Citation:

Eames, A. AND D. Vallero. Elongated Mineral Particulate Sampling and Analysis to Support Iron Range Community Exposure Estimates: Assessing Methodological Uncertainties. 2019 ASTM Michael E. Beard Conference, Denver, CO, April 04 - 05, 2019.

Impact/Purpose:

Presented at the 2019 ASTM Michael E. Beard Conference: Sampling, Analysis, Management of Asbestos, and other Microscopic Particles.

Description:

The EPA is considering elongated mineral particulates (EMP) measurements to augment the results of ongoing particulate matter (PM) monitoring and the recently completed occupational work conducted during the Minnesota Taconite Workers Study, which included epidemiological evidence of mesothelioma and other adverse health outcomes. Currently EMP sampling is the same as traditional asbestos methods, but the counting rules are modified to include all particles with an aspect ratio >3:1. Recently, Activity Based Sampling (ABS) with air filters as personal monitoring devices has been the gold standard for airborne PM exposure sampling. EMP air filters are analyzed by transmission electron microscopy (TEM), phase contrast microscopy (PCM) or scanning electronic microscopy (SEM). SEM can be useful in characterizing a single EMP, but has generally not been used in asbestos analysis in asbestos analysis due to its intermediate resolution, but recent improvements have allowed detection of fibrils; however contrast with background may be poor for some EMPs, especially if a high contrast substrate is not used (NIOSH). Often PCM is utilized because it is cheaper than TEM, and the analyzed substance is generally more well characterized beforehand (i.e. buildings, asbestos mine sites, etc.). In contrast, EMP can be composed of a variety of unknown minerals, and therefore TEM analysis is recommended. TEM is paired with energy-dispersive spectroscopy (EDS) and energy-dispersive X-ray analysis (EDXA) to identify mineral composition, which is important when thinking about toxicity of EMP. For soils, a sample is collected and analyzed by polarizing light microscopy (PLM) or TEM. There are a variety of methods associated with these. One problem is a lack of homogeneity in soil samples- incremental sampling methods are being investigated to deal with this. Although TEM has a higher magnification and the method is preferable for toxicity estimates, other than re-analysis, no independent method is yet available to assess accuracy of the results. The uncertainty for taconite EMP exposure estimates is greater than for its subclass, asbestos. In vivo studies have been conducted on taconite EMP are limited for but a few constituencies, e.g. ferroactinolite and grunerite by Cook et al. (2016). In vivo studies have shown that EMP acid leaching results in an increased dose over time. Mineral composition of an EMP varies substantially by location, making representativeness difficult for large areas in the Iron Range. The lack of taconite EMP exposure data from the 1950s and 1960s increases the uncertainty of linkages between taconite EMP and mesothelioma, which has a long latency period. ABS in the Iron Range is missing, which could otherwise be used to calculate exposures from data on the release of fibers from soil into the breathing zone; noting that ABS results from other areas, e.g. Libby, will differ substantially from the taconite exposures. Indoor exposure data is also unavailable. This discussion is intended to receive comments and advice on next steps needed in the sampling, analysis and quality assurance documents, currently under development.

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