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Comparative Study
. 2006 Mar;3(1):48-66.
doi: 10.3390/ijerph2006030007.

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

L E Murr  1 , K F Soto, K M Garza, P A Guerrero, F Martinez, E V Esquivel, D A Ramirez, Y Shi, J J Bang, J Venzor 3rd
Affiliations
Comparative Study

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

L E Murr et al. Int J Environ Res Public Health. 2006 Mar.

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.

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Figures

Figure 1:
Figure 1:
(a) PM (average) size (dp) range versus PM abundance as a percent of the total PM analyzed. Note that 93% of PM, were crystalline while 80% of all PM were aggregates. (b) Primary particle component sizes (size ranges) versus percent of the aggregated PM in (a). Note that >95% of all primary particles were PM1; 57% were PM0.1. PM collected in the El Paso, TX, USA outdoor air.
Figure 2:
Figure 2:
Elemental occurrence as a percent (%) of all collected PM in Fig. 1(a). Elements <1% not shown include W.
Figure 3:
Figure 3:
Carbon nanotube and related carbon (fullerene) nanoparticle aggregate in the El Paso, TX, USA outdoor air. (a) Bright-field TEM image. (b) Dark-field TEM image using the diffracted regime within the objective-aperture double exposure in the SAED pattern insert. Prominent hexagonal graphite (a = 0.25 nm, c = 0.67 nm) diffraction rings are indicated in the SAED pattern insert.
Figure 4:
Figure 4:
Carbon nanotubes and other carbon nanocrystal polyhedra (a) composing PM aggregates collected on the University of Texas at El Paso, TX, USA campus. Note in (b) the closed multiwall carbon nanotube structures and other fullerene morphologies readily observable at the aggregate edges. The collection site was roughly 100 m from a natural gas-burning power plant.
Figure 5:
Figure 5:
Complex aggregate composed of a mixture of carbon nanotube and related carbon nanoparticles and silica (SiO2) nanocrystal particles. (a) Bright-field TEM image with corresponding EDS spectrum showing C (Kα) and Si (Kα) peaks. The oxygen peak is suppressed in the X-ray emission competition. (b) Dark-field TEM image slightly shifted from (a) showing predominantly SiO2 strongly diffracting nanocrystals (reference X). The principal diffraction regimes marked 1 and 2 in the SAED pattern insert are characterized by overlapping (002)C/(101)SiO2 and (100)C/(200)SiO2 diffraction, respectively [26].
Figure 6:
Figure 6:
Typical PM example (dp ≅ 1μm: 1.5μm × 0.6μm) of carbon nanotube / nanocrystal polyhedra aggregate collected from the roof-top exhaust of a natural gas water heater.
Figure 7:
Figure 7:
Large (∼2 μm) carbon nanotube aggregate collected from a kitchen natural gas burner exhaust stream. The estimated primary nanoparticle (MWCNTs and fullerene nanopolyhedra) number is ∼8000. The TEM image shows only about one-fourth of the total aggregate.
Figure 8:
Figure 8:
(a) Typical aggregate of carbon nanotubes and other fullerene polyhedra collected above a kitchen propane gas stove burner. (b) Magnified view of the aggregate in (a) showing a cluster of carbon (concentric) nanoshell structures (A) and a concentric, faceted, polyhedron (p). The SAED pattern insert show the principal graphite (graphene) reflections. The (002) diffraction ring corresponds to graphene (d) spacings of 0.34 nm. The propensity of carbon nanotubes of various length-to-diameter ratios (aspect ratios) relative to fullerene nanopolyhedra is roughly 9-to-1.
Figure 9:
Figure 9:
Examples of DPM collected in the vicinity of an area truck stop in El Paso, TX, USA. (a) Dense, BC-like aggregate of carbon spherules. Note diffuse diffraction rings in SAED pattern insert. (b) Complex, branched clusters of carbon spherules. SAED pattern insert shows crystalline diffraction rings [36].
Figure 10:
Figure 10:
(a) DPM collected from a diesel bus location showing variations in carbon spherule aggregate structures (small and large spherule aggregates). SAED pattern insert shows well-defined graphite diffraction rings. (b) Complex, branched, carbon spherule aggregate characteristic of wood burning (WPM). Note similarity with DPM in Fig. 9(b). The EDS insert shows only carbon.
Figure 11:
Figure 11:
Early morning view (southwest) of particulate/smoke in version on the El Paso, TX USA/Juarez, Mexico border. (a) December, 2004. Arrow at left denotes reference at Asarco stack. R demotes the Rio Grande River. Juarez mountains are in the background. El Paso and Juarez city centers are at left out of view. (b) December, 1998. Arrows marked S show small smoke sources.
Figure 12:
Figure 12:
Particulate matter collected from a burning fire (TPM). (a) Small branched, aggregate fragment. The SAED pattern insert shows prominent graphite reflections. (b) Example of large, aggregated, branched particle. The image shows only about half of the aggregated particle.
Figure 13:
Figure 13:
Simple chicken wire models of carbon nanotubes. (a) Zig-zag type single wall. (b) Chiral tube. (c) Magnified view of (b). (d) Chiral tube growing over the zig-zag tube in (a). (e) Chiral tube growing over an arm-chair type tube. Arrows indicate growth direction.
Figure 14:
Figure 14:
Chicken wire model of carbonaceous spherule formed by overlapping (turbostratic) graphene fragments. (a) and (b) show two views of the spherule. (c) is a magnified view of (b).
Figure 15:
Figure 15:
Comparative cytotoxicites of chrysotile asbestos surrogate BC, and surrogate carbon nanotube aggregates (MWCNT-R) to murine macrophage cells at a concentration of 5 μg/mL. (a) 2 days, (b) 7 days, (c) 14 days.
Figure 16:
Figure 16:
El Paso, TX, USA City map showing survey responses by zip code.
Figure 17:
Figure 17:
Clinical and El Paso city-wide survey data and comparisons. (a) City-wide asthma incidence (M-males, F-females; HM (Hispanic males), HF (Hispanic females). (b) Comparison of current (kitchen) gas stove exposure: clinical and city-wide respondents. (c) Comparison of continuous (or long-term) kitchen gas stove exposure: clinical and city-wide respondents.
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