Occurrence and toxicity of halobenzoquinones as drinking water disinfection byproducts

Halobenzoquinones (HBQs) are emerging unregulated drinking water disinfection byproducts (DBPs) that are more toxic than regulated DBPs. This study aimed to determine the distribution and formation of HBQs in drinking water from water treatment plants in China, compare their chronic cytotoxicity and their induction of chromosomal damage in Chinese hamster ovary cells, and analyze the correlation of HBQ toxicity with their physicochemical parameters. Two HBQs, 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ) and 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ), were detected in finished water and tap water in China. The concentrations were in the ranges of <2.6-19.70 ng/L for 2,6-DCBQ and <0.38-1.8 ng/L for 2,6-DBBQ. Chemical oxygen demand and residual chlorine were positively correlated with HBQ formation. The HBQ concentration was lower in a drinking water treatment plant using chlorine dioxide. High Ca2+ in tap water decreased the HBQ level. The rank order of HBQ by cytotoxicity was 2-chloro-1,4-benzoquinone > 2,3-diiodo-1,4-benzoquinone > 2,6-diiodo-1,4-benzoquinone > 2,6-dibromo-1,4-benzoquinone > 2,5-dibromo-1,4-benzoquinone > 2,5-dichloro-1,4-benzoquinone > 2,6-dichloro-1,4-benzoquinone > tetrachloro-1,4-benzoquinone > 2,3,6-trichloro-1,4-benzoquinone, and for their genotoxicity, 2,5-dichloro-1,4-benzoquinone > 2,6-dichloro-1,4-benzoquinone > 2,3-diiodo-1,4-benzoquinone > 2,6-diiodo1,4-benzoquinone > tetrachloro-1,4-benzoquinone > 2,5-dibromo-1,4-benzoquinone > 2,6-dibromo-1,4-benzoquinone > 2,3,6-trichloro-1,4-benzoquinone. The cytotoxicity of six dihalo-HBQs was negatively correlated with the octanol-water partition coefficient (r = -0.971, P < 0.05), molar refractivity (r = -0.956, P < 0.05), energy of the highest occupied molecular orbital (EHOMO) (r = -0.943, P < 0.05), and polar surface area (r = -0.829, P < 0.05). The genotoxicity of these three pairs of dihalo-HBQisomers followed the same order as their EHOMO values. This study reveals the occurrence and formation of HBQs in drinking water in China and systematically evaluates the chromosomal damage caused by nine HBQs in mammalian cells. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the distribution and formation of halobenzoquinones in drinking water in China, comparing their cytotoxicity and genotoxicity, and analyzing the correlation of their toxicity with physicochemical parameters. It was found that the concentration of HBQs was influenced by water treatment methods and water quality parameters, with certain factors being negatively correlated with the cytotoxicity of the compounds.