Quantification of short and long asbestos fibers to assess asbestos exposure: a review of fiber size toxicity

Our plain-English summary of Quantification of short and long asbestos fibers to assess asbestos exposure: a review of fiber size toxicity, by G. Boulanger, P. Andujar, J.C. Pairon, et al (Environmental Health, 2014).

The study

• Authors: G. Boulanger, P. Andujar, J.C. Pairon, M.A. Billon-Galland, C. Dion, P. Dumortier, P. Brochard, A. Sobaszek, P. Bartsch, C. Paris, M.C. Jaurand
• Journal: Environmental Health
• Published: 2014;13:59
• Type of article: Review
• Cited by: 113 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The fibrogenicity and carcinogenicity of asbestos fibers are dependent on several fiber parameters including fiber dimensions. Based on the WHO (World Health Organization) definition, the current regulations focalise on long asbestos fibers (LAF) (Length: L ≥ 5 μm, Diameter: D < 3 μm and L/D ratio > 3). However air samples contain short asbestos fibers (SAF) (L < 5 μm). In a recent study we found that several air samples collected in buildings with asbestos containing materials (ACM) were composed only of SAF, sometimes in a concentration of ≥10 fibers.L-1. This exhaustive review focuses on available information from peer-review publications on the size-dependent pathogenetic effects of asbestos fibers reported in experimental in vivo and in vitro studies. In the literature, the findings that SAF are less pathogenic than LAF are based on experiments where a cut-off of 5 μm was generally made to differentiate short from long asbestos fibers. Nevertheless, the value of 5 μm as the limit for length is not based on scientific evidence, but is a limit for comparative analyses. From this review, it is clear that the pathogenicity of SAF cannot be completely ruled out, especially in high exposure situations. Therefore, the presence of SAF in air samples appears as an indicator of the degradation of ACM and inclusion of their systematic search should be considered in the regulation. Measurement of these fibers in air samples will then make it possible to identify pollution and anticipate health risk.

In plain English

This French expert working group's review covered human, animal and cell studies of fiber size and harm. It also re-analysed earlier air samples by electron microscopy. Regulators count only fibers at least 5 micrometers long, under 3 micrometers wide and over three times longer than wide; shorter such fibers were called short asbestos fibers (SAF). Of 105 asbestos-positive indoor samples from Paris-area public buildings (1997 to 2004), 40 held only SAF. The average SAF share ranged from 70% to 96% by material. Chrysotile was the main type found. In 192 samples from 7 industrial sectors, SAF averaged 16.3 fibers per milliliter. Reviewed experiments found short fibers less active than long ones, though at high doses they could cause inflammation, lung fibrosis and pleural reactions. Reviewed human studies linked short, thin fibers with lung cancer, but since exposures to different sizes were correlated, a specific role for short fibers could not be determined. The authors concluded SAF toxicity cannot be dismissed and both short and long fibers in air samples should be considered. The buildings were not representative of all French buildings.

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: Review of epidemiological, animal and cell-culture literature on fiber size and asbestos toxicity, combined with original re-analysis by transmission electron microscopy (TEM) of previously collected air samples, carried out within an ANSES expert working group
• Who was studied: Re-analysed air samples: 105 indoor samples from 64 public buildings in the Paris area (1997 to 2004); 115 outdoor samples from the Ile de France area (1993 to 1995); 192 occupational samples representative of 7 industrial sectors, first analysed by phase contrast microscopy at IRSST (Québec) between 1990 and 2006, then re-analysed by TEM. The literature reviewed covered human, animal (mainly rats, mice, hamsters, monkeys) and cell studies.
• Exposure: Short asbestos fibers (SAF: length under 5 micrometers, diameter under 3 micrometers, length-to-diameter ratio above 3) compared with long asbestos fibers (LAF: length 5 micrometers or more, with the same diameter and ratio limits). Mainly chrysotile in the air samples, with some amphibole, mainly amosite. The reviewed studies used chrysotile, crocidolite, amosite, anthophyllite and tremolite.
• Main results:
  • Indoor public-building samples: of 105 samples positive for asbestos, 40 contained only SAF, sometimes in concentrations above 10 fibers per liter.
  • Indoor samples: concentrations reached up to 630.9 fibers per liter for SAF and 16.3 fibers per liter for WHO (regulatory) fibers.
  • Indoor samples: the average percentage of SAF among total fibers ranged from 70% (sprayed asbestos) to 96% (asbestos cement). Mean SAF concentrations ranged from 91 fibers per liter (heat insulation) to 0.9 fibers per liter (asbestos cement).
  • Indoor samples: chrysotile was present in more than 90% of positive samples.
  • Outdoor Ile de France samples (115): only chrysotile was found. Median and maximum concentrations were 0.12 and 0.47 fibers per liter for fibers longer than 5 micrometers, and 0.32 and 2.73 fibers per liter for SAF.
  • Occupational samples (192, from 7 industrial sectors, originally analysed by IRSST, Québec, and re-analysed by TEM): average and maximum concentrations were 16.3 and 505.2 fibers per milliliter for SAF.
  • From the reviewed experimental studies: SAF were less active than LAF, but SAF in high doses could cause inflammation, interstitial pulmonary fibrosis and pleural reactions.
  • From the reviewed human data: exposure to longer fibers was associated with higher lung cancer rates, but no definite conclusion could be drawn for the other size classes.
  • From the reviewed recent human studies: exposure to short, thin fibers was associated with lung cancer risk, and these fibers were the majority of those counted by TEM.
  • The authors stated that it cannot yet be determined whether this association of short fibers with lung cancer reflects correlations among fiber-size categories or a specific role of short fibers in carcinogenesis.
  • From the reviewed animal biopersistence studies: results conflicted, showing either shorter or longer biopersistence of SAF compared with LAF.
• The authors' conclusion: The authors concluded that the toxicity of SAF cannot be dismissed. They also concluded that both LAF and SAF in air samples should be taken into consideration, and that SAF may indicate degradation of asbestos-containing materials.
• Limitations the authors state:
  • The buildings sampled were not representative of all French buildings.
  • Samples of short fibers used in experiments are hard to prepare and usually contain a small percentage of long fibers.
  • Uncertainties in the epidemiological data did not allow a formal conclusion about whether SAF have a low carcinogenic effect or none.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Fiber Dimensions.

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