Detection of Erionite and Other Zeolite Fibers in Soil by the Fluidized Bed Preparation Methodology

Our plain-English summary of Detection of Erionite and Other Zeolite Fibers in Soil by the Fluidized Bed Preparation Methodology, by D. Berry, J. Januch, L. Woodbury, et al (The Microscope, 2019).

The study

• Authors: D. Berry, J. Januch, L. Woodbury, D. Kent
• Journal: The Microscope
• Published: 2019;67(4):147-158
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

Erionite is a zeolite mineral that can occur as fibrous particles in soil. Inhalation exposure to erionite fibers may result in increased risk of diseases, such as mesothelioma. Low level detection of mineral fibers in soils has traditionally been accomplished using polarized light microscopy (PLM) methods to analyze bulk samples providing detection limits of around 0.25% by weight. This detection level may not be sufficiently low enough for protection of human health and is subject to large variability between laboratories. The fluidized bed asbestos segregator (FBAS) soil preparation method uses air elutriation to separate mineral fibers, such as erionite, from soil particles with higher aerodynamic diameter and deposits those mineral fibers onto filters that can be quantitatively analyzed by microscopic techniques, such as transmission electron microscopy (TEM). In this study, performance evaluation (PE) standards of erionite in soil with nominal concentrations ranging from 0.1% to 0.0001% by weight were prepared using the FBAS soil preparation method and the resulting filters were analyzed by TEM. The analytical results of this study illustrate a linear relationship between the nominal concentration of erionite (as % by weight) in the PE standard and the concentration estimated by TEM analysis expressed as erionite structures per gram of test material (s/g). A method detection limit of 0.003% by weight was achieved, which is approximately 100 times lower than typical detection limits for soils by PLM. The FBAS soil preparation method was also used to evaluate authentic field soil samples to better estimate the concentrations of erionite in soils on a weight percent basis. This study demonstrates the FBAS preparation method, which has already been shown to reliably detect low levels of asbestos in soil, can also be used to quantify low levels of erionite in soil.

In plain English

This laboratory study tested whether the fluidized bed asbestos segregator (FBAS), a soil preparation method, could detect erionite, a fibrous zeolite, in soil. It did not study people or disease. The authors mixed Rome, Oregon erionite into Arvada, Colorado test soil at known levels of 0.1%, 0.01%, 0.001% and 0.0001% by weight. The FBAS uses air to lift fibers from soil onto filters, which were examined by transmission electron microscopy. Measured and known levels were approximately linear. However, only about 20% of the added erionite was recovered at levels of 0.001% or higher, and repeat filters varied. Defining the detection limit as the level detected 80% of the time, which the authors called arbitrary, the limit was about 0.003%, versus about 0.25% for polarized light microscopy. Using the erionite standards, the authors estimated about 0.005% for Dunn County, North Dakota road gravel and 0.28% for Montana quarry gravel near Custer National Forest. Dunn County fibers included erionite and offretite, but the Montana fibers were identified as offretite. The authors concluded the method worked for both prepared standards and field samples.

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: Laboratory method evaluation (performance evaluation study) of a soil preparation method followed by transmission electron microscopy; no human or animal subjects
• Who was studied: Performance evaluation standards made from 50 g of Arvada, Colorado test soil spiked with erionite at four nominal levels, with five filter replicates per standard. Also archived field soil samples collected by the USEPA in 2008: two gravel samples from unpaved roads in Dunn County, North Dakota (DCRD-10, DCRD-16) and one from a gravel quarry near Custer National Forest, Montana (Custer-1), with three filter replicates each.
• Exposure: Erionite obtained in May 2008 from federal land outside Rome, Oregon, processed to a specimen averaging 87% to 90% erionite. The field samples contained erionite and offretite (zeolite fibers). No asbestos was tested in this study.
• Main results:
  • Measured concentrations in the performance evaluation standards were approximately linear with the known concentrations: R2 of 0.72 for individual samples and 0.93 for group means
  • Recovery was about 20% for the standards at nominal levels of 0.001% or higher; reported concentrations were consistently low
  • Within-laboratory coefficients of variation ranged from 0.35 to 1.49 and were higher at lower nominal levels
  • Defining the detection limit as the level detected with 80% probability (an arbitrary choice), the method detection limit was about 0.003% by weight
  • This detection limit was well below typical polarized light microscopy limits: about 0.25% by point counting and less than 1% by visual area estimation
  • Field samples: Dunn County road samples had 8E+04 to 2E+05 structures per gram; the Custer National Forest quarry sample had 8E+06 structures per gram
  • Using the linear model built from the erionite standards, the authors estimated about 0.005% for the Dunn County road samples and about 0.28% for the Custer National Forest quarry sample, which they reported as erionite concentrations; the Custer fibers were identified as offretite
  • The method detected erionite fibers in soil that polarized light microscopy had reported as non-detect (Dunn County sample DCRD-16)
  • Of eight structures whose diffraction patterns could be indexed, four of five from the Rome standards were erionite; the fifth Rome structure and all three Dunn County and Custer structures were offretite
  • Both erionite and offretite were identified in the Dunn County samples; fibers in the Custer National Forest quarry sample were identified as offretite
  • Fiber size distributions from FBAS-prepared Dunn County soil were generally similar to those in air samples collected during activity-based sampling on Dunn County roads
• The authors' conclusion: The authors concluded that the FBAS preparation method works for both spiked standards and authentic field samples for detecting erionite fibers, with a detection limit much lower than conventional techniques. They also suggested it provides useful data to inform risk managers on locations where human exposure has the potential to be higher.
• Limitations the authors state:
  • Recovery was low: only a fraction of the erionite added to the standards was captured on the filter
  • Results varied between replicate filters, more so at lower concentrations, mainly because of low structure counts
  • Precision was much worse for results reported as mass percent than as structures per gram
  • Fiber mass was only roughly approximated by assuming a rectangular solid shape
  • Electron beam damage to zeolite fibers made it difficult to capture diffraction patterns
  • The 80% detection probability used to define the detection limit was an arbitrary choice

Topics

Medical terms in this study, explained in our Lexicon: erionite, Zeolite, Mesothelioma, Mineral Fiber, Polarized Light Microscopy (PLM), Transmission Electron Microscopy (TEM).

Related studies

• A total sample preparation method for the measurement of airborne asbestos and other fibers by optical and electron microscopy — N. Kohyama, S. Kurimori (1996)
• CT findings in malignant pleural mesothelioma related to nonoccupational exposure to asbestos and fibrous zeolite (erionite) — C. Erzen, M. Eryilmaz, et al. (1991)
• Global geological occurrence and character of the carcinogenic zeolite mineral, erionite: A review — J.P. Patel, M.S. Brook, et al. (2022)
• Preparation of extrapulmonary tissues and body fluids for quantitative transmission electron microscope analysis of asbestos and other mineral particle concentrations — P.M. Cook (1979)
• Technical note: improved methodology for analyses of acid detergent fiber and acid detergent lignin — E. Raffrenato, M.E. Van Amburgh (2011)
• Airborne fiber control in buildings during asbestos material removal by amended water methodology — R.N. Sawyer, A.N. Rohl, et al. (1985)

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