Cytotoxicity, mutagenicity, and genotoxicity of emerging drinking water disinfection byproducts

  • Author / Creator
    McGuigan, Claire Frances
  • Drinking water disinfection byproducts (DBPs) are formed unintentionally when organic matter in raw water reacts with disinfectants used to kill pathogens. Epidemiological studies have shown that an increased risk of bladder cancer is associated with consumption of chlorinated water, but little is known of the toxicity of many DBPs. This thesis examined the cytotoxic, mutagenic, and genotoxic properties of phenazine and halobenzoquinone (HBQ) DBPs in human cells. Cytotoxicity was examined with an impedance-based real-time cell analysis (RTCA) instrument, mutagenicity was examined with the Ames test (bacterial reverse mutation assay), and genotoxicity was examined with the alkaline comet assay. Phenazine showed differential toxicity in human cell lines, producing an antiproliferative cytotoxic effect in HepG2 cells but a genotoxic effect in T24 cells. The BJ/XPA RTCA in vitro assay was developed and validated to provide high-throughput screening of cytotoxicity and nucleotide excision repair (NER)-mediated DNA damage simultaneously. Selected HBQs were examined with the BJ/XPA assay; the position, type, and number of substitutions on the benzoquinone ring affected cytotoxicity. All tested HBQs caused substitution mutations in the Ames test under at least some of the experimental conditions. 2,6-dichloro-3-methyl-1,4-benzoquinone (DCMBQ) was the most potent HBQ compound tested, demonstrating cytotoxicity, mutagenicity, and genotoxicity. Follow-up experiments indicated that N-acetylcysteine, a ROS scavenger, reduced cytotoxicity and genotoxicity when added concomitantly with DCMBQ. Both the cytotoxic and genotoxic effects of DCMBQ appeared to be mediated, at least in part, by the formation of reactive oxygen species. DCMBQ-induced genotoxicity appeared to be refractory to repair and may involve formation of complex oxidatively generated clustered lesions. Additional in vitro and in vivo studies are required for HBQ DBPs, particularly DCMBQ, to further determine their toxic effects. In summary, the original contributions of this research are: 1) the development of a novel in vitro method to simultaneously assess cytotoxicity and NER-mediated genotoxicity; 2) new information on the cytotoxic, mutagenic, and genotoxic properties of halobenzoquinone DBPs; 3) discovery of cytotoxic and genotoxic properties of phenazine; and 4) evidence of potential toxic mechanisms of action of DCMBQ.

  • Subjects / Keywords
  • Graduation date
    Spring 2014
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.