Browsing by Author "Fiss, Edward Matthew"

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    The Chlorination of Pharmaceuticals and Other Phenolic Compounds in the Presence of Iodide
    Fiss, Edward Matthew (Virginia Tech, 2009-04-01)
    Pharmaceuticals and personal care products (PPCPs) include a wide range of chemicals such as prescription and over-the-counter drugs, fragrances, diagnostic agents, and a litany of other compounds commonly added to household products such as sunscreens, soaps, toothpastes, and deodorants. If present in natural waters, PPCPs can come into contact with disinfectants during drinking water treatment processes. PPCPs are already known to form a variety of disinfection byproducts (DBPs) when oxidized by free chlorine, including trihalomethanes (THMs) and haloacetic acids (HAAs), many of which are known carcinogens. Salts, such as iodide, are also often present in natural water systems. Iodide is known to form a much more reactive oxidant, free iodine, when it reacts with free chlorine. Free iodine can react with organic compounds in waters to form iodinated byproducts, many of which have been shown to form in higher yields and to be more toxic than their chlorinated analogues. For this reason, it is necessary to more fully understand the fate of PPCPs during drinking water processes. The overall goals of this study are to 1) elucidate reaction mechanisms and product formation potentials for PPCP oxidation by free chlorine in the presence of iodide and 2) develop a computer model that can act as a predictive tool to aid in the assessment of potential risks resulting from PPCPs in source waters. Through the course of this research, a model was developed that could fit reaction rate parameters and accurately predict solution reactivity for a range of substituted phenols as well as PPCPs including bisphenol-A and triclosan. Past studies utilizing pseudo-first-order rate constants to determine a reaction rate over-simplified the analysis of halogen substitution reactions. Free chlorine reaction rate constant values were updated from the literature since the mechanism for electrophilic substitution was found to be different than stated in currently published literature. The involvement of H₂OCl⁺ was found to be negligible. The mechanism for the electrophilic substitution of phenolic compounds by free iodide was also different from current literature findings. We found that I₂, rather than H₂OI⁺, was an extremely important species for free iodine reactions and must be considered when analyzing the reaction kinetics. Finally, we found that small amounts of iodide can significantly affect product formation pathways thereby causing preferential formation of iodinated products and a potential increase in the total product formation. In general, the reaction kinetics were highly dependent upon the pH, iodide to free chlorine ratio, and the reactivity of the phenolic compound, and our model was able to successfully address changes in each of these variables. An LFER was developed that showed a linear relationship between reaction rates and the pKa of a phenolic compound. It is believed that the model developed can be used as a predictive tool to estimate reactivity of natural waters for a range of phenolic PPCPs simply by using the compounds pKa.
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    Formation of Chloroform and Other Chlorinated Byproducts by the Chlorination of Antibacterial Products
    Fiss, Edward Matthew (Virginia Tech, 2006-08-03)
    Triclosan is a widely used antibacterial agent found in many personal hygiene products. While it has been established that pure triclosan and free chlorine readily react, interactions between triclosan-containing products and free chlorine have not previously been analyzed. Sixteen double-blinded solutions including both triclosan-containing (1.14-3.12 mg triclosan/g product) and triclosan-free products were contacted with free chlorine. Products detected included (chlorophenoxy)phenols, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and chloroform. The daughter product yields were found to be highly variable and were dependent on the antimicrobial product investigated, the free chlorine to triclosan ratio, and the temperature at which the study was conducted. Lowering the temperature from 40 to 30 oC resulted in a decreased yield from 0.50 to 0.37 moles chloroform/mole triclosan after 1 minute of reaction time with [HOCl]initial = 4.0 mg/L as Cl2. Chloroform molar yields decreased to 0.29 when the initial chlorine concentration was reduced to 2.0 mg/L for a constant temperature of 40 oC. Field experiments, in which Atlanta and Danville tap waters were augmented with various soap products, exhibited differential results from the laboratory experiments in that different product yields were observed. These differences are attributed to the chlorine demand of constituents in the tap water. Higher chlorine to triclosan ratios tend to produce high levels of chloroform, while lower chlorine to triclosan ratios tend to form higher amounts of chlorophenols and (chlorophenoxy)phenol intermediates. The results from this study suggest that the chloroform produced by these reactions can be substantial under some conditions.