Acute toxicity evolution during ozonation of mono-chlorophenols and initial identification of highly toxic intermediates

Acute toxicity changes during ozonation of 2-chlorophenol (2-CP), 3-chlorophenol (3-CP) and 4-chlorophenol (4-CP) under various conditions were studied using the luminescence inhibition test. Though the concentrations of mono-chlorophenols (CPs) and TOC decreased constantly, the acute toxicity evidently increased with reaction time until a maximum value was reached during ozonation of 2-CP at pH 3 to 7, 3-CP at pH 3 to 10, and 4-CP at pH 3 and 5. Principal component analysis (PCA) was applied to understand the relationships between acute toxicity and other physicochemical parameters. The intense interrelations between acute toxicity and SUVA₂₈₀ were evident under all the pH conditions for 2-CP and 3-CP, and except at pH 12 for 4-CP, which implied that high-weight intermediates were formed and contributed to the increased toxicity. SUVA₂₈₀ was a possible surrogate measure of acute toxicity during the ozonation of all three CPs. Profiling of acute toxicity in ozonated CPs was conducted using solid phase extraction with a series of different cartridges, high performance liquid chromatography (HPLC) fractionation and the luminescence inhibition bioassay. Considering the acute toxicity evolution under different conditions and profiles of acute toxicity in HPLC fractions, the highly toxic intermediates probably included same non-chlorine carboxylic acids though the three CPs had different substituent positions with higher polarity than their parent compounds. In this study, the acute toxicity evolution during ozonation of CPs and the forcing agents were thoroughly discussed. Therefore, ozonation is expected to be carefully operated and monitored, and toxicity tests should be used to evaluate whether effluent detoxification takes place.