Role of temperature on the cytotoxicity of drinking water upon chlorination in the presence of CuO.

Average temperatures are growing globally with climate change, which in turn increases water temperatures in distribution systems. Cupric oxide (CuO), a pipe corrosion product, has been reported to enhance the formation of disinfection byproducts (DBPs) in drinking water at ambient room temperature. The influence of water temperature on the DBP-associated mammalian cell cytotoxicity of chlorinated drinking waters in the presence of CuO was investigated in this study. Results showed that the presence of CuO increased the Chinese hamster ovary cell cytotoxicity of chlorinated drinking water, irrespective of temperature. However, increasing the temperature from 20 to 60 °C decreased the bioassay-based measured cytotoxicity caused by nonvolatile fractions, albeit a slight increase in the calculated additive cytotoxicity from (semi-)volatile known DBPs. Therefore, the contribution from the latter one to total cytotoxicity increased from 21 % to 48 % in the presence of CuO when the temperature increased from 20 to 60 °C. Using Fourier transform ion cyclotron resonance mass spectrometry, ratios of Cl/C and Br/C in the identified formulas from nonvolatile fractions were positively correlated with cytotoxicity. The presence of CuO decreased carbon number but increased O/C and Br/C of formulas. Yet, the CuO-induced promoting effects decreased by 4-13 % at 60 °C compared with 20 °C. Structures of 24 halogenated DBPs were deciphered, including 3 aliphatic, 4 alicyclic and 17 aromatic substances. Despite the reduction in cytotoxicity of nonvolatile fractions at relatively high water temperature, promoting effects of CuO and heat on volatile DBP exposure risks should also be taken into consideration. This work provides insights into the role of temperature on water cytotoxicity in copper-containing distribution systems and household plumbing.