Identification of novel disinfection byproducts in pool water: Chlorination of the algaecide benzalkonium chloride

The maintenance of public swimming pools requires numerous technological steps. One of the most important issues involves microbiological safety. Benzalkonium chloride (BAC) encompasses homologous alkylbenzyldimethylammonium chlorides with various alkyl chains, in particular C12 and C14, and is known as a popular algaecide for keeping water clean. In addition to BAC, NaOCl and UV-irradiation are also used to treat pool water as additional technological steps. Therefore, BAC itself can become a precursor of disinfection byproducts (DBPs). High-performance liquid chromatography – tandem mass spectrometry (HPLC-MS/MS), with accurate mass measurements, has allowed the discovery of several groups of DBPs that are related to BAC in public pool water in Arkhangelsk (Russia). These DBPs include numerous isomeric monochlorinated derivatives ([C21H37ClN]+ and [C23H41ClN]+), hydroxyl derivatives ([C21H38NO]+ and [C23H42NO]), carbonyl ([C21H36NO]+ and [C23H40NO]+), and dicarbonyl derivatives ([C21H34NO2]+ and [C23H38NO2]+). In addition, chlorinated alcohols, ketones and ketoalcohols of BAC were also detected, including [C21H35ClNO]+, [C21H37ClNO]+ and [C21H35ClNO2]+ for BAC-12; and [C23H39ClNO]+, [C23H41ClNO]+ and [C23H39ClNO2]+ for BAC-14. MS/MS allowed reliable elucidation of the structures of novel DBPs, proving that chlorination starts via radical substitution in the long aliphatic chains of BAC. UV-irradiation dramatically accelerates the reaction completely destroying the original compounds in less than an hour, while the array of the intermediate products remains the same as in the dark. The formation of other DBPs proceeds due to further reactions of these primary products. The concentrations of novel DBPs in pool water reach μg L−1 levels. These conclusions were proved by conducting model reactions of BAC with NaOCl.