BACKGROUND: Chloronitrobenzenes (CINBs) are a family of toxic and bio-resistant organic compounds. Ozone treatment is specifically suitable for partial or complete oxidation of non-biodegradable components. However, few studies on the decomposition of CINBs by ozone are available, and kinetics and mechanisms of CINBs ozonation have not been thoroughly investigated. The kinetics and mechanism of ozonation degradation of CINBs in aqueous solution were investigated, and the contribution of both molecular ozone and hydroxyl radicals was also evaluated. RESULTS: The results demonstrated that the decomposition of CINBs was a pseudo-first-order reaction with respect to the pollutant concentration and the overall rate constant increased with an increase in pH. It declined, however, with an increase in pollutant and radical scavenger concentration. Furthermore, TOC removal rate was significantly lower than that of CINBs, but the same order o-CINB < m-CINB < p-CINB was followed. Ozonation could not reduce TOC significantly, p-chlorophenol, p-nitrophenol, 2-chloro-5-nitrophenol and 5-chloro-2-nitrophenol were detected as primary degradation intermediates in ozonation of p-CINB. Rate constants of the direct reaction between ozone and CINBs at 25 degrees C had been found to be lower than 1 M-1 S-1. More than 95% of CINBs removal was due to hydroxyl radical oxidation at pH >= 7. CONCLUSION: Advanced oxidation processes may be the preferred choice for the elimination of CINBs from the environment. (C) 2008 Society of Chemical Industry