Identifying novel high-molecular weight disinfection byproducts in engineered water systems

Drinking water in the United States is usually disinfected using chlorine. This disinfection is important for inactivating pathogens like E. coli, which can make people sick. However, chlorine also reacts with chemicals that are naturally present in water to form disinfection byproducts (DBPs), some of which may be harmful to human health. There are potentially thousands of different DBPs, yet only a few DBPs are well studied and regulated in drinking water. The well studied DBPs include chemicals like chloroform that are very low in molecular weight. In contrast, there is very little known about the high molecular weight DBPs that form in chlorinated drinking water. Therefore, this project will use several state-of-the-art mass spectrometry techniques to study and identify high molecular weight DBPs for the first time. Natural waters (e.g., lakes and rivers) and engineered waters (e.g., drinking and wastewater) contain mixtures of thousands of organic chemicals. This dissolved organic matter (DOM) reacts with disinfectants during drinking and wastewater treatment to form toxic disinfection byproducts (DBPs). The complexity of DOM has prevented a full understanding of its composition and reactivity, even with advanced analytical techniques. Importantly, only a fraction of disinfected water toxicity can be explained by known low molecular weight DBPs, demonstrating that investigation of unknown higher molecular weight DBPs is warranted. In addition, there is a disconnect between different fields of research. Researchers who focus on DOM often use high-resolution mass spectrometry techniques to identify thousands of formulas in a sample, yet this approach lacks data validation and cannot be used to identify structures. In contrast, contaminant researchers spend significant effort to overcome the noise of “background” DOM to identify and quantify individual compounds. These siloed analytical approaches present an opportunity, which will be addressed by this project. The project will develop a transferrable method for data collection and analysis that can be used for characterizing DOM, which has the potential to transform the way scientists view and analyze complex mixtures. The research will combine advances in mass spectrometry, new computational tools, and techniques from non-target analysis of contaminants to more fully unravel DOM. During Objective 1, a wide range of formula assignment methods will first be systematically evaluated. In addition, formula validation approaches will be developed for both Fourier transform-ion cyclotron resonance and Orbitrap mass spectrometry with the goals of expanding the chemical space of analysis of DOM. During Objective 2, contaminant-focused methods, including suspect screening and semi-quantitation, will be applied to DOM for the first time. During Objective 3, these techniques will be applied to investigate the hundreds to thousands of high-molecular weight DBPs that are detected by high-resolution mass spectrometry when DOM reacts with chlorine. Throughout this project, data and methods will be made publicly available to environmental engineers and chemists. This project will improve our understanding of DOM and will provide critical knowledge about the composition and formation mechanisms of high-molecular weight DBPs. While chlorination of water produces potentially thousands of DBPs, only a fraction of these species have been identified and the known DBPs do not sufficiently explain the toxicity of chlorinated water. Therefore, the information generated by this project is important for informing future toxicity studies and developing strategies to limit the formation of toxic DBPs. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.