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Description of key information

The only relevant exposure route is considered to be via inhalation. In case the substance is swalloved it is expected to pass through the body unaltered, due to the low solubility. The substance is not able to pass the dermal barrier. The toxic effect of the substance is by mechanical irritation only, which can lead to increased pulmonary macrophages at high exposure concentrations. 
It was concluded from the key study, that inhalation of FMMVF fibres give rise to increased pulmonary macrophages as well as any other inert/inorganic particulate is expected to do. The effect from FMMVF fibres were of a reversible nature, when exposure was ceased. Occasional bronchoalveolar neoplasms were found in all dose groups, including the negative control. No mesotheliomas were observed in the fibre exposed animals, thus there is no statistical evidence for a carcinogenic effect.
whereas it is expected that the mechanical effect of the fibres will have minor effect under low dose exposure conditions due to the clearance capacity of the lungs.

Key value for chemical safety assessment

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Dose descriptor:
NOAEC
30 mg/m³
Study duration:
chronic
Species:
rat

Additional information

In the selected key study, by McConnell et al 1994 it was concluded that there was no significant evidence for a carcinogenic effect by the fibers investigated. The experimental setup, long-term inhalation with rats is considered the most relevant for the evaluation of possible adverse effects for humans.

In the disregarded study by McConnell et al 1999 a single mesothelioma was found in one animal out of 250 exposed to FMMVF fibres. This study was performed on Hamster. A workshop panel under IARC concluded in 2001 that for long-term assessment of fibrosis and/or carcinogenic effect, only studies on rats should be evaluated. Therefore the study was disregarded as inappropriate for the evaluation of the possible adverse effects of FMMVF fibres on humans.


Repeated dose toxicity: inhalation - systemic effects (target organ) respiratory: lung

Justification for classification or non-classification

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