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A Feasibility Study on the Geophysical Response to Nanoparticles in the Subsurface
Citation:
WERKEMA, D. D., D. R. GLASER, R. Joyce, D. Hawkins, E. Atekwana, AND G. Z. Abdel Aal. A Feasibility Study on the Geophysical Response to Nanoparticles in the Subsurface. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-10/105, 2010.
Impact/Purpose:
The growth in research, development, and production of nano-scale materials has been dramatically increased over the past few decades. This growth has resulted in an estimated 900 nanotechnology enabled products, both consumer and commercial, utilizing the unique properties of nanomaterials (Maynard, 2006). Nanomaterials are used in the global marketplace. The behavior of these materials in the environment may constitute a new class of non-biodegradable pollutants of which environmental scientists have very little understanding.
Description:
The research presented herein aims to determine if a spectral induced polarization (SIP) response exists due to nanoparticles in a saturated sand matrix. If a SIP response is realized in such an experimental setting, then it is feasible that SIP may be capable of delineating nanoparticles in the subsurface. The following five nanoparticles were studied: zinc oxide (nZnO), cerium dioxide (nCeO2), titanium dioxide (nTiO2), zero valent iron (nZVI), and silver (nAg); in two separate experiments. In Experiment 1, the SIP detection threshold for various concentrations of nano-oxides and nano-metals is presented. The results show the nanometals, especially nAg, revealed the largest SIP response in the imaginary conductivity component. The nano-oxides showed very little SIP response. Therefore, Experiment 2, investigated the relationship between the SIP breakthrough and the geochemical breakthrough of nAg in flow-through columns. The chemical and SIP break through curves (BTCs ) showed very close qualitative similarity. The BTCs revealed that lower concentrations of nAg were transported more readily than higher concentrations, which also revealed the SIP discrepancy between these concentrations. Overall, the results from these feasibility experiments suggest that SIP methods hold promise in the mapping and monitoring of nano-metals in unconsolidated sand matrices if the concentrations of the nano-metals are near the detectability level. Our results suggest that electronic conductance appears to be the dominant conductivity mechanism for the SIP measurements. Additional experiments are in progress to address various solution chemistries, heterogeneous geologies, and other complications, which inevitably occur at field sites and the sensitivity of other geophysical methods to nanoparticles.