Cytotoxicity Assessment and Environmental Fate of Halogenated 4-Hydroxy-Benzaldehydes in Drinking Water

Halogenated 4-hydroxy-benzaldehydes (HHBALs) are a class of aromatic disinfection byproducts (DBPs) with relatively high cytotoxic potency. However, their cytotoxicity and environmental fate in drinking water remain unclear, which must be systematically addressed. The concentration level of HHBALs in tap water samples from 15 major cities in China ranges from several tens to hundreds of ng/L, and the median lethal concentration of HHBALs to Chinese hamster ovary cell is 78.52–638.27 μM, which is comparable to the cytotoxic potency of aliphatic nitrogenous DBPs. The risk quotient analysis revealed that the contributions of HHBALs to DBP-associated toxicity are relatively small. The species-specific second-order rate constants for the reactions between HHBAL species and water molecules, as well as reactive chlorine species (HOCl, NH 2 Cl, and NHCl 2 ), were determined via kinetic model simulation. These findings suggest that HHBALs exhibit high stability during hydrolysis and chloramination and poor stability during chlorination. Based on the identification of over 20 transformation products, the degradation of HHBALs mainly occurs at the carbon atom linked to the aldehyde group, with polychlorinated phenols and halogenated nitrophenols being confirmed as the major products during chlorination and chloramination, respectively. Therefore, the risk of HHBALs in drinking water is relatively low, but their transformation products may merit greater attention.