Redox-Directed Identification of Toxic Transformation Products During Ozonation of Aromatics

Abstract

The toxicity assessment of transformation products (TPs) formed in oxidative water treatment is crucial but challenging because of their low concentration, structural diversity, and mixture complexity. Here, this study developed a novel redox-directed approach for identification of toxic TPs without the individual toxicity and concentration information. This approach comprised an integrated process of the sodium borohydride reduction, fluorescence excitation-emission matrix characterization, high-resolution mass spectrometry detection, and subsequent ecological toxicity prediction. The redox-directed identification of primary causative toxicants was experimentally tested for the increased nonspecific toxicity observations in the ozonated effluents of model aromatics. Reduction reaction caused a remarkable decrease in toxicity and increase in fluorescence intensity, obtaining a good linear relation between them. More than ten monomeric or dimeric p-benzoquinone (p-BQ) TPs were identified in the ozonated effluents, with predicted toxicities toward fish and green algae 1–2 orders of magnitude higher than their precursors. These together indicated that the identified p-BQ TPs are primary toxicity contributors. It was further verified through parallel sodium sulfite reduction and actual wastewater ozonation experiments. The redox-directed approach facilitated the revelation of primary toxicity contribution, illustrating emerging p-BQs are a concern for aquatic ecosystem safety in the oxidative treatment of aromatics-contaminated wastewater.

Keywords: advanced oxidation processes, p-benzoquinones, nonspecific toxicity, sodium borohydride reduction, fluorescence enhancement