Combustion-generated nanoparticulates in the El Paso, TX, USA / Juarez, Mexico Metroplex: their comparative characterization and potential for adverse health effects

Our plain-English summary of Combustion-generated nanoparticulates in the El Paso, TX, USA / Juarez, Mexico Metroplex: their comparative characterization and potential for adverse health effects, by L.E. Murr, K.F. Soto, K.M. Garza, et al (International Journal of Environmental Research and Public Health, 2006).

The study

• Authors: L.E. Murr, K.F. Soto, K.M. Garza, P.A. Guerrero, F. Martinez, E.V. Esquivel, D.A. Ramirez, Y. Shi, J.J. Bang, J. Venzor
• Journal: International Journal of Environmental Research and Public Health
• Published: 2006;3(1):48-66
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

In this paper we report on the collection of fine (PM1) and ultrafine (PM0.1), or nanoparticulate, carbonaceous materials using thermophoretic precipitation onto silicon monoxide/formvar-coated 3 mm grids which were examined in the transmission electron microscope (TEM). We characterize and compare diesel particulate matter (DPM), tire particulate matter (TPM), wood burning particulate matter, and other soot (or black carbons (BC)) along with carbon nanotube and related fullerene nanoparticle aggregates in the outdoor air, as well as carbon nanotube aggregates in the indoor air; and with reference to specific gas combustion sources. These TEM investigations include detailed microstructural and microdiffraction observations and comparisons as they relate to the aggregate morphologies as well as their component (primary) nanoparticles. We have also conducted both clinical surveys regarding asthma incidence and the use of gas cooking stoves as well as random surveys by zip code throughout the city of El Paso. In addition, we report on short term (2 day) and longer term (2 week) in vitro assays for black carbon and a commercial multiwall carbon nanotube aggregate sample using a murine macrophage cell line, which demonstrate significant cytotoxicity; comparable to a chrysotile asbestos nanoparticulate reference. The multi-wall carbon nanotube aggregate material is identical to those collected in the indoor and outdoor air, and may serve as a surrogate. Taken together with the plethora of toxic responses reported for DPM, these findings prompt concerns for airborne carbonaceous nanoparticulates in general. The implications of these preliminary findings and their potential health effects, as well as directions for related studies addressing these complex issues, will also be examined.

In plain English

The authors combined three kinds of work in El Paso, Texas. First, they collected airborne particles outdoors over nearly two years, and separately in about five propane and five natural-gas kitchens, for electron microscope study. Of 225 fully analyzed outdoor particles, 42% contained carbon. The authors reported that about half the carbon-containing particles were carbon nanotube aggregates, which they linked to gas burning, though the article's figures for this share conflict. Levels above kitchen gas burners exceeded outdoor levels. Soot from diesel, wood and burning tires looked the same. Second, they exposed mouse macrophage cells to black carbon, a commercial multi-wall carbon nanotube material, and chrysotile asbestos as a reference. All three killed cells, and the carbon materials were slightly less toxic than chrysotile. Third, they surveyed 38 clinic patients, all asthmatic, and 200 'city-wide' respondents interviewed on the University of Texas at El Paso campus. Roughly 34% of city-wide respondents reported asthma, and roughly 90% of respondents currently used gas. Given migration and hereditary factors, the authors concluded that the link between gas use and asthma may be circumstantial.

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: Mixed descriptive study: electron microscope (TEM) characterization of airborne particles collected outdoors and in kitchens, laboratory (in vitro) cell-culture cytotoxicity assays, and questionnaire surveys of clinic asthma patients and other respondents
• Who was studied: Outdoor airborne particles collected over nearly 2 years at sites in El Paso, Texas (street corners, parking lots, truck stops, freeways, bus garages, gas exhausts). Separately, about 5 propane and 5 natural-gas kitchens were sampled; the article gives no duration for the kitchen sampling. For the cell work, a murine (mouse) alveolar macrophage cell line was used. For the surveys, there were 38 clinic patients, all asthmatic, who filled out questionnaires during 2003-2005. There were also 200 'city-wide' respondents interviewed in person on the University of Texas at El Paso campus, whose home zip codes were spread across the city.
• Exposure: Combustion-generated fine and ultrafine carbon particles (diesel, wood and tire soot, black carbon, carbon nanotube aggregates from gas burning) and kitchen gas stove use. In the cell assays: black carbon (Vulcan XC-72), a commercial multi-wall carbon nanotube aggregate (MWCNT-R), and chrysotile asbestos as a reference material.
• Main results:
  • Of 225 fully analyzed outdoor particles, 93% of PM1 were crystalline and 80% of all particles were aggregates
  • Among the analyzed outdoor particles, 42% contained carbon (also 33% silicon, 27% copper, 15% aluminum, 13% iron, 12% calcium, 10% sulfur)
  • The authors described about half of the carbon-containing particles as carbon nanotube aggregates, printed as '~10%'. Elsewhere they said nanotube aggregates account for 20% or less of outdoor airborne carbon, so what this percentage is a share of is unclear.
  • Outdoor carbon nanotube aggregates averaged roughly 10 to the 2nd to 10 to the 3rd (about 100 to 1,000) per cubic meter
  • Above kitchen gas burners, carbon nanotube aggregate concentrations averaged about 10 to the 3rd to 10 to the 5th per cubic meter. This was roughly 10 to the 2nd to 10 to the 3rd times the outdoor level, though the authors still described it as a relatively low concentration.
  • Burning-tire soot was microstructurally identical to diesel and wood-burning soot
  • In the mouse macrophage assays, black carbon and the multi-wall carbon nanotube material were slightly less cytotoxic than chrysotile asbestos, but all materials were cytotoxic
  • Cell killing increased with time for chrysotile asbestos, while the carbon materials showed a more constant killing ability
  • Cells killed by the carbon nanotube material showed features of both apoptosis and necrosis; cells killed by chrysotile asbestos showed an apoptotic mechanism
  • Among the 200 city-wide survey respondents, asthma incidence was roughly 34%
  • In the city-wide survey, 30% of Hispanic females and 16% of Hispanic males reported asthma
  • Among city-wide respondents with asthma, 51% were smokers
  • Roughly 90% of survey respondents currently used gas
• The authors' conclusion: The authors concluded that, considering migration of people with asthma and hereditary factors, the link between gas use or exposure and asthma may be circumstantial rather than problematic
• Limitations the authors state:
  • The clinical survey had only 38 respondents and was biased to include only asthmatics
  • Atmospheric factors such as sunlight, ozone and hydroxyl radicals may complicate the biological effects seen in cell assays
  • High asthma incidence in southwestern cities may reflect migration and heredity as much as airborne particles

Topics

Medical terms in this study, explained in our Lexicon: Macrophage, Chrysotile.

Related studies

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• Inhalable particles and pulmonary host defense: in vivo and in vitro effects of ambient air and combustion particles — G.E. Hatch, E. Boykin, et al. (1985)
• Biopersistence and potential adverse health impacts of fibrous nanomaterials: what have we learned from asbestos? — V.C. Sanchez, J.R. Pietruska, et al. (2009)
• Cytotoxicity and reactive oxygen species generation from aggregated carbon and carbonaceous nanoparticulate materials — K.M. Garza, K.F. Soto, et al. (2008)
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