Bioanalytical assessment of toxicity change during ozonation of methyl paraben and its halogenated derivatives

Abstract

Methylparaben (MeP), a common ingredient in personal care products, is frequently detected in aquatic environments at concentrations ranging from ng/L to μg/L. Its halogenated derivatives, including mono- (Cl-MeP and Br-MeP) and di-halogenated (diCl-MeP, Br,Cl-MeP, diBr-MeP) forms, are also prevalent due to the transformation of MeP during water chlorination. Previous research has indicated that MeP and halo-MePs can undergo oxidative degradation during water treatment processes like ozonation, potentially giving rise to toxic transformation products. However, relevant information on this matter is currently limited. This study aimed to assess the toxicity of transformation products formed during the ozonation of MeP and halo-MePs using bioanalytical methods, specifically in vitro bioassays covering oxidative stress response (Nrf2) and genotoxicity (p53 alone and p53 with S9 activation). Each paraben, prepared at a concentration of 100 M, underwent treatment with ozone concentration ranging from 0 from 230 M in the presence of tert-butanol (as OH radical scavenger). The resulting samples were analyzed using both the bioassays and HPLC/UV for residual paraben concentrations. The results showed measurable bioactivities in Nrf2 and p53 with S9 activation for the parabens, but negligible activities (below LOQ) in p53 alone. In addition, the bioactivites of ozonated samples were significantly higher than those of MeP and halo-MePs prior to ozonation, with increases of up to ~25-fold for Nrf2 and ~5-fold for p53/S9. These heightened bioactivities persisted even after the complete degradation of parent parabens by ozone, indicating the presence of persistent toxic transformation products. Future studies should focus on the identification of these toxic byproducts, and the efficacy of post-treatment processes such as biological filtration for their removal should be assessed.