Exposure and In Vitro Hazard Characterization of Microplastic Dusts Released from Machining of Boron Nitride Nanotube-Enabled Composites Along Its Lifecycle

Details

• Personal Author:
  Stueckle, Todd A. ; Kim, S. H. ; Afshari, Aliakbar A. ; Guppi, S. ; Bunker, Kristin ; Lersch, Traci L. ; Casuccio, Gary ; Friend, Sherri A. ; Erdely, Aaron ; Lee, Eun Gyung
• Description:
  Background and Purpose: Boron nitride nanotubes possess unique electrical insulation and radiation shielding abilities for use in light weight ceramics and flame-retardant insulation applications. Enabling plastic and epoxy resin composites with nanomaterials can affect technological performance and particle release characteristics during use scenarios, including nano- and microplastic release. The current study aimed to characterize airborne particle release during controlled machining of BNNT-enabled epoxy composites, evaluate the effect of weathering on airborne particle release, and conduct an initial hazard characterization of collected respirable particulate using macrophages. Methods: Three different BNNT-enabled epoxy composites (0%, 1%, and 4% BNNT by weight) were sanded (n=3-5 repeats for each composite) in a controlled laboratory apparatus using zirconium aluminum sandpaper. Direct reading instruments were used to quantify released particle number and size distributions while offline filter samples assessed particle concentration, morphology, elemental composition, and BNNT protrusions by electron microscopy. Next, composites were weathered under UV light and water for 2,016 hours, followed by sanding described above. A subset of weathered composites underwent immersion testing with increasing amounts of disruptive energy to evaluate release of BNNT from the epoxy matrix. Lastly, respirable dust suspensions in cell culture were characterized to determine particle morphology and hydrodynamic size. Differentiated human macrophages were exposed to respirable BNNT composite particulate (0 - 20 µg/cm2) in submerged culture for 24 hours and assayed for cytotoxicity, mechanism of cell death, reactive oxygen species, and mitochondrial membrane polarization. Results: 4% BNNT epoxy released significantly more particulate (41,000 particles/cm3) than 0% and 1% composites (30,000 particles/cm3). Respirable sized particles on collected filters were agglomerated averaging 3 microns in size and were 68% and 89% carbon-based on a number concentration and mass basis, respectively. BNNT protrusions were found on particle surfaces albeit in low number (0.2 - 2% with at least one BNNT protrusion). Weathering increased particle release of 4% composite during sanding (61,000 particles/cm3) compared to non-weathered composite. Free release of BNNT was observed in weathered 4% BNNT epoxy samples under immersion and light sonication conditions. Collected respirable BNNT epoxy sanding dust exposure (Zavg 1.73 - 1.93 µm) caused dose-dependent increase in cytotoxicity (i.e. LDH) and a 10-15% decrease in live cell count due to mixed pyroptosis and apoptosis in human macrophages. A dose-dependent increase in intracellular reactive oxygen species and no change on mitochondrial membrane polarization were also observed. No clear difference between BNNT % loading and macrophage response was observed. Conclusions: Our current findings indicate that BNNT % loading and weathering affects particle number release during machining processes in part due to the number and strength of BNNT surface bonding with the epoxy matrix. Percent loading of BNNT had minimal effect on human macrophage response to machined respirable epoxy particulate. Description provided by NIOSH
• Subjects:
  • Boron Compounds
  • Dust
  • Nanostructures
  • Nanotubes, Carbon
  • Occupational Health
  • Particulate Matter
  • Safety
• Keywords:
  • Boron nitride; Nanotubes; Nanoplastics; Particulates; Airborne particles; In vitro study; Macrophages
• Source:
  Toxicologist 2025 Mar; 204(S1):464
• ISSN:
  1096-6080
• Document Type:
  Text
• Genre:
  Abstract or Summary
• Place as Subject:
  Pennsylvania ; Philadelphia Region OSHA ; West Virginia
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  HELD - Health Effects Laboratory Division ; RHD - Respiratory Health Division
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  2 pdf pages
• Volume:
  204
• NIOSHTIC Number:
  nn:20071583
• CAS Registry Number:
  • Boron nitride (CAS RN 10043-11-5)
• Federal Fiscal Year:
  2025
• NORA Priority Area:
  Manufacturing
• Peer Reviewed:
  False
• Download URL:
  https://stacks.cdc.gov/view/cdc/259358/cdc_259358_DS1.pdf
• File Type:
  [PDF - 276.43 KB]
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:2cb6d8ba3b6ab9445b0066afd804922ea2dc6c0c48de4399b31f23dbd467adcb0dc9a7cfdc06a43fa622805f47448d29d9b14e83ac38bd3ce92fce6fe3d8f622