Grantee Research Project Results
Final Report: Assessment of the Environmental Impacts of Nanotechnology on Organisms and Ecosystems
EPA Grant Number: R832635Title: Assessment of the Environmental Impacts of Nanotechnology on Organisms and Ecosystems
Investigators: Bonzongo, Jean-Claude J. , Kopelevich, Dmity , Bitton, Gabriel
Institution: University of Florida
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2005 through September 30, 2008
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: Nanotechnology , Safer Chemicals
Objective:
The overall goal of this project was to develop an understanding of the potentially complex interplay between manufactured nanomaterials (MNs) and the health of organisms and ecosystems. Experimental and computational research was driven by the following broad hypothesis: “chemical elements used in the production of MN could lead to environmental dysfunctions due to: (1) the potential toxicity of these elements and their derivatives; and (2) the
nanometer-size that make MN prone to bio-uptake/bioaccumulation and (3) the large surface area which might lead MN to act as carriers/delivers of pollutants adsorbed onto them”. To address this hypothesis, toxicity studies using microbiotests as screening tool and experimental investigations on environmental implications and transport of toxic MN were conducted.These experimental studies were complemented by molecular dynamic (MD) simulations to investigate events on very small time- and length-scales. MD simulations were also used to assess the contribution of different types of intermolecular interactions and chemical reactions to the permeation of MNs into cell interior, as well as the potential of MNs to damage cell membranes and cell death. With regard to toxicity of MNs, well-established small-scale toxicity tests or microbiotests including the Daphnia acute toxicity test, the Selenastrum capricornutum chronic toxicity test, and the MetPLATE™ assay were used. In addition, batch experiments conducted to assess: (i) the short-term impacts of MNs on microbial driven sedimentary biogeochemical processes; and (ii) the bioavailability of MN-bound pollutants. Soil columns were also used in preliminary studies to assess the impacts of soil physicochemical characteristics as well as MN suspension chemistry on MN mobility in porous media. Finally, the modling component investigated: (1) the effect of size and shape of MNs on their transport through cellular membranes; (2) the effect of nanoparticles embedded in a cellular membrane on several of the key membrane properties. In particular, elastic energy of the membrane was measured in order to assess membrane deformation and possible instability caused by an embedded nanoparticle; and (3) the effect of a nanoparticle embedded in a membrane on the distribution of lateral pressure inside the membrane. This is because a substantial change of the lateral pressure is likely to affect energy thresholds for opening and closing of ion channels in the membrane. This, in turn, may affect the balance between ions inside and outside of the cell, potentially leading to the cell swelling or even rupturing due to a build-up of osmotic pressure. These studies were performed using coarse-grained molecular dynamics simulations which approximate small groups of atoms as coarse-grained beads, thus enabling exploration of the system dynamics on relatively large length- and time-scales. The cellular membrane was modeled as a phospholipid bilayer. Other constituents of the membrane were neglected in this project. The following carbon-based nanoparticles were considered: fullerene, C60, fullerenol, C60(OH)10, and single-wall carbon nanotubes of lengths up to 9 nm.
Summary/Accomplishments (Outputs/Outcomes):
This research combined experimental and computational components to investigate the potential implications of MNs on organisms. The main findings can be summarized as follows:
•Toxicity studies based on the use of several micro-biotests emphasizing the interactions of MNs with (i) biochemical processes (i.e. the MetPLATE test), (ii) the growth of a unicellular freshwater green algae (P. subcapitata), and (iii) the survival of an aquatic invertebrates (C.dubia and D. pulex), showed that both the fluids used to disperse MNs and MNs themselves can exhibit different degrees of toxicity. The latter varies as a function of MN concentrations and test organisms. The use of different toxicity methods is therefore necessary to avoid erroneous results. This is because different test organisms respond differently to different toxicants. Amongst the nano-metal particles tested, nano-silver and nano-copper displayed the highest toxicity. Aqueous fullerene suspensions prepared by use of organic solvent (THF) and SWNT suspensions in Gum Arabic (a non-toxic surfactant used in this study) showed higher degrees of toxicity as compared to water sonicated suspensions. Although the toxicity mechanisms were not addressed experimentally in this study, the toxicity of these MNs could be attributable to their ability to generate highly reactive and toxic free radicals, their degree of purity as toxic impurities increase toxicity, or simple surface interaction with cell membranes.
•The suspension of selected toxic MNs (i.e. C60, nano-silver, and nano-copper) in natural water matrices with varying DOC content and ionic strength showed that toxicity results obtained from laboratory experiments that use drastic MNs suspension methods may not be realistic. It was found that the suspensions of MNs in natural waters varied significantly with water chemistry and particle chemical composition and reactivity.
•Using soil columns to assess the transport of SWNTs in heterogeneous porous media, it was found that soil texture/characteristics and solution chemistry (i.e. the composition of the liquid used to suspend SWNTs) affect the transport of this highly hydrophobic MN, as surface charges of the MNs influence their adsorption and dispersion in the porous media. Finally, the use of a convection-dispersion model was able to accurately predict SWNTs transport in sandy soils, with a strong correlation between data obtained experimentally and simulated ones. However, it is worth noting that this modeling approach is rather preliminary as we continue to improve our ability to study MN transport in natural soil column, while addressing the analytical challenges associated with the complexity of soil leachate matrices.
•The effects of C60 , nano-Ag and CdSe quatum dots on sediment microbial activity were studied in slurries. C60 appeared to be highly toxic to bacteria involved in organic matter oxidation, primarily nitrate and nitrite reducers. Nano-silver and CdSe quantum dots were less toxic at tested concentrations, but gave the indication of potential pronounced negative effects on microorganisms at much higher concentrations.
•The fate and transformation of an example pollutant adsorbed onto MNs indicated that under specific environmental conditions, MNs could act as carriers of the pollutant adsorbed onto them. If this constitutes an advantage with regard to medical research, it could have negative implications in the environment.
•The modeling component of this research focused primarily on investigation of the transport of carbon-based nanoparticles across cell lipid membranes, as well as their potential to negatively impact the cell membranes functions. The calculated free energy profiles demonstrate that there is no significant energy barrier to enter the bilayer for any of the nanoparticles studied. Most of the transport time is spent inside the bilayer and the hydrophobic interior of a lipid bilayer acts as a trap for hydrophobic particles. The “trapping” effect is significantly increased with particle size. In addition, the nanoparticle shape significantly affects its transport rate. Overall, based on our molecular dynamics simulations, the following effects of tested MNs on cell membranes were observed:
•Carbon nanotubes embedded in lipid membranes lead to the membrane softening.
•Inclusion of carbon nanotubes into a membrane leads to perturbation of the lateral pressure profile within the membrane. However, this perturbation is localized and is unlikely to affect function of membrane proteins.
•Carbon nanotubes, fullerenes, and fullerenols located at their equilibrium positions inside a lipid membrane introduce relatively small and localized perturbations to the membrane energy. This implies that interactions between these nanoparticles and other membrane inclusions (such as membrane proteins) are relatively weak when the nanoparticles are located at their equilibrium positions.
•Nanoparticles entering a membrane experience strong coupling with the membrane undulations. This coupling is characterized by significant changes of the membrane shape in response to a small displacement of a nanoparticle. Therefore, the nanoparticles may significantly affect membrane function during their transport in the membrane. It was observed that none of the considered nanoparticles experienced a significant energy barrier to permeate into a lipid membrane. However, there is a substantial barrier for transport of the particles across the membrane, since the hydrocarbon core of the membrane and the interface between lipid tails and heads act as traps for hydrophobic and amphiphilic nanoparticles, respectively. The “trapping” effect is significantly increased with nanoparticle size. In addition, the shape of nanoparticles significantly affects their transport rate. The following effects of nanoparticles on the membranes were observed:
•Carbon nanotubes embedded in lipid membranes lead to the membrane softening.
•Inclusion of carbon nanotubes into a membrane leads to perturbation of the lateral pressure profile within the membrane. However, this perturbation is localized and is unlikely to affect function of membrane proteins.
•Carbon nanotubes, fullerenes, and fullerenols located at their equilibrium positions inside a lipid membrane introduce relatively small and localized perturbations to the membrane energy. This implies that interactions between these nanoparticles and other membrane inclusions (such as membrane proteins) are relatively weak when the nanoparticles are located at their equilibrium positions.
•Nanoparticles entering a membrane experience strong coupling with the membrane undulations. This coupling is characterized by significant changes of the membrane shape in response to small displacements of nanoparticles. Therefore, the nanoparticles may significantly affect membrane function during their transport in the membrane.
Conclusions:
These findings suggest the following direction of future research:
•Investigate effects of membrane softening induced by nanoparticles on the membrane functions involving its deformations (e.g., endocytosis).
•Investigate effects of the significant membrane deformations observed during the nanoparticle transport on the membrane stability, as well as on function of membrane proteins.
•Validate model predictions with laboratory based experiments.
Overall, the combination of toxicological, biogeochemical, and modeling expertise in the assessment of the potential impacts of MN on biota and the environment appears to be ideal in order to advance discovery as well as our understanding of the behavior, fate, and impact of MN in the environment. At the very least, our findings suggest that MN introduction to natural systems should be limited until more is known on their environmental implications.
Journal Articles on this Report : 4 Displayed | Download in RIS Format
Other project views: | All 14 publications | 5 publications in selected types | All 4 journal articles |
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Gao J, Bonzongo J-CJ, Bitton G, Li Y, Wu C-Y. Nanowastes and the environment: using mercury as an example pollutant to assess the environmental fate of chemicals adsorbed onto manufactured nanomaterials. Environmental Toxicology and Chemistry 2008;27(4):808-810. |
R832635 (2007) R832635 (Final) |
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Griffitt RJ, Luo J, Gao J, Bonzongo J-C, Barber DS. Effects of particle composition and species on toxicity of metallic nanomaterials in aquatic organisms. Environmental Toxicology and Chemistry 2008;27(9):1972-1978. |
R832635 (2007) R832635 (Final) |
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Tasseff RA, Kopelevich DI. Molecular modeling of nanoparticle transport across lipid bilayers. University of Florida. Journal of Undergraduate Research 2006;7(4). |
R832635 (2006) R832635 (2007) R832635 (Final) |
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Gao, J. I. E., Sejin Youn, Anna Hovsepyan, Verónica L. Llaneza, Yu Wang, Gabriel Bitton, and Jean-Claude J. Bonzongo. Dispersion and toxicity of selected manufactured nanomaterials in natural river water samples: effects of water chemical composition. Environmental science & technology 43 2009;43(9): 3322-3328. |
R832635 (Final) |
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Supplemental Keywords:
Manufactured nanomaterials, toxicity, dispersion, natural waters, mobility, porous media, trojan effect, molecular dynamic simulations, mechanisms, cell-nanomaterial interactions, Health, Scientific Discipline, Health Risk Assessment, Risk Assessments, Biochemistry, biological pathways, nanochemistry, bioavailability, nanotechnology, manufactured nanomaterials, nanomaterials, toxicologic assessment, biogeochemistry, cellular response to nanoparticles, nanoparticle toxicity, bioaccumulation, biochemical researchProgress 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.