A risk assessment for exposure to grunerite asbestos (amosite) in an iron ore mine

Our plain-English summary of A risk assessment for exposure to grunerite asbestos (amosite) in an iron ore mine, by R.P. Nolan, A.M. Langer, R. Wilson (Proceedings of the National Academy of Sciences of the United States of America, 1999).

The study

• Authors: R.P. Nolan, A.M. Langer, R. Wilson
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 1999;96(7):3412-9
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The potential for health risks to humans exposed to the asbestos minerals continues to be a public health concern. Although the production and use of the commercial amphibole asbestos minerals-grunerite (amosite) and riebeckite (crocidolite)-have been almost completely eliminated from world commerce, special opportunities for potentially significant exposures remain. Commercially viable deposits of grunerite asbestos are very rare, but it can occur as a gangue mineral in a limited part of a mine otherwise thought asbestos-free. This report describes such a situation, in which a very localized seam of grunerite asbestos was identified in an iron ore mine. The geological occurrence of the seam in the ore body is described, as well as the mineralogical character of the grunerite asbestos. The most relevant epidemiological studies of workers exposed to grunerite asbestos are used to gauge the hazards associated with the inhalation of this fibrous mineral. Both analytical transmission electron microscopy and phase-contrast optical microscopy were used to quantify the fibers present in the air during mining in the area with outcroppings of grunerite asbestos. Analytical transmission electron microscopy and continuous-scan x-ray diffraction were used to determine the type of asbestos fiber present. Knowing the level of the miner's exposures, we carried out a risk assessment by using a model developed for the Environmental Protection Agency.

In plain English

The authors assessed miners' risk from a small grunerite asbestos (amosite) seam in an iron ore mine. Analysis confirmed the mineral, and 24 drill core and blast samples showed no other asbestos type. In 179 personal air samples, fibers at least 5 micrometers long averaged 0.05 per milliliter (highest 0.39); shorter fibers were not counted. 13.4% exceeded the then-current OSHA limit of 0.1; none exceeded the MSHA mining limit. The authors calculated it would take 75 to 265 years of daily mine shifts to inhale the fiber count found in lungs of five British amosite factory mesothelioma cases. They used an Environmental Protection Agency model assuming risk proportional to exposure. For an assumed 45-year-old worker at the average measured level, it gave lifetime cancer risks per 100,000 of 0.1 (nonsmokers) and 0.6 (smokers) for 22 days of bench removal (unsampled; exposure uncertain), and 0.01 and 0.06 for two assumed exposure days of a 30-day drilling job. The highest exposure suggested risks up to seven times greater. The authors concluded mine exposures were several factors of ten below those of the reviewed worker groups.

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: Risk assessment that combined a geological and mineralogical survey of the seam, an air sampling program, a review of published mortality and lung-content studies of exposed workers, and calculations with an Environmental Protection Agency (EPA) risk model
• Who was studied: Miners working in the part of an iron ore mine containing the asbestos seam. The article does not name the mine. 326 air samples were analyzed: 147 area samples and 179 personal samples from drilling, shovel, production truck, track dozer and blast jobs. Sampling dates are not given.
• Exposure: Airborne grunerite asbestos (amosite) fibers released during mining of a localized seam in an iron ore mine. The fibers were counted by phase-contrast optical microscopy using standard NIOSH-MSHA methods, which counted fibers at least 5 micrometers long. They were characterized by analytical transmission electron microscopy.
• Main results:
  • Three bulk samples from highly fibrous seams were analyzed by polarized light microscopy, continuous-scan x-ray diffraction and analytical transmission electron microscopy. The authors stated that the identification criteria were not ambiguous.
  • No other asbestos fiber type was detected in 24 blast pattern and drill core samples.
  • Personal air samples (179): the mean concentration was 0.05 fiber per ml and the highest was 0.39 fiber per ml. Both figures count fibers at least 5 micrometers long.
  • Fibers shorter than 5 micrometers, and those too thin to see by phase-contrast microscopy, were not counted. Including all fiber sizes, the authors estimated total concentrations of 0.33 fibers per ml by one method and 1.18 fibers per ml by another.
  • No personal sample exceeded the MSHA asbestos standard of 2 fiber per ml.
  • 13.4% of personal samples exceeded the OSHA asbestos standard of 0.1 fiber per ml, which the article (published 1999) describes as current.
  • The authors compared the mine with a British grunerite asbestos factory, where an earlier study examined lung tissue from 14 lung cancer and 5 mesothelioma cases. They calculated that 75 to 265 years of daily 8-hour shifts in the mine would be needed to inhale a number of fibers similar to that found in the lungs of the factory mesothelioma cases. This calculation assumed no clearance of fibers from the lungs.
  • The authors took exposure in the Paterson, New Jersey amosite factory to be at least 30 fibers per ml. On that basis, they calculated that about 300 years of exposure in the iron ore mine would equal 6 months of work in that factory. In the factory, no mesotheliomas occurred with less than 6 months of exposure.
  • Scenario I was a 22-day bench removal. No air sampling was done at that site, so the authors assumed fiber levels similar to the mine measurements and a worker aged 45. The EPA model gave a lifetime total cancer risk of 0.1 in 100,000 for nonsmokers and 0.6 in 100,000 for smokers.
  • Scenario II was roughly 30 days of remaining drilling: 28 days in the sill, assumed to contain no asbestos, and two days in the waste iron formation. The estimated lifetime risk for the two exposure days was 0.1 in 1,000,000 (0.01 per 100,000) for nonsmokers and 0.6 in 1,000,000 (0.06 per 100,000) for smokers.
  • The highest measured exposure (0.39 fiber per ml) was seven times the mean. The authors took this to suggest the most extreme risk is seven times greater than their estimates.
• The authors' conclusion: The authors concluded that exposures measured in the iron ore mine were several factors of ten lower than the occupational exposures in the worker groups studied in the literature they reviewed.
• Limitations the authors state:
  • For the 22-day scenario, no air sampling was done at that site, and it is uncertain whether any asbestos exposure took place.
  • The EPA model was built from cohorts with exposures orders of magnitude higher than in the mine. Risk was extrapolated linearly to the low mine exposures.
  • Lung tissue counts included fibers of all lengths, while the air counts covered only longer fibers. Total airborne fiber levels therefore had to be estimated by two methods, whose results differed 3.6-fold.
  • The mean exposure used in the risk calculation assumed all counted fibers were asbestos.
  • The lung-burden comparison assumed no clearance of fibers from the lung, an assumption the authors describe as pessimistic.
  • Air fiber concentrations in the Paterson factory were never measured, so the comparison relies on the authors' estimate of that exposure.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Crocidolite.

Medical terms in this study, explained in our Lexicon: Grunerite, Amosite, Asbestos, Amphibole Asbestos, Riebeckite, Crocidolite, Analytical Transmission Electron Microscopy (ATEM), X-Ray Diffraction (XRD).

Related studies

• Rapporteur's Report Session 3: exposure to grunerite (amosite) asbestos: historical perspectives of the health effects — G.W. Gibbs (2008)
• Lung mineral fibers of former miners and millers from Thetford-Mines and asbestos regions: a comparative study of fiber concentration and dimension — A. Nayebzadeh, A. Dufresne, et al. (2001)
• Rapporteur's Report Session 4: grunerite asbestos (amosite) and tremolite-ferroactinolite asbestos: risk of environmental mesothelioma — J.F. Gamble (2008)
• Talc and amosite/crocidolite preferentially deposited in the lungs of nonoccupational female lung cancer cases in urban areas of Japan — H. Yamada, H. Hashimoto, et al. (1997)
• Human health effects associated with the commercial use of grunerite asbestos (amosite): Paterson, NJ; Tyler, TX; Uxbridge, UK — J. Ribak, G. Ribak (2008)
• Risk of asbestosis in crocidolite and amosite mines in South Africa: an erratum — L.M. Irwig, R.S. du Toit, et al. (1984)

Browse more research in Proceedings of the National Academy of Sciences of the United States of America, or return to medical research.