Abstract

Adsorption and dissipation of the three acetanilide herbicides alachlor, metolachlor and propachlor in soils at different moisture contents (30, 60 and 90% of soil field capacity) and different temperatures (10, 25 and 40℃) were performed with Tauyuan clay loam, Nantou loam and Kaohsiung sandy loam.  In the adsorption experiment, equilibrium was reached within 4 hr and the adsorption of herbicides in the soil-water system increased with increasing temperature.  The results indicate that the sorption isotherm agreed with the linear and Freundlich equations, while the dissipation rate of the herbicides increased with increasing soil temperature and soil moisture content.  The dissipation rate for three herbicides in soils followed the order : alachlor > propachlor > metolachlor.  The half lives for alachlor, metolachlor and propachlor were 8.6, 9.4 and 22.8 days, respectively, in the Nantou loam soil under soil moisture at 90% of field capacity and 40℃.  The order of dissipation rate in the different soils was Nantou loam > Kaohsiung sandy loam > Tauyuan clay loam for the three herbicides.  In non-sterilized soils, the dissipation rate of these herbicides was significantly higher than that in sterilized soils.  The movement of the herbicides in Kaohsiung sandy loam was faster than in Tauyuan clay loam and Nantou loam.  In addition, the movement of propachlor in the soils was faster than that of alachlor and metolachlor.  The possible contamination of groundwater by these herbicides was assessed using the behavior assessment model (BAM) and the groundwater pollution-potential model (GWP) indicate that propachlor may contaminate the groundwater of Kaohsiung sandy loam under the local meteorological conditions. 

Keywords: Adsorption; Movement; Dissipation; Alachlor; Metolachlor; Propachlor; Groundwater