Protecting the nanotechnology workforce: a new protocol for characterization of filter-captured nanomaterials from occupational exposure assessments

N. Neu-Baker, D. Smith, A. Segrave, J. Beach, I. Zurbenko, K. Dunn, S. Brenner
SUNY Polytechnic Institute Colleges of Nanoscale Science & Engineering,
United States

Keywords: worker health and safety, human exposure, methods development, hyperspectral imaging, metrology

Summary:

The nanotechnology workforce is growing along with the rapid commercialization of nanotechnology, with an estimated 6 million workers by 2020;1 however, risk assessment for nanotechnology workers is still in its infancy because occupational exposure assessment strategies and physiologic and health outcomes related to exposure to engineered nanomaterials (ENMs) have not yet been well characterized. Due to the novel physicochemical properties that emerge at the nanoscale, ENMs may be more toxic than their bulk counterparts.2–5 The rapid growth and projected acceleration of nanotechnology creates urgency in understanding and mitigating the potential health risks associated with exposure to ENMs. The most significant hurdle holding back exposure science, risk assessment, and the development of safety guidelines for the nanotechnology workforce is the lack of validated analytical techniques that accurately identify and characterize ENMs captured in occupational settings. The associated costs, time, and lack of standardization of existing methods make it impossible for industries to implement exposure assessment programs or comply with new or forthcoming recommended exposure limits for ENMs. This project advances the state of the science by developing and testing a new protocol for analysis of ENMs on filters by: further developing a novel hyperspectral imaging (HSI) method for high-throughput screening; evolving best-known methods for direct visualization of filter-captured ENMs by developing and incorporating advanced techniques into the new protocol; and testing the new protocol on real-world samples obtained during occupational exposure scenarios with semiconductor workers on-site. Industrially-relevant metal oxide ENMs (SiO2, Al2O3, CeO2) serve as the materials of interest due to their high-volume use in semiconductor and other manufacturing processes.6–11 The researchers are at the forefront in HSI methods development for rapid direct visualization and characterization of ENMs12–16 and are further developing HSI as a quantitative screening tool for filter samples by calibrating over a series of positive controls, calculating the limit of detection, and defining a screening procedure, including a round-robin calibration analysis and estimation of accuracy, precision, and bias to assess the transferability of the new protocol. The current method for direct visualization of ENMs by transmission electron microscopy (TEM) was created two decades ago for micron-sized asbestos.17 For samples that meet the threshold for further analysis, our protocol creates a guideline for determining which advanced analytical modality should be utilized for a given sample based on the properties of the exposure the investigator is interested in: the protocol incorporates environmental scanning electron microscopy with energy-dispersive x-ray spectroscopy, scanning TEM-EDS, x-ray photoelectron spectroscopy, and electron energy loss spectroscopy to yield physicochemical data relevant to ENM reactivity and toxicity. Round-robin analyses are integral to protocol development to confirm reproducibility and identify strengths and limitations. We will work proactively with semiconductor industrial partners to test the new protocol on field samples obtained during occupational exposure scenarios. The new protocol will drastically improve the efficiency, utility, and impact of performing occupational exposure assessments for ENMs and will deliver key physicochemical characterization data of toxicological significance, thus bridging exposure and toxicology research and underpinning comprehensive risk assessment for human health.