Type of Document Dissertation Author Fiss, Edward Matthew URN etd-04172009-132140 Title The Chlorination of Pharmaceuticals and Other Phenolic Compounds in the Presence of Iodide Degree PhD Department Environmental Engineering Advisory Committee
Advisor Name Title Vikesland, Peter J. Committee Chair Dietrich, Andrea M. Committee Member Edwards, Marc A. Committee Member Little, John C. Committee Member Tanko, James M. Committee Member Keywords
- free chlorine
- drinking water
Date of Defense 2009-04-01 Availability restricted AbstractPharmaceuticals 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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