Grantee Research Project Results
2009 Progress Report: Agglomeration, Retention, and Transport Behavior of Manufactured Nanoparticles in Variably-Saturated Porous Media
EPA Grant Number: R833318Title: 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: January 1, 2009 through December 31,2009
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 (NPs) 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.Progress Summary:
During the second year of this project, we focused on measuring magnetite mobility in model porous media (e.g., sand) under different solution chemistry (pH and ionic strength) and in the presence of different concentrations of humic acid, in line with the project objective #2. We also examined aggregation behavior of TiO2 NPs but no useable results have been obtained to date. Tasks completed and major finding are summarized below.
Materials and method of column experiments
The magnetite NPs used in our column experiments were synthesized using a co-precipitation method, which was described in the previous progress report. The particles were stabilized using trace amount of surfactant TMAH and had an average size of 58.0±0.3 nm, measured by dynamic light scattering (DLS). For all experiments, magnetite NP concentration of 30 mg/L was used. Elliott soil humic acid (HA) standard (1S102H, International Humic Substances Society (IHSS)) was used to represent natural organic matter, which was filtered through 0.45 µm nylon membrane filters, and the pH of the filtrate was adjusted to 6.7. Zeta potential of magnetite NP suspensions at pH 5 and ionic strength 1 mM, at pH 10 and ionic strength 1, 5, 10, 15, 25 mM, and with 2, 5, 10 ppm HA were measured using a ZetaSizer Nano. Quartz sand (Accusand 40/60, Unimin Corporation, Le Sueur, MN) with diameter of 300-355 µm and an average surface zeta potential of -59.95 mV was used. The column was 10-cm long and 3.8 cm in inside diameter and wet-packed. Experiments were run at all the conditions specified above. Breakthrough curves and particle depth-distribution profiles were constructed. Collision efficiencies were calculated to quantify NP retention.
Major findings
1. Effect of pH. Effect of pH was evaluated at pH 5 and 10. At pH 5 magnetite particles and the sand grains possess oppositely-charged surfaces so that attachment occurs under favorable conditions. As a result, there was < 10% retention of the input magnetite particles due to strong electrostatic attraction. On the other hand, the particles and sand grains are like-charged at pH 10 leading to unfavorable deposition conditions; therefore, there is minimal retention of magnetite particles due to electrostatic repulsion.
2. Effect of ionic strength. Effect of ionic strength was examined at pH 10 (i.e., unfavorable condition). As expected, increasing solution ionic strength increases magnetite particle retention hence decreases transport. This is likely cause by two reasons: 1) zeta potential of magnetite particles becomes less negative as ionic strength increases reducing repulsion; and 2) agglomeration of magnetite particles increases as ionic strength increases enhancing removal by straining. Results also indicate that the increased magnetite removal at higher ionic strength can be attributed to increased retention in both primary and secondary energy minima.
3. Effect of HA. Addition of HA modifies the surface charge status of magnetite particles therefore their aggregation and transport behavior. At pH 5 (favorable condition for attachment), we found that 2 ppm HA was not enough to change the nature of interaction between magnetite particles and sand, however, 10 ppm HA was sufficient to reverse the sign of charge of magnetite particles and enhanced their transport considerably as compared to without HA addition or at 2 ppm HA concentration. At pH 10 (unfavorable condition for attachment), on the other hand, HA addition at both 2 and 5 ppm decreased magnetite retention and increased transport at any given ionic strength. In the presence of HA, increased magnetite retention at higher ionic strength was mostly due to retention in the primary minimum. While the overall transport of magnetite particles showed an increasing trend with the addition of HA, retention by straining was found to increase when HA concentration was high, possibly due to blocking of pores by the large HA molecules. Therefore, effects of HA on magnetite NP behavior are complex and can vary depending on properties of the NP, solution chemistry, as well as HA concentration. Given the complex nature of natural organic matter in the subsurface, these effects are expected to be even less predictable.
Future Activities:
We will conduct column experiments under unsaturated flow conditions. Studies reported in the literature on transport of nanoparticles in porous media have mostly used particles larger than 100 nm. Our on-going work involves using truly nano-sized particles (5 nm and 50 nm) so that their behavior can be compared with their larger counterparts.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 15 publications | 6 publications in selected types | All 6 journal articles |
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Zhu H, Han J, Xiao JQ, Jin Y. Uptake, translocation, and accumulation of manufactured iron oxide nanoparticles by pumpkin plants. Journal of Environmental Monitoring 2008;10(6):713-717. |
R833318 (2009) R833318 (Final) |
Exit |
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
, RFA, Health, Sustainable Industry/Business, Sustainable Environment, Risk Assessments, Technology for Sustainable Environment, contaminated sediments, ecological risk assessment, fate and transport, bioavailability, nanotechnology, manufactured nanomaterials, human exposure, nanomaterials, groundwater contamination
Progress 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.