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Potential for metal contamination by direct sonication of nanoparticle suspensions
Citation:
Betts, J., M. Johnson, P. Rygiewicz, G. King, AND C. Andersen. Potential for metal contamination by direct sonication of nanoparticle suspensions. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 32(4):889-893, (2013).
Impact/Purpose:
Engineered nanoparticles (ENPs) have been recognized as valuable components of novel technologies and are currently being used in a variety of consumer products due to their unique physical, chemical, and electrical properties. The properties that make these particles functionally unique also may make them uniquely toxic to biological systems. Western Ecology Division scientists have been examining the potential toxicity of ENP to plants and soil organisms to determine if terrestrial ecosystems may be impacted by environmental release of ENPs. When conducting toxicity experiments using ENPs, it is critical to accurately characterize particle suspensions in order to 1) allow replication of the experiments among laboratories, and 2) link any toxic responses with specific particle/suspension attributes. During a series of experiments to evaluate the toxicity of titanium dioxide (TiO2) nanoparticles on terrestrial plants, Western Ecology Division scientists found large batch to batch variability in suspensions, despite following standardized mixing procedures widely reported in the literature. In addition, aluminum (Al) contamination from an unknown source was discovered in the suspensions. Using a suite of analytical techniques, it was determined that direct sonication, a procedure used to disperse particles using a metal ‘horn’ immersed in the suspension, was releasing small particles of an Al- containing alloy into the suspensions from the tip via erosion of the metal. Although sonicator tip erosion has been previously reported, it was found that the alloy contaminants had a measureable size distribution and electrical potential that interfered with the ability to characterize solutions using commonly employed instruments. In addition to interfering with suspension characterization, Al contamination may lead to unwanted biological toxicity caused independently of the ENPs under study. The results provide important information for other research laboratories using direct sonication since contamination may be hindering their ability to accurately characterize their test suspensions and potentially adding an additional toxicant to their test solutions.
Description:
There is a growing need to examine the potential toxicity of engineered nanoparticles (ENPs) to establish regulations protective of environmental health and safety. During a series of experiments to evaluate the toxicity of titanium dioxide (TiO2) nanoparticles on terrestrial plants, we found an unexpectedly broad range of particle sizes despite following standardized mixing procedures. In addition, aluminum (Al) contamination from an unknown source was discovered (using Scanning Electron Microscopy [SEM]) on the surface of plant tissue exposed to the particles, in what appeared to be TiO2-NP agglomerates. Using a suite of analytical techniques [Dynamic Light Scattering (DLS), Phase Analysis Light Scattering (PALS), X-Ray Diffraction (XRD), Silicon Drift Detector Energy Dispersive X-Ray Spectrometry (SDD-EDS), SEM and Electron Probe Microanalysis (EPMA)], we determined that the source of the Al was an Al-containing Ti alloy, released from the sonicator probe during direct sonication of our ENP test suspensions. Although sonicator tip erosion has been previously reported, we found that the alloy particles had a measureable size distribution and zeta potential () that altered our DLS and PALS measures. In addition to interfering with suspension characterization, Al contamination may lead to unwanted biological toxicity caused independently of the ENPs under study. Our findings suggest that caution be used when employing direct sonication for preparing nanoparticle test suspensions due to the potential interferences of these particles in toxicological assessments.
