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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:
1990-04-17 to 1991-04-04
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
equivalent or similar to
OECD Guideline 403 (Acute Inhalation Toxicity)
GLP compliance:
Test type:
standard acute method
Limit test:

Test material

Specific details on test material used for the study:
- Name of test material (as cited in study report): Sodium Molybdate
- Physical state: white crystalline powder
- Stability: stable
- Analytical purity: 99.9%
- Storage condition of test material: in the dark at room temperature
- Production date: 1990-04-12
- Other: prior to use in this study a subsample was sent to Microm Hills Ltd., Orpington, Kent where it was air-milled to the extent technically feasible

Test animals

Details on test animals and environmental conditions:
- Source: Charles River UK Limited, Margate, Kent, UK
- Age at study initiation: 6 - 8 weeks
- Weight at study initiation: ca. 200g
- Housing: 5 per sex per cage
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: at least 5 days

- Temperature (°C): 18 - 24 °C
- Humidity (%): 35 - 65%

Administration / exposure

Route of administration:
inhalation: dust
Type of inhalation exposure:
whole body
clean air
Details on inhalation exposure:
- Exposure apparatus: Wright dust generator
- Exposure chamber volume: 120 L
- Method of holding animals in test chamber: cages of stainless mesh partitioned to provide 10 individual animal compartments
- Source and rate of air: clean dried compressed air was connected to the dust generator and flow rate was 25 L/min
- Method of particle size determination: Two samples were taken using a Marple model 296 cascade impactor.
- Temperature, humidity, pressure in air chamber: the air temperature was measured and recorded at the start of the exposure and then at 30 min intervals during the 4-hour exposure, relative humidity was calculated from the recorded data for the water vapour content and temperature of the chamber air

- Brief description of analytical method used: five air samples were taken from the chamber during the exposure. Each air sample was withdrawn through a weighed glass fibre filter (Whatman GF/A) held in an open face filter holder, at a rate of 4 L/min. The volume of the air sample was measured with a wet-type gas meter. The filters were reweighed to determine the concentration of the test substance in the chamber air.

Analytical verification of test atmosphere concentrations:
Duration of exposure:
4 h
The mean concentration of Sodium molybdate was 1.93 mg/L
No. of animals per sex per dose:
Control animals:
Details on study design:
- Duration of observation period following administration: 14 days
- Frequency of observations: at least two times per day for clinical signs
- Frequency of weighing: every day
- Necropsy of survivors performed: yes
- Food and water consumption: the daily mean intakes of food and water for each rat were calculated from the recorded data
- Other examinations performed:
at the end of the 14 day observation period, the rats were subjected to a detailed macroscopic examination. The lungs were removed, dissected clear of surrounding tissue and weighed in to order to calculate the lung to body weight ratio. Lungs, Liver and Kidneys were preserved buffered 10% formalin. Fixed lungs were embedded in paraffin wax and four-micron sections were prepared, stained with haematoxylin and eosin and examined under the light microscope.

Results and discussion

Effect levels
Dose descriptor:
Effect level:
> 1.93 mg/L air
Based on:
test mat.
Exp. duration:
4 h
There were no deaths during the study.
Clinical signs:
During exposure:
Partial closing of the eyes was seen in rats exposed to Sodium molybdate. This sign is considered to be consistent with a non-specific response to exposure to high concentration of dust.
During the observation period:
No signs of toxicity were observed.
Body weight:
Small losses in body weight or a reduced rate of body weight gain were observed in rats exposed to Sodium molybdate for up to three days after exposure. Subsequently the rate of body weight gain of the exposed rats was similar to that of the control rats.
Gross pathology:
Macroscopic pathology:
The lungs of two control rats had dark areas on the surface of the lungs and the lungs of one male rat exposed to Sodium molybdate were congested (animal 95).
Microscopic pathology:
No changes considered to be of toxicological significance were observed in the lung sections examined.
Other findings:
Food consumption:
Food consumption was reduced for two days following exposure to Sodium molybdate. Subsequently, food consumption for exposed rats was similar to that for control rats.

Water consumption:
Water consumption was increased on Day 3 of the observation period and also, in male rats only, on day 4 after exposure.

Lung to body weight ratio:
The lung weight for one male rat (animal 95) exposed to Sodium molybdate was higher than normal. The ratio was considered to be within normal limits for all other rats.

Any other information on results incl. tables

Table 1: Concentrations of Sodium Molybdate
Sample Time Test Item in air (mg/L)
2.1 0h : 30 min 2.01
2.2 1h : 00 min 1.85
2.3 2h : 00 min 1.94
2.4 3h : 00 min 1.93
2.5 3h : 50 min 1.91
  mean 1.93

Variation: 8%

Table 2: Particle Size Distribution
Sample Time taken Stage Particle size range (µm) Amount collected (mg) % of total % respirable (< 3.5 µm a.d.)
PSD1 1h : 40 min 3 9.80 0.37 42.50 31.00%
4 6.00 0.09 10.30
5 3.50 0.14 16.10
6 1.55 0.27 31.00
7 0.93 0.00 0.00
8 0.52 0.00 0.00
Filter 0.00 0.00 0.00
PSD2 3h : 30 min 3 9.80 0.34 30.60 20.70%
4 6.00 0.31 27.90
5 3.50 0.23 20.70
6 1.55 0.23 20.70
7 0.93 0.00 0.00
8 0.52 0.00 0.00
Filter 0.00 0.00 0.00
mass median aerodynamic diameter: 6.9 µm; standard geometric diviation: 2.71 

Applicant's summary and conclusion

Interpretation of results:
GHS criteria not met
In conclusion, under the conditions of the test, the LC50 of Sodium molybdate is greater than 1.93 mg/L.
Executive summary:

In an acute inhalation toxicity study equivalent to OECD 403, groups of young male and female Sprague-Dawley rats (5 per sex) were exposed via inhalation route to Sodium molybdate (99.7% purity) for 4 hours to the whole body at a mean concentration of 1.93 mg/L. Animals then were observed for 14 days. No mortality or distinct clinical signs were observed after exposure to Sodium molybdate. Since no mortality occured during the 14-day observation period, the LC50 for both sexes is greater than 1.93 mg/L.