Grantee Research Project Results
2008 Progress Report: The Effect of Surface Coatings on the Environmental and Microbial Fate of Nanoiron and Feoxide Nanoparticles
EPA Grant Number: R833326Title: The Effect of Surface Coatings on the Environmental and Microbial Fate of Nanoiron and Feoxide Nanoparticles
Investigators: Lowry, Gregory V. , Tilton, Robert D. , Alvarez, Pedro J. , Kim, Chris , Minkley, Edwin
Institution: Carnegie Mellon University , Chapman University , Rice University
EPA Project Officer: Aja, Hayley
Project Period: September 1, 2006 through August 31, 2009
Project Period Covered by this Report: May 1, 2007 through October 31,2008
Project Amount: $400,000
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: Nanotechnology , Safer Chemicals
Objective:
- Determine how different classes of common NP surface coatings affect the rate and extent of nanoiron oxidation, and the mobility of the oxidized products formed under environmental conditions representative of a contaminated aquifer.
- Evaluate the rate and extent of microbial nanoiron oxidation and changes in mobility, and determine how different classes of NP surface coatings affect the ability of soil bacteria to facilitate these changes.
- Determine how surface coatings affect NP interactions with soil bacteria and their bactericidal or stimulatory properties.
- Investigate the effect of coated and uncoated nanoiron and Fe-oxides on microbial populations that may participate in the remediation process. These include populations that are biostimulated by cathodic hydrogen produced during iron corrosion, such as dehalorespirers that dechlorinate the target pollutants, dissimilatory iron reducers that reactivate the iron surface if occluded by inert Fe(III) oxides, methanogens that compete for H2, and homoacetogens that produce acetate from inorganic carbon to commensally feed the other bacteria.
Progress Summary:
Aim 1. Determine the influence of surface coatings on the fate of nanoiron in natural soil-water systems.
1.1. Evaluate the effect of surface coatings and porewater geochemistry on the rate and extent of nanoiron oxidation in soil microcosms (killed controls).
Progress.
NZVI modification and characterization. Nanoscale zerovalent iron (NZVI) particles purchased from Toda America (Onada, Japan) (Liu, et al., 2005) were modified with by physisorption of polyelectrolytes as described in Phenrat, et al., 2008. Poly(styrene sulfonate) with molecular weights of 70 and 1000 kg/mol (PSS70K and PSS1M), carboxymethyl cellulose with molecular weights of 90 and 700 kg/mole (CMC90K and CMC700K), and polyaspartate with molecular weights of 2.5 and 10 kg/mole (PAP2.5K and 10K) were compared. The adsorbed polymer layer was characterized and its properties correlated with the ability to prevent rapid aggregation and sedimentation of NZVI dispersions. Particle size distributions were determined by dynamic light scattering during aggregation. The order of effectiveness to prevent rapid aggregation and stabilize the dispersions was PSS70K (83%)>≈PAP10K (82%)>PAP2.5K (72%)>CMC700K (52%), where stability is defined operationally as the volume percent of particles that do not aggregate after one hour. The stable fractions with respect to both aggregation and sedimentation correlate well with the adsorbed polyelectrolyte mass and thickness of the adsorbed polyelectrolyte layers as determined by Oshima’s soft particle theory. This fundamental understanding of the relationship between the polymer adsorbed layer properties and its ability to stabilize particles against aggregation allows for prediction of NP stability from several simple measurements of the polymer-modified particle properties.
Oxidation of bare RNIP and effect of groundwater solutes and dissolved oxygen. Initial studies have been conducted to assess the effect of groundwater solutes and dissolved oxygen on the rate and extent of oxidation, and on the types of oxidation products formed as this may affect the transport and toxicity of the particles. Initial experiments were conducted in the absence of soil and bacterial activity.
Bare NZVI particles (10 g/L) were aged for a period of 1 month and 6 months in water that had been sparged with N2(g) for 15 min with 10 mN common groundwater anions (NO3-, SO42-, HCO3- , PO42-, and Cl-) individually. A series of reactors with varying concentrations of NO3- (0.2, 1, 3, 5, and 10 mN) were prepared, aged for 1 month, and analyzed in the same fashion. A 10 g/L batch of bare NZVI was allowed to age while air was bubbled through in order to mimic an environmental system with excess dissolved oxygen. X-ray absorption spectroscopy (XAS) was conducted at Stanford Synchrotron Radiation Laboratory (SSRL) wiggler magnet beamline 10-2 under anaerobic conditions. To successfully identify all mineral phases present in batch studies, a model compound database of Fe mineral extended X-ray absorption fine structure (EXAFS) spectra also was compiled.
The samples aged over a period of 1 month show distinct degrees of passivation of the nanoparticle surface toward oxidation by water. The anions listed in increasing passivation ability are: NO3-, HPO42-, SO42-, Cl-, and HCO3-. It has been noted previously that anions in high enough concentrations can passivate iron surfaces (Liu, et al., 2007; Cornell, Schwertmann, 2003). As the samples were allowed to age for a longer period of time, oxidation progressed for most samples to an oxidation state close to that of NZVI that had been aged in the absence of anions. Nitrate and sulfate passivated the surface sufficiently to halt complete oxidation over 6 months. Nitrate has been long known to passivate the surface of iron toward oxidation and reaction but the mechanism of passivation remains unclear. Sulfate may be involved in a surface precipitation reaction due to the detection of Fe-S mineral species in the EXAFS least squared fitting of some samples.
When anions are present in solution the formation of maghemite within the oxide layer is detectible and, in the case of NZVI aged in the presence of phosphate vivianite, Fe3(PO4)2·8H2O, was formed. In addition Fe-S minerals, e.g., schwertmannite and pyrite, were detected in some of the samples, even those without added sulfate. This result is plausible given that the particles contain significant amounts of sulfur, probably a remnant of the method of synthesis (Nurmi, et al., 2005). Although batch samples aged for 1 month only contained Fe0 and Fe3O4, the 6 month aged samples did show the presence of tertiary mineral phases. The presence of dissolved oxygen altered the Fe-oxide phases formed. After 24 hours of exposure to O2-saturated water, there was a small portion of the NZVI that had visibly turned from black to dark brown. EXAFS LCF analysis of these particles revealed the significant growth of maghemite within the oxide layer, and a rapid reduction in the amount of Fe0 present in the particles. The growth of maghemite likely is due to a conversion from magnetite of the oxide layer that occurs after the electrons from the core have been depleted. Besides the increased amount of oxidation, the dramatic increase in rate of oxidation in the presence of dissolved oxygen has critical implications toward the speciation and reactivity, especially the reducing power, of NZVI when released into the environment.
EXAXFS characterization of NZVI aged in the presence of bacteria in natural aquifer media from Alameda Point, CA, will be measured to determine the effect of bacteria on the rate and extent of NZVI oxidation and on the Fe-oxides formed.
Fate of NP coatings. Because the NP coating affects reactivity and mobility in the environment, it is important to understand if the adsorption of the surface coatings on the NPs is reversible or irreversible, and the time scale over which desorption occurs. We measured the rate and extent of desorption of polyelectrolyte coatings used to stabilize NZVI, including polyaspartate (PAP MW=2.5 kg/mol and 10 kg/mol), carboxymethyl cellulose (CMC MW=90 kg/mol and 700 kg/mol), and polystyrene sulfonate (PSS MW=70 kg/mol and 1000 kg/mol). In all cases, desorption of polyelectrolyte was slow, with less than 30 wt% desorbed after 4 months. The higher MW polyelectrolyte had a greater adsorbed mass and a slower desorption rate for PAP and CMC. NZVI mobility in sand columns after 8 months of desorption was similar to freshly modified NZVI, and significantly greater than unmodified NZVI aged for the same time under identical conditions. Based on these results, polyelectrolyte modified nanoparticles will remain more mobile than their unmodified counterparts even after aging. Because the coatings do not readily desorb, the potential for toxicity should be that for the coated NZVI rather than for bare NZVI. Similarly, tests regarding the transport of NZVI should be performed using the coated material, which is the relevant form upon release into the environment. This work has been presented at several national meetings and is submitted for publication in ES&T.
Aim 2. Determine the effect of nanoparticle surface coatings on bacteria-NP interactions and NP impact on soil microbial health and diversity.
2.1. Elucidate the interactions of coated and uncoated NPs with soil bacteria
2.2. Assess the role of particle dose and surface coatings/charge on the bactericidal properties of nanoiron and Fe-oxide NPs.
Metal nanomaterials have been shown to have bactericidal properties (Stoimenov, et al., 2002; Panacek, et al., 2006; Lee, et al., 2008). We expect that polymer coated NZVI will be less toxic to soil bacteria than uncoated NZVI. The coated NZVI may encounter bacteria in either an aerobic or anaerobic environment and may be fully oxidized or have zero-valent iron remaining in the particle during the encounter. The viability of Escherichia coli cells in the presence of NZVI particles that have no coatings and with particles that have a PSS or PA polymer coating was measured under anaerobic and aerobic conditions.
The cell loss after exposure to 100 ppm of bare NZVI containing 28% Fe0 is similar to the results of Lee, et al. (2008), which showed a 3 log unit loss of viable cells over the initial 10 minutes. The results here show a 3 log unit loss of cells over a 1 hour time period. NZVI particles that were aged and contain less Fe0 (7%) also show bactericidal properties. The bare particles are toxic to the cells in both aerobic and anaerobic conditions, although the effect is lessened in aerobic systems. This may be due to passivation of the surface that occurs when the particles are exposed to oxygen as demonstrated in the EXAFS characterization of NZVI in the presence of DO. In contrast, polymer coated particles have little effect on the cells under anaerobic conditions. Visual inspection of the culture tubes shows that after approximately 15 minutes of exposure with the bacteria, the bare nanoparticles are no longer aggregating and remain in suspension. This indicates that the particles and cells are attaching to each other. For PAA and PSS-coated particles, there was always some fraction of particles that would sediment out of the suspension, indicating that the polymer coated particles and the cells were not attaching to each other.
In summary, the steric and electrosteric hindrances appear to prevent the polymer coated particles and cells from attaching. The attachment of the bare NZVI particles is causing the loss of cell viability. The strong reducing capabilities of the nanoiron may cause the inactivation, but the ability to cause this appears to be proportional to the proximity of the NZVI to the cells. The results of this study will be submitted for publication in ES&T.
2.3. Determine the influence of coated and uncoated nanoiron and Fe-oxide NPs on the relative proliferation/attenuation of coexisting anaerobic species.
The effect of coated and uncoated nanoiron and Fe-oxides on microbial populations that may participate in the remediation process was investigated. These include populations that are biostimulated by cathodic hydrogen produced during iron corrosion, such as dehalorespirers that dechlorinate the target pollutants, dissimilatory iron reducers that reactivate the iron surface if occluded by inert Fe(III) oxides, methanogens that compete for H2, and homoacetogens that produce acetate from inorganic carbon to commensally feed the other bacteria.
Our results indicate that even though NZVI initially inhibits dechlorinating bacteria in mixed cultures, TCE dechlorination activity recovers following the oxidation and passivation of NZVI. Furthermore, from the ethene production analysis and H2 consumption measurement, we conclude that H2 produced by NZVI via cathodic corrosion can be utilized as an electron donor by dechlorinating bacteria as electron donor. These findings suggest that NZVI treatment followed by microbial reductive dechlorination is a promising remedial strategy for source zones impacted with chlorinated ethene DNAPL.
Future Activities:
Future Activities are described in each section above. There are no anticipated delays in completing the work.
Journal Articles on this Report : 7 Displayed | Download in RIS Format
Other project views: | All 17 publications | 8 publications in selected types | All 7 journal articles |
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Erbs J, Berquo T, Reinsch B, Lowry G, Banerjee S, Penn R. Reductive dissolution of arsenic-bearing ferrihydrite. GEOCHIMICA ET COSMOCHIMICA ACTA 2010;74(12):3382-3395. |
R833326 (2008) |
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Kim H-J, Phenrat T, Tilton RD, Lowry GV. Fe0 nanoparticles remain mobile in porous media after aging due to slow desorption of polymeric surface modifiers. Environmental Science & Technology 2009;43(10):3824-3830. |
R833326 (2008) |
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Levard C, Reinsch B, Michel F, Oymanhi C, Lowry G, Brown G. Sulfidation Processes of PVP-Coated Silver Nanoparticles in Aqueous Solution:Impact on Dissolution Rate. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2011;45(12):5260-5266. |
R833326 (2008) |
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Li Z, Greden K, Alvarez P, Gregory K, Lowry G. Adsorbed Polymer and NOM Limits Adhesion and Toxicity of Nano Scale Zerovalent Iron to E. coli. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2010;44(9):3462-3467. |
R833326 (2008) |
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Phenrat T, Long TC, Lowry GV, Veronesi B. Partial oxidation (“aging”) and surface modification decrease the toxicity of nano-sized zerovalent iron. Environmental Science & Technology 2009;43(1):195-200. |
R833326 (2008) |
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Phenrat T, Liu Y, Tilton RD, Lowry GV. Adsorbed polyelectrolyte coatings decrease Fe0 nanoparticle reactivity with TCE in water:conceptual model and mechanisms. Environmental Science & Technology 2009;43(5):1507-1514. |
R833326 (2008) |
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Reinsch B, Forsberg B, Penn R, Kim C, Lowry G. Chemical Transformations during Aging of Zerovalent Iron Nanoparticles in the Presence of Common Groundwater Dissolved Constituents. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2010;44(9):3455-3461 |
R833326 (2008) |
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Supplemental Keywords:
Environmental nanotechnology, Health, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, Health Risk Assessment, Risk Assessments, Biochemistry, Risk Assessment, fate and transport, microbial indicators, bioavailability, nanotechnology, surface coating, nanoiron, biochemical research, exposure assessmentRelevant Websites:
PI’s personal home page: www.ce.cmu.edu/~glowry Exit
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.