Grantee Research Project Results

2007 Progress Report: Agglomeration, Retention, and Transport Behavior of Manufactured Nanoparticles in Variably-Saturated Porous Media

EPA Grant Number: R833318
Title: Agglomeration, Retention, and Transport Behavior of Manufactured Nanoparticles in Variably-Saturated Porous Media
Investigators: Jin, Yan , Xiao, John
Institution: University of Delaware
EPA Project Officer: Aja, Hayley
Project Period: March 1, 2007 through February 28, 2011
Project Period Covered by this Report: September 1, 2006 through August 31,2007
Project Amount: $399,035
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Environmental and Human Health Effects of Manufactured Nanomaterials: a Joint Research Solicitation-EPA, NSF, NIOSH, NIEHS (2006) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Nanotechnology , Safer Chemicals

Objective:

The production of significant and increasing quantities of synthetic nanomaterials and our very limited knowledge on their potential environmental and health effects have caused increasing public concerns. The overall objective of the proposed project is to develop an understanding of the fate of nanoparticles released into the subsurface environments. We hypothesize that nanoparticles are likely to be mobile and have the potential to contaminate water resources either as contaminants themselves or by facilitating the transport of other toxic substances. We propose to conduct a comprehensive study to systematically investigate the major processes that control the movement of nanoparticles in the subsurface under environmentally relevant conditions. Our specific objectives are to (1) determine agglomeration behavior of nanoparticles under different solution chemistry (pH, ionic strength, and presence of dissolved humic material), (2) measure mobility of nanoparticles in model porous media under both saturated and unsaturated flow conditions; and (3) experimentally elucidate the attachment and retention mechanisms of nanoparticles at various interfaces at the pore scale.

Approach:

We will use TiO₂ and Fe nanoparticles as models representing two major categories of nanoparticles that have been used or have the potential to be used in large quantities commercially. Agglomeration of nanoparticles will be evaluated in batch experiments by dynamic light scattering. Transport and potential transformation will be studied with a series of laboratory column experiments using model sand of various surface properties. Sorption and reaction models will be combined with transport models to describe the transport experiments quantitatively. An innovative approach of using confocal microscopy to visualize and analyze particle-particle and particle-interface interactions in micromodels will provide resolution high enough to reveal detailed particle arrangement in bulk solution and at interfaces to elucidate the mechanisms involved in particle attachment and retention at the pore scale.

Progress Summary:

During the first year of this project, we focused on evaluating the agglomeration potential of magnetite nanoparticles (NPs) in batch experiments, in line with the project objective #1. Tasks completed to date and major finding are summarized as follows.

1. Synthesis and characterization of magnetite NPs. Magnetite particles were synthesized using a co-precipitation method, mixing, with strong magnetic stirring, 0.5 M FeCl₃•6H₂O (Sigma-Aldrich) and 1 M FeCl₂•4H₂O followed by addition of 0.7 M NH₄OH. The precipitated particles were washed with DI water and stabilized using surfactant TMAH. The average size of the resulting magnetite NPs is 58.0±0.3 nm, measured by dynamic light scattering (DLS). The structure and morphology of the particles were examined using XRD and TEM.

2. Agglomeration of magnetite NPs. Agglomeration of magnetite nanoparticles was evaluated in batch experiments by DLS over a wide range of solution pH (3 to 10) and ionic strength (1 to 50 mM). Special focus was given to the effect of adding dissolved humic acid (HA) on the stability and agglomeration kinetics of magnetite NPs at various pH and ionic strength. We found that magnetite agglomeration increases with increasing ionic strength and addition of HA made magnetite suspension more stable at high ionic strength than in absence of HA. The particles agglomerated quickly at pHs close to the point zero of charge (PZC), which was measured using ZetaSizer Nano, but were stable at pHs below or above the PZC. Addition of HA enhanced magnetite particle agglomeration at pHs below PZC but promoted stability above it.

3. Atomic force microscope (AFM) was used to observe magnetite NP-NP interactions at different pH and ionic strength as well as NP-HA interactions. Results agreed well with results from the batch agglomeration experiments.

4. The classic DLVO theory explained the observed magnetite agglomeration behavior well. To account for magnetic attraction between the particles, an apparent Hamaker constant was fitted and used in the DLVO calculations.

Expected Results:

The proposed project integrates experiments across disciplines (environmental soil physics/hydrology and physics/material science) and scales (column, batch, and pore scale). The results of the proposed study will lead to better understanding of particle-particle and particle-interface interactions at the microscopic level, as well as particle agglomeration, retention, and movement in porous media under various chemical (pH, ionic strength, presence of dissolved humic material) and physical (variable water content) conditions at macroscopic scale. We expect to provide conclusive evidence about the conditions under which transport of NPs is expected and the quantitative magnitude of the process. Such information will contribute to the overall understanding of how nanomaterials interact with the natural environment and provide scientific basis for determining exposure pathways and developing exposure guidelines, which is the first element in risk assessment to quantify potential human health effects.

Future Activities:

Results from the batch agglomeration studies provided framework for the design of column experiment to examine magnetite NP mobility through model porous media. These experiments are in progress. Also planned for the second project year are batch experiments with TiO₂ NPs, to compare their behavior with magnetite NPs. Corresponding column transport experiments will also be conducted with TiO₂ NPs.

Journal Articles:

No journal articles submitted with this report: View all 15 publications for this project

Supplemental Keywords:

Manufactured nanomaterials, elemental iron, iron oxides, titanium, dioxide, fate and transport, human health effect, agglomeration, vadose zone, environmentally conscious manufacturing, public policy, hydrology, modeling, health risk assessment, risk assessments, environmental contaminants, environmental science, physics
, Sustainable Industry/Business, Health, RFA, Technology for Sustainable Environment, Risk Assessments, Sustainable Environment, bioavailability, manufactured nanomaterials, nanomaterials, contaminated sediments, ecological risk assessment, groundwater contamination, human exposure, fate and transport, nanotechnology

Progress and Final Reports:

Original Abstract

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.