The contamination of Lake Superior with amphibole gangue minerals

Our plain-English summary of The contamination of Lake Superior with amphibole gangue minerals, by A.M. Langer, C.M. Maggiore, W.J. Nicholson, et al (Annals of the New York Academy of Sciences, 1979).

The study

• Authors: A.M. Langer, C.M. Maggiore, W.J. Nicholson, A.N. Rohl, I.B. Rubin, I.J. Selikoff
• Journal: Annals of the New York Academy of Sciences
• Published: 1979;330:549-72
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

Abstract

Iron ore called taconite is mined in the Biwabik Iron Formation in the Eastern Mesabi region of the Mesabi Range, in eastern Minnesota. After mining, ore is shipped to Silver Bay, Minnnesota for processing and wet magnetic extraction. Tailings from the process are dumped, as a slurry, into a man-made containment delta constructed in Lake Superior. Submicroscopic amphibole fibers and/or cleavage fragments, a component of the gangue, apparently escape from the delta at Silver Bay, and enter Lake Superior. These particles contaiminate the potable water supplies of municipalities drawing directly from the lake. One of the gangue minerals is the amphibole grunerite, whose asbestiform variety is called amosite. Major emphasis of this study was directed at identification of submicroscopic particle pollutants, based on morphology, structure and chemical composition. Quantitative determination of fibrous amphibole phases, present in a range of water samples, was undertaken. Transmission electron microscopy, selected area electron diffraction, and an electron microprobe technique was used for identification and enumeration and this information was compared with data sets determined from standards. Grunerite fiber and/or acicular cleavage fragments, in some instances indistinguishable from asbestiform grunerite, are present in the tailings, lake water and drinking water of a number of municipalities, a result of contamination of the lake at the Silver Bay milling operation. This amphibole is found in drinking water in concentrations which range from 0.6 to 2.8 X 10(6) fiber/liter. The risk to health, associated with direct ingestion of grunerite fiber is unknown and is extrapolated from the asbestiform grunerite (amosite) data base. The biological activity of other fibrous amphiboles observed, unrelated to any asbestiform silicate variety, is presently unknown and warrants investigation.

In plain English

This laboratory study examined mineral fibers from taconite (iron ore) tailings that the Reserve Mining Company discharged into Lake Superior at Silver Bay, Minnesota. The authors took samples from the plant's tailings launders, from the lake, and from tap water in towns drawing water from the lake. They identified fibers by electron microscopy, electron diffraction and chemical analysis, comparing them with reference minerals. Table 4 lists 14 to 70 million amphibole fibers per liter in six Duluth water samples, though the text states about 14 to 65 million. One New York City tap water sample contained none. Calculated from average fiber-type proportions, grunerite was 0.6 to 2.8 million fibers per liter and actinolite 3.1 to 15.4 million. Two percent of Duluth water fibers were indistinguishable from asbestiform grunerite (amosite). The authors said their figures may be conservative, and that it is unknown whether the asbestos property carries down to such small fibers. They concluded that the health risk of drinking grunerite fiber is unknown and is extrapolated from amosite data, and that the effects of ingesting these fibers warrant investigation.

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: Laboratory mineralogical analysis of tailings and water samples (electron microscopy, electron diffraction, electron microprobe chemistry, compared with mineral standards). It is not a study of human health outcomes.
• Who was studied: Water samples came from Reserve Mining Company tailings launders, directly from Lake Superior, and from tap water in municipalities drawing from the lake. Table 4 reports six Duluth, Minnesota samples and one New York City tap water sample. Chemical plots covered 91 fibers from tailings and 192 fibers from Duluth tap water. Sampling dates are not given.
• Exposure: Amphibole fibers and fragments in lake and drinking water, coming from taconite processing tailings (Biwabik Iron Formation, Peter Mitchell pit). These were grunerite (some indistinguishable from asbestiform grunerite, amosite), cummingtonite, actinolite, and hornblende fragments.
• Main results:
  • Table 4 lists total fibrous amphibole counts for six Duluth samples of 65, 20, 20, 70, 14 and 15 million fibers per liter, a range of 14 to 70 million. Sample 4 had 70 million.
  • The article's text states the total amphibole fiber content of drinking water as about 14 to 65 million fibers per liter. This conflicts with the 70 million listed in Table 4.
  • Grunerite fiber in drinking water ranged from 0.6 to 2.8 million fibers per liter, and a portion of these were identical to asbestiform grunerite
  • Actinolite fiber in drinking water ranged from 3.1 to 15.4 million fibers per liter
  • The per-sample concentrations of individual fiber types in Table 4 were calculated by applying average tap water proportions. They were not counted separately for each sample.
  • Of the fibers in Duluth municipal water, 4% were grunerite, 22% actinolite and 47% cummingtonite
  • Two percent of the fiber in Duluth municipal water was indistinguishable from asbestiform grunerite (amosite)
  • Tap water contained less grunerite fiber (up to 4%) than the tailings (some 7%)
  • The one New York City tap water sample showed zero fibrous amphiboles in Table 4
  • Masses of amphibole in drinking water were calculated at 0.4 to 40 micrograms per liter
  • More than half of the fibrous amphiboles in drinking water were less than 1 micron long and less than 0.2 microns wide, which was smaller than the amosite standard
  • The authors estimated exposure for a person drinking one liter of Duluth water per day. Ingested fibers identical with amosite would be orders of magnitude below occupational exposure. Fibrous grunerite and actinolite combined would approach the exposure levels of asbestos workers.
• The authors' conclusion: The authors concluded that the health risk of directly ingesting grunerite fiber is unknown and is extrapolated from the asbestiform grunerite (amosite) data. They also concluded that the effects of ingesting fibrous amphiboles, including grunerite in all its forms, are unknown and warrant investigation.
• Limitations the authors state:
  • The reported concentrations may be conservative because of the identification criteria used
  • Fibers too thick or too thin to give a diffraction pattern were left out of the analysis
  • Time constraints meant not every particle could be rotated for further diffraction, which left uncertainty for some 'possible' amphiboles
  • Mass estimates depended on assumed fiber thickness and varied by a factor of 2 to 3
  • It is unknown what form the fibers had in the mine, and whether the asbestos property carries down to submicroscopic fibers

Mines named here

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

• Penge mine, Transvaal

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Group, Taconite, Mesabi Range, Tailings, Cleavage Fragment, Grunerite, Asbestiform, Amosite.

Related studies

• Ingested mineral fibers: elimination in human urine — P.M. Cook, G.F. Olson (1979)
• Asbestos in public water supplies: discussion of future problems — J.P. Hills (1979)
• Asbestos-contaminated drinking water: its impact on household air — J.S. Webber, S. Syrotynski, et al. (1988)
• Distribution of chemical carcinogens in aquatic environments — H.F. Kraybill (1976)
• Asbestos in water — (1981)
• Epidemiological studies on ingested asbestos — J. Hopkins (1984)

Browse more research in Annals of the New York Academy of Sciences, or return to medical research.