Investigation on the durability of man-made vitreous fibers in rat lungs

Our plain-English summary of Investigation on the durability of man-made vitreous fibers in rat lungs, by B. Bellmann, H. Muhle, O. Kamstrup, et al (Environmental Health Perspectives, 1994).

The study

• Authors: B. Bellmann, H. Muhle, O. Kamstrup, U.F. Draeger
• Journal: Environmental Health Perspectives
• Published: 1994;102 Suppl 5(Suppl 5):185-9
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Two types of sized stonewool with median lengths of 6.7 and 10.1 microns and median diameters of 0.63 and 0.85 microns, and crocidolite with fibers of median length of 4.8 microns and median diameter of 0.18 microns were instilled intratracheally into female Wistar rats. A single dose of 2 mg in 0.3 ml saline was used for the stonewool samples and 0.1 mg in 0.3 ml saline for crocidolite. The evenness of distribution of fibers in the lung was checked by scanning electron microscopy (SEM). Five animals per group were sacrificed after 2 days, 1, 3, 6, and 12 months. After low-temperature ashing of the lungs about 200 fibers per animal were analyzed by SEM for length and diameter. The number and mass of fibers in the total lung were calculated. For the stonewool samples the decrease in the number of fibers in the lung ash followed approximately first order kinetics resulting in half-times of 90 and 120 days. The analysis of fiber number and diameter of different length fractions was used to estimate the contribution of three processes of fiber elimination: transport by macrophages for short fibers, breakage of fibers, and dissolution of fibers. (The process of transport by macrophages was found fastest for fibers with length < 2.5 microns). For the elimination of critical fibers with length > 5 microns, the breakage and dissolution were the most important processes. The breakage of fibers was predominant for one of the stonewool samples. The preferential type of the mechanism of fiber elimination is dependent on chemical composition and size distribution.

In plain English

In this animal experiment, female Wistar rats received one dose of one of three materials into the windpipe. Two were stonewools at 2 mg: MMVF21, a commercial basalt-based stonewool, and stonewool HT, modified with more alumina. Crocidolite asbestos (0.1 mg) was a comparison expected to be highly durable. Five rats per group were killed at intervals up to 12 months; fibers in their ashed lungs were counted and measured by electron microscopy. Based on fiber numbers, lung half-times were 111 days for stonewool HT (95% confidence limits 98 to 127), 257 for MMVF21 (195 to 376) and 665 for crocidolite (320, with no finite upper limit). Fibers longer than 40 micrometres broke in the lung for all three materials. Thicker MMVF21 fibers were probably reduced by dissolution; some stonewool HT fibers showed corrosion. The authors concluded that breakage and dissolution were both important reasons for the drop in the number of critical fibers longer than 5 micrometres, and that elimination was fastest for stonewool HT and slowest for crocidolite. The article's abstract gives different stonewool half-times (90 and 120 days).

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 (single intratracheal instillation in rats, with lungs examined at set times afterwards)
• Who was studied: Female Wistar rats weighing about 200 g. Five animals per group were killed at each time point: for the stonewool groups at 2 days, 2 weeks, 1, 3, 6 and 12 months (the tables show no 2-week data), and for crocidolite at 2 days, 6 and 12 months.
• Exposure: The test fibers were a basalt-based stonewool (MMVF21) and stonewool HT fiber (a modified stonewool with increased alumina content), each at 2 mg in 0.3 ml saline. A special preparation of UICC crocidolite with an increased fraction of long fibers was given at 0.1 mg in 0.3 ml saline as a positive control. Median fiber lengths were 6.7, 10.1 and 4.8 micrometres, and median diameters were 0.63, 0.85 and 0.18 micrometres, for MMVF21, stonewool HT and crocidolite respectively.
• Main results:
  • Fiber elimination followed approximately first-order kinetics. Half-times calculated from fiber numbers were 665 days for crocidolite (95% confidence limits 320 days to an upper limit printed as infinity), 257 days for MMVF21 (195 to 376) and 111 days for stonewool HT (98 to 127).
  • Mean fibers per lung for MMVF21 fell from 124.1 million at 2 days to 50.8 million at 12 months.
  • Mean fibers per lung for stonewool HT fell from 40.2 million at 2 days to 4.5 million at 12 months.
  • Mean fibers per lung for crocidolite were 197.5 million at 2 days, 99.9 million at 6 months and 135.2 million at 12 months.
  • The size distribution of fibers in the lung did not change significantly up to 12 months, except that stonewool HT fibers shifted toward thicker diameters over time.
  • For crocidolite, the authors interpreted the faster loss of the longest fibers as breakage in the lung.
  • For crocidolite, fibers thicker than 0.2 micrometres stayed constant in number from 6 to 12 months, which the authors took as a sign of high durability.
  • For MMVF21, fibers longer than 20 micrometres were eliminated fastest, which the authors attributed to breakage.
  • For MMVF21, from 3 to 12 months fibers thicker than 1.25 micrometres were eliminated significantly faster than thinner ones, probably due to dissolution.
  • For stonewool HT, all length fractions over 10 micrometres were eliminated relatively fast, with the highest elimination rate in the thinner diameter fractions.
  • For stonewool HT, electron microscopy showed some fibers with uneven diameter due to corrosion.
• The authors' conclusion: The authors concluded that breakage of fibers longer than 40 micrometres was common to MMVF21, stonewool HT and crocidolite. They concluded that both breakage and dissolution are important reasons for the decrease in the number of critical fibers longer than 5 micrometres. They found that the overall elimination rate increased in the order crocidolite, MMVF21, stonewool HT, even though mean fiber diameter also increased in that order.

Topics

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

Medical terms in this study, explained in our Lexicon: Vitreous, Crocidolite, Scanning Electron Microscopy (SEM), Low-Temperature Ashing, Macrophage.

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