Inhalation exposure to respirable crystalline silica (RCS) during the fabrication of engineered stone-based kitchen countertops has been on the rise in recent years and has become a significant occupational health problem in the United States and globally. Little is known about the presence of nanocrystalline silica (NCS), i.e., particles below 100 nm. We present a methodology to quantify the crystalline silica content in the sub-100 nm size fraction of the aerosol released during engineered stone fabrication using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Aerosol was generated in a test chamber designed per EN 1093-3 and sampled using cascade impactors. XRD and FTIR analysis showed the presence of both α-quartz (15-60%) and cristobalite (10-50%) polymorphs in all size fractions. With increasing particle size, the cristobalite content increased. Seventy percent of the total aerosol mass in the sub-100 nm fraction was found to be crystalline silica, qualitatively confirmed by electron diffraction and electron energy loss spectroscopy. The presence of other minerals was detected in all size fractions; no polymeric resin binder was detected in the sub-100 nm fraction. Although the sub-100 nm fraction was about 1% of the aerosol mass, it accounted for 4-24% of the aerosol surface area based on the total lung deposition. If the surface area is a more relevant exposure metric, the assessment of the efficacy of current engineering control systems using mass as an exposure metric may not provide adequate protection.

Copper-based preservatives consisting of micronized and nanoscale copper particles have been widely used in applications for wood protection. The widespread use of these preservatives along with the potential release of copper-containing nanoparticles (Cu NPs) during the life cycle of treated wood, has raised concerns over the impacts on the environment and occupational exposure. Along with assessing the potential hazards of these materials, a critical step is determining the chemical and morphological characteristics of the copper species released from copper-treated wood. Therefore, a combination of scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) was utilized to characterize and differentiate the released copper-containing particles based on their structures, sizing, and chemical properties. Airborne wood dust samples were collected during the abrasion and sawing of micronized copper (MC) treated wood in a laboratory testing system. Based on the signature Cu L2,3 edge of EEL spectra, three different copper species (i.e., basic copper carbonate, copper, and copper-wood complex) were identified as major components of the embedded particles in wood dust. In addition, two types of individual Cu NPs consisting of basic copper carbonate and copper were identified. The variation of morphologies and chemical properties of copper-containing particles indicates the importance of copper-wood interactions to determine the formation and distribution of copper species in wood components. Our findings will advance the fundamental understanding of their released forms, potential transformation, and environmental fate during the life cycle.

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The extensive use of carbon nanomaterials such as carbon nanotubes/nanofibers (CNTs/CNFs) in industrial settings has raised concerns over the potential health risks associated with occupational exposure to these materials. These exposures are commonly in the form of CNT/CNF-containing aerosols, resulting in a need for a reliable structure classification protocol to perform meaningful exposure assessments. However, airborne carbonaceous nanomaterials are very likely to form mixtures of individual nano-sized particles and micron-sized agglomerates with complex structures and irregular shapes, making structure identification and classification extremely difficult. While manual classification from transmission electron microscopy (TEM) images is widely used, it is time-consuming due to the lack of automation tools for structure identification. In the present study, we applied a convolutional neural network (CNN) based machine learning and computer vision method to recognize and classify airborne CNT/CNF particles from TEM images. We introduced a transfer learning approach to represent images by hypercolumn vectors, which were clustered via K-means and processed into a Vector of Locally Aggregated Descriptors (VLAD) representation to train a softmax classifier with the gradient boosting algorithm. This method achieved 90.9% accuracy on the classification of a 4-class dataset and 84.5% accuracy on a more complex 8-class dataset. The developed model established a framework to automatically detect and classify complex carbon nanostructures with potential applications that extend to the automated structural classification for other nanomaterials.

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The bioprocessing of CeO2 nanoparticles after uptake in lung tissues is compared with the formation of nanoparticles after inhalation of CeCl3 aerosols. In both cases, high-resolution TEM/STEM analyses indicate that cerium phosphate nanoparticles (NPs) had precipitated in phagolysosomal regions within macrophages. Importantly, the primary particle size, morphology, and agglomeration tendencies of the NPs were strikingly similar. Formation of cerium phosphate NPs after bioprocessing of inhaled CeO2 crystals proceeds via dissolution, ion transport, followed by nucleation and growth [1]. Application of 2D and 3D elemental maps of the NP bioprocessing stages and corresponding tissue interactions provide insights on the breakdown mechanisms, formation of new precipitates, size, and morphology changes of the original delivered NPs, and ion transport phenomena that result in secondary particle formation. Particle size and morphology are very similar for all of the cerium phosphate NPs, suggesting a common underlying precipitation mechanism independent of whether the metal ions are derived from dissolution of nanoparticles (CeO2) or from instilled metal ions (CeCl3).

Journal Article In vivo formation of Ce-phosphate Nanoparticles following Intratracheal Instillation of CeCl3: Subcellular sites, Nanostructures, Precipitation Mechanisms and Nanoparticle 3D-Alignment Get access Uschi M Graham, Uschi M Graham National Institute for Occupational Safety and Health, Cincinnati, OH, USA Search for other works by this author on: Oxford Academic Google Scholar Chen Wang, Chen Wang National Institute for Occupational Safety and Health, Cincinnati, OH, USA Search for other works by this author on: Oxford Academic Google Scholar Joseph Fernback, Joseph Fernback National Institute for Occupational Safety and Health, Cincinnati, OH, USA Search for other works by this author on: Oxford Academic Google Scholar Alan K Dozier, Alan K Dozier National Institute for Occupational Safety and Health, Cincinnati, OH, USA Search for other works by this author on: Oxford Academic Google Scholar Lawrence Drummy, Lawrence Drummy Air Force Research Laboratory, Dayton, OH Search for other works by this author on: Oxford Academic Google Scholar Krishnamurthy Mahalingam, Krishnamurthy Mahalingam Air Force Research Laboratory, Dayton, OH Search for other works by this author on: Oxford Academic Google Scholar Ramon M Molina, Ramon M Molina Harvard T.H. Chan School of Public Health, Boston, MA, USA Search for other works by this author on: Oxford Academic Google Scholar Nagarjun V Konduru, Nagarjun V Konduru Harvard T.H. Chan School of Public Health, Boston, MA, USA Search for other works by this author on: Oxford Academic Google Scholar M Eileen Birch, M Eileen Birch National Institute for Occupational Safety and Health, Cincinnati, OH, USA Search for other works by this author on: Oxford Academic Google Scholar Joseph D Brain Joseph D Brain Harvard T.H. Chan School of Public Health, Boston, MA, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 1342–1343, https://doi.org/10.1017/S1431927617007371 Published: 04 August 2017

Journal Article Workplace Monitoring of Airborne Carbon Nanomaterials by HRTEM Get access M Eileen Birch, M Eileen Birch Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar Chen Wang, Chen Wang Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar Joseph E Fernback, Joseph E Fernback Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar H Amy Feng, H Amy Feng Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar Quinn T Birch, Quinn T Birch Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar Alan K Dozier Alan K Dozier Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S3, 1 July 2016, Pages 1910–1911, https://doi.org/10.1017/S1431927616010394 Published: 25 July 2016

In many wood preservative formulations, copper-based components are usually used as primary biocides to protect wood structures against microbial, fungal, and insect decay [1]. The wood preservation industry has recently introduced a particulate copper (i.e., micronized copper or MC) system as a replacement for ionized copper preservative in pressure-treated lumber (PTL) [2]. The use of MC treated wood in workplaces has raised concerns over the potential exposure of workers to the wood dust that contains micronized/nanoscale copper particles [3-4]. However, there is a lack of information about identification and characterization of copper particles in wood dust generated by the processing of MC treated PTL.

Journal Article Characterization of Sulfonated Polysulfone Polymers by EELS Get access Chen Wang, Chen Wang Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar Stephen J Paddison, Stephen J Paddison Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37996, USA Search for other works by this author on: Oxford Academic Google Scholar John R Dunlap, John R Dunlap Advanced Microscopy and Imaging Center, University of Tennessee, Knoxville, TN 37996, USA Search for other works by this author on: Oxford Academic Google Scholar Gerd Duscher Gerd Duscher Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 1679–1680, https://doi.org/10.1017/S1431927615009174 Published: 23 September 2015

Journal Article Observations of in vivo Processing of Metal Oxide Nanoparticles by Analytical TEM/STEM Get access Uschi M Graham, Uschi M Graham Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, Ohio, 45226Center for Applied Energy Research, University of Kentucky, Lexington, KY 40511 Search for other works by this author on: Oxford Academic Google Scholar Alan K Dozier, Alan K Dozier Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, Ohio, 45226 Search for other works by this author on: Oxford Academic Google Scholar Giinter Oberdorster, Giinter Oberdorster School of Medicine and Dentistry, University of Rochester, Rochester, NY 14642 Search for other works by this author on: Oxford Academic Google Scholar Chen Wang, Chen Wang Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, Ohio, 45226 Search for other works by this author on: Oxford Academic Google Scholar Michael T Tseng, Michael T Tseng Department of Anatomical Sciences and Neurobiology, University of Louisville, Louisville, KY, 40204 Search for other works by this author on: Oxford Academic Google Scholar Joseph E Fernback, Joseph E Fernback Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, Ohio, 45226 Search for other works by this author on: Oxford Academic Google Scholar M Eileen Birch, M Eileen Birch Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, Ohio, 45226 Search for other works by this author on: Oxford Academic Google Scholar Burtron H Davis Burtron H Davis Center for Applied Energy Research, University of Kentucky, Lexington, KY 40511 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 2287–2288, https://doi.org/10.1017/S1431927615012210 Published: 23 September 2015

Journal Article Combine Simulation and Experiment EELS to Characterize Ionomer Conformation Get access Chen Wang, Chen Wang Division of Applied Research and Technology, National Institute for Occupational Safety and Health, Cincinnati, OH, 45226, USA Search for other works by this author on: Oxford Academic Google Scholar Stephen J Paddison, Stephen J Paddison Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37996, USA Search for other works by this author on: Oxford Academic Google Scholar Gerd Duscher Gerd Duscher Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 21, Issue S3, 1 August 2015, Pages 1653–1654, https://doi.org/10.1017/S1431927615009046 Published: 23 September 2015

The side chain effects on the PTFE backbone conformation in the family of perfluorosulfonic acid ionomers were first investigated with electron energy-loss spectroscopy and first principles calculations.

The hydrated morphologies of sulfonated poly(phenylene) sulfone (sPSO2) ionomers as a function of equivalent weight (EW), molecular weight (MW), and water content were investigated by using mesoscale dissipative particle dynamics (DPD) simulations. The morphological changes were characterized by analyzing the water distribution and plotting the radial distribution functions for the water particles. The results were compared to typical PFSA ionomers (i.e., Nafion and Aquivion) to evaluate the effects of backbone and side chain chemistry. Our results show that water is more likely to be equally distributed within the hydrophilic domains of the sPSO2 ionomers particularly at low water content, which is in contrast to strong phase separation observed in PFSA ionomers at the same level of hydration. As the degree of sulfonation is increased (i.e., decreasing the EW), well-connected water clusters develop in the sPSO2 ionomers even at low water content which are less affected by changes in the MW than observed for PFSA ionomers. The size of the water clusters is estimated to be from 1.2 to 1.5 nm (compared to ∼ 3.5 nm in Nafion) at a water content of 7H2O/SO3H, which is consistent with results determined from previous experiments. This suggests that the high proton conductivity observed in the sPSO2 ionomers is due to the well-connected hydrophilic pathways.

Broadband Dielectric Spectroscopy is employed to investigate the link between hydrated morphology, local water dynamics and charge transport in a series of commercially available Perfluorosulfonic Acid (PFSA) membranes of different equivalent weights and hydration levels[1-2]. Different experimental set-ups are used to determine dielectric properties of both dry and hydrated membranes in a wide frequency range spanning more than 11 orders of magnitude. The dielectric spectra are dominated by long-range proton conduction on the low frequency regime and local water dynamics at higher frequencies. The results are discussed within the framework of recent studies of charge transport in nano-confined membranes. References 1. K.-D. Kreuer, M. Schuster, B. Obliers, O. Diat, U. Traub, A. Fuchs, U. Klock, S. J. Paddison and J. Maier, J. Power Sources, 178, 499 (2008). 2. G. A. Giffin, G. M. Haugen, S. J. Hamrock, and V.D. Noto, Journal of the American Chemical Society, 135 (2), 822-834 (2013).

The morphology of dry and hydrated perfluorosulfonic acid (PFSA) ionomers at cryo and room temperature is examined using TEM/STEM with EELS capability. Z-contrast imaging was utilized to identify the micro-phase separation of the hydrophilic side chains containing water and the hydrophobic polytetrafluoroethylene (PTFE) backbones. The results compare very favourably with hydrated morphologies obtained through mesoscale dissipative particle dynamics (DPD) simulations. The cryo-STEM images of plunge-frozen samples was also found to agree with morphologies based on SAXS experiments.