Molecular characteristics of saturated halogenated disinfection byproducts in chlorinated urban eutrophic lake water elucidated by ultrahigh-resolution mass spectrometry

Lake eutrophication affects the molecular composition of aquatic dissolved organic matter (DOM) and halogenated disinfection byproducts (Xn-DBPs). However, the effects of autochthonous DOM on the Xn-DBPs formation during disinfection of natural eutrophic water from the perspective of biological metabolism are still poorly revealed. Herein, the natural urban eutrophic lake (UEL) water with slight eutrophication was employed to elucidate the discrepancies in Xn-DBPs formation between autochthonous and allochthonous DOM based on the ultrahigh-resolution mass spectrometry. The increased operational taxonomic units, microbial cell density and relative abundance of genus Microcystis in the collected samples indicated the slight algal bloom of the lake. The prefiltration decreased the total number of Xn-DBPs in the chlorinated UEL water. The number and its proportion of nitrogenous Xn-DBPs in chlorinated UEL water samples were significantly larger (p < 0.05) than those for chlorinated SRNOM. Microbes dominated by Microcystis contributed largely to releasing autochthonous DOM due to the microbial cell lysis and microbe-derived Xn-DBPs species upon disinfection. The Xn-DBPs species mainly derived from microorganisms were highly saturated, reduced, bioavailable, nitrogenous, and toxic but lowly oxidized and aromatic than terrestrially derived Xn-DBPs species. Moreover, the connection between microbial lipid metabolism and Xn-DBPs species exclusively identified in chlorinated UEL water indicated the considerable contribution of lipid metabolites to saturated Xn-DBPs species. Our findings not only shed light on the effects of algae on the molecular composition of DOM and Xn-DBPs species but also deepen the understanding towards the formation mechanisms of microbe-derived Xn-DBPs species from the view of microbial metabolic pathways.