Revealing Molecular Connections between Dissolved Organic Matter in Surface Water Sources and Their Cytotoxicity Influenced by Chlorination Disinfection

Dissolved organic matter (DOM) is the primary precursor of disinfection products (DBPs) during chlorination. However, the compositional characteristics of DOM transformation during the chlorination process in different source waters and its relationship to cytotoxicity remain understudied. Here, we used high-resolution mass spectrometry to evaluate chlorination-induced molecular-level changes in DOM derived from different surface water sources. We correlated DOM components with the cytotoxicity profiles of selected DBPs using new alternative methods with predictive toxicological assessments. Our findings indicate a selective chlorination of DOM in natural waters and a tendency for lignin and protein conversion during the manual chlorination process. The reactivity of bioactive compounds decreased in the order of lignin > protein > tannin or ConAC. The cytotoxicity of DOM from source waters is mainly attributed to lignin- and protein-like compounds within the CHO and CHNO groups. Additionally, mitochondrial damage is a highly sensitive indicator of DOM-induced cytotoxicity. The toxicity profiles of DBPs revealed 37 common toxicity-driving components characterized by low mass, medium H/C ratio, low O/C ratio, reduction state, and hydrophobicity. Our findings highlight the need to exploit the health effects of DOM and provide substantial experimental evidence for the necessity to remove potential toxicants.