Evidence and reconstruction of airborne asbestos from unconventional environmental samples

Our plain-English summary of Evidence and reconstruction of airborne asbestos from unconventional environmental samples, by J.S. Webber, M. Getman, T.J. Ward (Inhalation Toxicology, 2006).

The study

• Authors: J.S. Webber, M. Getman, T.J. Ward
• Journal: Inhalation Toxicology
• Published: 2006;18(12):969-73
• Type of article: Historical article
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The understanding of historical ambient asbestos concentrations is critical to exposure mapping and retrospective health impact studies involving asbestos related diseases. Two presentations at the University of Montana Center for Environmental Health Sciences Asbestos Conference (July 28, 2005) introduced novel methods for detecting evidence of past airborne asbestos contamination. In each of these studies, transmission electron microscopy was used to identify and measure asbestos fibers collected in samples from unconventional environmental sources. In the first study, paleolimnology, analytical transmission electron microscopy, particle-separation techniques, and empirical aerosol-sediment modeling were combined to provide the first measurements of airborne asbestos concentrations prior to the 1980s. In an upstate New York study area, airborne concentrations of chrysotile followed its 20th-century usage, with highest concentrations near mid-century (approximately 0.1 fibers/cm3), followed by a decrease in the last quarter century. Airborne concentrations of anthophyllite asbestos (a contaminant from nearby talc mines and mills) increased from <0.004 to 0.022 fibers/cm3 from 1847 to 1995. In the second study, tree bark and core samples were collected from areas near the asbestos-contaminated vermiculite mine in Libby, MT. We originally hypothesized that trees in the areas surrounding the mine could serve as reservoirs for ambient amphibole fibers. Though gravimetric reduction of a tree core sample did not indicate the presence of amphibole fibers, transmission electron microscopy analysis of bark samples yielded substantial amphibole fiber concentrations ranging from 14 to 260 million amphibole fibers/cm2. Based on these preliminary results, we conclude that trees in the Libby valley can serve as reservoirs for amphibole fibers, and that a continued potential for exposure exists for those who harvest contaminated wood.

In plain English

This article described two studies presented at a University of Montana asbestos conference in July 2005. Both used transmission electron microscopy to find asbestos in unusual environmental samples. In the first, the authors dated lake sediment layers downwind and upwind of a talc mining area in upstate New York to estimate past airborne asbestos levels. Reconstructed chrysotile levels rose to more than 0.1 fiber/cm3 toward the mid-20th century, then fell. Anthophyllite asbestos, a talc contaminant, peaked at about 0.02 fiber/cm3 around 1966. It was higher than at the upwind lake. A pilot sediment core near Libby, Montana, gave an estimated airborne level of about 0.01 fibers/cm3 around 1980. In the second study, tree bark at and just outside the restricted area of the former Libby vermiculite mine contained 41 to 530 million amphibole fibers per gram. None were detected in a control sample from Albany, New York. Based on these preliminary results, the authors concluded that Libby-valley trees can serve as reservoirs for amphibole fibers, with continued potential exposure for people who harvest contaminated wood. A repeat analysis of one bark sample gave significantly different results.

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: Article summarizing two conference presentations: a paleolimnology (dated lake-sediment) reconstruction of past airborne asbestos and a preliminary tree-bark sampling study; fuller methods are published elsewhere
• Who was studied: Sediment cores from Sixberry Lake (downwind) and Clear Lake (upwind) of a talc mining and milling area in upstate New York; a sediment core collected in 2002 from a marsh about 5 km northeast of Vermiculite Mountain near Libby, MT; bark and core samples from trees at three locations near the former W. R. Grace vermiculite mine, plus one control bark sample from Albany, NY
• Exposure: Airborne chrysotile and anthophyllite asbestos (anthophyllite being a contaminant of locally mined fibrous talc) in New York; amphibole fibers (winchite, richterite, tremolite) from the asbestos-contaminated Libby vermiculite mine
• Main results:
  • New York study: reconstructed airborne chrysotile concentrations rose to more than 0.1 fiber/cm3 toward the middle of the 20th century and dropped in the last quarter of the century
  • New York study: airborne concentrations reconstructed from sediments of about 1979 (0.02 fibers/cm3) closely matched the earliest ambient concentrations measured by TEM at that time
  • New York study, downwind lake: maximum reconstructed airborne anthophyllite asbestos concentrations were about 0.02 fiber/cm3, from about 1966
  • New York study: anthophyllite asbestos concentrations correlated with annual local talc production (r2 = .80, p less than .001) and were much higher (p = .004) than concurrent concentrations at the upwind control lake
  • New York study: all of the chrysotile fibers and more than 70% of the anthophyllite asbestos fibers were too narrow to be detected by phase-contrast light microscopy
  • Libby pilot sediment study: a slice from about 1980 contained winchite, richterite and tremolite fibers at 2.4 × 10^8 fibers per gram of dried sediment
  • Libby pilot sediment study: applying the collection efficiency from the New York study gave an estimated airborne concentration of about 0.01 fibers/cm3
  • Tree bark study: bark collected at the mine site and directly outside the U.S. EPA-restricted area contained 41 to 530 million fibers per gram
  • Tree bark study: concentrations expressed per exposed bark surface area ranged from 14 to 260 million amphibole fibers/cm2
  • Tree bark study: no amphibole fibers were detected in the control bark sample from Albany, NY
  • Tree core samples were not analyzed by TEM because their residues after ashing were consistently less than 0.5% of the original mass
• The authors' conclusion: The authors concluded, from preliminary results, that trees in the Libby valley can serve as reservoirs for amphibole fibers and that a continued potential for exposure exists for those who harvest contaminated wood; they also stated that the New York and Libby studies demonstrated paleolimnology's ability to reconstruct historic airborne concentrations
• Limitations the authors state:
  • The authors described the tree bark results as preliminary
  • The bark ashing protocol was inconsistent: a second preparation and analysis of one bark sample gave significantly different results, attributed to a thicker subsample with less exposed surface per gram
  • The per-area bark concentrations were approximations, based on an estimated exposed surface area of about 2 cm2 per subsample
  • Isotope dating of the Libby sediment core was somewhat mixed, possibly because animals stirred the shallow sediment

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Transmission Electron Microscopy (TEM), Analytical Transmission Electron Microscopy (ATEM), Chrysotile, Anthophyllite, Talc, vermiculite, Amphibole Group, Gravimetric Reduction.

Related studies

• Reconstruction of a century of airborne asbestos concentrations — J.S. Webber, K.W. Jackson, et al. (2004)
• Separation and characterization of respirable amphibole fibers from Libby, Montana — J.S. Webber, D.J. Blake, et al. (2008)
• Simultaneous airborne dust samples with konimeter, thermal precipitator and dosimeter in asbestos mines — R.S. du Toit, T.C. Gilfillan (1977)
• Comparison of direct and indirect methods of measuring airborne chrysotile fibre concentration — C. Eypert-Blaison, S. Veissiere, et al. (2010)
• An evaluation of potential occupational exposure to asbestiform amphiboles near a former vermiculite mine — J.F. Hart, T.M. Spear, et al. (2009)
• Amphibole asbestos in tree bark--a review of findings for this inhalational exposure source in Libby, Montana — T.J. Ward, T.M. Spear, et al. (2012)

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