Accumulation of ingested asbestos fibers in rat tissues over time

Our plain-English summary of Accumulation of ingested asbestos fibers in rat tissues over time, by K. Patel-Mandlik, J. Millette (Environmental Health Perspectives, 1983).

The study

• Authors: K. Patel-Mandlik, J. Millette
• Journal: Environmental Health Perspectives
• Published: 1983;53:197-200
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

With the use of the transmission electron microscope, asbestos fibers have been assessed in kidney cortex of four groups of rats previously exposed to intermediate-range feeding grade chrysotile asbestos. Newborn rats, from mothers gavaged with asbestos during pregnancy, were gavaged twice a week at the dose level of 50 mg/kg beginning at age day 7 until their natural death or sacrifice. The rats were divided into four groups by age: 0-200, 200-400, 400-600 and 600-800 days. Of the 20 rats comprising the four test groups, 17 were positive, average fiber recovery being 5.34 X 10(3)/mg dry weight. Average fiber level in control tissues was 0.23 X 10(3)/mg dry weight. Fiber recovery in tissues from control animals was shown to be significantly lower (p less than 0.005) than that from test tissues. Test groups showed highly significant differences (p less than 0.005) from each other in the fiber levels. Dose-response relationship was not significant (0.05 less than p less than 0.1). The length distribution and the alterations in morphology of the recovered fibers are described. This study is consistent with the passage of chrysotile asbestos across the gastrointestinal wall.

In plain English

In this animal experiment, the authors used transmission electron microscopy to count chrysotile asbestos fibers in rat kidney cortex. Rats whose mothers were gavaged (fed by stomach tube) with asbestos during pregnancy were themselves gavaged with feeding-grade chrysotile twice a week at 50 mg per kg from day 7. They examined 20 exposed rats, five in each of four age-at-death groups (0-200, 200-400, 400-600 and 600-800 days), plus four controls. Fibers were found in 17 of the 20. Exposed rats averaged 5.34 x 10^3 fibers per mg dry weight, significantly more than controls (0.23 x 10^3; p less than 0.005). Levels were highest at 400-600 days and lowest at 0-200 days. No straight-line relationship with cumulative dose was found. For Class A, B and C fibers combined, a curved relationship reached p less than 0.08, counted as significant only because the authors accepted p values below 0.1; Class A and B fibers alone showed none. The authors concluded the study was consistent with chrysotile passing across the gastrointestinal wall. They noted that the fiber classes rested on their personal judgment.

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: long-term (chronic) gavage study in rats, with kidney tissue examined by transmission electron microscopy
• Who was studied: Sprague-Dawley rats taken from an unpublished carcinogenicity study. Rats that died of natural causes between ages 0 and 800 days were sorted into four age-at-death groups. Kidney tissue came from 20 randomly selected exposed rats (five per age group) and 4 control rats (one per age group).
• Exposure: Feeding-grade intermediate-range chrysotile asbestos (Environmental Health Sciences Sample No. 109C). Mothers were gavaged during pregnancy. Pups were gavaged twice a week at 50 mg per kg body weight from day 7 until death, so older rats had received a larger cumulative dose.
• Main results:
  • Chrysotile fibers were found in the kidney cortex of 17 of the 20 exposed rats.
  • Average fiber level: 5.34 x 10^3 fibers per mg dry weight in exposed rats and 0.23 x 10^3 per mg dry weight in control rats. The Results section gives the control figure as 0.2 x 10^3.
  • Fiber levels in control rats were significantly lower than in exposed rats (p less than 0.005).
  • Among exposed rats, Class A+B+C fiber levels were highest in the 400-600 day group (9.63 plus or minus 4.1 x 10^3 per mg dry weight) and lowest in the 0-200 day group (1.57 plus or minus 1.4 x 10^3 per mg dry weight), per Table 1.
  • No linear relationship was found between cumulative dose (age) and fiber count. For Class A+B+C fibers, a quadratic (rise then fall) relationship reached p less than 0.08. The authors called this significant only by accepting p values below 0.1. The article's own abstract calls the dose-response relationship not significant (0.05 less than p less than 0.1).
  • No dose relationship was observed when only Class A+B fibers were counted.
  • Fiber lengths in exposed rats ranged from 0.08 to 5.71 micrometres, with group medians from 0.23 to 0.46 micrometres. Shorter fibers outnumbered longer ones: on average 77.4% of Class A+B fibers were 0-0.5 micrometres long (Table 2).
  • Bundles and clusters of fibrils were found in all age groups and made up 25.8% of total fibers.
• The authors' conclusion: The authors concluded the study was consistent with chrysotile asbestos passing across the gastrointestinal wall. In the Discussion they wrote that finding fibers in the kidney cortex of gavaged rats shows that migration occurs.
• Limitations the authors state:
  • Fibers were sorted into Classes A, B, C and D using the authors' personal judgment of how the fibers looked.
  • Microprobe analysis, which would have been more precise, could not be used.
  • Fiber diameter could not be meaningfully measured, because some degraded fibers were swollen or lacked sharp edges.
  • Degraded fibers may not all have been identifiable, so the authors considered the counts conservative. Mass concentration was not computed.
  • The clumping of fibrils into bundles and clusters might have been caused by the preparation procedure.
  • The analysis of one rat's lung and omentum was too limited to say anything about fiber retention in those organs.
  • The health significance of the many short fibers retained is not known.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Dose-response relationship.

Related studies

• Collagen accumulation over time in the murine lung after exposure to crocidolite asbestos or Libby amphibole — A.M. Smartt, M. Brezinski, et al. (2010)
• Transmigration of ingested asbestos — M.E. Meek (1983)
• Ingested mineral fibers. Do they penetrate tissue or cause cancer? — P. Gross, R.A. Harley, et al. (1974)
• Review of published studies on gut penetration by ingested asbestos fibers — P.M. Cook (1983)
• Quantitative assessment of chrysotile fibrils in the bloodstream of rats which have ingested the mineral under different dietary conditions — M. Weinzweig, R.J. Richards (1983)
• Ingested mineral fibers: elimination in human urine — P.M. Cook, G.F. Olson (1979)

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