title: The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry.
abstract: 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 μm in length and 0.2-0.5 μm in width. Therefore, the current standard NIOSH Method 7400, which only counts EMP >5 μm 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.].
authors: a Division of Environmental Health Sciences, School of Public Health, University of Minnesota , Minneapolis , Minnesota.
authors: Jooyeon
authors: J
authors: Hwang
authors: Gurumurthy
authors: G
authors: Ramachandran
authors: Peter C
authors: PC
authors: Raynor
authors: Bruce H
authors: BH
authors: Alexander
authors: Jeffrey H
authors: JH
authors: Mandel
mesh_terms: D000395:Air Pollutants, Occupational / Q000032:analysis* / Q000737:chemistry; D017636:Asbestos, Amphibole / Q000032:analysis / Q000737:chemistry; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D019570:Inhalation Exposure / Q000032:analysis*; D007501:Iron; D016014:Linear Models; D008906:Mining; D008910:Minnesota; D016273:Occupational Exposure / Q000032:analysis*; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis* / Q000737:chemistry; D017640:Silicates
chemical_list: D000395:Air Pollutants, Occupational; D017636:Asbestos, Amphibole; D052638:Particulate Matter; D017640:Silicates; C026703:taconite; D007501:Iron
keywords: NIOSH 7400; elongate mineral particles (EMP); size-based definitions for EMP exposures; taconite