Quantitative assessment of chrysotile fibrils in the bloodstream of rats which have ingested the mineral under different dietary conditions

Our plain-English summary of Quantitative assessment of chrysotile fibrils in the bloodstream of rats which have ingested the mineral under different dietary conditions, by M. Weinzweig, R.J. Richards (Environmental Research, 1983).

The study

• Authors: M. Weinzweig, R.J. Richards
• Journal: Environmental Research
• Published: 1983;31(2):245-55
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Samples of hepatic portal blood derived from control rats and from animals ingesting chrysotile asbestos were examined for the presence of mineral fibers. Only fibrils (97% less than 1 micron) were detected in the blood samples of both control and chrysotile-exposed rats. Total fibril counts per milliliter of blood revealed that in 6 out of 15 of the dietary experiments, the chrysotile-exposed groups had significantly higher counts than the equivalent controls. The actual quantity of chrysotile mineral (by counts or mass) which may be persorbed upon passage through the gastrointestinal tract and enter the blood stream is minute in comparison with the ingested dose.

In plain English

This was an animal experiment at University College, Cardiff. It asked whether chrysotile asbestos eaten in food can reach the bloodstream. Male rats were fed UICC chrysotile A, or a short-fiber "prepared" chrysotile sample, mixed into margarine. There were five feeding schedules, some with single doses and some after weeks of daily feeding. Each exposed rat had a matched control rat fed plain margarine. Blood from the hepatic portal vein, which drains the intestine, was taken 1 to 48 hours after feeding and examined by electron microscopy. Only very small fibrils were found, 97% under 1 micrometre long. They were present in the blood of every control rat as well as in exposed rats. Exposed groups had significantly higher counts than controls in 6 of the 15 feeding experiments, and five of these six were at 7 hours after eating. In one schedule, two exposed groups had significantly lower counts than controls. The authors concluded that minute quantities of chrysotile fibrils can enter the portal blood of some animals after ingestion. They added that this seemed independent of dose and fiber size and was not easy to reproduce. They said laboratory contamination could not be ruled out.

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 (rats fed chrysotile in their diet; blood examined by transmission electron microscopy)
• Who was studied: Male MRC-hooded rats aged 4 to 9 months, each test rat matched with a control rat, at University College, Cardiff, Wales. The total number of rats is not stated. The authors refer to 24 control animals examined (experiments 1 and 2), and the work ran over a period of 3 years.
• Exposure: UICC chrysotile A, or a "prepared" chrysotile sample with over 90% of fibers under 5 micrometres long, blended with 1 g of margarine. Five regimes were used: (1) 50 mg/day for 1 month then a single 50 mg dose; (2) a single 50 mg dose; (3) 50 mg/day for 1 month then single doses of 50, 30, 15 or 1 mg; (4) single doses of 50 mg, 1 mg, 10 micrograms or 0.1 micrograms of prepared chrysotile; (5) 10 micrograms of prepared chrysotile daily, then single doses of 50 mg, 1 mg or 10 micrograms. Controls were fed margarine only.
• Main results:
  • Only fibrils were found in the blood of both control and exposed rats. 75% were below 0.42 micrometres long and 97% were below 1 micrometre long.
  • Blood from every control rat contained asbestos fibrils, although controls were housed separately and no fibrils were detected in the drinking water.
  • Across all regimes, exposed groups had significantly higher fibril counts than controls in 6 of the 15 dietary experiments. A significant increase at 7 hours after ingestion was common to five of these six positive results.
  • Experiment 1 (rats given 50 mg/day chrysotile for 4 weeks before a final dose): counts were significantly different from controls at 1, 7, 12 and 24 hours (experiment 1a) and at 2, 7 and 24 hours (experiment 1b). At 7 hours the mean fibrils per grid opening were 52.2 (SD 20.1) in 1a and 49.7 (SD 20.4) in 1b, versus 6.1 (SD 7.5) and 5.8 (SD 3.0) in the matching controls.
  • Experiment 2 (single 50 mg dose of UICC chrysotile A, no prior exposure): counts were significantly different from controls only at 7 hours.
  • Experiment 3 (prior 50 mg/day, then final doses of 1 to 50 mg): only the 2- and 12-hour samples from the 30 mg group were significantly higher than controls. There was no significant increase at 7 hours and no increase with increasing dose.
  • Experiment 4 (single doses of prepared chrysotile, 0.1 micrograms to 50 mg): the only significant difference from controls was in rats given 1 mg, at 7 hours.
  • Experiment 5 (prior daily prepared chrysotile, then single doses): two exposed groups had significantly lower fibril counts than unexposed rats.
  • In recovery tests with known amounts of chrysotile added to blood, 65 to 70% of the fibrils were recovered by the processing method.
• The authors' conclusion: The authors concluded that minute quantities of chrysotile fibrils can enter the hepatic portal blood of some animals after natural ingestion. They said this seemed independent of ingested dose and original particle size and was not easy to reproduce. They described the amount, as a percentage of the ingested dose, as minute, and said the physiological consequences are unknown.
• Limitations the authors state:
  • Wide variation between experiments suggested inconsistencies in sample preparation.
  • Contamination of samples by the operator or from the air was considered quite possible, given the minute numbers detected and the fibrils found in control animals.
  • Variable airborne contamination in the laboratory over the 3-year period could not be excluded.
  • The quantity by weight of fibrils in the blood could not be estimated accurately.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Fibril, Mineral Fiber.

Related studies

• Pulmonary effects in rats inhaling size-separated chrysotile asbestos fibres or p-aramid fibrils: differences in cellular proliferative responses — D.B. Warheit, M.A. Hartsky, et al. (1996)
• Changes in numbers and dimensions of chrysotile asbestos fibers in lungs of rats following short-term exposure — V.L. Roggli, A.R. Brody (1984)
• Ingested mineral fibers. Do they penetrate tissue or cause cancer? — P. Gross, R.A. Harley, et al. (1974)
• Chronic effects of dietary exposure to amosite asbestos and tremolite in F344 rats — E.E. McConnell, H.A. Rutter, et al. (1983)
• An assessment of the fibrogenic potential of very short 4T30 chrysotile by intratracheal instillation in rats — I. Lemaire, D. Nadeau, et al. (1985)
• Experimental lung tumors following specific intrabronchial application of chrysotile asbestos. Longitudinal light and electron microscopic investigations in rats — E. Fasske (1988)

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