Closing the gap of known and unknown halogenated nitrogenous disinfection byproducts in water: Advanced mass spectrometry techniques

Halogenated nitrogenous disinfection byproducts (X-NDBPs) are unregulated but toxicologically relevant DBPs of public health concern. The formation of X-NDBPs occurs via substitutions of halogens to carbon (XC-NDBPs) or nitrogen (XN-NDBPs). XC-NDBPs are relatively stable and widely present, while XN-NDBPs are generally unstable and difficult to detect in water. Stable X-NDBPs have shown significantly higher toxicity than the regulated DBPs and are forcing agents in the cytotoxicity of disinfected water among known DBPs. Evidence suggests that unknown X-NDBPs are present in tap water. Mass spectrometry (MS) techniques are the most powerful tools for identification of unknown X-NDBPs. Here, we critically evaluate the analytical and toxicological studies of known X-NDBPs, as well as recent advances in MS techniques for identification of unknown X-NDBPs. This review highlights gaps, challenges, and the need for development of simplified sampling techniques, identification of reactive nitrogenous organics in source water, and identification of missing X-NDBPs in disinfected water.