Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry

Our plain-English summary of Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry, by J. Hwang, G. Ramachandran, P.C. Raynor, et al (The Annals of Occupational Hygiene, 2013).

The study

• Authors: J. Hwang, G. Ramachandran, P.C. Raynor, B.H. Alexander, J.H. Mandel
• Journal: The Annals of Occupational Hygiene
• Published: 2013;57(8):966-78
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Since the 1970s, concerns have been raised about elevated rates of mesothelioma in the vicinity of the taconite mines in the Mesabi Iron Range. However, insufficient quantitative exposure data have hampered investigations of the relationship between cumulative exposures to elongate mineral particles (EMP) in taconite dust and adverse health effects. Specifically, no research on exposure to taconite dust, which includes EMP, has been conducted since 1990. This article describes a comprehensive assessment of present-day exposures to total and amphibole EMP in the taconite mining industry. Similar exposure groups (SEGs) were established to assess present-day exposure levels and buttress the sparse historical data. Personal samples were collected to assess the present-day levels of worker exposures to EMP at six mines in the Mesabi Iron Range. The samples were analyzed using National Institute for Occupational Safety and Health (NIOSH) methods 7400 and 7402. For many SEGs in several mines, the exposure levels of total EMP were higher than the NIOSH Recommended Exposure Limit (REL). However, the total EMP classification includes not only the asbestiform EMP and their non-asbestiform mineral analogs but also other minerals because the NIOSH 7400 cannot differentiate between these. The concentrations of amphibole EMP were well controlled across all mines and were much lower than the concentrations of total EMP, indicating that amphibole EMP are not major components of taconite EMP. The levels are also well below the NIOSH REL of 0.1 EMP cc(-1). Two different approaches were used to evaluate the variability of exposure between SEGs, between workers, and within workers. The related constructs of contrast and homogeneity were calculated to characterize the SEGs. Contrast, which is a ratio of between-SEG variability to the sum of between-SEG and between-worker variability, provides an overall measure of whether there are distinctions between the SEGs. Homogeneity, which is the ratio of the within-worker variance component to the sum of the between-worker and within-worker variance components, provides an overall measure of how similar exposures are for workers within an SEG. Using these constructs, it was determined that the SEGs are formed well enough when grouped by mine for both total and amphibole EMP to be used for epidemiological analysis.

In plain English

This study measured airborne elongate mineral particles (EMP) at taconite mines on Minnesota's Mesabi Iron Range. From January 2010 to May 2011, 232 workers at six mines (one eastern, five western) wore personal air samplers. Workers were sorted into exposure groups by job. Light microscopy counted 'total EMP' in all samples except 18 excluded as overloaded or damaged; it cannot tell asbestiform from non-asbestiform particles. A subset was checked by electron microscopy for amphibole EMP: cummingtonite–grunerite and actinolite. Total EMP was higher overall at eastern mine A. Its highest single result was about 22 times the NIOSH recommended limit, 0.1 particles per cubic centimeter. At mine F, every job group was below that limit. Amphibole EMP levels were much lower than total EMP. All western-zone amphibole results were below the detection limit. Amphibole levels exceeded the NIOSH limit only in a few job groups at mine A, with three individual measurements above it. The authors concluded that amphibole EMP are not major components of taconite EMP. They also concluded the job groups, grouped by mine, suit epidemiological study of total EMP.

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: Occupational exposure assessment study using personal air sampling, with workers grouped into similar exposure groups (SEGs) and analysis of variance components
• Who was studied: 232 workers at six taconite mines in the Mesabi Iron Range, north-eastern Minnesota. Mine A was in the eastern zone (56 workers). Mines B–F were in the western zone (176 workers). Sampling ran from January 2010 to May 2011. 1298 samples were analyzed by PCM and 275 by TEM. Workers were placed in 28 SEGs, of which 27 were monitored.
• Exposure: Elongate mineral particles in taconite dust. 'Total EMP' was counted by NIOSH 7400 phase contrast microscopy: any mineral particle longer than 5 µm with an aspect ratio of at least 3:1. 'Amphibole EMP' was identified by NIOSH 7402 transmission electron microscopy; the amphiboles found were cummingtonite–grunerite and actinolite. Three chrysotile asbestiform EMP were found and excluded from the analyses. 18 samples were excluded because they were overloaded or had damaged filters.
• Main results:
  • Total EMP concentrations were higher overall in mine A (eastern zone). The highest single total EMP exposure, 2.2 particles per cubic centimeter, was about 22 times the NIOSH REL of 0.1 particles per cubic centimeter.
  • Mine F had the lowest total EMP concentrations. Total EMP for every SEG at that mine was below the NIOSH REL.
  • In the western zone (mines B–F), all amphibole EMP results were below the limit of detection.
  • Amphibole EMP concentrations were much lower than total EMP concentrations. They were generally below the NIOSH REL of 0.1 particles per cubic centimeter, except for a few SEGs in mine A (eastern zone). Three individual measurements exceeded the NIOSH REL for amphibole EMP.
  • Of the 21 SEGs present in both zones, 62% (13 of 21) had significantly different total EMP levels between the eastern and western zones.
  • In the western zone, pelletizing operators had the highest total EMP exposure levels of any SEG.
  • Contrast between SEGs for total EMP was 0.740 in the eastern zone and 0.130 in the western zone taken as a whole.
• The authors' conclusion: The authors concluded that total EMP exceeded the REL for many SEGs in several mines, but that total EMP does not necessarily mean regulated asbestiform EMP. They found amphibole EMP well controlled and not major components of taconite EMP. They concluded that their SEGs, grouped by mine, are appropriate for use in an epidemiological study for total EMP.
• Limitations the authors state:
  • NIOSH 7400 (used for total EMP) cannot distinguish asbestiform from non-asbestiform EMP.
  • The authors judged that TEM (NIOSH 7402) can more conservatively be said to separate amphibole from non-amphibole EMP, rather than asbestiform from non-asbestiform.
  • Many samples were below the limit of detection, especially TEM samples in the western zone. Values below the limit were set at half the limit, and this lowered the estimated within-worker variability in the west.
  • The Janitor SEG could not be monitored because janitors are independent contractors.

Topics

Medical terms in this study, explained in our Lexicon: elongate mineral particles (EMPs), Taconite, Mesothelioma, Iron Range, Cumulative Exposure, Amphibole Group, Personal Breathing Zone Sample, NIOSH.

Related studies

• The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry — J. Hwang, G. Ramachandran, 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)
• A review of mortality associated with elongate mineral particle (EMP) exposure in occupational epidemiology studies of gold, talc, and taconite mining — J.H. Mandel, 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)

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