Influence of water matrix components and peroxide sources on the transformation products and toxicity of tebuthiuron under UVC-based advanced oxidation processes

Coupling of UV-C irradiation to different peroxides (H2O2, S2O82- and HSO5-) has great potential to degrade persistent organic compounds due to the formation of HO center dot or SO4 center dot- species. However, an in-depth comparison between the perfor-mance of different UV-C/peroxide processes as a function of (i) target compound degradation, (ii) generated transforma-tion products and (iii) lethal/sub lethal toxicity effects has not yet been performed. To this end a comparison study was carried out to evaluate the effectiveness of different UV-C/peroxide processes using the herbicide tebuthiuron (100 or 500 mu g L-1) as a model pollutant. TBH degradation experiments were performed at lab-scale in real municipal wastewa-ter treatment plant effluent and distilled water. Faster degradation occurred by increasing peroxide concentration from 735 to 2206 mu mol L-1 in the municipal wastewater treatment plant effluent, mainly for S2O82-. Experiments performed in the presence of peroxide trapping agents - HO center dot and SO4 center dot- (methoxibenzene) or HO center dot (2-propanol) - revealed that oxida-tion in the UV-C/S2O82- system occurs mainly through SO4 center dot-. Lower toxicity for the MWWTP effluent was obtained after oxidative treatments using hydrogen peroxide or monopersulfate as oxidants which react mainly through HO center dot radicals. Two mechanistic pathways were proposed for tebuthiuron degradation: (i) hydrogen abstraction by HO center dot (H2O2 and HSO5-) and (ii) electron transfer by SO4 center dot- (S2O82-). In addition, one unprecedented transformation product was identified. In conclusion, results emphasize the relevance of comparing the degradation of toxic compounds in the presence of different peroxide sources and matrices and simultaneouly evaluating responses chemical and biological endpoints.