Grantee Research Project Results
Final Report: Hysteretic Accumulation and Release of Nanomaterials in the Vadose Zone
EPA Grant Number: R832529Title: Hysteretic Accumulation and Release of Nanomaterials in the Vadose Zone
Investigators: Kibbey, Tohren C.G. , Sabatini, David A.
Institution: University of Oklahoma
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 2005 through August 31, 2009
Project Amount: $375,000
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Environmental and Human Health Effects of Manufactured Nanomaterials: A Joint Research Solicitation - EPA, NSF, NIOSH (2005) RFA Text | Recipients Lists
Research Category: Human Health , Safer Chemicals , Nanotechnology
Objective:
The objectives of this work were to study the vadose zone accumulation and release of a wide range of manufactured nanomaterials, with emphasis on hysteretic interactions with air/water interfaces and specific mineral surfaces. Nanomaterials can enter the vadose zone through infiltration of atmospheric dispersions, or from groundwater contaminated by landfill leachate or other sources. Depending on the nature of the materials and interactions with critical interfaces, the vadose zone may either provide a sink for nanomaterials, preventing their spread throughout the environment, or a long-term contaminant source.
The work was divided into three primary tasks, each with a specific purpose for achieving the objectives of the study:
Task 1. Batch adsorption/adhesion experiments
Purpose: to assess adsorption/adhesion affinities with critical liquid/solid and liquid/air interfaces.
Task 2. Saturated deposition/dispersion transport experiments
Purpose: to evaluate dynamic interactions between nanomaterials and mineral surfaces.
Task 3. Dynamic hysteretic unsaturated transport experiments
Purpose: to provide detailed information about the effects of wetting/drying history, infiltration, and unsaturated soil behavior on the accumulation and release of nanomaterials.
Experiments were conducted using a range of experimental systems, ranging from custom-designed miniature pressure cells (used for miniature dynamic wetting/drying/infiltration experiments) to large (as tall as six feet or more) custom-designed columns (used for experiments examining the effects of heterogeneity). Other experiments needed to interpret results (e.g., saturated transport experiments) were conducted in parallel with unsaturated experiments. After refining methods needed for the experiments and conducting experiments to better understand the mechanisms behind the deposition of nanoparticles during dynamic unsaturated flow, the project focused on understanding hysteretic retention and release of nanoparticles under dynamically changing wetting/drying conditions.
A wide range of nanomaterials selected for study during the project, but most detailed experiments were conducted with four specific nanomaterials: titanium dioxide (TiO2), tin (IV) oxide (SnO2), fullerene C60, and polystyrene latex nanospheres.
Porous media used in miniature dynamic wetting/drying/infiltration experiments to date have included two sizes of glass beads as well as fine sands in selected experiments. Large column experiments have used both coarse and fine sands.
Summary/Accomplishments (Outputs/Outcomes):
The results of this work found that air/water interfaces play a significant role in retention and release of nanoparticles during dynamic unsaturated conditions. In cases where there nanoparticles have little affinity for solid surfaces, the formation of air/water interface during drainage (drying), and the elimination of air/water interface during imbibition (wetting), controls the retention and release of nanoparticles. Because porous media with smaller mean grain sizes tend to exhibit greater interfacial area at a particular saturation, retention as a function of saturation tends to be greater for finer-grained materials under unsaturated conditions; i.e., finer materials such as silts are likely to form a greater sink for nanoparticles in the unsaturated zone than coarser materials such as coarse sands. At higher saturations, nanoparticle retention is likely driven by adsorption to air/water interfaces. However, at lower saturation, retention tends to become much more significant, and is likely driven by film straining. This is particularly true during dynamic drainage, as nanoparticle-containing water channels in porous media shrink, trapping nanoparticles against solid surfaces.
Repeated wetting/drying appears to trap many nanoparticles. That is, nanoparticles retained when interfaces are formed during drainage may be released during imbibition, but are recaptured during subsequent drainage events. Flooding the porous medium with water appears to release highly mobile nanoparticles (i.e., those with very little affinity for the solid surface). However, nanoparticles which are strongly retained during drainage tend not to be released to a significant extent during subsequent flooding, even if they were suspended and mobile prior to drainage, and the flooding solution is designed to create conditions that should mobilize nanoparticles.
Conclusions:
The environmental significance of this result is that retention of strongly-retained nanoparticles in the unsaturated zone may be nearly irreversible in some cases, so the unsaturated zone may provide a sink the significantly limits mobility and risk. However, there are a number of nanoparticles and conditions for which there is little retention by unsaturated interfaces (e.g., fullerene under many conditions), so the role of the unsaturated zone is likely to vary significantly for different nanoparticles.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 8 publications | 4 publications in selected types | All 2 journal articles |
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Type | Citation | ||
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Chen L, Sabatini DA, Kibbey TCG. Role of the air-water interface in the retention of TiO2 nanoparticles in porous media during primary drainage. Environmental Science & Technology 2008;42(6):1916-1921. |
R832529 (Final) |
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Chen L, Sabatini DA, Kibbey TCG. Retention and release of TiO2 nanoparticles in unsaturated porous media during dynamic saturation change. Journal of Contaminant Hydrology 2010;118(3-4):199-207. |
R832529 (Final) |
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Supplemental Keywords:
Health, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, Health Risk Assessment, Risk Assessments, Biochemistry, Risk Assessment, nanochemistry, contaminated sediments, fate and transport, bioavailability, carbon fullerene, nanotechnology, nanomaterials, vadose zone, soil pollution, exposure assessmentProgress and Final Reports:
Original AbstractThe 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.