For definition of Groups, see Preamble Evaluation.
VOL.: 68 (1997) (p. 283)
Chem. Abstr. Name: Wollastonite
Wollastonite is a calcium silicate mineral that occurs naturally in deposits in several areas of the world. Wollastonite has been mined in commercial quantities since the 1950s and its production is increasing with its use as a replacement for asbestos. Wollastonite breaks down during processing (crushing and grinding) into fibres of varying aspect ratios. High-aspect ratio wollastonite is used mainly as an asbestos replacement in construction and insulation board and automotive friction products, and in plastics and rubber. Powdered (milled) wollastonite, including small amounts of synthetic wollastonite, is used mainly in ceramics (the major current application of wollastonite) and in metallurgy. Occupational exposure to wollastonite occurs during its mining, milling, production and use.
5.2 Human carcinogenicity data
In the only available small cohort mortality study of workers in a wollastonite quarry, the observed numbers of deaths from all cancers combined and lung cancer were lower than expected.
5.3 Animal carcinogenicity data
Wollastonite was tested for carcinogenicity in an inhalation study in rats. No increase in tumour incidence was observed, but the number of fibres with a length > 5 mm and a diameter <3 mm was relatively low (about 54 fibres/mL). Therefore, this study has only a limited value for an evaluation of carcinogenicity.
Four grades of wollastonite of different fibre sizes were tested for carcinogenicity in one experiment in rats by intrapleural implantation. There was no information on the purity of the four samples used. A slight increase in the incidence of pleural sarcomas was observed with three grades, all of which contained fibres greater than 4 mm in length and less than 0.5 mm in diameter. Pleural sarcomas were not observed after implantation of the grade that contained relatively few fibres with these dimensions.
In two studies by intraperitoneal injection in rats using two samples of wollastonite (one from India and one of unspecified origin with median fibre lengths of 8.1 mm and 5.6 mm, respectively), no intra-abdominal tumours were found.
5.4 Other relevant data
Evidence from wollastonite miners suggests that occupational exposure can cause impaired respiratory function and pneumoconiosis. However, animal studies have demonstrated that wollastonite fibres have low biopersistence and induce a transient inflammatory response compared to various forms of asbestos. A two-year inhalation study in rats at one dose showed no significant inflammation or fibrosis.
A sample of wollastonite from China produced morphological transformation of Syrian hamster embryo cells. A sample of wollastonite from Québec, Canada, induced polyploidy but not chromosomal aberrations in cultured Chinese hamster lung cells.
There is inadequate evidence in humans for the carcinogenicity of wollastonite.
There is inadequate evidence in experimental animals for the carcinogenicity of wollastonite.
Wollastonite cannot be classified as to its carcinogenicity to humans (Group 3).
For definition of the italicized terms, see Preamble Evaluation
Previous evaluation: Suppl. 7 (1997) (p. 377)
See Also: Toxicological Abbreviations