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Detection of Silver Nanoparticles in Vadose Zone Environments using Complex ConductivityMeasurements
Atekwana, E., G. Abdel Aal, AND D Werkema. Detection of Silver Nanoparticles in Vadose Zone Environments using Complex ConductivityMeasurements. Presented at 20th European Meeting of Environmental and Engineering Geophysics, Athens, GREECE, September 14 - 18, 2014.
Nanoparticles are emerging in great numbers within the global marketplace as a result of their remarkable size dependent properties that allow for their beneficial use in science, medicine, engineering and technology. Among metal nanoparticles, silver nanoparticles possess many superior properties, such as increased electrical conductivity, antimicrobial activity, catalytic effect, etc. (Kabashin et al., 2003). In fact, silver nanoparticles are used in more than 300 known consumer products which accounts for nearly a fourth of these products. However, very little is known about the effects that the increased and widespread use of silver nanoparticles could have on the environment (Benn, 2008). Therefore, the ntroduction of silver nanoparticles into the natural environment through their life cycle via accidents, product breakdown, or waste is imminent and demands the development of techniques to detect their presence and transport in the subsurface. Compared with conventional soil and water sampling and laboratory analysis, near surface geophysical techniques provide such a potential. In particular, the complex conductivity method is a well-established geophysical method that is sensitive to the presence of metals and very small physiochemical changes that occur at the grain fluid interface (e.g. Seigel et al., 1997). The vadose zone is the source and initial location of nearly all contaminants that initiate at the surface. However, there is no single study to address the complex conductivity signatures of silver nanoparticles under such partially saturated conditions characteristic indicative of vadose zone conditions. To date there is only one study in the literature that used complex conductivity to investigate the presence of nanoparticles under fully saturated conditions (Joyce et al., 2012). In this study, we investigate the complex conductivity response of silver nanoparticles in porous media under (1) different Ag nanoparticle concentration and (2) different saturation conditions.
The emergence of engineered nano-materials (ENMs) in the global marketplace and their accidental introduction into the subsurface pose a potential risk to the environment and public health. There is a need for the development of techniques to detect their presence and transport in the subsurface. Complex conductivity measurements have been shown to be sensitive to the presence of metals. Laboratory experiments were conducted to investigate the complex conductivity response of silver (Ag) nanoparticles in a sand column under different nanoparticle concentrations (0, 2, 4, 6, 8 and 10 mg/g) and moisture content (5%, 10%, 15%, 20% and 30%). Complex conductivity measurements were obtained between 0.1-1000 Hz. The results showed that at different water saturation the magnitude of the imaginary conductivity component increased by one order with increasing concentration of Ag nanoparticles with minimal changes in the real conductivity component. On the other hand, at different concentrations of Ag nanoparticles the magnitude of the imaginary conductivity and real conductivity components increased by one and a half order and one order of magnitude, respectively. Our results demonstrate that complex conductivity measurements are sensitive to the presence of nanoparticles in unsaturated porous media which potentially could be used in guiding the detection and remediation processes of such contaminants within the vadose zone.