Bioassays and chemical analyses were performed to study the effect of hydrophobic dissolved organic matter (HoDOM) extracted from a municipal waste compost (MWC) on the behavior of triflusulfuron methyl in soil and water. Bioassays with oilseed rape showed that HoDOM in culture solution lowered the effective dose 50 of triflusulfuron methyl by up to 4.8 times. Equilibrium dialysis experiments showed that in aqueous solution triflusulfuron methyl was adsorbed to HoDOM (K(OC) of 446.5 mL g(-1)). The half-life in water (pH 7.0) was increased from 52 to 76 days in the presence of HoDOM, but this cannot completely explain its phytotoxicity, as bioassays lasted for 21 days only. On the other hand, the addition of HoDOM to soils did not change the degradative behavior of triflusulfuron methyl. Fluorescein diacetate hydrolysis showed that HoDOM in soil did not significantly influence soil microbial activity, which may explain the above result on degradation in soil. Furthermore, in batch equilibrium experiments on soil, triflusulfuron methyl was only weakly adsorbed and the presence of HoDOM significantly modified the isotherm form. Results suggest that although the addition of exogenous HoDOM from MWC to soil did not influence the herbicide's persistence, its enhanced mobility could be of environmental concern and may deserve further research.