Reconstruction of a century of airborne asbestos concentrations

Our plain-English summary of Reconstruction of a century of airborne asbestos concentrations, by J.S. Webber, K.W. Jackson, P.P. Parekh, et al (Environmental Science & Technology, 2004).

The study

• Authors: J.S. Webber, K.W. Jackson, P.P. Parekh, R.F. Bopp
• Journal: Environmental Science & Technology
• Published: 2004;38(3):707-14
• Type of article: Historical article
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Airborne asbestos concentrations have been reconstructed for the entire 20th century for the first time through a combination of paleolimnological methods, particle-separation techniques, and analytical transmission electron microscopy. Pb concentrations and respirable aerosol mass concentrations in air and sediments yielded collection efficiencies of approximately 3000 m3 of air per gram of lake sediment. Airborne concentrations of chrysotile, the most common type of asbestos, reconstructed from control lake sediments echoed chrysotile's usage during the 20th century, with the highest concentrations mid-century (approximately 0.1 fibers/cm3) and then decreasing in the last quarter century. Reconstructed airborne concentrations of anthophyllite asbestos, a byproduct of local talc mining and milling, increased from <0.004 to 0.022 fibers/cm3 from 1846 to 1967. These anthophyllite concentrations during the approximately 100-year period of talc mining correlated well (r2 = 0.80, p < 0.01) with annual production of local talc and were much higher (p = 0.004) than concurrent concentrations in a control lake located upwind of the mines and mills. All of the chrysotile and more than 70% of the anthophyllite asbestos fibers were too narrow to be detected by phase-contrast light microscopy, the method used to measure airborne fiber concentrations before approximately 1980.

In plain English

The authors estimated past airborne asbestos levels in northern New York State by analyzing dated layers of lake-bottom sediment with transmission electron microscopy. Sediment cores were collected from nine lakes. Analysis centered on Clear Lake, about 8 km downwind of the local talc industry, and Sixberry Lake, a control lake upwind of the mines and mills. Sediment fiber counts were converted to air concentrations using factors derived from lead and aerosol data. In the control lake, reconstructed chrysotile ranged from less than 0.006 to 0.129 fibers/cm3, rising in the middle of the 20th century and declining steeply in its last quarter. In Clear Lake, anthophyllite asbestos rose to 0.022 fibers/cm3 by 1966 and was correlated over time with local talc production (r2 = 0.80, p less than 0.01). It was significantly higher than in the control lake (p = 0.004). All of the chrysotile fibers detected, and more than 70% of the anthophyllite fibers, were too narrow to be seen by phase-contrast light microscopy. The authors concluded that the patterns pointed toward talc-related activities as the source of the anthophyllite. They noted added uncertainty in applying their conversion factors to asbestos fibers.

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: Environmental reconstruction study (paleolimnology): dated lake sediment cores were analyzed by transmission electron microscopy, comparing a study lake downwind of talc operations with an upwind control lake
• Who was studied: Lake sediment cores from St. Lawrence County, northern New York State. The study lake was Clear Lake, about 8 km downwind of the talc industry near Gouverneur. The control lake was Sixberry Lake, upwind. Eight sections from each core, spanning the mid-1800s to 1995, were analyzed for asbestos.
• Exposure: Airborne asbestos fibers deposited in lake sediments: chrysotile (linked to general asbestos use), anthophyllite asbestos (linked to local talc mining and milling), and tremolite and actinolite asbestos
• Main results:
  • Averaged collection efficiencies used to convert sediment fiber counts to air concentrations were 3.0 × 10^3 cubic meters of air per gram of sediment for the study lake and 1.9 × 10^3 for the control lake
  • Reconstructed airborne chrysotile concentrations from the control lake ranged from less than 0.006 to 0.129 fibers/cm3
  • In the control lake, chrysotile rose sharply in the middle of the 20th century and declined steeply in the last quarter of the century, which the authors linked to asbestos use and its legislated reduction
  • In the study lake, anthophyllite asbestos concentrations increased during the 20th century, reaching 0.022 fibers/cm3 by 1966
  • Anthophyllite concentrations in the study lake were much higher (p = 0.004) than concurrent concentrations in the upwind control lake
  • Mean 20th-century airborne anthophyllite concentrations were 0.016 fibers/cm3 in the study lake and 0.001 fibers/cm3 in the control lake, a 16-fold difference
  • Study-lake airborne anthophyllite asbestos concentrations were significantly correlated over time with local talc production (r2 = 0.80, p less than 0.01)
  • Tremolite asbestos was detected only in study-lake sediments, at low concentrations with no time trend, and a maximum of 0.007 fibers/cm3 at the beginning of the 20th century
  • All of the chrysotile fibers detected, including those longer than 5 µm, were too narrow to be resolved by phase-contrast light microscopy (PCM)
  • More than 70% of anthophyllite fibers were below PCM resolution
  • The majority of anthophyllite fibers detected were shorter than 5 µm
• The authors' conclusion: The authors concluded that the spatial, time-related and compositional trends pointed strongly toward talc-related activities as the source of the elevated airborne anthophyllite asbestos at the study lake
• Limitations the authors state:
  • Applying the collection efficiencies, derived from lead and aerosol mass, to asbestos fibers adds uncertainty. The results are a first-order estimate.
  • Blank samples showed nonuniform chrysotile contamination, attributed to the filters. The authors subtracted thin chrysotile fibers resembling the contaminants (fibrils thinner than 0.05 µm and bundles thinner than 0.1 µm) from all raw counts.
  • Many fibers could not be identified as a specific mineral because they fell between two minerals, for example between anthophyllite and talc
  • The authors note that some contend the anthophyllite fibers in the talc are actually talc intergrowths

Topics

The National Library of Medicine indexes this study under subjects our site covers: Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Analytical Transmission Electron Microscopy (ATEM), Chrysotile, Anthophyllite, Talc.

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