Characterization and Formation of Iodinated Disinfection Byproducts from Organic and Inorganic Precursors

Many drinking water sources are impacted by medical waste that contain iodinated contrast media (ICM) or their biodegradation products. When dissolved iodine enters a drinking water treatment plant, it can be a precursor to iodinated disinfection byproducts (I-DBPs) in the finished water, such as iodinated trihalomethanes (I-THMs) and iodoacids (IAs), that have higher relative toxicity compared to regulated DBPs. The goal of this research was to advance our understanding of I-DBP formation in drinking water and evaluate strategies to reduce consumer exposure. The first objective was to develop a method for resolving and quantifying four IAs from nine other haloacetic acids in a drinking water matrix, since current methods lack sensitivity and quality assurance for measuring their occurrence. With a multi-step extraction process that utilizes liquid-liquid and solid-phase extractions, four IAs were reproducibly concentrated from ng/L to the µg/L levels required for detection. The second objective was to evaluate medical waste-impacted surface waters in the US state of North Carolina that are used as downstream drinking water sources. The surface waters receiving such wastewater residues showed measurable levels of organic iodine and downstream drinking water treatment plants had I-DBPs in the finished water. Non-target chemical analysis confirmed that ICMs and their transformation products were responsible for at least a portion of the total organic iodine load in the drinking water source. In the third objective, organic iodine was also tracked through each unit process in the drinking water treatment plant to evaluate I-DBP formation. Utilizing adsorption isotherms, an optimized use of powdered activated carbon was proposed to meet the plant’s current usage objective for taste and odor control while decreasing I-DBP formation in the finished water. When free chlorine was applied at any location in the treatment plant and total dissolved iodine was present, I-THMs formed. Once in the distribution system, I-THMs degraded in the presence of residual disinfectant leading to spatial variability in the water delivered to the consumers. This research demonstrates that I-DBP precursors can originate from anthropogenic sources thus increasing the need for drinking water source protection together with enhanced treatment processes to ensure a high-quality drinking water for consumers.Doctor of Philosoph