Desalination of Seawater: Comprehensive Nontarget Assessment of Disinfection Byproducts

Due to growing populations and water scarcity, desalination is increasingly used to generate safe drinking water. A concern is the potential formation of more toxic brominated and iodinated disinfection byproducts (DBPs) in the finished drinking water. While desalination technologies remove much of the organic matter and bromide/iodide precursors to DBP formation, lower molecular weight, uncharged compounds and salts are not completely removed. We present a comprehensive nontarget identification of DBPs from desalination, using a broadscreen, comprehensive approach with gas chromatography (GC)-high resolution-mass spectrometry (MS) to identify DBPs produced in desalinated waters treated with chlorine, chlorine dioxide, ozone, chloramine, and UV. We include real desalinated waters from three large desalination plants in the United Arab Emirates, along with controlled laboratory treatments of these waters, allowing a direct comparison of different disinfectants. Mammalian cell cytotoxicity analyses for new desalination DBPs are also reported, along with whole-water toxicology for treated desalinated waters. Fifty-five DBPs were identified, including many reported for the first time in desalinated water, including a new dibromomethyl-pyrazole, along with haloketones, haloaldehydes, halonitromethanes, haloamides, and >2 carbon haloacids. Di- and tribromophenols had greater cytotoxicity compared to corresponding regulated di- and trihaloacetic acids. Reverse osmosis (RO)-treated waters had higher cytotoxicity than distilled waters (multistage flash and multieffect distillation). Of the RO-treated waters, samples treated with ozone-chlorine had highest cytotoxicity, followed by UV, ozone, and chloramine, consistent with increased formation of more toxic bromonitromethanes and dibromoacetic acid with ozone-chlorine. However, DBP levels in the treated desalinated waters and whole-water cytotoxicity were lower than found in typical drinking waters, suggesting that, despite increased formation of brominated DBPs, desalination may produce safer water overall.