Cytotoxicity of Halogenated Tyrosyl Compounds, an Emerging Class of Disinfection By-Products.

Halogenated amino acids and peptides are an emerging class of disinfection by-products (DBPs), having been detected in drinking water and in washed food products. However, the toxicological significance of these emerging DBPs remains unclear. In this study, the cytotoxicity of eight halogenated tyrosyl compounds was investigated in Chinese hamster ovary (CHO) cells using real-time cell analysis (RTCA). Di-halogenated tyrosyl compounds are more cytotoxic than their mono-halogenated analogues. The cytotoxicity of the di-halogenated compounds is associated with their ability to induce intracellular reactive oxygen species (ROS), suggesting that oxidative stress is an important toxicity pathway of these compounds. Pearson correlation analysis of the cytotoxicity (IC50 values) of these compounds with eight physiochemical parameters showed strong associations with their lipophilicity (logP) and reactivity (polarizability, ELUMO). Finally, cytotoxicity testing of the concentrated extracts of a chloraminated mixture of eight dipeptides with bromide or iodide showed the cytotoxicity of these mixtures in the order: iodinated peptides > brominated peptides >/= chlorinated peptides. These results demonstrate that halogenated peptide DBPs are toxicologically relevant, and further research is needed to understand the implications of long-term exposure for human health.