The primary aim of this study was to gain an understanding of how different concentrations of chloride ions affect the oxidation of methyl t-butyl ether (MTBE) in the Fenton system. Oxidation of MTBE in a chloride-free reaction mixture was rapid and very effective, but was inhibited even by the lowest chloride concentrations employed. After 90 min of reaction in the presence of 0.05-1 M of chloride ions, the effectiveness of MTBE degradation dropped to 97-68%, respectively. It was found that the inhibition of Fenton's reaction by chloride ions depends on two factors, thus, complexation and radical scavenging. Under the experimental conditions of the current study, comparison of rate constants for possible degradation reactions showed that most of the (OH)-O-center dot radicals formed by the reaction of H2O2 with Fe2+ were consumed by Cl-. The influence of chloride ions on the degradation of four intermediate products in identical system was also studied: in chloride-free solution under the same experimental conditions, t-butyl alcohol (TBA) was the major by-product, followed by t-butyl formate (TBF) and acetone. In the process of degradation, the distribution of MTBE intermediates varied with the different chloride concentrations. Furthermore, by varying the concentrations of Fe2+ and H2O2, it was possible to track the behavior of MTBE degradation products in the Fenton system in order to find optimal conditions for saline wastewater treatment. (c) 2006 Elsevier B.V. All rights reserved.