A New Group of Heterocyclic Nitrogenous Disinfection Byproducts (DBPs) in Drinking Water: Role of Extraction pH in Unknown DBP Exploration

pH adjustment prior to extraction is an important step in water sample pretreatment processes for exploration of new/unknown disinfection byproducts (DBPs) in drinking water. To achieve a better extraction efficiency, the pH of a water sample is usually adjusted to a low level (e.g., < 0.5) to ensure that target DBPs are in their neutral forms. However, such a practice may elude some amphoteric DBPs (especially those nitrogenous DBPs with multiple functional groups), which can accept protons at a low pH and lose protons at a high pH. In this study, with careful extraction pH selection and optimization, we first report the detection and identification of a new group of heterocyclic nitrogenous DBPs, halogenated pyridinols, in simulated drinking water using ultra performance liquid chromatography/electrospray ionization-triple quadrupole mass spectrometry and time-of-flight mass spectrometry, including 5-chloro-3-pyridinol, 2-bromo-3-pyridinol, 2,6-dichloro-4-pyridinol, 2,6-dibromo-3-pyridinol, 3-bromo-2-chloro-5-pyridinol, 5-bromo-2-chloro-3-pyridinol, 3,5,6-trichloro-2-pyridinol, and 2,4,6-tribromo-3-pyridinol. On the basis of the speciation of dissociated chemical species and recovery tests at different extraction pH values, it was found that, only at a pH of 3.0, all the eight new DBPs could achieve recoveries of >50%. With subsequent instrumental parameter optimization, the method detection and quantitation limits of the eight new DBPs were determined to be 0.04-1.58 and 0.15-4.11 ng/L, respectively. The optimized method enabled an accurate detection of the eight new DBPs in two real drinking water samples. Further aided with in vivo developmental and acute toxicity assays using zebrafish embryos, the developmental and acute toxicity of the new DBPs were found to be slightly lower than those of halogenated benzoquinones but dozens of times higher than those of commonly known DBPs such as tribromomethane and iodoacetic acid.

Automated summary

Adjusting pH prior to extraction is crucial in water sample pretreatment for studying new disinfection byproducts. This study successfully detected a new group of nitrogenous DBPs in drinking water, with recovery rates of over 50% achieved at a pH of 3.0. The optimized method allowed for accurate detection of these DBPs with limits ranging from 0.04-1.58 ng/L, and toxicity assays indicated lower toxicity compared to halogenated benzoquinones but higher than commonly known DBPs.