Study On Simulation Of Adsorption, Degradation And Transportation Of Pesticide Butachlor In Sandy Loamy Soil

Butachlor (N-Butoxymethyl- -chloro-N-2,6-diethylphenyl-acetamide) is one of the three highest produced herbicides (Butachlor, Acetochlor and Glyhosate), it is widely used for selective control of grass weeds in rice production in China. In this paper, laboratory experiments were processed to investigate the fate and mobility of butachlor in a loamy soil. First, to characterize the adsorption property of butachlor in the loamy, adsorption isotherms were determined by using the batch experiment, and it was conformed to the Freundlich equation. In addition, adsorption estimates can be based on a varies of physical and chemical properties (i.e., n-octanol/water partition coefficient, melting point and water solubility, chromatography, equal tension and specific volume and so on). In general, the parameter of Sw, Kow, Koc, and P can estimate the sorption coefficient of pesticide (Kf) better than guide the behavior and fate of chemicals in soil-water environments. Second, degradation of butachlor is mainly by microbial metabolism; photodegradation and volatilization is limited. To acquire degradation rate constant in the loamy soil, the half-life of butachlor was determined by the incubation experiment. Third, miscible displacement experiments were carried out in saturated homogeneous soil under steady-state flow at a specific pore water velocity separately, and the dynamics of flux concentration for tracer (chloride) and the variation of butachlor after 24h and 48h pulse input was obtained. At the same time, miscible displacement experiments were processed in unsaturated homogeneous soil under unsteady-state flow at a specific water pressure, and the dynamics of flux concentration for butachlor after 48h pulse input and the residue concentration of different depths in the soil column was obtained.In respect of modeling, HYDRUS-1D software was used. Using a tracer's BTC, hydraulic dispersion coefficient could be obtained by solving an inverse problem of the CDE; Applying the software HYDRUS-1D based on the local equilibrium assumption model and nonequilibrium assumption model to describe the transport of butachlor in the soil columns. It was shown that the two-site nonequilibrium model provided a useful approach to better quantify environmental fate of butachlor. By the best-fit parameters optimized from Exp.3, the dynamics of the flux and residue concentration and cumulative leaching quantity for butachlor at different conditions of the soil column from Exp.l and Exp.2 were analysed.