Effect of dissolved organic matter on chlorotoluron sorption and desorption in soils

A batch equilibrium techniques was used to examine the effect of dissolved organic matter (DOM) extracted from both non-treated sludge (NTS) and heat-expanded sludge (HES) on the sorption and desorption of chlorotoluron (3-(3-chloro-p-tolyl)-1,1-dimethylurea) in two types of soils, a yellow fluvo-aquic and a red soil from China. Without DOM, sorption of chlorotoluron was significantly greater (P < 0.05) in the red soil than in the yellow fluvo-aquic soil. However, with DOM the effect was dependent on the soil type and nature of DOM. Chlorotoluron sorption was lower in the yellow fluvo-aquic soil than in the red soil, suggesting that with the same DOM levels the yellow fluvo-aquic soil had a lower sorption capacity for this herbicide. Application of DOM from both NTS and HES led to a general decrease in sorption to the soils and an increase in desorption from the soils. Desorption of chlorotoluron also significantly increased (P < 0.05) with an increase in the DOM concentration. Additionally, for sorption and desorption, at each DOM treatment level the NTS treatments were significantly lower (P < 0.05) than the HES treatments. This implied that non-treated sludge had a greater effect on the sorption and desorption of chlorotoluron than heat-expanded sludge.