Investigating Relationships Between Artificial Sweeteners and Water Quality: Waste Impact Indicators and Disinfection Byproduct Precursors

Abstract

Artificial sweeteners (ASs) are highly stable, man-made sugar alternatives used in many low and no-calorie foods and beverages. The massive consumption of ASs by the general population has resulted in their wide occurrence in waste and environmental waters. Wastewater treatment is not designed to remove ASs and therefore detection of ASs can be used as indicators of human impact on environmental waters. Chapter 1 includes a critical review of literature on ASs and re-assessment of the specificity and stability assumptions that led to their use as waste-water indicators. I drew attention to accurate characterizing of waste sources before interpreting AS impact on receiving water bodies to account for specificity and natural variation in occurrence. Further, I emphasized the importance of sensitive and reliable analytical methods to facilitate proper utilization of ASs as WW impact indicators. In Chapter 2, a high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method was developed for sensitive (ng/L) detection of two ASs, acesulfame (ACE) and sucralose (SUC) without sample preconcentration. The method was used to investigate the occurrence of ACE and SUC in 10 publicly accessible surface water bodies in the Thompson Region. SUC was only present at two sites while ACE was detected in every sample. Therefore, ACE is a better indicator for future water quality studies on human waste-impact in the Thompson Region surface waters. In Chapter 3, I examined the application of ACE as a urine indicator in recreational waters. Water disinfection is essential to prevent the transmission of waterborne pathogens but unintentionally results in the formation of disinfection byproducts (DBPs). Nitrogenous compounds in urine can react with chlorine disinfectants to form irritating N-DBPs in swimming pools. Rapid HPLC-MS/MS analysis identified 100% occurrence of ACE in pool and hot tub samples from two Canadian cities. The recreational water samples contained significantly greater concentrations of ACE compared to the input tap water controls. Approximate estimates of 30 and 75 L of urine were calculated to be required to account for the average ACE in two pools. In Chapter 4, I moved to examine ASs as potential DBP precursors. Previous studies have identified halobenzoquinones (HBQs) as more cyto- and genotoxic in vitro than commonly regulated DBPs. I therefore examined a commonly used AS, aspartame, an aromatic dipeptide composed of phenylalanine, aspartic acid, and methanol, as a precursor to 2,6-dichloro-1,4-benzoquinone (DCBQ). Under controlled chloramination conditions, HPLC-MS/MS analysis confirmed aspartame and phenylalanine as precursors of DCBQ. Further, dissolving one AS package (Equal® Original) in a cup of authentic tap water containing residual monochloramine can increase DCBQ concentration. Additionally, the presence of aspartame in water was found to reduce the transformation of DCBQ to HO- DCBQ. Boiling pre-treatment of tap water reduced residual chloramine, increased pH and significantly decreased the concentration of DCBQ. In Chapter 5, I further examined formation of HBQs from aromatic amino acids (AAAs). Determining HBQ precursors is essential to reduce their formation in drinking water. AAAs share structural similarities and are readily found in natural water bodies. DCBQ and 2,3,6-trichloro-1,4-benzoquinone (TriCBQ) formation was quantified with HPLC-MS/MS after chlorination of each AAA (phenylalanine, tyrosine, and tryptophan). Additionally, water sources high in bromide ions have been found to produce higher proportions of Br-DBP analogues after disinfection. Br-DBP species are more toxic than the corresponding chlorinated compounds. In the presence of bromide, chlorination of all AAAs yielded 2,6-dibromo-1,4-benzoquinone (DBBQ) in addition to DCBQ. This thesis investigates ASs and their relation to water quality. Ubiquitous occurrence of ACE in B.C. surface waters and Canadian swimming pools and hot tubs provides a baseline for future waste impact studies on these environmental waterbodies. The confirmation of aspartame and phenylalanine as DCBQ precursors under chloramination and AAAs as HBQ precursors under chlorination conditions warrants further investigation into human exposure to DBPs via consumption of beverages prepared with disinfected tap water.