Investigation of the Biodurability of Wollastonite and Xonotlite

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 pm 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 pm 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. -Environ Health Perspect 102 (Suppl 5):191-195 (1994)

A Review of the Toxicology and Epidemiology of Wollastonite

“…These surface-treated wollastonites have not been studied extensively. However, Bellmann and Muhle (1994) have studied the biopersistence of surface-treated wollastonite (WOLLASTOCOAT 1001 and 1005, NYCO Minerals) and found that these materials had half-times similar to those of the untreated materials also tested (NYAD G and NYAD 1250)-all samples tested cleared rapidly (half-times between 18 and 22 days). In view of the critical role of biopersistence in fiber toxicity, this study is noteworthy and demonstrates that these coatings (at least at the concentrations typically used) would not have an impact on the pathogenicity of wollastonite.…”

“…Among the fibers tested, only xonotlite [Ca 6 Si 6 O 17 (OH) 2 ] had a more rapid elimination time (<2 days). Bellmann and Muhle (1994) concluded that "The relatively fast dissolution of the test materials, which are all composed of a calcium silicate base, should minimize the health effects related to respired fibers" (p. 194). They also concluded "The coating of wollastonite in Wollastocoat had no effect on the elimination process" (p. 191).…”

Mesothelial Cell Proliferation and Biopersistence of Wollastonite and Crocidolite Asbestos Fibers

“…This stock of crocidolite asbestos fibers induced malignant mesotheliomas after weekly intraperitoneal injections in 40-50% of mice (Kane and Macdonald, 1993). The size distribution of NYAD 1250 was described previously (Bellmann and Muhle, 1994).…”

Comparative Investigations of the Biodurability of Mineral Fibers in the Rat Lung

“…Usually 200 fibers per animal were analyzed for size distribution. Further details are presented elsewhere (17).…”