土壌内におけるアシュラムの吸着・脱離と移動

抄録

Adsorption and desorption of asulam, a polar herbicide, on decomposed granite (DG), two sand size fractions of DG (0.212-0.425mm and 0.075-0.150mm), and two natural loam soils werestudied under both batch and transport conditions. In the batch experiments, equilibrium was obtainedwithin the first 10 minutes in the DG soils and after 36 hours in the organic matter-rich loam soils.Freundlich isotherm models best describe the measured adsorption/desorption data. Asulam adsorptionwas highly correlated with Cation Exchange Capacity (CEC) for the five soils, suggesting that both soilorganic matter and clay minerals controlled sorption. Different sorption time-dependency (kinetics) wereobserved when comparing initially non-polluted with initially already asulam-polluted soil. During thetransport (micro-column) experiments, significant differences in the shape and tailing of the breakthroughcurves and in asulam retardation were observed for the two soil types. A Two-Sites Non-Equilibrium (TNE) model was used to describe and interpret the transport measurements. Pronounced non-equilibriumsorption and transport processes in the more organic and clay-rich loam soil gave a significant tailing ofbreakthrough curves while a symmetric breakthrough was seen for the more coarse-tetured DG, probablydue to the immediate sorption equilibrium in the DG. Slightly different values of pesticide retardationfactors were obtained from the batch and transport experiments in the case of loam soil, likely due to theobserved sorption non-equilibrium, sorption non-linearity, and sorption hysteresis processes.