Effect of dissolved organic matter on mobility and activation of chlorotoluron in soil and wheat

Chlorotoluron is a pesticide that is moderately absorbed and fairly mobile and leaching in soils. Dissolved organic matter (DOM) plays a critical role in affecting the environmental behavior of pesticides. In this study, we report the effect of DOM extracted from sludge (SL) and straw (ST) on chlorotoluron sorption/desorption and mobility using several techniques including batch experiment, soil column, soil thin-layer chromatography and bioefficacy estimation. Application of DOM (SL and ST) at 50 and 150 mg DOC L-1 decreased the sorption of and increased desorption of chlorotoluron in soils. Freundlich constant K-f values (sorption) of chlorotoluron for SL1 (50 mg DOC L-1 sludge extract) and SL2 (150 mg DOC L-1 sludge extract) treatments were 0.06 and 0.04, respectively, which were significantly lower than the value (0.29) for the control. The respective values for treatments of M (50 mg DOC L-1 straw extract) and ST2 (150 mg DOC L-1 straw extract) were 0.04 and 0.02. Mobility of chlorotoluron was tested in packed soil columns and soil plate. Addition of DOM to both systems significantly increased the mobility of chlorotoluron and the total concentration of chlorotoluron in the leachate in columns. Biological analysis with wheat plant revealed that application of DOM reduced the chlorotoluron accumulation in tissues at lower concentration of chlorotoluron and increased its accumulation at higher level of chlorotoluron. Finally, we analyzed FT-IR spectral and fluorescence for DOMs and found that more unsaturated components and amine were present in DOM-ST than in DOM-SL These results may help our understanding of the general role of DOMs in regulating the activation and mobility of organic chemicals (e.g. herbicide and contaminants) in the ecosystem. (c) 2008 Elsevier B.V. All rights reserved.