Historical ambient airborne asbestos concentrations in the United States - an analysis of published and unpublished literature (1960s-2000s)

Our plain-English summary of Historical ambient airborne asbestos concentrations in the United States - an analysis of published and unpublished literature (1960s-2000s), by A. Abelmann, M.E. Glynn, J.S. Pierce, et al (Inhalation Toxicology, 2015).

The study

• Authors: A. Abelmann, M.E. Glynn, J.S. Pierce, P.K. Scott, S. Serrano, D.J. Paustenbach
• Journal: Inhalation Toxicology
• Published: 2015;27(14):754-66
• Type of article: Historical article, Review
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Outdoor concentrations of airborne asbestos have been measured throughout the US over time. However, a thorough review and analysis of these data has not been conducted. The purpose of this study is to characterize asbestos concentrations in ambient air by environment type (urban, rural) and by decade, using measurements collected in the absence of known asbestos emission sources. A total of 17 published and unpublished studies and datasets were identified that reported the results of 2058 samples collected from the 1960s through the 2000s across the US. Most studies did not report asbestos fiber type, and data based on different analytical methods (e.g. Phase Contrast Microscopy, Transmission Electron Microscopy, etc.) were combined in the dataset; however, only fibers ≥5 μm in length were considered. For a small subset of the measurements (n = 186, 9.0%), a conversion factor was used to convert mass-based data (e.g. ng/m(3)) to count-based values (i.e. f/cc ≥5 μm). The estimated overall mean and median ambient asbestos concentrations for the 1960s through 2000s were 0.00093 f/cc and 0.00022 f/cc, respectively. Concentrations generally increased from the 1960s through the early 1980s, after which they declined considerably. While asbestos use decreased throughout the 1970s, these results indicate that ambient concentrations peaked during the early 1980s, which suggests the possible contribution of abatement or demolition activities. Lastly, ambient asbestos concentrations were higher in urban than rural settings, which is consistent with the greater use of asbestos-containing materials in more densely populated areas.

In plain English

This review pooled outdoor air measurements of asbestos taken across the United States from the 1960s to the 2000s. It used only samples collected away from known asbestos sources such as mines or shipyards. It combined 16 studies and reports (381 samples) with an unpublished RJ Lee Group dataset (1,677 urban samples, 1986 to 1998), for 2,058 samples from at least 40 states. Only fibers 5 micrometres or longer were counted. Fiber types were mostly not distinguished, and data from different microscope methods were combined. The overall mean was 0.00093 and the median 0.00022 fibers per cubic centimetre. Urban samples had a mean of 0.0011 and rural samples 0.00039. The share of samples above a cut-off of 0.0046 did not differ significantly between urban and rural samples (8.1% versus 3.9%). That share was 20% in the 1980s, significantly different from all other decades, and 0% in the 2000s. The authors concluded that concentrations were higher in urban areas, likely peaked in the 1980s, and declined afterwards. They noted that many samples were below detection limits, and that falling detection limits might explain part of the trend.

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: Review and pooled statistical analysis of published and unpublished outdoor (ambient) air sampling data
• Who was studied: 2,058 outdoor air samples from at least 40 US states, collected from the 1960s to the 2000s. They came from 16 published studies and reports (381 samples) and an unpublished RJ Lee Group dataset (1,677 urban samples, 1986 to 1998).
• Exposure: Airborne asbestos in outdoor air sampled away from known or potential emission sources. Only fibers 5 micrometres or longer were counted. Fiber type was mostly not reported. Results from phase contrast microscopy (PCM), transmission or other electron microscopy (TEM/EM), scanning electron microscopy (SEM) and the ISO method were combined. 186 mass-based samples (9.0%) were converted to fiber counts.
• Main results:
  • Across all 2,058 samples, the estimated mean was 0.00093 fibers per cubic centimetre (f/cc) and the median was 0.00022 f/cc.
  • Mean concentrations were 0.0011 f/cc in urban settings (1,954 samples) and 0.00039 f/cc in rural settings (102 samples).
  • Median concentrations were 0.00050 f/cc in urban settings and 0.000020 f/cc in rural settings.
  • 8.1% of urban samples and 3.9% of rural samples exceeded the cut-off of 0.0046 f/cc. The cut-off was the 95th percentile of the reported detection limits. This difference was not statistically significant (p = 0.13).
  • The 1970s was the only decade with both urban and rural samples. In that decade, 19% of rural samples and 4.6% of urban samples exceeded the cut-off, a statistically significant difference (p = 0.017).
  • Mean concentrations by decade were 0.0012 f/cc (1960s), 0.0011 f/cc (1970s), 0.0022 f/cc (1980s), 0.0016 f/cc (1990s) and 0.000017 f/cc (2000s).
  • The share of samples above the cut-off was 4.7% in the 1960s, 6.8% in the 1970s, 20% in the 1980s, 1.7% in the 1990s and 0% in the 2000s.
  • The 1980s proportion above the cut-off was statistically significantly different from that of every other decade.
  • Most of the higher 1980s concentrations came from samples collected in the early 1980s.
  • Mean and median concentrations from PCM samples were higher than those from TEM and SEM samples.
• The authors' conclusion: The authors concluded that ambient asbestos concentrations were higher in urban than rural environments. They also concluded that concentrations likely peaked sometime in the 1980s and appear to have declined since then.
• Limitations the authors state:
  • Data from different analytical methods were combined.
  • PCM cannot tell asbestos from other fibers, so including PCM data may have inflated concentrations in some subsets.
  • A high percentage of samples were below the detection limit in some subsets, especially the later decades. This was 99.2% of 1990s samples and 92.6% of 2000s samples.
  • Apparent trends over time may partly reflect detection limits getting lower over time rather than real decreases in concentration.
  • Relevant studies may have been missed.
  • Studies were not weighted, although data quality likely varied.
  • The choice of conversion factor for mass-based data could affect the results.
  • The unpublished RJ Lee Group dataset made up most of the data. When the authors reran the analysis without it, the overall trends and conclusions did not change.

Topics

Medical terms in this study, explained in our Lexicon: phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Abatement, Asbestos-Containing Material (ACM).

Related studies

• Historical ambient airborne asbestos concentrations in the United States — M.M. Finkelstein (2016)
• Response to Letter to the Editor Regarding "Ambient Asbestos Fiber Concentrations and Long-Term Trends in Pleural Mesothelioma Incidence Between Urban and Rural Areas in the United States (1973-2012)" by Finkelstein — K.A. Keeton, M.E. Glynn, et al. (2018)
• Authors' response to Finkelstein's letter to the editor regarding our recent review of ambient airborne asbestos concentrations (Abelmann et al., 2015) — A. Abelmann, M.E. Glynn, et al. (2016)
• Exposure to airborne asbestos during removal and installation of gaskets and packings: a review of published and unpublished studies — A.K. Madl, K. Clark, et al. (2007)
• Letter Concerning: Glynn ME, Keeton KA, Gaffney SH, Sahmel J. Ambient Asbestos Fiber Concentrations and Long-Term Trends in Pleural Mesothelioma Incidence Between Urban and Rural Areas in the United States (1973-2012). Risk Analysis 2018;38(3):454-471 — M.M. Finkelstein (2018)
• Reconstruction of a century of airborne asbestos concentrations — J.S. Webber, K.W. Jackson, et al. (2004)

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