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Acute Toxicity: inhalation

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acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2010-08-16 to 2011-12-07
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
OECD Guideline 436 (Acute Inhalation Toxicity: Acute Toxic Class Method)
Version / remarks:
GLP compliance:
yes (incl. QA statement)
signed 2009-11-12
Test type:
acute toxic class method
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
Cobalt oxide
EC Number:
EC Name:
Cobalt oxide
Cas Number:
Molecular formula:
Test material form:
solid: particulate/powder
migrated information: powder
Details on test material:
- Name of test material (as cited in study report): Cobalt monoxide
- Molecular formula: CoO
- Molecular weight: 74.9 g/mol
- Physical state: grey/brown powder
- Storage condition of test material: ambient temperature, closed container, dry, in an airtight bag
- Melting point: 1830°C
- Water solubility: 4.88 mg/L (20°C, OECD 105)

Test animals

Crj: CD(SD)
Details on test animals or test system and environmental conditions:
- Source: Charles River Laboratories Research Models and Services Germany GmbH, Sandhofer Weg 7, 97633 Sulzfeld, Germany
- Age at study initiation: males: 49 - 52 days; females: 63 - 65 days
- Weight at study initiation: males: 207 - 280 g; females: 218 - 257 g
- Fasting period before study: feeding was discontinued approx. 16 hours before exposure; only tap water was then available ad libitum.
- Housing: granulated textured wood (Granulat A2, J. Brandenburg, 49424 Goldenstedt, Germany) was used as bedding material for the cages. The cages were changed and cleaned twice a week. During the 14-day observation period, the animals are kept by sex in groups of 2 - 3 animals in MAKROLON cages (type III plus).
- Diet (ad libitum, for exception please refer to "Fasting period before study" above): Commercial diet, ssniff® R/M-H V1534 (ssniff Spezialdiäten GmbH, 59494 Soest, Germany)
- Water (ad libitum): Drinking water
- Acclimation period: at least 5 adaptation days; the animals were randomised before use. They were acclimatised to the test apparatus for approx. 1 hour on 2 days prior to testing. The restraining tubes did not impose undue physical, thermal or immobilization stress on the animals.

- Temperature: 22°C±3°C (maximum range)
- Relative humidity: 55% ± 15% (maximum range)
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:
inhalation: dust
Type of inhalation exposure:
nose only
clean air
Mass median aerodynamic diameter (MMAD):
>= 3.284 - <= 3.791 µm
Geometric standard deviation (GSD):
>= 2.76 - <= 3.05
Details on inhalation exposure:
- Exposure apparatus: the study was carried out using a dynamic inhalation apparatus (RHEMA-LABORTECHNIK, 65719 Hofheim/Taunus, Germany)(air changes/h (≥ 12 times)) with a nose-only exposure of the animals according to KIMMERLE & TEPPER. The apparatus consists of a cylindrical exposure chamber (volume 40 L) which is able to hold 10 animals in pyrex tubes at the edge of the chamber in a radial position.

- System of generating particulates/aerosols: the dust of the test material was generated with a rotating brush dust generator (RBG 1000, PALAS GmbH Partikel und Lasermesstechnik,76229 Karlsruhe, Germany)(concentrations of 0.05 to 5 mg/L air). The generator was fed with compressed air (5.0 bar) from a compressor (ALUP Kompressorenfabrik, 73257 Köngen, Germany) (air was taken from the surrounding atmosphere of the laboratory room and filtered using an in-line disposable gas-filter).
The dust of the test material at the concentration of 0.05 mg/L air was generated with a Dust Generator acc. to Bundschuh (TSE Systems GmbH, 61352 Bad Homburg, Germany).
At the bottom of the exposure chamber, the air was sucked off at a lower flow rate than it was created by the dust generator in order to produce a homogenous distribution and a positive pressure in the exposure chamber (inflow 900 L/h, outflow 800 L/h).
A manometer and an air-flow meter (ROTA Yokogawa GmbH & Co. KG, 79664 Wehr/Baden, Germany) were used to control the constant supply of compressed air and the exhaust, respectively. Flow rates were checked hourly and corrected if necessary.
The exhaust air was drawn through gas wash-bottles.

- Method of particle size determination: an analysis of the particulate size distribution was carried out twice during the exposure period using a cascade impactor according to MAY (MAY, K.R. Aerosol impaction jets, J.Aerosol Sci. 6, 403 (1975), RESEARCH ENGINEERS Ltd., London N1 5RD, UK.).
The dust from the exposure chamber was drawn through the cascade impactor for 5 or 10 minutes at a constant flow rate of 5 L/min. The slides were removed from the impactor and weighed on an analytical balance (precision 0.1 or 0.01 mg). Deltas of slides’ weight were determined.
The mass median aerodynamic diameter (MMAD) was estimated by means of nonlinear regression analysis. The 32 μm particle size range and the filter (particle size range < 0.5 μm) were not included in the determination of the MMAD in order not to give undue weight to these values.
The Geometric Standard Deviation (GSD) of the MMAD was calculated from the quotient of the 84.1%- and the 50%-mass fractions, both obtained from the above mentioned non-linear regression analysis.
In addition, a sample of approx. 10 g test material was taken from the exposure chamber to determine the particle size distribution (volume) with a CILAS 715 Sizer by My-Tec GmbH, 91325 Adelsdorf, Germany. This determination was non-GLP.

- Temperature, humidity, oxygen content, carbon dioxide content: the oxygen content in the inhalation chamber was 21%. It was determined at the beginning and at the end of the exposure with a DRÄGER Oxygen-analysis test set (DRÄGER Tube Oxygen 67 28 081). Carbon dioxide concentration did not exceed 1%.
Temperature and humidity were measured once every hour with a climate control monitor (testo 175-HZ data logger).

The whole exposure system was mounted in an inhalation facility to protect the laboratory staff from possible hazards.

The exposure was initiated by placing the animals’ noses into the exposure chamber after equilibration of the chamber concentration for at least 15 minutes (t95 approximately 8 minutes).

Before initiating the study with the animals, a pre-test was carried out with the exposure system in order to verify that under the experimental settings chosen, the limit concentration of 5 mg/L air could be achieved by gravimetric analysis.

The tests with the main study animals and the recovery animals were conducted in the same inhalation chamber but on different days. Between the exposure times the chamber was cleaned carefully.

- Brief description of analytical method used: the actual dust concentration in the inhalation chamber was measured gravimetrically with an air sample filter (Minisart SM 17598 0.45 μm) and pump (Vacuubrand, MZ 2C) controlled by a rotameter. Dust samples were taken once every hour during the
exposure. For that purpose, a probe was placed close to the animals' noses and air was drawn through the air sample filter at a constant flow of air of 5 L/min for 1 or 10 minutes. The filters were weighed before and after sampling (accuracy 0.1 or 0.01 mg). The correct loading of the filter was checked by the airflow via the rotameter and by a positive weight increase of the filter after the sampling period of 1 or 10 minutes.
- Samples taken from breathing zone: yes

TEST ATMOSPHERE (if not tabulated)
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.):
Main study:
- 0.05 ± 0.00 mg/L air: MMAD: 3.285 µm; GSD: 2.96
- 0.11 ± 0.01 mg/L air: MMAD:3.284 µm; GSD: 2.77
- 0.53 ± 0.02 mg/L air: MMAD: 3.537 µm; GSD: 2.76
Satellite group:
- 0.05 ± 0.00 mg/L air: MMAD: 3.435 µm; GSD: 3.05
- 0.10 ± 0.01 mg/L air: MMAD: 3.791 µm; GSD: 2.77
- 0.53 ± 0.02 mg/L air: MMAD: 3.715 µm; GSD: 2.68
- 1.07 ± 0.01 mg/L air: MMAD: 3.535 µm; GSD: 2.79
- 5.06 ± 0.03 mg/L air: MMAD: 3.698 µm; GSD: 2.66
Analytical verification of test atmosphere concentrations:
please refer to "details on inhalation exposure" above
Duration of exposure:
4 h
Main study:
actual concentration: 0.05 ± 0.00, 0.11 ± 0.01, and 0.53 ± 0.02 mg/L air
Satellite group:
actual concentration: 0.05 ± 0.00, 0.10 ± 0.01, 0.53 ± 0.02 , 1.07 ± 0.01 and 5.06 ± 0.03 mg/L air
No. of animals per sex per dose:
Main study: 5 males/5 females
Satellite group: 3 males/3 females
Control animals:
Details on study design:
- Duration of observation period following administration: 24 hours (satellite group) and 14 days (main study)
- Frequency of observations and weighing: during and following exposure, observations were made and recorded systematically; individual records were maintained for each animal. Careful clinical examinations were made at least twice daily until all symptoms subsided, thereafter each working day. Observations on mortality were made at least once daily (in the morning starting on test day 2) to minimize loss of animals to the study, e.g. necropsy or refrigeration of those animals found dead and isolation or sacrifice of weak or moribund animals.
Cageside observations included, but were not limited to: changes in the skin and fur, eyes, mucous membranes, respiratory, circulatory, autonomic and central nervous system, as well as somatomotor activity and behaviour pattern.
Particular attention was directed to observation of tremor, convulsions, salivation, diarrhoea, lethargy, sleep and coma. The animals were also observed for possible indications of respiratory irritation such as dyspnoea, rhinitis etc..
Individual weights of animals were determined once during the acclimatisation period, before and after the exposure on test day 1, on test days 3, 8 and 15 and at time of death. Changes in weight were calculated and recorded when survival exceeded one day. At the end of the test, all surviving animals were weighed and sacrificed.
- Necropsy of survivors performed: yes
Necropsy of all main study and satellite animals was carried out and all gross pathological changes were recorded:
- Satellite animals: necropsy at 24 hours after cessation of exposure, as this is likely to be the time at which any signs of respiratory irritation would have manifested;
- Main study animals: necropsy at the end of the 14-day observation period, also to assess whether any respiratory tract irritation persists or abates.
Autopsy and macroscopic inspections of animals which died prematurely were carried out as soon as possible after exitus.
- Histopathology:
All main study and satellite animals were subjected to the same level of histopathological examination upon necropsy at the end of the respective observation period. During histopathology, attention was paid to alterations that might be indicative of respiratory irritation, such as hyperaemia, oedema, minimal inflammation, thickened mucous layer.
The following organs of all animals were fixed in 10% (nose, i.e. head without brain, eyes and lower jaw) or 7% (other organs) buffered formalin for histopathological examination:
- Nose (5 levels of the nasal turbinates):
The tip and level 1 of the nose were taken from a cut just anterior to the incisor teeth. With tip removed, level 2 was taken approximately 2 mm posterior to free tip of the incisor teeth. Level 3 was cut through the incisive papilla. Level 4 was cut through the middle of the second palatal ridge, which is located just anterior to the molar teeth. Level 5 was cut through the middle of the molar teeth. All sections were embedded face down to yield a section from the anterior section, except the nose tip was embedded posterior surface down.
- Larynx
- Trachea
- Lungs (five levels)
Paraffin sections were prepared of all above mentioned organs and stained with haematoxylin-eosin.
The LC50 was calculated according to FINNEY (Probit analysis).

Results and discussion

Effect levelsopen allclose all
Dose descriptor:
Effect level:
0.06 mg/L air (analytical)
Based on:
test mat.
Exp. duration:
4 h
Dose descriptor:
Effect level:
0.07 mg/L air (analytical)
Based on:
test mat.
Exp. duration:
4 h
Dose descriptor:
Effect level:
0.06 mg/L air (analytical)
Based on:
test mat.
Exp. duration:
4 h
Main study:
- 0.05 mg/L air: 1/5 male and none of 5 female animals died prematurely.
- 0.11 mg/L air: all animals died prematurely until test day 4.
- 0.53 mg/L air: all animals died prematurely until test day 3.
Satellite group:
- 0.05 mg/L air: no animal died prematurely.
- 0.11 mg/L air: 2/3 male and none of 3 female satellite animals died prematurely.
- 0.53 mg/L air: 3/3 male and 1/3 female satellite animals died prematurely.
- 1.07 mg/L air: 2/3 male and 3/3 female animals died prematurely
- 5.06 mg/L air: 3/3 male and 1/3 female animals died prematurely.
Clinical signs:
other: - 0.05 mg/L air: Main study: slight ataxia and slight dyspnoea in all male and female animals. Satellite group: slight ataxia and slight dyspnoea in 3/3 male and 3/3 female animals. - 0.11 mg/L air: Main study: slight ataxia and slight dyspnoea in all
Body weight:
Body weight gain could not be calculated as all animals died not later than test day 4 (concentrations of 0.10 to 5.06 mg/L air). Two of the 5 female animals at 0.05 mg/L air appeared to be reduced in body weight gain.
Gross pathology:
A concentration of 0.05 mg/L air revealed marbled or blood-stained lungs in 9 of 16 or 7 of 16 animals, respectively. Haemorrhagic lungs were observed in all animals at concentrations of 0.1 to 5 mg/L air.
Other findings:
- 0.05 mg/L air: test item-related histopathological changes were noted in the lungs, but not in the nose, larynx and trachea.
- 0.10, 0.53, and 1.07 g/L air: test item-related histopathological changes were observed in the nose and lungs but not in the trachea.
(Please also refer for results to "Attached background material" below).

Applicant's summary and conclusion

Interpretation of results:
Category 2 based on GHS criteria
LC50 (4 hours): 0.06 mg/L air (males)
LC50 (4 hours): 0.07 mg/L air (females) and
LC50(4 hours) : 0.06 mg/L air (males and females combined).
According to the EC Regulation No. 1272/2008 and subsequent regulations, the test item is classified as Category 2.