Investigation of exposures to commercial asbestos in northeastern Minnesota iron miners who developed mesothelioma

Our plain-English summary of Investigation of exposures to commercial asbestos in northeastern Minnesota iron miners who developed mesothelioma, by W.M. Brunner, A.N. Williams, A.P. Bender (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: W.M. Brunner, A.N. Williams, A.P. Bender
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S116-20
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A 70% excess of mesothelioma, an asbestos-related cancer, has been reported among men in northeastern Minnesota, where iron mining has been the major industry. The Minnesota Department of Health has studied iron miners who developed mesothelioma to identify possible sources of asbestos exposure. A database of all Minnesota residents diagnosed with mesothelioma between 1988 and 1996 was linked to a database of approximately 72,000 current and former Minnesota iron-mining employees to identify cases who had ever worked in the mining industry. The job histories of the cases were examined to determine if any of their jobs could have involved exposure to commercial asbestos. Seventeen individuals diagnosed with mesothelioma in Minnesota between 1988 and 1996 were found to have worked in the iron mining industry. Of the 15 for whom adequate work histories were available, 14 had identifiable sources of exposure to commercial asbestos in jobs held both inside and outside of the mining industry. The time between employment in these asbestos-exposed occupations and the diagnosis of mesothelioma is consistent with the 20 or more year latency period that has been observed in other studies of this cancer.

In plain English

This Minnesota Department of Health case series looked for sources of commercial asbestos (commercially available asbestos and asbestos-containing materials) among iron miners who developed mesothelioma. The authors linked records of all Minnesota residents diagnosed with mesothelioma from 1988 to 1996 to a cohort of about 72,000 iron-mining employees. Of 340 men with mesothelioma, 17 had worked in iron mining. None of the 92 women with mesothelioma were in the cohort. Two of the 17 men had peritoneal mesothelioma. Exposure was judged from job titles, work histories, interviews and expert panels, not measurements. Taconite dust was not assessed. Of 15 men with adequate work histories, 14 had jobs with possible or probable commercial asbestos exposure: 11 probable and 3 possible. These were mining jobs such as carpenter and plumber, non-mining jobs, or both. One had no apparent occupational source; for two, significant gaps in their job histories prevented assessment. The authors concluded that commercial asbestos exposure was the likely cause of mesothelioma in this case series, but that other causes could not be ruled out. The study had no comparison group.

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: Case series, using record linkage between the state cancer registry and an iron miner cohort, with a qualitative exposure assessment
• Who was studied: Minnesota residents diagnosed with mesothelioma from 1988 to 1996 (340 men, 92 women), linked to the Minnesota Iron Miner cohort of about 72,000 people who worked in northeastern Minnesota iron mining between the 1930s and the early 1980s. The linkage found 17 male former iron-mining employees with mesothelioma.
• Exposure: Commercial asbestos (commercially available asbestos and asbestos-containing materials such as insulation) in mining and non-mining jobs. It was judged qualitatively from job titles and histories, more than 350 worker interviews and company assessment panels. Exposure to taconite dust was not assessed.
• Main results:
  • Two of the 17 iron-mining employees with mesothelioma had peritoneal mesothelioma; the other 15 had pleural mesothelioma. Age at diagnosis ranged from 55 to 82.
  • None of the 92 female Minnesotans diagnosed with mesothelioma between 1988 and 1996 were found in the iron miner cohort.
  • Occupational histories were complete enough to evaluate for 15 of the 17 cases.
  • Of the 15 cases with adequate histories, 14 had potential exposure to commercial asbestos: 11 had jobs with probable exposure and 3 had jobs with possible exposure.
  • One of the 15 had no apparent occupational exposure to commercial asbestos based on the available information.
  • For 2 of the 17, a potential source of exposure could not be determined because the jobs they held for significant portions of their work histories were unknown.
  • Of the 14 with possible or probable exposure, mining jobs were the only identified source for 4, non-mining jobs the only identified source for 4, and both for 6.
  • Mining jobs rated as having potential commercial asbestos exposure included carpenter, maintenance mechanic and plumber.
  • Non-mining jobs with potential exposure included boiler operator, sheet metal worker and worker at the Conwed plant in Cloquet. Two of the 17 had also worked at Conwed.
  • The time between work in these asbestos-exposed jobs and diagnosis was consistent with a latency period of 20 or more years.
• The authors' conclusion: The authors concluded that their findings show an unquantified risk of mesothelioma among former Minnesota iron miners. They suggested that commercial asbestos exposure, inside and outside the mining industry, is the likely cause of mesothelioma in this case series. They added that at least one miner had no identifiable source and other causes cannot be ruled out.
• Limitations the authors state:
  • As a case series, the study had no control group, so exposures among people without mesothelioma could only be assumed.
  • The mesothelioma risk among miners could not be quantified, and it is not solely attributable to exposures in the mining workplace.
  • Exposure assessment was based on job titles and occupational histories from existing records, not actual monitoring data.
  • Next of kin could not be contacted for more information about work histories.
  • Nothing was known about non-occupational asbestos exposures, such as hobbies, the home environment or a spouse's job.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Mesothelioma, Peritoneal mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Asbestos Exposure, Latency.

Related studies

• A case-control study of mesothelioma in Minnesota iron ore (taconite) miners — C.S. Lambert, B.H. Alexander, et al. (2016)
• Occupational exposures and lung cancer risk among Minnesota taconite mining workers — E.M. Allen, B.H. Alexander, et al. (2015)
• The search for asbestos within the Peter Mitchell Taconite iron ore mine, near Babbitt, Minnesota — M. Ross, R.P. Nolan, et al. (2008)
• Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry — J. Hwang, G. Ramachandran, et al. (2013)
• Risk assessment due to environmental exposures to fibrous particulates associated with taconite ore — R. Wilson, E.E. McConnell, et al. (2008)
• Cancer incidence among Minnesota taconite mining industry workers — E.M. Allen, B.H. Alexander, et al. (2015)

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