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EC number: 604-314-4
CAS number: 142844-00-6
Overload effects at 30mg/m3 – together with various problems specifically associated with the hamster study – casts considerable doubt on the validity of the positive results obtained in these studies
Table 1 - Summary of exposure and results for the rat high dose
Number of Animals at risk
Concentration of Non-fibrous particles <3µm diameter
(mean no. of particles/ml)
Aerosol fibre dimensions
Geometric mean (GSD)
"After service" Kaolin
This study was designed to test the toxicity and
carcinogenicity of RCF at extreme conditions, but the experimental
exposure exceeded any meaningful maximum tolerated dose (lung burden).
The material under discussion is classified as a category 2 carcinogen
under DSD (1B under CLP), largely on the basis of the experiments
reported in this section. However, the positive results obtained at
30mg/m3 in both rats and hamsters were from somewhat unreliable studies,
and self classification would lead to classification as 3 under DSD and
2 under CLP.
There are reports of injection studies with relevant materials that may
be somewhat informative. For example, Miller BG, Searl A, Davis JMG,
Donaldson K, Cullen RT, Buchanan D and Soutar CA (1999) Influence of
fibre length, dissolution and biopersistence on the production of
mesothelioma in the rat peritoneal cavity.Ann Occup Hyg43(3):155-166)
reported that, in IP studies, the same RCF1 sample used in the lifetime
inhalation studies was no more potent than rockwool, while RCF4 (a
heated ‘after service’ fibre sample) produced no tumours at all.
studies suffer from the assumption that 30mg/m3was a maximum
tolerated dose. Later studies have indicated that this dose level was in
fact around five times the true MTD. The presence of many non-fibrous
particles in the RCF samples was also a key problem. (See:Mast,
R.W. et al. (2000) A retrospective review of the carcinogenicity of
refractory ceramic fiber in two chronic Fischer 344 rat inhalation
studies: An assessment of the MTD and implications for risk assessment.
Inhalation Toxicology, 12, 1141–1172;andBellmann,
B. et al (2001) Effects
of nonfibrous particles on ceramic fiber (RCF1) toxicity in rats.
Inhalation Toxicology, 13, 877-901).
In German regulation, the results of intraperitoneal injection studies
are used to classify fibrous dusts. Unfortunately we have no access to
the full audited reports on the studies used in the German deliberations
and therefore have not included any of those results here.
Carcinogenicity: via inhalation route (target organ): respiratory:
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