Aerodynamic and Chemical Characteristics of Six Engineered Nanomaterial Powders

Abstract

Six engineered nanomaterial (ENM) powders (nano-diamond, nano-silver, nano-titanium dioxide, single walled carbon nanotubes, multi-walled carbon nanotubes, and C60 fullerenes) were investigated to determine their aerodynamic and chemical characteristics. Materials were suspended in a controlled environmental chamber, collected on filters and cascading deposition impactors (MOUDI), and then underwent gravimetric and chemical analysis using standard atmospheric aerosol methodologies. The chemical analyses included examining elemental/organic carbon (EC/OC), soluble metals by ICP-MS, organics by TD-GCMS, and reactive oxygen species (ROS) macrophage assay. Chemical composition and toxicity were compared to urban ambient PM values to give context to the ENM results, allowing a relative assessment of aerosol characteristics and the risks associated with ENM emissions. The results show that ENM particle suspensions generally exist in the accumulation or coarse particle mode range, while large mass concentrations of Aitken-nuclei mode particles were not observed. Key findings include the following: the organic and elemental carbon analysis of the carbon structured ENM could not adequately reconstruct the mass of these carbon based materials, suggesting the carbon structure of these samples is too refractive or the carbonaceous material is not oxidized sufficiently to allow accurate quantification with standard thermal-optical EC/OC analysis; the materials exhibited very low quantities of PAHs and alkanes, with the majority of these constituents below detection limits; a select group of soluble metals were detected in concentrations similar to those observed in urban ambient samples on a mass per mass basis, and lastly, the biological activity of the ENM was found to be small (by in-vitro ROS macrophage assay), especially when compared to the activity of atmospheric PM2.5 in an urban location in the US.