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Description of key information

In an acute oral toxicity study (OECD 401) young adult Crl:CD (SD) rats (5 animals per sex and dose) were orally exposed to the source substance Sodium molybdate in corn oil at concentrations of 3200, 5000 and 6400 mg/kg bw. Mortality occurred within the different dose groups. The oral LD50 for both sexes was considered to be 4233 mg/kg body weight. This value equals 3136 mg/kg bw of the target substance Molybdenum disilicide.

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 the inhalation route to the source substance Sodium molybdate (99.7% purity) for 4 hours to the whole body at a mean concentration of 1.93 mg/L. No mortality or distinct clinical signs were observed after exposure to Sodium molybdate. The LC50 for both sexes was considered to be greater than 1.93 mg/L.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records
Reference
Endpoint:
acute toxicity: oral
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
For justification of read-across please refer to the read-across report attached to IUCLID section 13.
Reason / purpose:
read-across source
Sex:
male/female
Dose descriptor:
LD50
Effect level:
4 233 mg/kg bw
Based on:
test mat.
Mortality:
After a single oral dose of Sodium molybdate at a concentration of 3200 mg/kg bw three male and one female died within 5 hours after treatment. At 5000 mg/kg bw one male died and two female animals died within 2 days after treatment. After treatment with 6400 mg/kg bw all animals died within 2 hours after treatment.
Clinical signs:
Piloerection was observed in all rats within five minutes after treatment. This sign was accompanied on Day 1 and/or later intervals by:
- hunched posture, waddling and pallor of the extremities in all rats dosed at 3200 and 5000 mg/kg bw , less commonly among rats treated at 6400 mg/kg
- lethargy and decreased respiratory rate in all rats dosed at 5000 mg/kg and less commonly among rats treated at 3200 and 6400 mg/kg
- ptosis in all rats dosed at 5000 mg/kg and less common cases at 3200 mg/kg
- diarrhoea in a majority of rats dosed at 500 mg/kg and less commonly among rats treated at 6400 mg/kg
- prostration, preceding death, in one female treated with at 5000 mg/kg

Recovery of surviving rats was complete by day 3 (3200 mg/kg), day 4 (males at 5000 mg/kg) and day 6 (females at 5000 mg/kg)
Body weight:
Slightly low body weight gains for a majority of surviving rats on day 8. All rats achieved anticipated bodyweight gains during the second week of the study.
Gross pathology:
No macroscopic abnormalities were observed

Preliminary study:

The results indicated that the acute median lethal oral dose (LD50) to male and female rats of Sodium molybdate was greater than 1000 mg/kg body weight.

Interpretation of results:
GHS criteria not met
Conclusions:
In conclusion, the oral LD50 value in rats after treatment with Sodium molybdate was 4233 mg/kg body weight.
Executive summary:

In an acute oral toxicity study (OECD 401) young adult Crl:CD (SD) rats (5 animals per sex and dose) were orally exposed to Sodium molybdate in corn oil at concentrations of 3200, 5000 and 6400 mg/kg bw. Animals were observed for 14 days. All animals died in the high dose group. At 5000 mg/kg bw one male died and two female animals died and at 3200 mg/kg bw three male and one female died. There were treatment related clinical signs and slight changes in body weight. No treatment-related gross pathology abnormalities were observed after 14 days. Based on the mortality occured after treatment with Sodium molybdate, the oral LD50 value both in female and male Crl:CD (SD) rats was considered to be 4233 mg/kg body weight. Based on the LD50 for administered Sodium molybdate the LD50 for the target substance Molybdenum disilicide can be calculated with 3136 mg/kg bw (not accounting for differences in solubility/bioavailability).

 

This information is used in a read-across approach in the assessment of the target substance.

For justification of read-across please refer to the attached read-across report (see IUCLID section 13).

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
3 136 mg/kg bw
Quality of whole database:
Guideline study

Acute toxicity: via inhalation route

Link to relevant study records
Reference
Endpoint:
acute toxicity: inhalation
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
For justification of read-across please refer to the read-across report attached to IUCLID section 13.
Reason / purpose:
read-across source
Analytical verification of test atmosphere concentrations:
yes
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 1.93 mg/L air
Based on:
test mat.
Exp. duration:
4 h
Mortality:
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.

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 
Interpretation of results:
GHS criteria not met
Conclusions:
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.

This information is used in a read-across approach in the assessment of the target substance.

For justification of read-across please refer to the attached read-across report (see IUCLID section 13).

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Acute toxicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

No data is available for Molybdenum disilicide (target substance). Thus, available data from Sodium molybdate was used in a read-across approach. Due to a lower water solubility of Molybdenum disilicide compared to Sodium molybdate the resulting bioavailability (toxicity potential) would also be expected to be lower. Therefore, the read across to the source substance Sodium molybdate is adequately protective. Details on the read-across rational are provided in section 13.

In an acute oral toxicity study (OECD 401) young adult Crl:CD (SD) rats (5 animals per sex and dose) were orally exposed to Sodium molybdate in corn oil at concentrations of 3200, 5000 and 6400 mg/kg bw. Mortality occurred within the different dose groups. The acute median lethal oral dose (LD50) to male and female rats was calculated using the method of Finney (1971, Probit Analysis). The oral LD50 for both sexes was calculated to be 4233 mg/kg body weight. This value equals 3136 mg/kg bw of the target substance Molydenum disilicide.

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 the inhalation route to Sodium molybdate (99.7% purity) for 4 hours to the whole body at a mean concentration of 1.93 mg/L (higher concentrations technically not possible). No mortality or distinct clinical signs were observed after exposure to Sodium molybdate. The LC50 for both sexes was considered to be greater than 1.93 mg/L.


Justification for classification or non-classification

Based on the available data Molybdenum disilicide does not warrant classification for acute toxicity. LD50 values for the oral route are above the limit values of the relevant OECD guidelines. The LC50 value received from an acute inhalation study was greater than 1.93 mg/L (as Sodium molybdate).