Applying definitions of "asbestos" to environmental and "low-dose" exposure levels and health effects, particularly malignant mesothelioma

Our plain-English summary of Applying definitions of "asbestos" to environmental and "low-dose" exposure levels and health effects, particularly malignant mesothelioma, by B.W. Case, J.L. Abraham, G. Meeker, et al (Journal of Toxicology and Environmental Health. Part B, Critical Reviews, 2011).

The study

• Authors: B.W. Case, J.L. Abraham, G. Meeker, F.D. Pooley, K.E. Pinkerton
• Journal: Journal of Toxicology and Environmental Health. Part B, Critical Reviews
• Published: 2011;14(1-4):3-39
• Type of article: Review
• Cited by: 82 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Although asbestos research has been ongoing for decades, this increased knowledge has not led to consensus in many areas of the field. Two such areas of controversy include the specific definitions of asbestos, and limitations in understanding exposure-response relationships for various asbestos types and exposure levels and disease. This document reviews the current regulatory and mineralogical definitions and how variability in these definitions has led to difficulties in the discussion and comparison of both experimental laboratory and human epidemiological studies for asbestos. This review also examines the issues of exposure measurement in both animal and human studies, and discusses the impact of these issues on determination of cause for asbestos-related diseases. Limitations include the lack of detailed characterization and limited quantification of the fibers in most studies. Associated data gaps and research needs are also enumerated in this review.

In plain English

This was a review prepared for a U.S. National Institute of Environmental Health Sciences workshop on asbestos; it reported no new data. The authors reviewed regulatory and mineralogical definitions of asbestos, covering chrysotile, a serpentine mineral, and the amphiboles crocidolite, amosite, anthophyllite asbestos, tremolite asbestos and actinolite asbestos. They noted that the two kinds of definition sometimes contradict one another. In their view, animal inhalation studies have been less effective in understanding low-level exposure, and all human studies are imperfect. They stated that environmental exposure is not always low-level, and that the environmental and household mesothelioma studies they had just described were all in high-exposure areas. Citing NIOSH county data for residents aged 15 and over in 2000–2004, they noted that Jefferson Parish, Louisiana, had 75 mesothelioma deaths over that period, an age-adjusted rate of 42.1 per million per year; 34.7% were women. The authors concluded that extrapolating risk from high to low exposure is fraught with uncertainty and that risk assessment must rest on detailed fiber characterization. They noted that most studies lacked such characterization.

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: Narrative state-of-the-science review prepared for an NIEHS workshop; no new data collected
• Who was studied: Published literature on asbestos definitions, exposure measurement in animal and human studies, and environmental and "low-dose" exposures and disease, particularly malignant mesothelioma
• Exposure: The six regulated asbestos minerals: chrysotile, crocidolite (riebeckite asbestos), amosite (cummingtonite-grunerite asbestos), anthophyllite asbestos, tremolite asbestos and actinolite asbestos. Other elongate minerals such as erionite and balangeroite were also discussed. Exposure settings covered naturally occurring asbestos, legacy exposures from former industrial sites, and household exposures.
• Main results:
  • The most commonly used regulatory definitions (e.g., OSHA, NIOSH, WHO) count structures longer than 5 µm with an aspect ratio of 3:1 (sometimes 5:1).
  • The authors stated that regulatory definitions evolved for practical analytical reasons. As a result, they may include particle categories that do not cause health effects or exclude some that do.
  • The authors noted that regulatory and mineralogical definitions of asbestos sometimes contradict one another.
  • The authors stated that animal inhalation studies have been less effective in understanding the impact of low-level fiber exposure.
  • Human studies vary in how thoroughly they characterize and quantify fibers. The authors stated that all are imperfect.
  • For tissue (lung) fiber burden studies, the authors described it as now generally accepted that laboratories may produce internally consistent results. Results from different laboratories should not be directly compared.
  • The authors stated that environmental exposure is not always low-level. The degree of exposure depends on disturbance of the source by human activity or natural events.
  • The authors described environmental and household mesothelioma outbreak studies, such as tremolite outbreaks and crocidolite outbreaks near mines and asbestos plants. They stated that all of these studies were performed in areas of high exposure, and that household exposures are difficult to separate from environmental ones in them.
  • The county rates in the NIOSH table reproduced in the review were age-adjusted death rates per million per year, for ages 15 years or over, over the most recent 5 years (2000–2004 per the cited NIOSH source). In three Minnesota taconite-mining counties, 44 of 46 cases were male.
  • Jefferson Parish, Louisiana, had 75 mesothelioma deaths over that 5-year period. This was an age-adjusted rate of 42.1 deaths per million per year, and 34.7% of the deaths were female.
• The authors' conclusion: The authors concluded that extrapolating from high to low exposure is fraught with uncertainty, whether it uses statistical (e.g., linear no-threshold) or mode-of-action-based models. They also concluded that assessing health risk from fibers must be based on detailed characterization of fiber lengths and diameters.
• Limitations the authors state:
  • Most studies in the reviewed literature lacked detailed characterization of fibers and quantified them only to a limited extent.
  • The list of community exposure studies discussed was not comprehensive and was not meant to be.
  • The section on environmental exposure excluded exposures in the built (indoor) environment, such as asbestos in buildings.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma.

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