Chrysotile asbestos in a California recreational area

Our plain-English summary of Chrysotile asbestos in a California recreational area, by W.C. Cooper, J. Murchio, W. Popendorf, et al (Science, 1979).

The study

• Authors: W.C. Cooper, J. Murchio, W. Popendorf, H.R. Wenk
• Journal: Science
• Published: 1979;206(4419):685-8
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004996).

Abstract

Dustfall along roads and trails being used recreationally in the Clear Creek area of San Benito County, California, located in the New Idria serpentinite, was found to be 90 percent or more chrysotile asbestos. Personal samplers worn by motorcyclists using one of the trails showed concentrations of airborne fibers ranging from 0.3 to 5.3 fibers per milliliter, according to methods prescribed for monitoring occupational exposures. The present workplace standard for brief exposures to asbestos is 10 fibers per milliliter; 5 fibers per milliliter is the proposed standard. The average total dust concentration estimated from personal samplers was approximately 20 milligrams per cubic meter of roughly 90 percent chrysotile. To our knowledge, this is the first demonstration of asbestos exposures of this magnitude, in size ranges known to be pathogenic, resulting from natural deposits not associated with mining, milling, or industrial use.

In plain English

This 1979 report measured chrysotile asbestos at the Clear Creek recreational area, federal land in San Benito County, California, on the naturally asbestos-bearing New Idria serpentine body. In 1978 the authors sampled settled dust near roads and trails. They also took personal air samples from six motorcycle riders and a patrolling ranger, and from one fixed site. Electron microscopy of five dustfall samples showed that more than 90 percent of the particles were chrysotile fibers. The text gives the riders' airborne fibers longer than 5 micrometers as 0.3 to 5.3 fibers per milliliter, though one table value reads 5.6. Total dust reached 61 milligrams per cubic meter. Many values were not far below the then-current workplace ceiling of 10 fibers per milliliter for 15 minutes, and two exceeded the proposed ceiling of 5. The authors concluded that the fibers could be hazardous if inhaled over long periods. They doubted that intermittent visitors had yet inhaled enough to pose a measurable risk, but admitted this could not be documented. They said sustained or frequently repeated exposures at such concentrations, especially by children, did not seem justifiable.

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: Environmental field measurement study: dustfall sampling plus personal breathing-zone air sampling, analyzed by light and electron microscopy and x-ray diffraction
• Who was studied: The Clear Creek recreational area (Bureau of Land Management land, San Benito County, California), sampled in spring and summer 1978. Dustfall was collected in 10 cans near the main road and side trails. Air samplers were worn by six motorcycle riders on three runs on 18 June 1978 and by one ranger on patrol, and one was placed at a fixed site. The area had 41,150 users in 1975, about 85 percent of them off-road vehicle operators.
• Exposure: Naturally occurring chrysotile asbestos in the New Idria serpentinite, raised as dust by vehicles (mainly motorcycles) on roads and trails. The authors state that the area is not affected by mining.
• Main results:
  • Dustfall in the four containers nearest the road ranged from 35 to 90 g/m2 per month. It was 22 and 23 g/m2 per month along two motorcycle trails, and 2 to 6 g/m2 per month in containers 15 to 150 m from the road.
  • Electron microscopy of five dustfall samples showed that more than 90 percent of the particles were fibrous, with the form and diffraction pattern of chrysotile.
  • The text states that airborne fibers longer than 5 micrometers on the personal samplers ranged from 0.3 to 5.3 fibers per milliliter, counted by the occupational light-microscopy method.
  • Table 1 as scanned lists 5.6 fibers per milliliter for run 1, rider position 2. This is above the 5.3 maximum stated in the text.
  • Compared with OSHA ceiling standards (current: 10 fibers per milliliter for a 15-minute period; proposed: 5 fibers per milliliter), many rider values were not far below the current ceiling, and two exceeded the proposed ceiling.
  • Total dust mass concentrations at Clear Creek were as high as 61 mg/m3.
  • The ranger's sampler, worn during a 47-minute patrol along about 5 km of road, showed 0.4 fibers per milliliter and 1.7 mg/m3 total dust.
  • Electron microscopy showed large numbers of fibers shorter than 5 micrometers, and chunks of chrysotile were not counted by light microscopy. The authors said this suggested total fiber exposures appreciably greater than the light-microscope counts.
• The authors' conclusion: The authors concluded that this was the first instance they knew of where naturally occurring airborne asbestos reached levels comparable to the workplace, and that the fibers could be hazardous if inhaled over long periods. They doubted that intermittent users had so far inhaled enough to constitute a measurable risk. They said that sustained or frequently repetitive exposures to such concentrations, especially by children, did not seem justifiable, and that restrictions or other protective measures should be considered.
• Limitations the authors state:
  • The sampling filter's intake was not matched to vehicle speed (not isokinetic), though the authors argue that breathing through the nose and mouth is similarly mismatched.
  • Chrysotile chunks in the respirable size range were not counted by light microscopy because of their shape.
  • Fiber count categories could not be added together, because the disease-causing potential of fibers shorter than 5 micrometers is not well established.
  • The authors' view that intermittent users so far face no measurable risk cannot be documented by epidemiological evidence.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, New Idria, Serpentinite, Occupational Exposure, Asbestos Exposure.

Related studies

• Additional comments on the study of the effect of population density on the results of the California Bay area study — P.M. Conforti (1983)
• Acid leaching studies of chrysotile asbestos from mines in the Coalinga region of California and from Quebec and British Columbia — A. Morgan (1997)
• Polymorphism of glutathione S-transferase M1 and lung cancer risk among African-Americans and Caucasians in Los Angeles County, California — S.J. London, A.K. Daly, et al. (1995)
• Residential proximity to naturally occurring asbestos and mesothelioma risk in California — X.L. Pan, H.W. Day, et al. (2005)
• Mortality among California highway workers — N. Maizlish, J. Beaumont, et al. (1988)
• A task-based assessment of parental occupational exposure to organic solvents and other compounds and the risk of childhood leukemia in California — C. Metayer, G. Scelo, et al. (2016)

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