The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry

Jooyeon Hwang, Gurumurthy Ramachandran, Peter C Raynor, Bruce H Alexander, Jeffrey H. Mandel

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Different dimensions of elongate mineral particles (EMP) have been proposed as being relevant to respiratory health end-points such as mesothelioma and lung cancer. In this article, a methodology for converting personal EMP exposures measured using the National Institute for Occupational Safety and Health (NIOSH) 7400/7402 methods to exposures based on other size-based definitions has been proposed and illustrated. Area monitoring for EMP in the taconite mines in Minnesota's Mesabi Iron Range was conducted using a Micro Orifice Uniform Deposit Impactor (MOUDI) size-fractionating sampler. EMP on stages of the MOUDI were counted and sized according to each EMP definition using an indirect-transfer transmission electron microscopy (ISO Method 13794). EMP were identified using energy-dispersive X-ray and electron diffraction analysis. Conversion factors between the EMP counts based on different definitions were estimated using (1) a linear regression model across all locations and (2) a location-specific ratio of the count based on each EMP definition to the NIOSH 7400/7402 count. The highest fractions of EMP concentrations were found for EMP that were 1-3 m in length and 0.2-0.5 m in width. Therefore, the current standard NIOSH Method 7400, which only counts EMP >5 m in length and ≥ 3 in aspect ratio, may underestimate amphibole EMP exposures. At the same time, there was a high degree of correlation between the exposures estimated according to the different size-based metrics. Therefore, the various dimensional definitions probably do not result in different dose-response relationships in epidemiological analyses. Given the high degree of correlation between the various metrics, a result consistent with prior research, a more reasonable metric might be the measurement of all EMP irrespective of size.[Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: figures detailing EMP concentration.]

Original languageEnglish (US)
Pages (from-to)613-624
Number of pages12
JournalJournal of occupational and environmental hygiene
Issue number9
StatePublished - Sep 2 2014


  • NIOSH 7400
  • elongate mineral particles (EMP)
  • sizebased definitions for EMP exposures
  • taconite


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