Carbon Nanotubes in Soils: Transport, Filtration, and Impact on Soil Microbial Community

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CBET-0828795ElimelechCarbon nanotubes (CNTs) are emerging in a variety of applications, including electronic, optical, medical, and structural composite technologies. Because of their anticipated role in large-scale industrial production, there is little doubt that CNTs will ultimately find their way into our aquatic environment. The unusual physicochemical characteristics of CNTs compared to other nanoparticles, particularly the very large aspect ratio and highly bundled (aggregated) state in aqueous solutions, preclude meaningful theoretical predictions of their aggregation and transport behavior. Furthermore, because of the lack of laboratory data on CNT transport in porous media, very little is known about their potential mobility and fate in subsurface environments. Of particular interest is the need to assess the potential contamination of groundwater aquifers by CNTs. Contamination of groundwater with CNTs may originate from landfill leachates, wastewater infiltration, and land applications. Therefore, understanding the extent of CNT transport in soils will be the key to predicting the risk of contamination of underlying groundwater aquifers. Furthermore, because of CNT retention within the soil profile, its impact on soil microbial ecology must be considered in light of recent studies indicating antibacterial effects of CNTs. The overall objective of the proposed research is to assess the extent of transport and retention of CNTs in soils and the impact of retained CNTs on the soil microbial community. Worst case scenarios for CNT transport in soils will be established, which will then enable them to predict the potential for contamination of underlying groundwater aquifers. Furthermore, they will establish the conditions under which retained CNTs influence the soil microbial ecology. Two hypotheses guide their research: (i) the mobility of CNTs in soils will be relatively limited as the large aspect ratio of the nanotubes and their highly aggregated (bundled) state will promote extensive removal by physicochemical filtration and straining, and (ii) because of their effective retention, particularly via straining, CNTs will accumulate in soils and thus will influence the soil microbial community. To complete the proposed work, they will: (1) select and characterize single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes MWNTs, (2) select and characterize soils and model porous media, (3) evaluate transport and retention of CNTs in packed columns, (4) evaluate mobilization (release) of retained CNTs by perturbations in solution chemistry, (5) assess the impact of retained CNTs on soil microbiology, and (6) evaluate worst case scenarios and potential effects on soil and groundwater. The research program will include the training of a doctoral student and two undergraduate students. Special modules on transport of nanomaterials in the environment and on the potential implications of nanomaterials on the geomicrobiology of subsurface environments will be added to undergraduate courses. They will work with the Yale Peabody Museum to develop appropriate modules for the museum's School Programs and Teacher's Workshops on environmental and societal impacts of nanotechnology.