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Description of key information

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

Key value for chemical safety assessment

Carcinogenicity: via inhalation route

Link to relevant study records
carcinogenicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
6th June 1988 - 14th November 1990
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
The exposure chosen was believed to be a maximum tolerated dose (MTD) but subsequent studies demonstrated that the MTD was exceeded by at least 5 fold. The test substance used was heavily contaminated with particles not normally present in workplace atmospheres and these contributed to the overload. (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. Inhal. Toxicol. 12:1141–1172; and Bellmann, B. et al (2001) Effects of nonfibrous particles on ceramic fiber (RCF1) toxicity in rats. Inhalation Toxicology, 13, 877-901).
Reason / purpose for cross-reference:
reference to same study
according to guideline
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
GLP compliance:
yes (incl. QA statement)
Fischer 344
Details on test animals or test system and environmental conditions:
- Source: Charles River Kingston stone ridge NY
- Age at delivery: 8 weeks
- Weight at study initiation: 130-150g ( on receipt at lab)

- Housing: individual cages
- Diet : ad libitum pelleted standard Kliba 343
- Water : ad libitum Geneva domestic supply
- Acclimation period:18 days

- Temperature (°C): 20C+/- 3
- Humidity (%): 30-70%
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12hours

IN-LIFE DATES: From:June 1988 To: Oct 1992
Route of administration:
Type of inhalation exposure (if applicable):
nose only
Details on exposure:
As described in Bernstein DM, Thevenaz P, Fleissner H, Anderson R,Hesterberg TW, Mast R 1995 Evaluation of the oncogenic potential of man-made vitreous fibers: the inhalation model Ann Occup Hyg 1995; 39(5):661-72
The aerosol was generated by a brush disperser, fed with test material .Static was neutralised using a 63 nickel radiation source. The airflow to each animal was 1 litre /min calculated to be laminar. The animals were restrained in Battelle tubes.
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
Fibres were collected on membrane filters and quanitified by weighing and using microscopy, fibres lengths were measured using light microsopy and diameters using SEM.
Duration of treatment / exposure:
104 weeks followed by 23 weeks recovery (until survival >20%).Animals were removed from exposure at 13, 26, 39, 52, 65 and 78 weeks. Some animals were sacrificed and others were allowed to recover
Frequency of treatment:
6 hours/day,5 days/week
Post exposure period:
Varied- animals were allowed to survive for various periods so that fibre clearance could be estimated.
Doses / Concentrations:
RCF4 - 206+-48
other: WHO f/ml
Doses / Concentrations:
RCF3 - 213+- 44
other: WHO f/ml
Doses / Concentrations:
RCF2 - 268+-45
other: WHO f/ml
Doses / Concentrations:
RCF1 -234+-35
other: WHO f/ml
No. of animals per sex per dose:
140 males
Control animals:
yes, concurrent vehicle
Details on study design:
.Dose selection rational: 30 mg/m3 was believed to be the maximum tolerated dose for RCF3 in a 56 day study it was assumed this exposure was the MTD for all man made fibres in all rodent species.
- Rationale for animal assignment (if not random): Random
Positive control:
NIEHS intermediate lengthChrysotile Asbestos Plastibest-20
dose 10+-3 mg/m3.(10,600 WHO f/ml)
Observations and examinations performed and frequency:
- Time schedule: twice daily prior and following exposure and once daily on non- exposure days

- Time schedule for examinations: each during acclimation period , weekly during the first 13 weeks and at least monthly thereafter

Sacrifice and pathology:
HISTOPATHOLOGY: Yes samples of the following tissues were taken for histopathogy:
Adrenal glands, Aorta, Brain, Cecum, Colon,Duodenum, Epididymides,Esophagus, Exorbital lacrimal glands, Eyes with optic nerve and Harderian gland,Femur, including joint, Heart, Ileum,Jejunum., Kidneys, Larynx,Liver,Lungs,Lymph nodes-mandibular,mediastinal,mesenteric,(celiac), Nasal cavity and turbinates,Pancreas,Pituitary gland,Prostate gland,rectum,Salivary gland- mandibular,subligual,sciatic nerve,seminal vesicles,skeletal muscle,skin,spinal- cord cervical,midthoracic,lumber,spleen,sternum with boane marrow,stomach,testes,thymaus,thyroid gland including parathyroid,tongue,trachea,urinary bladder, infused with formalin
All gross lesions,masses and suspected tumours were examined by a pathologist.
Other examinations:
Samples of neoplastic tissue were taken and sent frozen in liquid nitrogen to CIIT North Carolina 27709
Special purposes for lungs -examined under a dissection microscope for detection and indentification of small macroscopic lesions
Lungs were inflated with formaldehyde photographed and sections taken for histopathology after sacrifices at 13, 26, 39 and 52 weeks lungs were instilled with Karnowski's fixative and sampled as detailed in full study report. The histopathology of the lung was studied intensively in a method developed as the study progressed . In General the left lobe was sectioned along the main bronchus and the ventral half allocated to light microscopy . The dorsal half was sectioned in to two parts with the cranial half evaluated by scanning SEM. The right cranial lobe was evaluated by light microscopy and the accessory lobe was allocated to a study of lung fibre burden. The remaining tissues were archived. As a deviation to this procedure any relevant tissue showing marcoscopic lesions were also evaluated using light microscopy.
Body weight and organ weight were analysed using Dunnett's test ,age specific survival rates were calculated . Statistical evaluations for the neoplastic lesions was performed according to Peto et al 1980
Clinical signs:
no effects observed
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
Lung weight slight increase
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Fibrosis just reaching significance at Wagner grade 4
Histopathological findings: neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Lung and Mesothelial tumours were seen
Details on results:
Fibrosis and tumours occurred after the RCF exposure however this was in the presence of many non fibrous particles and at a lung burden that would result in the inhibition of macrophage mediated clearance, fibrosis and profound inflammation as a result this study should not be used for hazard identification of risk assessment.
Relevance of carcinogenic effects / potential:
Tumours caused by pulmonary overload are not relevant in assessing carcinogenic risk to humans.
Dose descriptor:
conc. level:
Effect level:
ca. 30 mg/m³ air
Based on:
test mat.
Basis for effect level:
other: see 'Remark'
Remarks on result:
other: Effect type: carcinogenicity (migrated information)

Table 1 - Summary of exposure and results for the rat high dose (30mg/m3) study




Test Species



Number of Animals at risk




Fibre type



Aerosol Concentration


f/ml (SD)





 Concentration of Non-fibrous particles <3µm diameter

(mean no. of particles/ml)




Aerosol fibre dimensions


Geometric mean (GSD)





(Wagner Grade)


Tumour Incidence



















(Fischer 344/N)






Air control










234 (35)

29.1 (5.2)


0.82 (1.89)

15.9 (2.4)





"After service" Kaolin

206 (48)

30.1 (7.8)


1.22 (1.68)

9.8 (3.8)





High Purity

213 (44)

29.2 (7.0)


0.85 (1.91)

17.4 (2.4)







268 (45)

28.9 (4.5)


0.88 (1.92)

12.8 (2.5)



















It is impossible to draw profound conclusions from this study as the lung burden of fibres and particles was considerably higher than could be tolerated without causing serious effects unrelated to the test material
Executive summary:

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).

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
30 mg/m³
Study duration:

Justification for classification or non-classification

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.

Additional information

These 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: lung