High-molecular-weight by-products of chlorine disinfection

Although drinking water chlorination has reduced the incidence of waterborne disease, the reactions of chlorine with organic matter can lead to the formation of >700 halogenated disinfection by-products (DBPs). Epidemiological studies have linked the consumption of chlorinated drinking water with bladder cancer. With studies indicating that the one- and two-carbon-atom DBPs of current interest account for only ~16% of disinfected water cytotoxicity, there is a need to identify toxicity drivers within the poorly characterized higher-molecular-weight (more than two carbon atoms) DBP fraction. In this Review, we outline the current knowledge regarding this fraction and discuss novel analytical approaches to characterizing the much wider variety of structures that it contains. We detail the products formed from the reactions of chlorine with different categories of precursor, including the characteristics of the elemental formulae of products identified by high-resolution mass spectrometry, the halogenated aromatic DBPs formed from precursors in pristine waters and the products derived from biopolymer-bound monomers in algal- or wastewater-impacted waters. Finally, we discuss the key challenges for research into this important, but until recently, mostly overlooked by-product fraction. Recent toxicological studies have indicated that the poorly characterized high-molecular-weight fraction of disinfection by-products may contribute more to toxicity than the carbon disinfection by-products of current research interest. This Review summarizes what is known about the high-molecular-weight fraction and suggests pathways for future research in this area.