Date of Graduation
Master of Science in Civil Engineering (MSCE)
Second Committee Member
Michelle Evans White
Cytotoxicity, DBPs, Mutagenicity
Bioassays have been used extensively to assess various toxicity endpoints of drinking water disinfection byproducts (DBPs), but an emphasis on single compounds prevails. In this research, DBP mixtures were assessed using a cytotoxicity test with Chinese Hamster Ovary (CHO) cells and an Ames fluctuation test with Salmonella typhimurium TA-98 and TA-100 with and without S9 rat liver homogenate. Seven whole mixture DBP concentrates were formulated using reconstituted natural organic matter (NOM) extracts from the Upper Mississippi River using scaled disinfectant dosing protocols with free chlorine and monochloramine in the presence and absence of added bromide. DBPs were identified by gas chromatography-mass spectrometry (GC-MS) and quantified with an electron capture detector (GC-ECD). Four trihalomethanes, three dihaloacetonitriles, 1,1-dichloro-2-propanone, chloropicrin, nine haloacetic acids, and dalapon were identified and quantified. Exogenous N-nitrosodimethylamine (NDMA) was added to two monochloramine-derived concentrates because the NOM did not include precursors for this known human carcinogen that forms in chloraminated waters. Five synthetic DBP analog mixtures were formulated based on the profiles of the whole mixture DBP concentrates. DBP mixture concentrates exerted mild cytotoxicity to CHO cells, approaching or reaching the LD50 in all seven concentrates, a result which could be only partially explained by the identified DBPs. In the Ames tests, no revertant wells were observed with the TA-98 bacterial strain, indicating the DBP-concentrates did not induce frameshift mutations in hisD3052. However, statistically significant increases in the number of revertant wells were observed in TA-100 in all seven DBP mixture concentrates, indicating base-substitution mutations in hisG46. Mutagenicity was greater with the DBP mixtures formulated with free chlorine and bromide, suggesting that bromine-substituted DBPs were important contributors. Exogenous NDMA had a synergistic effect in the concentrate formulated with monochloramine and bromide in the presence of S9 only, indicating NDMA was important in mammalian mutagenicity. However, none of the observed mutagenicity in TA-100 was explained by the nineteen identified DBPs and/or the associated interactions. Future work should focus on high resolution mass spectrometry techniques aimed at identifying additional DBPs in the mixture concentrates and assessing the mutagenicity of these DBPs.
Ghebremedhin, Y. (2019). Cytotoxicity and Mutagenicity of Disinfection Byproduct Mixtures Formulated Using Free Chlorine and Monochloramine. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/3453