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Administrative data

acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
available as unpublished report, no restrictions, fully adequate for assessment

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
according to
OECD Guideline 436 (Acute Inhalation Toxicity: Acute Toxic Class Method)
GLP compliance:
yes (incl. certificate)
TNO Triskelion, Utrechtseweg 48, 3704 HE Zeist, The Netherlands
Test type:
acute toxic class method
Limit test:

Test material

Test material form:
solid: particulate/powder
migrated information: powder
Details on test material:
- Name of test material (as cited in study report): Celitement
- Chemical name: Calcium hydrosilicate
- Physical state: White powder
- pH-value: 10.5
- Expiration date of the lot/batch: 12/2015
- Stability under test conditions: Hydration reaction with water
- Storage condition of test material: Room temperature protected from light, in original container in evacuated desiccator

Test animals

Details on test animals and environmental conditions:
- Source: Harlan Laboratories, The Netherlands.
- Age at study initiation: ca 8 weeks old
- Weight at study initiation: Mean body weight was 256 g for males and 180 g for females.
- Housing: The animals were housed in groups of three, separated by sex, in macrolon cages (type 4) with a bedding of wood shavings (Lignocel, Rettenmaier Rosenberg, Germany) and a piece of gnaw wood (from ABEDD, Austria) and shreds of paper (Enviro-dri, Shepherd Specialty Papers, Michigan, USA) as environmental enrichment.
- Diet: cereal-based (closed formula) rodent diet (Rat & Mouse No. 3 Breeding Diet, RM3) from a commercial supplier (SDS Special Diets Services, Whitham, England), ad libitum
- Water: tap-water suitable for human consumption ad libitum. In addition to the water supplied in bottles, and in response to their weakened condition, the animals were provided with a cup of HydroGel (ClearH2O, Portland, ME, USA) in the cage to prevent dehydration (period: day 1 - 3 of the observation period).
- Acclimation period: 14 days

- Temperature (°C): 22 ± 2
- Humidity (%): 45 - 65
- Air changes (per hr): about 10
- Photoperiod (hrs dark / hrs light): Sequence of 12 hours light and 12 hours dark.

Administration / exposure

Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
Details on inhalation exposure:
-Exposure equipment
The animals were exposed to the test atmosphere in a nose-only inhalation chamber, a modification of the design of the chamber manufactured by ADG Developments Ltd., Codicote, Hitchin, Herts, SG4 8UB, United Kingdom. The inhalation chamber consisted of a cylindrical stainless steel column, surrounded by a transparent cylinder. The column had a volume of 48 litres and consisted of a top assembly with the entrance of the unit, two mixing chambers, a rodent tube section and at the bottom the base assembly with the exhaust port. The rodent tube section had 20 ports for animal exposure. Several empty ports were used for test atmosphere sampling (for analysis of the actual concentration and particle size) and measurement of oxygen, carbon dioxide, temperature and relative humidity. The animals were secured in plastic animal holders (Battelle), positioned radially through the outer cylinder around the central column. Male and female rats were placed in alternating order. The remaining ports were closed. Only the nose of the rats protruded into the interior of the column. Habituation to the restraint of the animal holders was not performed because in our experience habituation does not help to reduce possible stress (Staal et al., 2012). In the experience of the test laboratory, the animal's body does not exactly fit in the animal holder which always results in some leakage from the high to the low pressure side. By securing a positive pressure in the central column and a slightly negative pressure in the outer cylinder which encloses the entire animal holder, dilution of test atmosphere by air leaking from the animal’s thorax to the nose was avoided. The unit was illuminated externally by normal laboratory fluorescent tube lighting. The total airflow through the unit was at least 1 L/min for each rat. The air entering the unit was maintained between 22 ± 3˚C and the relative humidity between 30% and 70%.

-Generation of the test atmosphere
The test atmosphere was generated using a turntable dust feeder (Reist and Taylor, 2000) and an eductor (Fox Valve Development Corp., Dover, NJ, USA; Cheng et al., 1989). The compartment of the dust feeder containing the test material was flushed with a stream of compressed dry air (about 5 L/min) to avoid clogging of the equipment. The test material was aerosolized in the educator which was supplied with humidified compressed air. The eductor was calibrated by measuring (in triplicate) the total flow at the driving air pressure used during exposure. To prevent clogging, the eductor was shaken using an electric shaker. The resulting aerosol was led to the top inlet of the exposure unit. From there, the aerosol was directed downward and led to the noses of the animals. At the bottom of the unit, the test atmosphere was exhausted. The animals were placed in the exposure unit after stabilization of the test atmosphere (T95 was 1.2 minutes). The period between the start of the generation of the test atmosphere and the start of exposure of the animals was 18 minutes.

-Analysis of exposure conditions
--Actual concentration: The actual concentration of the test material in the test atmosphere was measured by gravimetric analysis. Representative test atmosphere samples were obtained from the animals’ breathing zone by passing approximately 5 L test atmosphere at 5 L/min through fiber glass filters (Sartorius, 13400-47). Filters were weighed before sampling, loaded with a sample of test atmosphere, and weighed again. The actual concentration was calculated by dividing the amount of test material present on the filter by the volume of the sample taken. A total number of 11 samples was taken during exposure of the animals.
--Nominal concentration and generation efficiency: The nominal concentration was determined by dividing the total amount of test material used (by weight) by the total volume of air passed through the exposure unit. The generation efficiency was calculated from the actual and the nominal concentration (efficiency = actual concentration as percentage of nominal concentration.
--Particle size: Three particle size distribution measurements were carried out, one during preliminary generation of the test atmosphere and two during exposure. A 10-stage cascade impactor was used (2110k cascade impactor, Sierra instruments, Carmel Valley, California, USA). The Mass Median Aerodynamic Diameter and geometric standard deviation were calculated (Lee, 1972).
--Total airflow, temperature, relative humidity, and concentration of oxygen and carbon dioxide: The chamber airflow, temperature and relative humidity of the test atmosphere were recorded eight times during exposure. Airflow was measured by recording the driving air pressure of the eductor as a measure for the flow. The temperature and relative humidity were measured using an RH/T device (TESTO 635-1, TESTO GmbH & Co, Lenzkirch, Schwarzwald, Germany). The oxygen (Oxygen analyser type PMA-10, M&C Products Analysentechnik GmbH, Ratingen-Lintorf, Germany) and carbon dioxide (GM70, Vaisala, Helsinki, Finland) concentrations were measured once about halfway through the exposure period.
Analytical verification of test atmosphere concentrations:
Duration of exposure:
4 h
5.31 (± 0.46) g/m3
No. of animals per sex per dose:
Control animals:
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: On the exposure day, the animals were observed for clinical signs just before exposure, four times during exposure (about once per hour), and twice after exposure. During the observation period, each animal was observed daily in the morning hours by cage-side observations and, if necessary, handled to detect signs of toxicity. On working days, all cages were checked again in the afternoon. In weekends only one check per day was carried out. The body weight of each animal was recorded once during the acclimatization period (on day -1), and on days 0 (just before exposure), 1, 3, 7 and on day 14 prior to necropsy.
- Necropsy of survivors performed: yes, abdominal and thoracic organs were examined in situ for gross pathological changes, with particular attention to any changes in the respiratory tract.

Results and discussion

Effect levels
Dose descriptor:
Effect level:
> 5.31 mg/L air (analytical)
Based on:
test mat.
Exp. duration:
4 h
No mortality observed
Clinical signs:
other: Initially, the animals did not show any clinical abnormalities during exposure. About 1.5 hours after the start, moderate dyspnoea and shallow breathing were observed which persisted thoughout the 4-hour exposure period. In the last hour, all animals also
Body weight:
All animals showed exposure-related loss of body weight on the day after exposure. All animals had gained weight by day 3, and recovery of the initial body weight loss was observed by day 7. The animals displayed a normal growth in the second week of the observation period.
Gross pathology:
Macroscopic examination at necropsy revealed abnormalities in one female animal (displayed breathing abnormalities until day 6 ), consisting of white spots on the left lung lobe and a swollen uterus. The white spots on the lung were considered to be related to the exposure. The remaining two females and three males did not show any gross lesions.
Other findings:
- Actual concentration: The actual concentration of the aerosol in the test atmosphere during the exposure period was 5.31 g/m3 (±0.46, n=11) based on gravimetric analysis.
- Time to attain chamber equilibration: The time to reach 95% of the steady state concentration (T95) was about 1.2 minutes (based on a chamber volume of 48 L and an airflow of 116 L/min).
- Nominal concentration and generation efficiency: The nominal concentration – calculated from the consumption of test material, the airflow and the duration of test atmosphere generation – was 17.2 g/m3, indicating a generation efficiency of 31% (which is within the expected range for aerosol generation from a dry powder).
- Particle size measurement: Particle size was determined in duplicate during exposure. The mass median aerodynamic diameter was 3.07 and 3.05 μm, and the distribution of particle sizes had geometric standard deviations of 2.49 and 2.33, respectively. Approximately 57% of the mass of the aerosol present in the animals' breathing zone was contained in particles with an aerodynamic diameter smaller than 4 μm. During preliminary generation of the test atmosphere, using the same settings, similar values were found.
- Total airflow, temperature, relative humidity, and concentration of oxygen and carbon dioxide: The average chamber airflow was 116 L/min. The temperature and relative humidity in the exposure chamber were within the target range of 19-25°C and 30-70%, respectively. The measured temperature was between 21.4 and 21.7°C, and the relative humidity was between 40.2 and 43.2%. The oxygen and carbon dioxide concentrations in the exposure chamber, measured about halfway through the exposure period, were 20.7% (v/v) and 0.45% (v/v), respectively.

Applicant's summary and conclusion

Interpretation of results:
practically nontoxic
Migrated information Criteria used for interpretation of results: EU
Under the test conditions (OECD 436, GLP) the 4-hour LC50 of the test substance in rats is above 5.31 g/m3.
Executive summary:

In accordance to OECD guideline 436 and GLP, the acute inhalation toxicity of the test substance was examined in Wistar rats. Three rats per sex were exposed for four hours to a target limit concentration of 5 g/m3 and were kept for an observation period of 14 days. To detect adverse effects, clinical observations were made during and after exposure, body weight was determined before exposure (days -1 and 0) and on days 1, 3, 7 and 14, and animals were examined for gross pathological changes at the end of the observation period. The mean actual concentration during exposure was 5.31 (± 0.46) g/m3, based on gravimetric analysis. The mass median aerodynamic diameter of the particles in the aerosol was 3.07 and 3.05 μm (duplicate measurements) and the distribution of particle sizes had a geometric standard deviation of 2.49 and 2.33, respectively. All animals survived until scheduled sacrifice at the end of the 14-day observation period. During exposure, all animals showed moderate dyspnoea and shallow breathing, which was first observed about 1.5 hours after the start of exposure. In addition, a slightly decreased breathing rate was noticed in all animals at the last hourly observation. Multiple breathing abnormalities – such as sniffing, grunting, dyspnoea, shallow and irregular breathing at an increased rate – and general signs of discomfort (e.g. hypoactive behaviour, hunched posture, piloerection, blepharospasm) were observed shortly after exposure, which generally persisted until the next day. Several animals also showed a discharge from the nose and/or eyes, and nasal encrustations. Over the following days, the incidence of clinical abnormalities gradually decreased. Recovery of clinical abnormalities was observed by day 3-4 in most animals; one female displayed breathing abnormalities until day 6. All animals showed exposure-related loss of body weight on the day after exposure. By day 3, all animals had gained weight, and recovery of the initial body weight loss was by day 7. The animals displayed a normal growth in the second week of the observation period. Macroscopic examination at necropsy revealed white spots on the left lung lobe of the female rat with breathing abnormalities until day 6.The remaining three males and two females did not show any gross lesions at necrospy. It was concluded that the 4-hour LC50 of the test substance in rats is above 5.31 g/m3.