ORGANIC-CHEMICALS IN THE ENVIRONEMNT - FLUOMETURON SORPTION AND TRANSPORT IN DUNDEE SOIL

The mobility of a synthetic organic compound in soil is affected by degradation and sorption reactions. Sorption is often a nonequilibrium process, leading to greater mobility and increased potential for contamination of shallow groundwater. Accordingly, this study was undertaken to examine sorption kinetics of the herbicide fluometuron [N,N-dimethyl-N'-[3-(trifluoromethyl)-phenyl]urea] in Dundee silty clay loam (fine-silty, mixed, thermic Aeric Ochraqualfs), a common soil in the Mississippi Delta. Batch experiments indicated sorption equilibrium was achieved by 72 h contact time. Other data suggested little degradation of fluometuron within this time. The approach to equilibrium was characterized by an initially very rapid reaction, followed by a slower rate of sorption. This behavior could be equally well described by either a nonlinear two-site equilibrium/kinetic or equilibrium/diffusion model. Reaction parameters determined from the batch experiments were further validated by use in a transport model to predict fluometuron movement in this soil. Within parameter uncertainty, the two-site equilibrium/kinetic model gave accurate predictions of fluometuron mobility. Explicitly modeling time-dependent sorption as a diffusion process offered minor improvement in transport predictions.