Structural and mechanistic insights into halogenated disinfection byproducts of tannic acid with toxicity analysis during chloramination.

Chloramination is widely employed in water treatment due to its reduced formation of traditional disinfection byproducts (DBPs); however, the halogenated DBPs formed through reactions with organic precursors in matrices such as Suwannee River Natural Organic Matter (SRNOM) and wastewater remain incompletely characterized. Tannic acid, a prevalent phenolic precursor in these matrices, was systematically investigated in this study to elucidate the structural features, formation mechanisms, and toxicological risks of halogenated DBPs generated during chloramination. Using ultra-performance liquid chromatography coupled with high-resolution mass spectrometry (UPLCHRMS), we identified 28 chlorinated disinfection byproducts (Cl-DBPs) and 17 brominated disinfection byproducts (Br-DBPs) compounds, with molecular structures resolved for 13 Cl-DBPs and 8 Br-DBPs. Key intermediates, such as gallic acid derivatives, underwent halogenation via electrophilic substitution, nucleophilic attack, and decarboxylation, yielding aromatic, non-aromatic cyclic, aliphatic, and heterocyclic halogenated DBPs. These halogenated DBPs were detected in chloraminated SRNOM and wastewater effluents, demonstrating their environmental prevalence. In vitro cytotoxicity results showed the toxicity of identified 3,5-dichloro-4-hydroxybenzoic acid lies between that of monochloroacetamide and dichloroacetamide, underscoring its health impacts. In silico toxicity analysis using Quantitative Structure-Activity Relationship (QSAR) models predicted higher acute ecological toxicity for most Cl-DBPs and Br-DBPs compared to traditional DBPs such as monochloroacetamide and dichloroacetamide, with certain compounds exhibiting potential developmental toxicity and mutagenicity risks. This study underscores the pivotal role of tannic acid as a key DBP precursor, and emphasizes the need for advanced monitoring and risk mitigation strategies to address the emerging threats posed by these contaminants in treated water systems.