Grantee Research Project Results
2009 Progress Report: Environmental Transport, Biodegradation, and Bioaccumulation of Quantum Dots and Oxide Nanoparticles
EPA Grant Number: R833861Title: Environmental Transport, Biodegradation, and Bioaccumulation of Quantum Dots and Oxide Nanoparticles
Investigators: Aga, Diana S. , Banerjee, Sarbajit , Colon, Luis , Watson, David
Current Investigators: Aga, Diana S. , Watson, David , Colon, Luis , Banerjee, Sarbajit
Institution: University of Buffalo
EPA Project Officer: Aja, Hayley
Project Period: July 1, 2008 through June 30, 2011
Project Period Covered by this Report: July 1, 2008 through June 30,2009
Project Amount: $400,000
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Fate, Transport, Transformation, and Exposure of Engineered Nanomaterials: A Joint Research Solicitation - EPA, NSF, & DOE (2007) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
Objective:
This research aims to investigate the influence of size and surface chemistry of quantum dots (QD) (i.e. CdS and CdSe) and engineered metal oxide (MO) nanomaterials (i.e.CeO2, HfO2, ZrO2, TiO2) on their environmental mobility, biodegradation, and bioaccumulation. The specific goals are to: [1] characterize the influence of natural organic matter (NOM) on the surface functionalization, solubility, and stability of QD and MO suspensions, [2] examine the effects of NOM on the transport behavior and degradation of various formulations of QD and MO in soil columns, [3] determine the biodegradability of QD and MO in activated sludge systems as a function of surface functionalization; and [4] measure the bioaccumulation of QD and MO as a function of size and NOM concentration in a model organism (Eisenia fetida). We hypothesize that size, surface chemistry, bioavailability, and solubility of QD and MO are closely related parameters that affect the environmental fate and potential ecological impacts of QD and MO nanomaterials.
Progress Summary:
During the first year of this funding (2008-2009), we addressed the first two objectives of our research, focusing on the fate and transport behavior of QDs and MOs in water and in soil specifically, CdSe QDs, HfO2 and ZrO2 nanoparticles. The influence of NOM on these engineered nanomaterials was investigated using CdSe QDs and MOs synthesized in the Banerjee and Watson laboratories as well as commercially available QDs (EvitagTM, purchased froom Evident Technologies). We used the Suwannee River humic acid and fulvic acid standards (International Humic Substances Society) as model NOM.
Objective #1: Characterize the influence of natural organic matter (NOM) on the surface functionalization, solubility, and stability of QD and MO suspensions
Initial experiments focused on characterizing the solubility, phase transfer and dissolution of QDs and MOs upon interaction with NOM. For non-aqueous nanoparticles suspensions, the NOM-nanomaterial interactions were examined using simple phase transfer experiments, which demonstrated that hydrophobic QDs (CdSe QDs capped with trioctylphosphine oxide (TOPO), tetradecyl phosphonic acid (TDPA) or oleic acid (OA) in hexane suspensions can efficiently transfer into the aqueous phase in the presence of humic acids (HA) and fulvic acids (FA). Phase transfer proceeded for all QDs regardless of the surface-capping groups. No phase transfer was observed in the control set-ups where nanopure water was used. In the case of MOs (HfO2 -monoclinic, ZrO2-tetragonal and solid-solution HfxZr1-xO2-monoclinic and tetragonal MOs capped with TOPO), some selectivity dependent on crystal structure was evident, only allowing phase transfer of particles with monoclinic structure. Although some transfer of monoclinic MO nanoparticles were detected in nanopure water, the MOs were only stabilized in the presence of NOM. The phase transfer process was monitored and characterized using the following techniques: optical absorption and emission spectroscopies, Fourier transform infrared (FTIR) and Raman spectroscopy, dynamic light scattering (DLS) and zeta potential, inductively-coupled plasma mass spectrometry (ICP-MS), and transmission electron microscopy (TEM). Our experiments revealed that the nanoparticles were not completely degraded after phase transfer, but some leaching of the core metal was observed. Close interacting units of HA and QDs/MOs are evident from the TEM images, where the crystalline nanoparticles are agglomerated to amorphous HA/FA. QDs retained its optical absorption after phase transfer. The rate of phase transfer is also influenced by pH, ionic strength and the levels of HA/FA in solution. This NOM-mediated phase transfer has also been demonstrated using two natural surface water samples. These results reveal that NOM can provide a means by which these hydrophobic nanoparticles can enter the aquatic environment and release toxic elements like Cd2+ and/or Se2-. This demonstrates the importance of having stable surface capping ligands on the surfaces of these nanoparticles. Our phase transfer experiments also provided us a better understanding of the interactions between NOM and QDs/MOs. Two synergistic mechanisms can be deduced from our results: (1) hydrophobic interactions between non-polar functional groups of HA/FA and organic capping groups of QDs/MOs, and (2) displacement of capping groups by Lewis basic groups of HA/FA. The understanding of these mechanisms will be instrumental in predicting the fate and transport of these engineered nanomaterials. Our findings showing that even QDs with hydrophobic surface capping can be potentially transported into the aquatic environments upon interaction with natural organic matter is environmentally relevants. The NOM-mediated transfer of QDs gave rise to decreased particle sizes and some leaching of Cd2+ into aqueous solution as verified by emission spectroscopy and by inductively couple plasma mass spectrometry analysis. Fluorescence quenching of QD was observed in the presence of other substances in the sample matrix. For example, in the presence of humic or fulvic acids over time, when analyzed using capillary zone electrophoresis with laser induced fluorescence. Similar effects were observed for the aminefunctionalized QD (EvitagTM). The type of buffer also affects the fluorescence intensity by enhancing the signal, such as what was observed in CAPs buffer (N-cyclohexyl-3-aminopropanesulfonic acid) relative to water only. Therefore, it is crucial to have other analytical techniques for the accurate quantification of QD and degradation products in the samples.
Objective #2: Examine the effects of NOM on the transport behavior and degradation of various formulations of QD and MO in soil columns Soil column experiments were initiated using water-soluble suspensions of QDs (CdSe QDs capped with cysteine (CYS) or mercaptopropionic acid (MPA) and core-shell CdSe/ZnS QDs that is -COOH terminated) in active soil. Leaching was done using (1) 0.01M CaCl2 (as artificial rain) and, (2) 0.01M Na2EDTA (as Cd2+ chelator). In our experiments, both parent and aged residue leaching revealed that when leached with artificial rain (0.01M CaCl2), similar to Cd2+, the water-soluble QDs have negligible mobility in soil. It is evident in the analysis of the different soil fractions and leachates by graphite furnace atomic absorption spectroscopy (GFAAS) that Cd2+ and QDs are strongly retained by soil. However, when leached with a metal chelator, it appears that QDs behave differently from free Cd2+. EDTA enables the extraction of free Cd2+ (not QD bound) out of the soil column while majority of the QDs remain sorbed on the top soil after more than 10 column volumes. These results provide a possible approach to (1) studying QD degradation in soil (allowing the separation of free and intact QD) and (2) demonstrate effects of environmental chelators on the potential transport of these nanomaterials.
Future Activities:
For the second year, we will continue on to finish our first two objectives. The effects of pH, ionic strength and HA concentration on the solubility and stability of aqueous suspensions of QDs will be investigated. Phase transfer will also be continued for non-aqueous MO suspensions with varying surfacecapping groups to further examine what resulted to be a crystal-structure dependent phase transfer for MOs nanoparticles. The soil column experiments will also be continued for the second year, extending the materials studied to phase-transferred QDs and MOs. We will also start to collect preliminary data for the biodegradation and bioaccumulation experiments using commercially available QDs. Studies on the effect of QD on activated sludge bacteria will be initiated in the second year of funding.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 36 publications | 10 publications in selected types | All 10 journal articles |
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Depner SW, Kort KR, Banerjee S. Precursor control of crystal structure and stoichiometry in twin metal oxide nanocrystals. CrystEngComm 2009;11(5):841-846. |
R833861 (2009) R833861 (Final) |
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Navarro DA, Watson DF, Aga DS, Banerjee S. Natural organic matter-mediated phase transfer of quantum dots in the aquatic environment. Environmental Science & Technology 2009;43(3):677-682. |
R833861 (2009) R833861 (Final) |
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Supplemental Keywords:
bioavailability, soil contamination, nitrifying activated sludge bacteria, UV, IR Raman, Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, laser-induced fluorescence, heavy metals, Health, Scientific Discipline, Health Risk Assessment, Risk Assessments, biological pathways, nanochemistry, ecological risk assessment, quantum dots, bioavailability, nanotechnology, quantification of non-cancer risk, manufactured nanomaterials, nanomaterials, toxicologic assessment, biogeochemistry, nanoparticle toxicity, cellular response to nanoparticles, analysis of chemical exposure, bioaccumulationProgress 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.