The search for asbestos within the Peter Mitchell Taconite iron ore mine, near Babbitt, Minnesota

Our plain-English summary of The search for asbestos within the Peter Mitchell Taconite iron ore mine, near Babbitt, Minnesota, by M. Ross, R.P. Nolan, G.L. Nord (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: M. Ross, R.P. Nolan, G.L. Nord
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S43-50
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos crystallizes within rock formations undergoing intense deformation characterized by folding, faulting, shearing, and dilation. Some of these conditions have prevailed during formation of the taconite iron ore deposits in the eastern Mesabi Iron Range of Minnesota. This range includes the Peter Mitchell Taconite Mine at Babbitt, Minnesota. The mine pit is over 8 miles long, up to 1 mile wide. Fifty three samples were collected from 30 sites within areas of the pit where faulting, shearing and folding occur and where fibrous minerals might occur. Eight samples from seven collecting sites contain significant amounts of ferroactinolite amphibole that is partially to completely altered to fibrous ferroactinolite. Two samples from two other sites contain ferroactinolite degraded to ropy masses of fibers consisting mostly of ferrian sepiolite as defined by X-ray diffraction and TEM and SEM X-ray spectral analysis. Samples from five other sites contain unaltered amphiboles, however some of these samples also contain a very small number of fiber bundles composed of mixtures of grunerite, ferroactinolite, and ferrian sepiolite. It is proposed that the alteration of the amphiboles was caused by reaction with water-rich acidic fluids that moved through the mine faults and shear zones. The fibrous amphiboles and ferrian sepiolite collected at the Peter Mitchell Mine composes a tiny fraction of one percent of the total rock mass of this taconite deposit; an even a smaller amount of these mineral fragments enter the ambient air during mining and milling. These fibrous minerals thus do not present a significant health hazard to the miners nor to those non-occupationally exposed. No asbestos of any type was found in the mine pit.

In plain English

This was a mineralogical field survey of rock, not a study of people. The authors searched the Peter Mitchell Taconite Mine, an open pit near Babbitt, Minnesota, for asbestos or asbestos-like minerals. Over five days they collected 53 samples from 30 sites. They sampled only faulted, sheared or folded rock, where fibrous minerals might form, and examined the samples with X-ray and electron-microscope methods. Several samples contained the amphibole ferroactinolite, partly or completely altered into very fibrous crystals. Two samples held ropy masses made mostly of ferrian sepiolite, a clay mineral built of very thin fibers. One sample had small amounts of fibrous actinolite, and in four samples no fibers were detected. The authors proposed that acidic water moving through faults altered amphiboles that were not originally fibrous. They concluded that this material did not form the way true asbestos does and makes up a tiny fraction of one percent of the mine's rock. They stated that no asbestos of any type was found. Their statements about air levels and health relied on a separate study, not on measurements made here.

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: Mineralogical field survey and laboratory analysis of rock samples (no human subjects)
• Who was studied: 53 rock samples from 30 sites in the Peter Mitchell Taconite Mine pit (Biwabik iron formation), about 3 miles south of Babbitt, Minnesota, collected over a five-day period. A portion of a U.S. EPA ferroactinolite sample collected in 1975 was also examined.
• Exposure: No human exposure was studied. The minerals examined were the amphiboles ferroactinolite, grunerite and actinolite, and the clay mineral ferrian sepiolite. Samples were taken only from deformed rock zones.
• Main results:
  • Type 1 samples (10B, 10C, 20A, 20B, 21A, 24A, 24B and the EPA ferroactinolite sample) contained ferroactinolite and composite grunerite-ferroactinolite amphibole that had partially or completely altered to very fibrous crystallites.
  • Type 2 samples (5C and 13E): in sample 5C the ferroactinolite was degraded to a ropy mass composed mostly of ferrian sepiolite, made of very thin fibers. The thinnest fibers were less than 0.1 micrometre wide.
  • Type 3 sample 30B contained well-crystallized ferroactinolite and grunerite, plus small amounts of brownish fibrous actinolite and mats of decomposed amphibole.
  • Type 4 samples (13C, 13F, 21B and 29) showed blocky prismatic amphibole crystals, and no fibers were detected.
  • The authors proposed that water-rich fluids, acidified by oxidation of sulfide minerals, moved through the mine's faults and shear zones and chemically altered the amphiboles.
• The authors' conclusion: The authors concluded that the fibrous amphiboles and ferrian sepiolite make up a tiny fraction of one percent of the mine's rock. They concluded that the fibrous ferroactinolite is a low-temperature alteration product of non-fibrous amphibole and does not occur in the manner of true asbestos. The article's own abstract states that no asbestos of any type was found and that these minerals do not present a significant health hazard. Its statements on air concentrations and cancer risk are taken from a separate study (Wilson et al., 2008), not measured in this survey.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Actinolite.

Medical terms in this study, explained in our Lexicon: Taconite, Iron Range, Ferro-actinolite, Amphibole Group, Sepiolite, X-Ray Diffraction (XRD), Grunerite, Peter Mitchell Mine.

Related studies

• Mineralogical and microscopic evaluation of coarse taconite tailings from Minnesota taconite operations — L.M. Zanko, H.B. Niles, et al. (2008)
• A case-control study of mesothelioma in Minnesota iron ore (taconite) miners — C.S. Lambert, B.H. Alexander, et al. (2016)
• Risk assessment due to environmental exposures to fibrous particulates associated with taconite ore — R. Wilson, E.E. McConnell, et al. (2008)
• Mortality experience among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2014)
• Cancer incidence among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2015)
• Occupational exposures and lung cancer risk among Minnesota taconite mining workers — E.M. Allen, B.H. Alexander, et al. (2015)

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