiments on the estimated distribution coefficient of the three herbicides was also investigated. By changing the soil/solution ratio from 1:3 to 1:1, an increase in the distribution coefficient of imazamethabenz-methyl and chlorsulfuron was observed. On the other hand, the distribution coefficient of tribenuron-methyl decreased within the same range of soil/solution ratios. Results indicate that these herbicides, but especially chlorsulfuron and tribenuron-methyl, could be mobile in the soils studied. The effect of the soil/solution ratio or hysteresis in desorption seems to be more important than the isotherm nonlinearity in modeling the transport of these hebicides in soil.