Microstructures and nanostructures for environmental carbon nanotubes and nanoparticulate soots

Our plain-English summary of Microstructures and nanostructures for environmental carbon nanotubes and nanoparticulate soots, by L.E. Murr (International Journal of Environmental Research and Public Health, 2008).

The study

• Author: L.E. Murr
• Journal: International Journal of Environmental Research and Public Health
• Published: 2008;5(5):321-36
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

This paper examines the microstructures and nanostructures for natural (mined) chrysotile asbestos nanotubes (Mg3 Si2O5 (OH)4) in comparison with commercial multiwall carbon nanotubes (MWCNTs), utilizing scanning and transmission electron microscopy (SEM and TEM). Black carbon (BC) and a variety of specific soot particulate (aggregate) microstructures and nanostructures are also examined comparatively by SEM and TEM. A range of MWCNTs collected in the environment (both indoor and outdoor) are also examined and shown to be similar to some commercial MWCNTs but to exhibit a diversity of microstructures and nanostructures, including aggregation with other multiconcentric fullerenic nanoparticles. MWCNTs formed in the environment nucleate from special hemispherical graphene "caps" and there is evidence for preferential or energetically favorable chiralities, tube growth, and closing. The multiconcentric graphene tubes ( approximately 5 to 50 nm diameter) differentiate themselves from multiconcentric fullerenic nanoparticles and especially turbostratic BC and carbonaceous soot nanospherules ( approximately 8 to 80 nm diameter) because the latter are composed of curved graphene fragments intermixed or intercalated with polycyclic aromatic hydrocarbon (PAH) isomers of varying molecular weights and mass concentrations; depending upon combustion conditions and sources. The functionalizing of these nanostructures and photoxidation and related photothermal phenomena, as these may influence the cytotoxicities of these nanoparticulate aggregates, will also be discussed in the context of nanostructures and nanostructure phenomena, and implications for respiratory health.

In plain English

This single-author paper used electron microscopy to compare the structure of chrysotile asbestos with multiwall carbon nanotubes, soot and black carbon particles. The author examined a mined chrysotile sample from Quebec, Canada, commercial carbon nanotubes, and particles collected from indoor and outdoor air and from diesel exhaust, burning wood and tires, candles and gas burners. Individual chrysotile nanotubes had inner diameters of around 5 nm and outer diameters of about 30 nm. In microscope images, chrysotile and carbon nanotubes made by arc evaporation were almost indistinguishable. Carbon nanotubes were found in particles from gas and propane flames, and short chrysotile nanotubes were collected with soot near an interstate highway in El Paso, Texas. In lung-cell laboratory tests reproduced from the group's earlier work, asbestos, black carbon, natural gas blue-flame soot and commercial nanotubes were among the most cytotoxic (cell-damaging) samples. The author concluded that the two kinds of nanotubes are identical in microstructure and nanostructure in most respects. The author also noted that laboratory cell tests cannot predict long-term effects and that assumptions about long-term cancer effects of carbon nanotubes would be speculative.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Descriptive electron microscopy (SEM and TEM) characterization study of particle samples, with discussion of the author's group's previously published cytotoxicity and PAH data
• Who was studied: No people were studied. The samples were a small mined chrysotile sample from Quebec, Canada; commercial multiwall carbon nanotubes; commercial black carbon; airborne particles collected indoors and outdoors (including El Paso, Texas); and soots from diesel exhaust, wood, tires, candles and a natural gas cooking range. No sample counts are given.
• Exposure: Chrysotile asbestos nanotubes compared with multiwall carbon nanotubes (arc evaporation and nickel catalyst grown, plus combustion-generated) and with soot and black carbon particles. Human exposure doses were not studied.
• Main results:
  • Individual chrysotile asbestos nanotubes had inner (core) diameters of around 5 nm and outer diameters of about 30 nm.
  • Arc-evaporation-produced carbon nanotubes and chrysotile were almost indistinguishable in TEM images. Catalyst-grown carbon nanotubes looked distinct, with diameters from under 5 nm to about 25 nm.
  • Carbon nanotube aggregates collected indoors and outdoors, from sources such as a propane kitchen range and an industrial natural gas source, were over 2 micrometers in size and could contain more than 1000 individual nanotubes or fullerene-type nanoparticles.
  • The author stated that, given the many forms observed, it would be extremely difficult if not impossible to tell manufactured carbon nanotubes apart from combustion-generated ones in environmental pollution.
  • Candle, wood, diesel and tire soots were not notably distinguishable from one another by structure. Their primary spherules were about 20 to 60 nm in diameter.
  • Short chrysotile asbestos nanotubes were collected together with small soot aggregates in air near an interstate freeway in El Paso, Texas.
  • In lung cell (A549) test data reproduced from earlier work (Garza et al.), black carbon, natural gas blue-flame soot, asbestos and commercial carbon nanotubes were among the most cytotoxic samples.
• The authors' conclusion: The author concluded that chrysotile asbestos nanotubes and multiwall carbon nanotubes are identical in microstructure and nanostructure in most respects, and that both are cytotoxic and efficient generators of reactive oxygen species. For the statement that both produced mesothelial lesions in mice, the author relied on a separate study by other researchers (reference 75).
• Limitations the authors state:
  • Laboratory cell tests cannot predict long-term, chronic effects.
  • Short-term cell assays do not predict long-term lung responses or indicate cancer-causing or mutation-causing effects.
  • Assumptions about long-term cancer effects of carbon nanotubes would be speculative.
  • Different soot types are hard to recognize by electron microscope imaging.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Transmission Electron Microscopy (TEM).

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