Elevated Mammalian Cell Cytotoxicity of Chlorinated Drinking Waters in the Presence of CuO

It has been demonstrated previously that cupric oxide (CuO) can enhance the formation of one- to two-carbon-atom disinfection byproducts (DBPs) during water chlorination. Effects of CuO on the Chinese hamster ovary cell cytotoxicity of chlorinated water and the underlying mechanisms were investigated in this study. Results showed that 0.1 g L^-1 CuO elevated the cytotoxicity of chlorinated waters by 20% and 120% at initial bromide concentrations of 15 and 415 μg L^-1, respectively. Increasing the CuO dose increased the cytotoxicity induced by both known and unknown DBP fractions, and a more pronounced elevation was observed for the former one. Unknown fractions accounting for >70% of chlorinated water cytotoxicity were characterized by Fourier transform ion cyclotron resonance mass spectrometry. The presence of CuO decreased the average molecular weight (416.4 vs 412.3 Da) of assigned ∼2350 formulas after chlorination but increased the number of bromine-containing formulas (165 vs 328). The contribution of bromine addition/substitution pathways to the alteration of identified formulas in the presence of CuO almost doubled that in the absence of CuO. The preferential formation of brominated DBPs in the presence of CuO was ascribed to the higher formation rate constant of CuO-HOBr than that of CuO-HOCl complex and lower adsorption energies based on density functional theory calculations. This work provides insights into DBP-associated cytotoxicity and its mitigation strategies in copper-containing distribution systems.