Investigation of the biodurability of wollastonite and xonotlite

Our plain-English summary of Investigation of the biodurability of wollastonite and xonotlite, by B. Bellmann, H. Muhle (Environmental Health Perspectives, 1994).

The study

• Authors: B. Bellmann, H. Muhle
• Journal: Environmental Health Perspectives
• Published: 1994;102 Suppl 5(Suppl 5):191-5
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The in vivo durability of wollastonite materials, coated and uncoated, and of xonotlite was tested. Wollastonite is an anhydrous natural silicate and xonotlite is a hydrated synthetic calcium silicate. UICC crocidolite was used as a positive control with high durability. Using a dry-sizing technique, fractions from the stock materials were prepared according to the definition of "thoracic particulate mass" and "respirable particulate mass" of the American Conference of Governmental Industrial Hygienists. Fibers were instilled intratracheally into female Wistar rats, and the evenness of their distribution in the lung was checked by scanning electron microscopy (SEM). After serial sacrifices at 2 and 14 days, 1, 3, and 6 months, and low temperature ashing of the lung, the fibers were analyzed by SEM. The number and size distribution of fibers were investigated. The total number of crocidolite fibers decreased with a half-time of 240 days, but the number of fibers > 5 microns in length was unchanged after 6 months. The elimination kinetics of wollastonite fibers from the lung were relatively fast, with half-times of 15 to 21 days. The coating of wollastonite in Wollastocoat had no effect on this elimination process. For the thoracic fraction of wollastonite, the elimination from the lung was as fast as for the respirable particulate fraction. The elimination kinetics of xonotlite from the lung was very fast. This material consisted of single crystals of acicular morphology with a median length of 1.3 micron and of agglomerates of these crystals. More than 99% of single crystals and about 85 to 89% of the agglomerates were already eliminated 2 days after instillation.

In plain English

This animal experiment tested how long wollastonite and xonotlite stayed in rat lungs. Wollastonite, a natural calcium silicate, was tested uncoated and coated; xonotlite is a synthetic calcium silicate. Durable UICC crocidolite served for comparison. Female Wistar rats each received one 2 mg dose into the windpipe. Groups of five were killed at intervals up to 6 months, and lung fibers were counted by electron microscopy. Wollastonite half-times were 15 to 21 days (15 to 24 across all measures). After six months, 0.02 to 0.5% remained of the wollastonite mass found in the lungs at 2 days (about 0.6 to 2 mg). The authors reported the coating had no effect, though the thoracic fraction of NYAD G Wollastocoat 2075 had a significantly longer half-time, 21 days. Crocidolite's total fiber count had a half-time of 236 days (95% confidence limits 146 to 613), based on only two sacrifice dates; its fibers over 5 micrometres were unchanged at 6 months. Over 99% of xonotlite single crystals were gone after 2 days. The authors concluded that wollastonite cleared mainly by dissolution, and xonotlite faster still.

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: biodurability (lung clearance) study using intratracheal instillation in rats, with serial sacrifices
• Who was studied: Female Wistar rats of about 200 g body weight, five animals per group, at the Fraunhofer Institute of Toxicology and Aerosol Research, Hannover, Germany. Wollastonite and xonotlite groups were sacrificed at 2 days, 2 weeks, 1, 3 and 6 months. Crocidolite groups were sacrificed at 2 days and 6 months. The paper was presented at a September 1992 workshop.
• Exposure: A single dose of 2 mg of fibers in 0.3 ml salt solution, instilled into the trachea. Materials tested were thoracic and alveolar (respirable) size fractions of wollastonite (NYAD G, NYAD 1250, and the surface-modified NYAD G Wollastocoat 1001 and 2075) and of xonotlite (Promaxon). UICC crocidolite was used as a positive control with high durability.
• Main results:
  • For all wollastonite test materials, calculated half-times were between 15 and 24 days. Based on number of fibers, they were 15 to 21 days.
  • For all wollastonite test materials, the initial mass found in the lung 2 days after instillation was approximately 0.6 to 2 mg, calculated from the shape and density of particles
  • Six months after instillation, the wollastonite mass remaining was 0.02 to 0.5% of the initial lung burden (the mass found in the lung at 2 days), not of the 2 mg dose
  • The authors reported that the Wollastocoat coating had no effect on elimination
  • The half-time for the thoracic fraction of NYAD G Wollastocoat 2075 was significantly higher, at 21 days. The authors suggested this could be related to its greater fiber diameter.
  • For wollastonite, elimination of the thoracic fraction was as fast as elimination of the respirable fraction
  • UICC crocidolite: the half-time based on total number of fibers was 236 days (95% confidence limits 146 to 613)
  • The crocidolite half-times were calculated from sacrifice dates at 2 days and 6 months only
  • The number of crocidolite fibers longer than 5 micrometres was unchanged during 6 months
  • Xonotlite: more than 99% of single crystals and about 85 to 89% of agglomerates were eliminated 2 days after instillation. Its elimination was at least one order of magnitude faster than that of wollastonite.
• The authors' conclusion: The authors concluded that elimination of wollastonite fibers from the lung followed first-order kinetics and was mainly due to dissolution, with half-times of 15 to 21 days. Xonotlite was eliminated even faster. They also concluded that the relatively fast dissolution of these calcium silicate materials should minimize health effects related to respired fibers.

Topics

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

Medical terms in this study, explained in our Lexicon: Wollastonite, Silicate, UICC, Crocidolite, Scanning Electron Microscopy (SEM), Single Crystal, Acicular.

Related studies

• Investigation on the durability of man-made vitreous fibers in rat lungs — B. Bellmann, H. Muhle, et al. (1994)
• Fibrogenic effect of wollastonite compared with asbestos dust and dusts containing quartz — M. Cambelová, A. Juck (1994)
• Pulmonary toxicity of wollastonite in vivo and in vitro — E. Tátrai, Z. Kováciková, et al. (2004)
• Genotoxicity of dimethylnitrosamine in the presence of chrysotile asbestos UICC B and xonotlite — F. Denizeau, M. Marion, et al. (1985)
• Red blood cell damage by wollastonite: in vitro study — M. Aslam, M.J. Arif, et al. (1995)
• Mesothelial cell proliferation and biopersistence of wollastonite and crocidolite asbestos fibers — J.L. Macdonald, A.B. Kane (1997)

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