Assessment of asbestos body formation by high resolution FEG-SEM after exposure of Sprague-Dawley rats to chrysotile, crocidolite, or erionite

Our plain-English summary of Assessment of asbestos body formation by high resolution FEG-SEM after exposure of Sprague-Dawley rats to chrysotile, crocidolite, or erionite, by N.B. Gandolfi, A.F. Gualtieri, S. Pollastri, et al (Journal of Hazardous Materials, 2016).

The study

• Authors: N.B. Gandolfi, A.F. Gualtieri, S. Pollastri, E. Tibaldi, F. Belpoggi
• Journal: Journal of Hazardous Materials
• Published: 2016;306:95-104
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This work presents a comparative FEG-SEM study of the morphological and chemical characteristics of both asbestos bodies and fibres found in the tissues of Sprague-Dawley rats subjected to intraperitoneal or intrapleural injection of UICC chrysotile, UICC crocidolite and erionite from Jersey, Nevada (USA), with monitoring up to 3 years after exposure. Due to unequal dosing based on number of fibres per mass for chrysotile with respect to crocidolite and erionite, excessive fibre burden and fibre aggregation during injection that especially for chrysotile would likely not represent what humans would be exposed to, caution must be taken in extrapolating our results based on instillation in experimental animals to human inhalation. Notwithstanding, the results of this study may help to better understand the mechanism of formation of asbestos bodies. For chrysotile and crocidolite, asbestos bodies are systematically formed on long asbestos fibres. The number of coated fibres is only 3.3% in chrysotile inoculated tissues. In UICC crocidolite, Mg, Si, and Fe are associated with the fibres whereas Fe, P and Ca are associated with the coating. Even for crocidolite, most of the observed fibres are uncoated as coated fibres are about 5.7%. Asbestos bodies do not form on erionite fibres. The crystal habit, crystallinity and chemistry of all fibre species do not change with contact time, with the exception of chrysotile which shows signs of leaching of Mg. A model for the formation of asbestos bodies from mineral fibres is postulated. Because the three fibre species show limited signs of dissolution in the tissue, they cannot act as source of elements (primarily Fe, P and Ca) promoting nucleation and growth of asbestos bodies. Hence, the limited number of coated fibres should be due to the lack of nutrients or organic nature.

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In plain English

This animal study used high-resolution electron microscopy (FEG-SEM) and Raman spectroscopy to examine fibres and asbestos bodies (fibres coated with a deposit) in archived tissue slides from male and female Sprague-Dawley rats. In an earlier cancer-testing project, the rats had received a single 25 mg injection of UICC chrysotile, UICC crocidolite or erionite from Jersey, Nevada into the pleural or peritoneal space, and were monitored for up to 3 years. Asbestos bodies appeared on chrysotile and crocidolite fibres in less than 40 weeks, mainly on long fibres. None formed on the short erionite fibres at any time. Of the fibres observed in the tissues, 3.3% of chrysotile fibres and 5.7% of crocidolite fibres were coated. Expressed as a ratio of coated to uncoated fibres, these figures were 3.4% and 6.0%. Fibre crystallinity was preserved over time, but chrysotile showed signs of magnesium leaching. As part of a model they postulated, the authors stated their belief that few fibres were coated because nutrients from ferritin in phagocytes or blood plasma were limited. They cautioned that injected doses and fibre clumping may not reflect human inhalation.

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: Animal experiment: microscopy study of archived histological slides from a past long-term carcinogenicity bioassay in rats
• Who was studied: Male and female Sprague-Dawley rats given intraperitoneal or intrapleural injections and monitored up to 3 years after exposure. The number of rats is not stated in the text provided. The original bioassay was conducted by the Ramazzini institute in Bentivoglio, Bologna, Italy.
• Exposure: A single 25 mg injection of UICC chrysotile, UICC crocidolite or erionite from Jersey, Nevada (USA). The calculated number of fibres per 25 mg was 3.2 × 10^9 for chrysotile, 1.0 × 10^9 for crocidolite and 5.9 × 10^9 for erionite.
• Main results:
  • Asbestos bodies appeared in chrysotile- and crocidolite-injected tissues in less than 40 weeks but did not form on erionite fibres.
  • In erionite-injected tissues, no asbestos bodies were observed in any sample at any contact time.
  • In chrysotile-injected tissues, uncoated fibres were found in all examined samples, and 3.3% of the observed fibres were coated.
  • In crocidolite-injected tissues, most of the observed fibres were uncoated, and 5.7% were coated.
  • The ratio of coated to uncoated fibres was 3.4% for chrysotile and 6.0% for crocidolite. These are ratios to uncoated fibres, not percentages of all observed fibres.
  • The average size of chrysotile fibres that could produce asbestos bodies was 29.6 micrometres long and 0.5 micrometres in diameter.
  • The average size of crocidolite fibres that could produce asbestos bodies was 41.0 micrometres long and 0.86 micrometres in diameter.
  • For UICC crocidolite, magnesium, silicon and iron were associated with the fibres, while iron, phosphorus and calcium were associated with the coating.
  • For chrysotile fibres, the silicon-to-magnesium ratio rose with contact time: 1.49 in standard UICC chrysotile, 1.50 at 71 weeks, 2.09 at 80 weeks and 3.90 at 128 weeks. The authors attribute this to in vivo leaching.
  • Raman spectra showed that the crystallinity of most chrysotile fibres was preserved.
  • No correlation was found between the iron content of the fibres and the number of coated fibres.
  • The authors saw no noteworthy differences between asbestos bodies formed in the pleural and the peritoneal cavity.
• The authors' conclusion: The authors concluded that asbestos bodies do not form on very short fibres but nucleate on fibres longer than 10 micrometres. As part of a model they postulated, they stated their belief that the small number of coated fibres is due to the limited source of nutrients provided by ferritin from phagocytes or circulating in plasma.
• Limitations the authors state:
  • Fibre burdens from injection into the pleural or peritoneal space may be excessive or unreliable compared with inhalation by rats or humans.
  • Dosing was unequal in terms of number of fibres per mass for chrysotile compared with crocidolite and erionite.
  • Fibres may have clumped together during instillation.
  • The original injection study was done 26 years earlier. The injected fibres were not counted before injection, and the fibre numbers were calculated theoretically, so inaccuracies are possible.
  • Counts of coated versus uncoated fibres may be biased by the excessive fibre burden from instillation.
  • The apparent link between fibre iron content and asbestos body size had poor statistical significance because of the limited number of observations.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Body Formation, Chrysotile, Crocidolite, erionite, Asbestos Bodies, UICC, Habit.

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