Evaluation of public and worker exposure due to naturally occurring asbestos in gravel discovered during a road construction project

Our plain-English summary of Evaluation of public and worker exposure due to naturally occurring asbestos in gravel discovered during a road construction project, by R.A. Perkins, J. Hargesheimer, L. Vaara (Journal of Occupational and Environmental Hygiene, 2008).

The study

• Authors: R.A. Perkins, J. Hargesheimer, L. Vaara
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2008;5(9):609-16
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

During a repair and reconstruction project of an unpaved highway in a remote region of Alaska, workers discovered, after construction had commenced, that the materials used from a local material site contained asbestos (variously described as tremolite or actinolite). The regional geology indicated the presence of ultramafic rock, which often contains asbestos. Evaluation of asbestos exposure to workers, their equipment, and living quarters was required, as was the possible future exposure of workers and the general public to asbestos already used in the roadway construction. In addition, a decision was needed on whether to use materials from the contaminated site in the future. Of the almost 700 breathing zone air monitoring samples taken of the workers, 3% of the samples indicated exposures at or near 0.1 f/cc by the National Institute for Occupational Safety and Health (NIOSH) 7400 phase contrast microscopy (PCM) procedure. Thirty-six of the PCM samples underwent transmission electron microscopy (TEM) analysis by the NIOSH 7402 procedure, which indicated that about 40% of the fibers were asbestos. After classifying samples by tasks performed by workers, analysis indicated that workers, such as road grader operators who ground or spread materials, had the highest exposures. Also, monitoring results indicated motorist exposure to be much less than 0.1 f/cc. The design phase of any proposed construction project in regions that contain ultramafic rock must consider the possibility of amphibole contamination of roadway materials, and budget for exploration and asbestos analysis of likely materials sites.

In plain English

This article described an asbestos exposure evaluation on a gravel road reconstruction project on Mileposts 90 to 111 of Alaska's Dalton Highway, begun in May 2000. Workers then found that gravel from a local material site (MS 105) contained naturally occurring asbestos, identified as tremolite or actinolite. Of 564 analyzed time-weighted average breathing-zone samples from road workers, 548 were below the OSHA limit of 0.1 fibers per cubic centimeter (f/cc). The authors stated that about 3% of worker exposures were near or above that limit. The highest, 0.59 f/cc, came from a grader operator. Of 36 worker samples also checked by electron microscopy, 24 could be compared, and in those, on average 40% of counted fibers were asbestos. Most dust samples from workers' RVs and equipment cabs had more than 100,000 asbestos structures per square centimeter. Motorists driving with windows open behind dusty vehicles had time-weighted averages of 0.049 f/cc. The authors concluded that road workers had measurable but low exposures, well below the limit for most tasks. They noted that gravel-site sample sizes were too small for firm conclusions.

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 exposure assessment of a single road construction project: bulk material sampling, settled dust sampling, and personal and area air monitoring
• Who was studied: Workers on a reconstruction project covering about 20 miles of the Dalton Highway, Alaska (Milepost 90 to 111), begun in May 2000. The study also covered their RV living quarters and equipment, and motorists, through 9 personal samples from drivers and 38 roadside area samples.
• Exposure: Naturally occurring amphibole asbestos (tremolite or actinolite) in gravel from material site MS 105, used in the roadway and in the camp gravel pad. Exposure came through tasks such as grading, water truck driving, culvert work, bulldozing and backhoe loading, and through driving on the road.
• Main results:
  • Road workers: of 564 time-weighted average (TWA) breathing-zone samples analyzed by phase contrast microscopy, 548 were below the 0.1 f/cc OSHA limit, and 177 of those were below the limit of detection.
  • Road workers: the authors stated that about 3% of personal exposures were near or above the permissible exposure limit. The 16 TWA samples above 0.1 f/cc averaged 0.18 f/cc (Table II).
  • The highest single exposure, 0.59 f/cc, was from a grader operator in the cab. Applying the average 40% asbestos fraction, the authors estimated 0.24 f/cc for this sample. Grader operators had 4 of 87 samples over 0.1 f/cc.
  • Of 36 worker air samples analyzed by both methods, 12 could not be compared. In the 24 that could be compared, phase contrast microscopy averaged 0.073 f/cc and electron microscopy averaged 0.026 f/cc. On average, 40% of fibers counted were asbestos, mostly identified as actinolite.
  • At MS 105, short (20 to 30 minute) bulldozer samples during start-up and ground-breaking measured 0.13 to 0.204 f/cc by phase contrast microscopy and 0.101 to 0.104 f/cc by electron microscopy. Backhoe samples were below the limit of detection. The authors stated several tasks would have exceeded the limit had they continued for 8 hours.
  • Settled dust: 14 of 15 living-area samples and 7 of 9 equipment-cab samples contained more than 100,000 asbestos structures per square centimeter, which the authors described as high contamination (93% and 77%). Traces of chrysotile in the dust suggested that not all contamination came from MS 105.
  • After decontamination, about half of the aggressive air clearance samples were below the limit of detection. The highest was 0.005 f/cc.
  • Bulk roadway gravel: 5 of 10 samples were negative, 4 had 0.1% tremolite, and 1 had 0.4% tremolite and 0.1% actinolite. Of 7 gravel pad samples, 6 were negative and 1 had a trace (less than 1%) of tremolite.
  • Motorists driving with windows open behind dust-raising vehicles (9 samples): two short-term samples exceeded 0.1 f/cc, and TWA samples averaged 0.049 f/cc. Roadside area samples were highest at MP 107 to 109.5, averaging 0.064 f/cc.
• The authors' conclusion: The authors concluded that the Dalton Highway reconstruction caused measurable asbestos exposures to road workers, but at low concentrations, well below the OSHA permissible exposure limit for most tasks. They noted that exposures might have been much higher had a rock crusher been used.
• Limitations the authors state:
  • Only one short sample was taken for each operation at MS 105, too few for firm conclusions.
  • There is no definitive method to convert settled dust concentrations into personal airborne exposure.
  • Laboratories were inconsistent in identifying the asbestos type as tremolite or actinolite.
  • Because asbestos may have been clumped in the gravel, bulk samples may not have represented the average asbestos content of the pad.
  • It was not known how much of the road was built from MS 105 material. Roadway samples were taken only from the surface.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Actinolite, Tremolite.

Medical terms in this study, explained in our Lexicon: naturally occurring asbestos (NOA), Tremolite, Actinolite, Ultramafic Rocks, Asbestos Exposure, Air Sampling, NIOSH, phase contrast microscopy (PCM).

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