Cytotoxicity assessment of some carbon nanotubes and related carbon nanoparticle aggregates and the implications for anthropogenic carbon nanotube aggregates in the environment

Our plain-English summary of Cytotoxicity assessment of some carbon nanotubes and related carbon nanoparticle aggregates and the implications for anthropogenic carbon nanotube aggregates in the environment, by L.E. Murr, K.M. Garza, K.F. Soto, et al (International Journal of Environmental Research and Public Health, 2005).

The study

• Authors: L.E. Murr, K.M. Garza, K.F. Soto, A. Carrasco, T.G. Powell, D.A. Ramirez, P.A. Guerrero, D.A. Lopez, J. Venzor
• Journal: International Journal of Environmental Research and Public Health
• Published: 2005;2(1):31-42
• Cited by: 53 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Nanotechnology and nanomaterials have become the new frontier world-wide over the past few years and prospects for the production and novel uses of large quantities of carbon nanotubes in particular are becoming an increasing reality. Correspondingly, the potential health risks for these and other nanoparticulate materials have been of considerable concern. Toxicological studies, while sparse, have been concerned with virtually uncharacterized, single wall carbon nanotubes, and the conclusions have been conflicting and uncertain. In this research we performed viability assays on a murine lung macrophage cell line to assess the comparative cytotoxicity of commercial, single wall carbon nanotubes (ropes) and two different multiwall carbon nanotube samples; utilizing chrysotile asbestos nanotubes and black carbon nanoaggregates as toxicity standards. These nanotube materials were completely characterized by transmission electron microscopy and observed to be aggregates ranging from 1 to 2 microm in mean diameter, with closed ends. The cytotoxicity data indicated a strong concentration relationship and toxicity for all the carbon nanotube materials relative to the asbestos nanotubes and black carbon. A commercial multiwall carbon nanotube aggregate exhibiting this significant cell response was observed to be identical in structure to multiwall carbon nanotube aggregates demonstrated to be ubiquitous in the environment, and especially in indoor environments, where natural gas or propane cooking stoves exist. Correspondingly, preliminary epidemiological data, although sparse, indicate a correlation between asthma incidence or classification, and exposure to gas stoves. These results suggest a number of novel epidemiological and etiological avenues for asthma triggers and related respiratory or other environmental health effects, especially since indoor number concentrations for multiwall carbon nanotube aggregates is at least 10 times the outdoor concentration, and virtually all gas combustion processes are variously effective sources. These results also raise concerns for manufactured carbon nanotube aggregates, and related fullerene nanoparticles.

In plain English

This laboratory study tested how toxic several carbon materials were to a line of mouse lung immune cells (alveolar macrophages) grown in dishes. The materials were a commercial single-wall carbon nanotube powder, two commercial multiwall carbon nanotube samples and a commercial black carbon. A chrysotile asbestos specimen served as a comparison. All were examined under an electron microscope. All the materials, including the chrysotile, began to kill cells at 2.5 µg/mL, and the carbon materials gave responses similar to the chrysotile. At 5 µg/mL, black carbon was slightly less toxic. No IL-10 or IL-12, two immune signaling proteins, was detected. One multiwall sample closely resembled particles the authors collected from kitchen gas-stove exhaust. In questionnaires from 24 clinic patients with asthma symptoms, 83% of the women were currently exposed to gas cooking stoves. The authors concluded that the carbon materials showed the same toxicity to these cells as chrysotile asbestos above about 2 µg/mL. They suggested that such particles may contribute to asthma. They noted that cell studies are far from representing human lungs and that the clinic data may be biased.

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: Laboratory (in vitro) cytotoxicity experiment on a mouse lung macrophage cell line, with electron microscope characterization of the materials, plus a small preliminary questionnaire of asthma clinic patients
• Who was studied: Murine (mouse) alveolar macrophage cells (cell line printed as RAW 267.9), plus two dozen questionnaire respondents from an El Paso, Texas allergy and asthma clinic, aged 11 to 89, collected in Fall and Winter 2003-2004. Respondents were roughly 15% of patients and 75% were women.
• Exposure: Cells were exposed to single-wall carbon nanotubes (SWCNT-1, containing roughly 5% to 10% iron catalyst), two multiwall carbon nanotube samples (MWCNT-R and MWCNT-N), black carbon (Vulcan XC-72), and chrysotile asbestos as a toxicity comparator. Concentrations rose in doubling steps from 0.005 to 10 µg/mL for 48 hours. Patients were asked about current and continuous exposure to kitchen gas stoves.
• Main results:
  • All the test materials, including the chrysotile asbestos, began to cause cell death at a threshold of 2.5 µg/mL.
  • Essentially all of the carbon materials produced a cell-killing response similar to that of the chrysotile asbestos.
  • At 5 µg/mL, the black carbon was slightly less toxic than the carbon nanotube materials and the chrysotile asbestos.
  • No production of the immune signaling proteins IL-10 or IL-12 was detected in the treated cell cultures.
  • Multiwall carbon nanotube aggregates collected from kitchen gas-stove burner exhaust closely resembled the MWCNT-R test material.
  • Among the women in the clinic questionnaire sample, 83% were currently exposed to gas cooking stoves at home and 67% had been continuously exposed. All of the Hispanic women were currently exposed.
• The authors' conclusion: The authors concluded that black carbon, single-wall and multiwall carbon nanotube aggregates showed the same toxicity to mouse alveolar macrophage cells as chrysotile asbestos at concentrations above about 2 µg/mL. They suggested that carbon nanotube aggregates in the environment may contribute to allergies and/or asthma, especially with long-term exposure, and raised concerns about manufactured carbon nanomaterials.
• Limitations the authors state:
  • Cell culture studies do not include effects from interaction of the particles with the respiratory tract and nervous system.
  • Mouse cell lines are far from representing human lung function.
  • The clinic questionnaire data may be biased because all clinic patients were assumed to have some respiratory problem.
  • Exposure length and concentration for people are largely unknown, so risk is difficult to establish.
  • National gas-use and asthma-death data showed no specific association between gas use and asthma or asthma deaths.

Topics

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

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

Related studies

• Cytotoxicity and reactive oxygen species generation from aggregated carbon and carbonaceous nanoparticulate materials — K.M. Garza, K.F. Soto, et al. (2008)
• Fibrous nanocellulose, crystalline nanocellulose, carbon nanotubes, and crocidolite asbestos elicit disparate immune responses upon pharyngeal aspiration in mice — E.J. Park, T.O. Khaliullin, et al. (2018)
• Determination of cytotoxicity attributed to multiwall carbon nanotubes (MWCNT) in normal human embryonic lung cell (WI-38) line — J.S. Kim, K.S. Song, et al. (2010)
• Cytotoxic responses and potential respiratory health effects of carbon and carbonaceous nanoparticulates in the Paso del Norte airshed environment — K.F. Soto, L.E. Murr, et al. (2008)
• Cytotoxic effects of aggregated nanomaterials — K. Soto, K.M. Garza, et al. (2007)
• Toxicity evaluations of various carbon nanomaterials — M. Uo, T. Akasaka, et al. (2011)

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