Grantee Research Project Results
2007 Progress Report: Nanoparticle Stability in Natural Waters and its Implication for Metal Toxicity to Water Column and Benthic Organisms
EPA Grant Number: R833324Title: Nanoparticle Stability in Natural Waters and its Implication for Metal Toxicity to Water Column and Benthic Organisms
Investigators: Ranville, James , Butler, Barbara , Jackson, Brian
Institution: Colorado School of Mines , Dartmouth College
EPA Project Officer: Aja, Hayley
Project Period: April 15, 2007 through April 14, 2011
Project Period Covered by this Report: April 15, 2007 through April 14,2008
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:
The stated objectives for this research project were three-fold.
- Determine the stability (against aggregation and dissolution) of nanoparticles as a function of water composition.
- Determine the uptake, distribution, and elimination of metals from dissolved and nanoparticle phases within Daphnia magna organisms under variable water compositions.
- Determine the uptake, distribution, and elimination of metals from dissolved and aggregated nanoparticle phases within Hyalella azteca organisms under variable water compositions.
Progress Summary:
During the period 2007 – 2008 we have primarily focused our research efforts on the first two stated objectives. We looked at the stability of CdSe/ZnS quantum dots (QDs) in various water compositions as well as developed characterization techniques for metal-containing nanoparticles in aqueous media. We have also examined the acute toxicity of QDs to the test organism Daphnia magna. In our studies we only used QDs that are commercially sold (i.e., Evident Technologies and NN-Labs). Our decision to use commercially produced QDs is based on the observation that QD syntheses can vary greatly, and that different preparation methods can lead to different toxicities. It is thus our hope that by obtaining commercial QDs we are testing potential toxicities of the QDs that are the most widely distributed. Given the importance of nanoparticle characterization, in addition to working on the stated objectives, we have been developing two new approaches for nanoparticle characterization and detection.
Through fluorescence spectroscopy, serial filtrations, and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) we began to characterize the stability of CdSe/ZnS QDs in natural freshwaters. The QDs had been rendered water-soluble by the supplier using a polyethylene oxide (PEO) coating. We investigated the stability of two different size QDs (red and green emitting) as well as explored potential hardness/alkalinity effects by diluting QDs into deionized water and EPA hard water. Our results show that for all samples, no significant loss in fluorescence occurs within the first 100 hrs (4 days), but that partial degradation starts shortly after this. A full loss/degradation of fluorescence occurs for most QD samples after approximately 5 weeks. Total metals in solution were measured by ICP-AES at the beginning and the end of the experiment to monitor losses due to sorption to container walls or nanoparticle aggregation and settling. Serial filtrations at 3kDa were used to separate truly dissolved metals from partially degraded nanoparticulates. Filtration data demonstrated a presence of dissolved metals in solution, released from both green and red emitting QDs. The dissolved metal fraction represented as much as half the total metals in solution at the end of 5 weeks. This data suggests that these PEO coated nanoparticles are relatively resistant to aggregation in aqueous solutions, but that they degrade in reasonably short time period. This has important implications for the life cycle of QDs when introduced into our freshwater systems. Our next experiments will look at QDs with a different surface coating characteristics (i.e., ionic).
Using 48hr exposures, we also investigated the acute toxicity of QDs with two different CdSe core diameters, 2 nm green emitting QDs and 5 nm red emitting QDs. To explore potential particle effects we also examined two separate surface coatings, polyethylene oxide (PEO) and 11-mercaptoundecanoic acid (MUA), which are polar and anionic respectively (Evident Technologies, Troy NY and NN-Labs, Fayetteville AR). These coatings, which serve to render the QDs water stable, increase the hydrodynamic diameter of all QDs to approximately 25 nm. Thus, while the metal content of the red and green emitting QDs (2 nm vs. 5 nm) was substantially different, the total particle size was the same. Using a fluorescence scan of the QDs (400-800 nm) we monitored the QD concentrations during exposures. We found that PEO coated QDs remained well-dispersed throughout the 48 hr exposures with no significant change in QD concentration whereas MUA coated QDs had a higher tendency to aggregate. In addition, we characterized the QDs before and after exposure via filtrations and ICP-OES metal analysis (unfiltered, 0.02 μm and 3 kDa filtrations). The observed acute toxicity for 5 nm PEO-coated QD to Ceriodaphnia dubia gave an LC50 of about 3.5 nM QDs, which is equivalent to about 274 ppb Zn and 350 ppb Cd. The results for the QD were similar to that observed for dissolved Zn but much less toxic than dissolved Cd, suggesting that the mode of action for QD toxicity might be related to Zn toxicity. For experiments with 2.5 and 5 nm PEO-coated QD and Daphnia magna, an effect of size was observed in the preliminary results, with smaller QDs (2.5 nm) being more toxic on an equivalent metal basis than the 5 nm QDs.
Characterization of nanoparticles is difficult and there is a need for further development of analytical techniques. We are using field-flow fractionation (FFF) coupled directly to inductively coupled plasma-mass spectrometry (ICP-MS) to characterize the quantum dot suspensions. One interesting observation was that some production lots of the QD had, in addition to the 25 nm QD particles, smaller Zn-containing nanoparticles. The FFF-ICP-MS technique is very powerful for quantifying impurities in the suspensions.
Detection of engineered nanoparticles in environmental samples remains an unsolved problem. We are investigating the use of ICP-MS in a non-conventional way to detect individual nanoparticles at low concentration. By collecting data from the ICP-MS at millisecond intervals, nanoparticles can be detected as individual spikes in the ICP-MS signal for the element of interest in the nanoparticle. The size of the nanoparticle can be estimated if the geometry of the particle is known. We have preliminary data on Ag and iron oxide nanoparticle suspensions that suggest nanoparticles as small as about 5-10 nm can be observed at very low concentration.
Finally, we have attempted to identify QD uptake and distribution within Daphnia magna by using synchrotron micro X-ray fluorescence (XRF). X-ray fluorescence uses a hard X-ray beam to map metals in biological tissues. Our preliminary results showed accumulation of nanoparticles within exposed daphnids with particularly high accumulation in the gut. A group from Belgium recently published a paper describing this technique as applied to dissolved metal ecotoxicology (De Samber, 2008a,b). We will apply this method to quantitatively target organ specific nanocrystal distribution within the daphnids.
Future Activities:
We will continue the work on QD acute toxicity and expand the work to include chronic toxicity. The stability studies will be expanded to include the interaction of QD with natural suspended sediments. Finally, we will perform the toxicity experiments with benthic organisms to fulfill the third objective of the project.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 41 publications | 9 publications in selected types | All 9 journal articles |
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Type | Citation | ||
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Hassellov M, Readman JW, Ranville JF, Tiede K. Nanoparticle analysis and characterization methodologies in environmental risk assessment of engineered nanoparticles. Ecotoxicology 2008;17(5):344-361. |
R833324 (2007) R833324 (Final) |
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Supplemental Keywords:
Water, exposure, bioavailability, metals, environmental chemistry,, Health, Scientific Discipline, Health Risk Assessment, Risk Assessments, Biochemistry, biological pathways, nanochemistry, bioavailability, nanotechnology, 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.