Ioana Sizemore, Ph.D. (Committee Chair); Nicholas Reo, Ph.D (Committee Member); Michael Raymer, Ph.D. (Committee Member); David Dolson, Ph.D. (Committee Member); Jason Deibel, Ph.D. (Committee Member)
Doctor of Philosophy (PhD)
Silver nanoparticles (AgNPs) and ionic silver (Ag+) are known to be broad-spectrum antimicrobial agents. Recent studies show these agents may be an alternative to the most widely used drinking water disinfectant, chlorine. Chlorine is a toxic industrial chemical with a lethal concentration of 430 ppm after 30 minutes. Additionally, chlorine can react with naturally occurring materials to produce a number of disinfection byproducts such as chloroform and trihalomethanes. Some of these byproducts pose cancer risks in addition to other negative impacts to human health. These would be eliminated with the use of Ag+ or AgNPs. The main goal of this study was to show the less-explored electrochemically-synthesized silver colloid (eAg) is more effective than widely-used borohydride-capped silver nanoparticles (bAg) against the Gram-negative and water quality organisms (Escherichia coli, Klebsiella variicola, and Pseudomonas aeruginosa) at similar bacterial concentrations (e.g., 5x105 CFU mL-1) and at 0.1 mg L-1 silver, the secondary contaminant limit for drinking water. Silver colloids (eAg and bAg) were synthesized, concentrated, fractionated (5-17 nm), and their corresponding physico-chemical properties were determined and compared (e.g., size distribution, shape, surface chemistry and area). The minimum inhibitory concentration (MIC) and minimum bactericidal concentrations (MBC) for bacterial concentrations (5x105 CFU mL-1) were approximately 10 times lower for the eAg (approximately 3 mg L-1, 4 mg L-1) than bAg (approximately 35 mg L-1). These results were compared to the dose-dependent effect on bacterial concentration for the AgNPs at a steady concentration of 0.1 mg L-1, the health advisory level where no risk to health would be observed. The three types of bacteria exhibited a similar response to the three test agents, i.e., Ag+ was most effective, followed by eAg, and lastly bAg. These studies show that eAg is more effective than bAg and the antibacterial effectiveness may be demonstrated at the 0.1 mg L-1 health advisory level and show lower concentrations of eAg are needed than bAg to be effective drinking water disinfectants and effective without any by-products, such as nitrates or trihalomethanes.
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