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2006 Progress Report: Fate and Transport of Carbon Nanomaterials in Unsaturated and Saturated Soils

EPA Grant Number: R832535
Title: Fate and Transport of Carbon Nanomaterials in Unsaturated and Saturated Soils
Investigators: Pennell, Kurt D. , Abriola, Linda M. , Hughes, Joseph
Institution: Georgia Institute of Technology , Tufts University
EPA Project Officer: Lasat, Mitch
Project Period: October 1, 2005 through September 30, 2008
Project Period Covered by this Report: October 1, 2005 through September 30, 2006
Project Amount: $395,300
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Environmental and Human Health Effects of Manufactured Nanomaterials: A Joint Research Solicitation - EPA, NSF, NIOSH (2005)
Research Category: Nanotechnology , Health Effects

Description:

Objective:

Widespread production and application of manufactured nanomaterials is expected to increase dramatically over the next decade, which will inevitably lead to the release of carbon-based nanoparticles into the environment. Our current understanding of nanomaterial fate and transport in subsurface systems is extremely limited. For example, it is not known how nanomaterials will interact with soil matrices, whether or not nanoparticle transport can be accurately modeled using classical filtration theory, and how unsaturated soil conditions will impact nanomaterial transport and retention. The overall goal of this project is to expand our knowledge of carbon (C60) nanomaterial fate and transport in natural soils. The project focuses on three specific objectives: (1) investigate the fate and transport of C60 nanomaterials in water-saturated soils as a function of soil properties and systems parameters; (2) assess the effects of C60 nanomaterials on soil water retention, water flow, and transport in unsaturated soils; and (3) develop and evaluate numerical models to describe C60 nanomaterial transport, retention, and release in subsurface systems.

Progress Summary:

During the first year of the project, our research efforts focused on the measurement of C60 fullerene transport and retention in water-saturated soils and the development and evaluation of mathematical models to describe nanomaterial behavior in porous media. A total of 40 column experiments have been conducted to evaluate the effects of flow rate, soil particle size, and influent concentration on micro- and nanoparticle transport under water-saturated conditions. Aqueous suspensions of C60 aggregates, referred to as nano-C60, were prepared with fullerene-saturated (99.9%, Materials Electronics Corp.) tetrahydrofuran (THF) that was mixed with an equal volume of water and evaporated at 75°C to remove THF. The resulting suspension contained ∼60 mg/L of nano-C60 aggregates with an average diameter of 95 nm determined by dynamic light scattering (DLS). Borosilicate glass columns (2.5 cm diameter by 15 cm length) were packed with either 40–50 mesh Ottawa sand or borosilicate glass beads. Following complete water saturation, a non-reactive tracer study was performed to assess water flow characteristics and to obtain hydrodynamic dispersion coefficients. Discrete pulses of nano-C60 fullerene solutions were injected at two flow rates (0.11 or 0.95 mL/min) and two influent concentrations (6 and 30 mg/L). Concentrations of C60 fullerene in column effluent and solid phase extracts were determined by UV absorbance and total carbon analysis, while particle size distributions were quantified by DLS.

Effluent breakthrough curve data obtained from the nano-C60 column experiments were fit using the HYDRUS-1D model, which was modified to include a non-linear, rate-limited sorption expression to describe C60 retention. The numerical model successfully captured the characteristics of the effluent profiles and yielded detachment rate coefficients that approached zero, indicating that C60 deposition was irreversible under these experimental conditions. The larger attachment rate coefficients obtained for Ottawa sand, relative to glass beads, were consistent with later breakthrough of C60 from the Ottawa sand columns. The relatively flat C60 retention profiles obtained from column extracts are indicative of a limiting attachment capacity, which was consistent with batch measurements of C60 retention. These findings were supported by subsequent column experiments, in which no further attachment was observed when an additional two pore volumes of nano-C60 solution were introduced. Simulated maximum retention values obtained for the glass beads and Ottawa sand columns agreed well with experimentally determined values. These findings indicate that the rate of nano-C60 attachment is dependent upon the number of available deposition sites. At low ionic strength, nano-C60 was not retained by Ottawa sand and the corresponding breakthrough curves were identical to those obtained for the non-reactive tracer. These observations are consistent with predictions based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which indicate that in the presence of a very large repulsion energy barrier, nano-C60 deposition will not occur.

Future Activities:

In year 2 of the project, experimental work will involve measurements of nano-C60 transport and retention in a natural medium (Appling soil), as a function of Ottawa sand size fraction (20–30, 40–50, 80–100, and 100–140 mesh), and in the presence of stabilizing agents (e.g., surfactant and dissolved organic matter). Mathematical modeling efforts will focus on further refinement and validation of nanoparticle retention expression and on more detailed consideration of attractive and repulsive forces governing C60 retention and release in porous media.

Journal Articles:

No journal articles submitted with this report: View all 1 publications for this project

Supplemental Keywords:

nanoparticles, nanomaterials, carbon, particle, fullerene, fullerol, water, groundwater, soil, chemical transport, adsorption, retention, detachment, hydrology, modeling, mathematics, scaling., , ENVIRONMENTAL MANAGEMENT, Scientific Discipline, Health, Risk Assessment, Risk Assessments, Health Risk Assessment, Biochemistry, bioavailability, exposure assessment, biochemical research, nanotechnology, fate and transport, carbon fullerene, ecological risk assessment, soil pollution, ecotoxicogenomics, nanomaterials, contaminated sediments, structure function relationship

Progress and Final Reports:
Original Abstract

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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