Drinking water disinfection by-products: Toxicological impacts and biological mechanisms induced by individual compounds or as complex mixtures

The introduction of drinking water disinfection greatly reduced the incidence of waterborne diseases. However, the reaction between disinfectants and natural or synthetic organic matter in the source water can lead to an unintended consequence which is the formation of drinking water disinfection by-products (DBPs). Many DBPs are mutagenic, cytotoxic, genotoxic, carcinogenic, or teratogenic. Studies on the molecular mechanisms of toxic effects induced by DBPs, and the overall toxicity of DBP complex mixtures are limited. The objectives of this dissertation were to i) analyze the occurrence and comparative toxicity of the emerging haloacetaldehyde (HAL) DBPs, ii) investigate the molecular mechanism of DBP-induced toxicity by the haloacetic acids (HAAs), iii) develop a single well microplate-based ATP-protein assay as a novel toxicity metric for DBPs, iv) investigate the occurrence and in vitro mammalian cell toxicity of DBPs in European drinking water samples collected from the site where epidemiological studies on reproductive outcomes were being conducted (HIWATE), and v) determine the impact of iodinated X-ray contrast media (ICM) in the source water and the type of disinfectant on the overall toxicity of DBP mixtures. From this study, iodoacetaldehyde was identified as a new DBP and ten HALs induced in vitro cytotoxicity and genotoxicity in Chinese hamster ovary (CHO) cells. HALs were the second most cytotoxic DBP class among six DBP chemical classes reported in the literature. Three mono-halogenated HAAs (monoHAA) including chloroacetic acid, bromoacetic acid, and iodoacetic acid induced ATP depletion in CHO cells, and cellular ATP levels was recovered when they were simultaneously treated with pyruvate. The magnitude of monoHAA-mediated ATP depletion highly correlated with the monoHAA-induced inhibition kinetics of GAPDH and with diverse measurements of toxicity including cytotoxicity, genotoxicity, mutagenicity and teratogenicity published in the literature. A novel single well microplate-based ATP-protein assay was developed and with this assay, monoHAAs showed the greatest reduction in ATP levels while diHAAs showed a moderate reduction with higher concentration ranges. TriHAAs induced increases in ATP levels. The occurrence and in vitro mammalian cell toxicity of DBPs in the HIWATE study was investigated. The cytotoxic potency index values significantly correlated with the total number of identified DBPs and also with the concentration of 21 target DBPs. The genotoxic potency index values were not correlated with either of these metrics or with any DBP chemical class. In the ICM study, Iopamidol generated an enhanced level of CHO cell cytotoxicity and genotoxicity after disinfection, and the relative Iopamidol-mediated increase in toxicity was greater when chloramines was used as the disinfectant compared with chlorine. Four other ICMs (Iopromide, Iohexol, Diatrizoate and Iomeprol) expressed some cytotoxicity over the control, and expressed higher cytotoxicity when chlorinated. Only Iohexol enhanced genotoxicity compared to the chlorinated source water.