CHLORINE DIOXIDE OXIDATION OF TRICLOSAN IN WATER MATRIX: KENETICS STUDY AND INFLUENCES OF WATER CONSTITUENTS

This study focused on the kinetics and toxicity of triclosan (TCS) oxidized by chlorine dioxide and influences of coexisting organic matter (COM) in the aquatic environment. The results showed that approximately 92.18% of TCS (2.0 mu M) could be eliminated by ClO2 (30 04) within 30 s. The reaction between TCS and ClO2 followed second-order kinetic model, and the average rate constant, k(app), was 2.85x10(3) M-1 s(-1) at pH 7.0. The degradation efficiencies of TCS were obviously dependent on the concentrations of COM additives in the substrate solution. Primarily, the presence of cationic surfactant (CTAB) in low concentrations conveyed significantly promotional effects on the TCS-ClO2 reaction, while the catalytic effect was suppressed in high concentrations. The rate enhancement might be attributed to micellar surface catalysis of CTAB through the Coulomb attraction between the reactants and positively charged surfactant. However, inhibitory actions were observed in the spiked samples that contained humic acid, anionic (SDBS) or nonionic (Tween-80) surfactants with it being rather effective, which have been ascribed to the side reaction between ClO2 and COM. Furthermore, the acute toxicity quickly decreased before the disappearance of TCS and then increased gradually. The results indicated that some intermediates were more toxic and stable than TCS in the resulting solution, which may be pose potential health threat to consumers.