Integration of Evidence on Community Cancer Risks from Elongate Mineral Particles in Silver Bay, Minnesota

Our plain-English summary of Integration of Evidence on Community Cancer Risks from Elongate Mineral Particles in Silver Bay, Minnesota, by L.D. Dell, A.E. Gallagher, L.J. Yost, et al (Risk Analysis, 2021).

The study

• Authors: L.D. Dell, A.E. Gallagher, L.J. Yost, K.A. Mundt
• Journal: Risk Analysis
• Published: 2021;41(9):1674-1692
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The potential for cancer-related risks to community members from ambient exposure to elongate mineral particles (EMPs) in taconite processing has not been formally evaluated. We evaluated 926 ambient air samples including 12,928 EMPs (particle structures with length-to-width ratio ≥3:1) collected over 26 years near a taconite processing facility in Silver Bay, Minnesota. Eighty-two percent of EMPs were ≤3 μm in length and 97% of EMPs had an average aspect ratio <20:1. A total of 935 (7.3%) EMPs had length >5 μm and AR ≥3:1. Average ambient concentration of NIOSH countable amphibole EMPs over all years was 0.000387 EMPs per cubic centimeter (EMP/cm3 ). Of 12,765 nonchrysotile EMPs, the number of amphiboles with length and width dimensions that correlate best with asbestos-related carcinogenicity ranged from four (0.03%) to 13 (0.1%) and the associated ambient amphibole air concentrations ranged from 0.000003 to 0.000007 EMP/cm3 . After 65 years of taconite processing in Silver Bay, evidence of an increased risk of mesothelioma and lung cancer in community members who did not work in the taconite industry is lacking. The absence of an increased risk of asbestos-related cancer in the Silver Bay community is coherent with supporting evidence from epidemiological and toxicological studies, as well as ambient exposure data and lake sediment data collected in Minnesota Iron Range communities. Collectively, the data provide consistent evidence that nonasbestiform amphibole minerals lack the carcinogenic potential exhibited by amphibole asbestos.

© 2021 Ramboll US Consulting, Inc. Risk Analysis published by Wiley Periodicals LLC on behalf of Society for Risk Analysis.

In plain English

This article analysed air monitoring data and reviewed other published evidence. The authors analysed 926 air samples from 1996 to 2018, taken near a taconite plant and its tailings basin in Silver Bay, Minnesota. These held 12,928 elongate mineral particles (EMPs), examined by electron microscopy; all but 31 were at least three times longer than wide. Of these, 6,175 (48%) were amphiboles; of 2,569 with chemistry data, 69% were cummingtonite-grunerite and 30% actinolite. Of 12,765 non-chrysotile particles, 7.3% were longer than 5 µm, and 98% of amphiboles had shapes the authors called consistent with cleavage fragments. Amphibole particles longer than 5 µm averaged 0.000387 EMP per cubic centimeter, about 7.5 times below a lifetime community limit the authors derived from the NIOSH occupational limit. Only 4 to 13 amphibole particles met size definitions linked to asbestos cancer potency. No epidemiological studies of community members' cancer risk from these ambient particles were available. The authors concluded that any increased mesothelioma and/or lung cancer risk to residents from potential exposure to cleavage fragments longer than 5 µm emitted during taconite processing is "vanishingly small, and may be zero."

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: Descriptive analysis of existing ambient air monitoring data, combined with a narrative integration of other published epidemiological, toxicological and environmental evidence
• Who was studied: 926 ambient air samples (96-hour samples taken every 12th day) from two monitoring locations near the Northshore taconite processing facility and tailings basin in Silver Bay, Minnesota, 1996–2018. The samples contained 12,928 recorded EMPs, of which 31 had an aspect ratio below 3:1. No people were studied directly.
• Exposure: Ambient airborne elongate mineral particles from taconite processing, counted by transmission electron microscopy. Of the 2,569 amphibole EMPs with chemical composition, 69% were cummingtonite-grunerite and 30% were actinolite. Tremolite and hornblende were each less than 1%. The 160 chrysotile EMPs were excluded from further analysis.
• Main results:
  • Of the 12,928 EMPs in the samples, 6,175 (48%) had diffraction patterns consistent with amphibole minerals.
  • Of the 12,928 recorded EMPs, 31 had an aspect ratio below 3:1.
  • Only 7.3% of the 12,765 non-chrysotile EMPs were longer than 5 µm (with aspect ratio of 3:1 or more).
  • The average ambient air concentration of NIOSH-countable amphibole EMPs (longer than 5 µm) was 0.000387 EMP per cubic centimeter.
  • Only 48 (0.8%) of the amphibole EMPs had dimensions the authors described as commonly reported in amphibole asbestos: length over 5 µm, width under 1.5 µm, and aspect ratio of 20:1 or more.
  • Few amphibole EMPs met size definitions linked to asbestos cancer potency. The text gives 4 for Lippmann (2014), 4 for Stanton et al. (1981) and 13 for Berman and Crump (2003). Table I instead lists 10 for Stanton et al. and 4 for each of Lippmann's two definitions.
  • 6,075 (98%) of the 6,175 amphibole EMPs had aspect ratios of 20:1 or less. The authors described this size profile as consistent with a population of cleavage fragments.
  • The authors converted the NIOSH occupational limit into a 70-year continuous community limit of 0.0029 EMP per cubic centimeter. The 0.000387 average was about 7.5 times lower than this limit.
  • After adjusting for sampling duration and frequency, the authors estimated a continuous exposure concentration for community members of 0.000129 EMP per cubic centimeter.
  • From 2006 to 2018, rolling annual average concentrations of amphibole EMPs longer than 5 µm ranged from 0.000016 to 0.00077 EMP per cubic centimeter.
• The authors' conclusion: The authors concluded that, based on their integration of evidence, any increased risk of mesothelioma and/or lung cancer to Silver Bay residents from potential exposure to cleavage fragments longer than 5 µm emitted during taconite ore processing is vanishingly small and may be zero.
• Limitations the authors state:
  • No epidemiological studies of community members were available to evaluate cancer risks from ambient EMP exposure related to taconite mining.
  • Data on individual particles were not available for 2005.
  • The laboratory did not record features of asbestos needed to classify particles as ASTM Class 1 'asbestiform'.
  • The counting method used (MDH Method 852) cannot tell asbestiform fibers from cleavage fragments of the same mineral on a particle-by-particle basis.

Topics

Medical terms in this study, explained in our Lexicon: elongate mineral particles (EMPs), Taconite, Aspect Ratio (Length-to-diameter ratio), NIOSH, Amphibole Group, Mesothelioma, Lung Cancer, Iron Range.

Related studies

• The epidemiologic evidence for elongate mineral particle (EMP)-related human cancer risk — P. Boffetta, K.A. Mundt, et al. (2018)
• Non-asbestiform elongate mineral particles and mesothelioma risk: Human and experimental evidence — J.E. Goodman, M.J. Becich, et al. (2023)
• A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans — D.H. Garabrant, S.T. Pastula (2018)
• Dosimetry of inhaled elongate mineral particles in the respiratory tract: The impact of shape factor — B. Asgharian, T.P. Owen, et al. (2018)
• Measurement of elongate mineral particles: What we should measure and how do we do it? — E.J. Chatfield (2018)
• 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)

Browse more research in Risk Analysis, or return to medical research.