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Analytical Characterization of Halobenzoquinones as Emerging Disinfection Byproducts in Disinfected Water
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- Author / Creator
- Wang, Wei
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Water disinfection is necessary for killing pathogens, but it causes an unintended chemical risk from the formation of disinfection byproducts (DBPs). Epidemiological studies show a potential association of water disinfection with increased risk of bladder cancer. It is unknown what DBPs are responsible for the observed adverse health effects. The quantitative structure and toxicity relationship analysis predicts halobenzoquinones (HBQs) are potential bladder cancer carcinogens. The objectives of this study are to characterize the occurrence, formation, transformation, removal, and toxicity of HBQs as DBPs. An analytical methodology that can identify and quantify trace levels of new HBQs in water was essential for my research. Therefore, I first developed an analytical method using solid phase extraction–ultra-high performance liquid chromatography–tandem mass spectrometry (SPE-UHPLC-MS/MS) and applied it to study what HBQs are present in swimming pools. 2,6-dichloro-(1,4)benzoquinone (2,6-DCBQ) was widely present in swimming pool water at concentrations up to 100 times higher than its concentrations in the input tap water. Other HBQs 2,3,6-trichloro-(1,4)benzoquinone (TriCBQ), 2,3-dibromo-5,6-dimethyl-(1,4)benzoquinone (DMDBBQ) and 2,6-dibromo-(1,4)benzoquinone (2,6-DBBQ) were also identified in the water of some swimming pools but not in the input tap water. These additional HBQs formed in the pools were due to personal care products, higher levels of dissolved organic contents, higher chlorine doses, and higher water temperatures, as compared to tap water. To understand what precursors contribute to the formation of HBQs in water, I conducted laboratory-controlled chlorination experiments to characterize precursors of HBQs in source waters. The biopolymer fraction of natural organic matter (NOM) in source water was identified as the most important source of 2,6-DCBQ precursors based on statistical analysis. Lotions and sunscreens also contain precursors of 2,6-DCBQ and other HBQs in swimming pool water. To control HBQ formation in drinking water, I evaluated water treatment processes on the removal of HBQ precursors. Common treatments used in drinking water treatment plants (DWTPs), including coagulation, ozonation, and granular activated carbon, can partially remove or destroy HBQ precursors, but not substantially eliminate them. Anthracite/sand filtration and UV irradiation show negligible impact on HBQ formation. To understand the fate and behavior of HBQs in drinking water distribution systems, I examined the transformation of HBQs in laboratory experiments and in field samples. Using high-resolution quadrupole time-of-flight (QToF) MS, I found that HBQs were transformed to halo-hydroxyl-benzoquinones (OH-HBQs) at neutral pH in the laboratory experiments. An SPE-UHPLC-MS/MS method was developed to quantify HBQs and OH-HBQs in authentic drinking water samples. Using this method, I confirmed that OH-HBQs are DBPs in drinking water and that they increased with decrease of HBQs in several DWTPs. An in vitro toxicity study with CHO-K1 cells showed that HBQs are two-fold more toxic than OH-HBQs, and that both HBQs and OH-HBQs are significantly more toxic than the regulated DBPs. Finally, I studied the interaction of glutathione (GSH) with HBQs to elucidate potential mechanisms of HBQ toxicity. Mono-, di-, tri-, and tetra-GSH conjugates (GS-HBQs) were identified using LC-MS/MS in reaction mixtures. The glutathionylated conjugates were elevated with the increase in GSH levels. Halosemiquinone (HSQ) free radicals were gradually depleted with the increase in GSH levels using electron paramagnetic resonance spectroscopy. These results suggest that (1) reversible redox reactions between HBQs and halo-hydrobenzoquinones (HHQs) to form HSQ radicals and oxidize GSH to glutathione disulfide; (2) Michael addition of GSH on HBQs; and (3) nucleophilic substitution of the halo groups of HBQs by GSH. Unique desulfurized and disulfide GSH-DBBQ conjugates, and the substitution of the methyl group by GSH on 2,6-dichloro-3-methyl-(1,4)benzoquinone (DCMBQ) were also observed. Finally, the conjugates in HBQ-treated HepG2 cells were identified to be the same as those produced in the reaction of (5:1) GSH/HBQs. This dissertation confirms HBQs as a group of emerging DBPs and provides the occurrence data and the mechanisms of the formation and transformation of HBQs during water treatment. Evaluation of current treatments for removal of HBQ precursors provides information for DWTPs to control these DBPs. The analytical characterization combined with toxicity evaluation of HBQs stresses the importance of monitoring these DBPs compared to the regulated DBPs. The highly sensitive and specific analytical tools developed here enable future research on assessment of human exposure and health risk of HBQs. The research methodologies are useful for discovery of other potentially important DBPs.
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- Graduation date
- Spring 2016
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.