Comparison of soil sampling and analytical methods for asbestos at the Sumas Mountain Asbestos Site-Working towards a toolbox for better assessment

Our plain-English summary of Comparison of soil sampling and analytical methods for asbestos at the Sumas Mountain Asbestos Site-Working towards a toolbox for better assessment, by J. Wroble, T. Frederick, A. Frame, et al (PloS One, 2017).

The study

• Authors: J. Wroble, T. Frederick, A. Frame, D. Vallero
• Journal: PloS One
• Published: 2017;12(7):e0180210
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Established soil sampling methods for asbestos are inadequate to support risk assessment and risk-based decision making at Superfund sites due to difficulties in detecting asbestos at low concentrations and difficulty in extrapolating soil concentrations to air concentrations. Environmental Protection Agency (EPA)'s Office of Land and Emergency Management (OLEM) currently recommends the rigorous process of Activity Based Sampling (ABS) to characterize site exposures. The purpose of this study was to compare three soil analytical methods and two soil sampling methods to determine whether one method, or combination of methods, would yield more reliable soil asbestos data than other methods. Samples were collected using both traditional discrete ("grab") samples and incremental sampling methodology (ISM). Analyses were conducted using polarized light microscopy (PLM), transmission electron microscopy (TEM) methods or a combination of these two methods. Data show that the fluidized bed asbestos segregator (FBAS) followed by TEM analysis could detect asbestos at locations that were not detected using other analytical methods; however, this method exhibited high relative standard deviations, indicating the results may be more variable than other soil asbestos methods. The comparison of samples collected using ISM versus discrete techniques for asbestos resulted in no clear conclusions regarding preferred sampling method. However, analytical results for metals clearly showed that measured concentrations in ISM samples were less variable than discrete samples.

In plain English

This field study, by EPA authors, compared two ways of collecting soil at the Sumas Mountain Asbestos site: traditional discrete ("grab") samples and incremental sampling (ISM). It also compared three laboratory methods for measuring asbestos: CARB 435, ASTM D7521, and a fluidized bed asbestos segregator (FBAS) followed by electron microscopy. In autumn 2014, samples came from five areas on one Whatcom County property beside Swift Creek, where the asbestos is mostly naturally occurring chrysotile. Two of the five areas had elevated asbestos. The FBAS method found asbestos in nearly every sample, including where other methods found none, but its results varied the most. Variability in asbestos results did not differ significantly between ISM and grab samples, although ISM metal results were less variable. Asbestos was positively correlated with several metals, including magnesium and nickel. Asbestos was not detected in most activity-based (breathing-zone) air samples, possibly because of humid weather and vegetation, which limited soil-to-air comparisons. The authors concluded that the study did not identify a combination of methods giving reproducible soil asbestos data, though FBAS was the most sensitive method available.

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: Field comparison of soil sampling methods (incremental sampling versus discrete grab samples) and laboratory analytical methods for asbestos, with metals analysis and activity-based air sampling
• Who was studied: Soil from five decision units on a single Whatcom County-owned property next to Swift Creek at the Sumas Mountain Asbestos site. Field work took place the week of September 29, 2014. In each decision unit, five discrete samples and three ISM samples were collected, not counting quality-assurance duplicates.
• Exposure: Naturally occurring asbestos, mostly chrysotile, with a small percentage of actinolite fibers in some samples. The asbestos came from landslide material and from dredged creek sediments placed on the property.
• Main results:
  • Two of the five decision units (DUs 4 and 5) had elevated asbestos concentrations. The other three (DUs 1 to 3) had low concentrations.
  • Compared with the other methods, samples prepared by FBAS showed the greatest variability. However, the FBAS method identified asbestos in samples where the other methods did not.
  • In DUs 1 to 3, the ASTM D7521 method detected no asbestos by light microscopy. Electron microscopy of the fine fraction of these samples showed very low levels.
  • Variability in asbestos concentrations did not differ significantly between ISM and discrete samples.
  • With the CARB 435 method, ISM samples had lower relative standard deviations than discrete samples in DUs 4 and 5, the units where asbestos was consistently detected. The authors suggested this combination may give more reproducible results when asbestos is above about 1%.
  • With the ASTM D7521 method, discrete samples had lower relative standard deviations than ISM samples in 4 of 6 comparisons.
  • For metals, only two of the sixty sample sets (12 metals across 5 decision units; 3.3%) had a lower relative standard deviation for discrete samples than for ISM samples.
  • FBAS asbestos concentrations were positively correlated with chromium, cobalt, iron, magnesium, manganese and nickel. They were negatively correlated with aluminum, barium, calcium, sodium and zinc.
  • In this study's data, a calcium-to-magnesium ratio between 0.01 and 0.03 went along with asbestos concentrations above 1%.
  • Air samples had many non-detects. 75% of activity-based PCME results were non-detects, which limited the ability to relate soil to air concentrations.
  • In a qualitative comparison, air asbestos concentrations were markedly lower for DUs 1 to 3 than for DUs 4 and 5, consistent with the soil results.
• The authors' conclusion: The authors concluded that the study did not achieve its goal of identifying a combination of sampling, preparation and analytical methods that would give reproducible soil asbestos data. They found FBAS followed by ISO 10312 electron microscopy to be the most sensitive method available.
• Limitations the authors state:
  • Asbestos was not detected in most activity-based air samples, possibly because of high humidity and abundant ground cover.
  • Thirty increments per ISM sample may have been too few to account for the variability of asbestos in soil.
  • The methods report results in different units that are not necessarily interconvertible, which limited quantitative comparison.
  • Soil preparation techniques were not the same for all subsamples, which may have introduced differing error or variability.
  • Direct comparisons at lower concentrations were not possible because of many non-detects.
  • Fiber types not associated with the site, such as certain amphiboles, were found in lower-concentration samples, possibly indicating contamination during sample preparation. The authors stated that blank samples showed no asbestos, ruling out laboratory contamination.

Topics

Medical terms in this study, explained in our Lexicon: Superfund, Polarized Light Microscopy (PLM), Transmission Electron Microscopy (TEM).

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