Occurrence, Formation, and Oxidative Stress of Emerging Disinfection Byproducts, Halobenzoquinones, in Tea

Halobenzoquinones (HBQs) are frequently detected disinfection byproducts (DBPs) in drinking water with high toxicity and relevance to public health. In this study, we characterized the occurrence, formation, and oxidative stress of the HBQs in tea. 2,6-DCBQ and TetraC-1,2-BQ were identified in all prepared teas at total concentrations of 1.3-2.0 ng/L. 2,6-DCBQ originated from drinking water DBPs, while TetraC-1,2-BQ originated from tea leaves or were generated during tea polyphenol chlorination. HBQs in tea induced the formation of reactive oxygen species and semiquinone radicals, and the oxidative stress could be depleted by tea polyphenols, e.g., (-)-epigallocatechin gallate (EGCG). High-resolution mass spectrometry analysis indicated that the HBQs combined with EGCG and formed adducts at a ratio of 1:1 or 2:1 with the binding sites on the A ring and B ring of EGCG. The viability of HepG2 cells exposed to 50 μM 2,6-DCBQ was increased from 20.0% to 65.2% when 50 μM of EGCG was added. These results demonstrated that various HBQs can occur in tea due to the HBQ DBPs in drinking water, the leachate from tea leaves, and the chlorination of tea polyphenols; furthermore, the oxidative stress and cellular toxicity induced by HBQs in tea could be decreased by tea polyphenols. This is the first study to report HBQs in tea, elucidate the sources of HBQs, and assess relevant health risks.