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Carcinogenicity

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Description of key information

The two selected inhalation studies were both performed on rats, that is considered to be the most relevant model for the evaluation of inhalation toxicity to humans, as the lungs of rats closely resemble the human lung.
The result from the studies show no significant carcinogenic potential for FMMVF fibres, thus it can be concluded that there is limited evidence of carcinogenic potential.
A Life-time inhalation study on rats, conclude that there is no statistical evidence for carcinogenicity of FMMVF fibers.
The other study with 12 month exposure and 12 month recovery, indicated that exposure to FMMVF can induce fibrosis at very high exposure concentrations. Also some, 10.5% of the animals exposed developed adenomas, but no mesotheliomas were observed in the exposed animals. It is concluded that FMMVF fibers did not induce carcinogenesis.

Key value for chemical safety assessment

Carcinogenicity: via inhalation route

Endpoint conclusion
Dose descriptor:
NOAEC
30 mg/m³

Justification for classification or non-classification

In the two selected studies on carcinogenicity, no significant evidence could be demonstrated. Both studies were chronic toxicity studies and therefore relevant for the evaluation of potential adverse effects on human health. A NOAEL for carcinogenesis was established on the basis of the data in McConnell et al. therefore FMMVF fibres can be considered a possible carcinogen with a threshold of concern, that is above the tested highest dose 30 mg per m3, corresponding to 243 WHO fibres per cm3.

Additional information

The fibre types tested in the two selected studies complies with the definiton of FMMVF fibres. The experimental setup, chronic inhalation animal model is considered the most relevant laboratory model for evaluating the potential risk of airborne fibres to human health. Also the experimental animal, rat is considered the most relevant animal for evaluating the potential risk of airborne fibres to human health.

In McConnell et al 1994, it was concluded from the study that in very high doses the MMVF 21 and MMVF 22 fibers give rise to increase in pulmonary macrophages as well as could be expected from exposure to any other inert/inorganic particulate, but in a reversible manner, when exposure is ceased. Occasional bronchoalveolar neoplasms were found in all dose groups, including the unexposed control. No mesotheliomas were observed in the fiber exposed groups, consequently there was no statistical evidence for a carcinogenic effects of the two fiber types studied.

The Cullen et al 2000 study came to similar conclusions as McConnell et al. Animals exposed to 100/475 fibers at 4 times the exposure concentration as in McConnell, had a slightly higher level of fibrosis, than did unexposed control animals, although it was not statistically significant. The 100/475 fiber did not induce any carcinomas or mesotheliomas. Adenomas were present in 4 out of 38 animals , corresponding to 10.5%, compared to 1 out of 38, corresponding to 2.6% in unexposed control. The study therefore shows that FMMVF fibers possibly can induce development of fibrosis and adenomas at very high exposure concentrations, but there is no significant evidence for tumor development following inhalation exposure to the fibers.


Carcinogenicity: via inhalation route (target organ): respiratory: lung

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