Chemical and toxicological studies of disinfection byproducts produced by chloramination of acesulfame

The artificial sweetener acesulfame is widely used in considerable amounts in various foodstuffs and consumers products. Chemically, it is also remarkably stable, which means it passes through many domestic sewage treatment processes and readily enters the environment. Compared to other sweeteners, acesulfame has the highest occurrence in environmental compartments worldwide, raising comparable concern. Acesulfame can be degraded by powerful chemical disinfection treatment such as ozonation, chlorination and chloramination. Among these disinfection approaches, chloramination is being widely adopted by more and more countries worldwide, including the US, China, Australia and the United Kingdom. However, chloramination of acesulfame produces disinfection byproducts (DBPs) that could be more toxic than the original compound. At this stage, details of the transformation fate and related biological impact of DBPs from chloramination remain largely unknown. Our preliminary degradation study has revealed a progressive change of molecular profile and formation of chloraminated-substituted byproducts of acesulfame, and toxicity tests with mammalian cells showed that these DBPs are substantially mutagenic. Research that can decipher the chemical mechanism and assess the toxicity of acesulfame chloramination is therefore of pivotal importance to safe, effective drinking water treatment.

A primary objective of the present study is to trace the chemical transformation pathway of acesulfame undergoing chloramination. Chemical structures and identities of individual acesulfame DBPs / nitrogenous DBPs will be confirmed by comprehensive instrumental characterizations. Chemical data obtained will be used to establish the NH2 Cl-induced degradation mechanism. Biological testing will be carried out to thoroughly evaluate the impact of acesulfame DBPs on drinking water safety. Key parameters of acute toxicity and DNA damage will be quantified in mammalian cell assays to provide information relevant to human health. Finally, the presence of acesulfame DBPs will be screened in the water produced at treatment plants and in household water to reveal the urgency of the issue. The compilation of chemical and toxicological data in this study, complementing existing eco-environmental data, will not only consolidate the scientific foundation for comprehensive risk assessment on acesulfame, but also inform efforts to design and develop better disinfection methods for a sustainable and safe supply of this vital resource.

To this end, the present work sets out to assess the transformation of acesulfame during lab-simulated chloramination treatment. Through comprehensive instrumental analysis and characterization, structural identities of chloramination DBPs will be elucidated along with the reaction mechanism and pathways. In vitro assays based on Chinese hamster ovary cell CHO-K1 will be performed to obtained data of cytotoxicity and genotoxicity with relevance to human health. The occurrence of identified acesulfame DPBs will be evaluated in water produced at water treatment plant and household tap water in order to better assess the danger of acesulfame DBPs.