Niobium carbide

Endpoint summary

Description of key information

No substance specific data for acute toxicity of niobium carbide is available. For the read across partner niobium oxide acute toxicity data is available for the inhalation and oral route. For both routes no mortality has been reported.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

other: Original reference in foreign language (Russian).

GLP compliance:

not specified

Test type:

other: acute oral toxicity

Species:

rat

Strain:

not specified

Sex:

not specified

Route of administration:

oral: unspecified

Vehicle:

not specified

Sex:

not specified

Dose descriptor:

LD50

Effect level:

> 10 000 mg/kg bw

Based on:

not specified

Interpretation of results:

not classified

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

In an acute toxicity study rats were administered orally with niobium pentoxide. The oral LD50 exceeds 10000 mg/kg bw.

Executive summary:

In an acute oral toxicity study published by Davidova, 1991, rats were orally treated with niobium pentoxide. The LD50 value was presented to be greater than 10000 mg/kg bw. Based on comparable low solubility, niobium pentoxide is considered a suitable read across partner for niobium carbide.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

10 000 mg/kg bw

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2000-09-25 to 2001-03-20

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study. Niobium pentoxide used as read-across partner.

Qualifier:

according to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

standard acute method

Limit test:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River UK Limited, Margate, Kent, England
- Age at study initiation: 8-9 weeks
- Weight at study initiation: males: 259 - 298 g, females: 204 - 237 g
- Housing: in groups of 5/sex in stainless steel cages
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 9 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19.5 - 20.5
- Humidity (%): 39 - 68
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12 / 12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

clean air

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: snout-only exposure chambers were of cylindrical form (30 cm diamter, 45 cm height)
- Exposure chamber volume: 30 litres
- Method of holding animals in test chamber: animals were held for exposure in moulded polycarbonate restraining tubes, which were attached at evenly spaced ports in the cylindrical section of the chamber, and were designed to allow only the snout to project into the chamber
- Source and rate of air: a supply of clean, dry air was connected to the generator and the supply pressure was adjusted to give a flow rate of 15 litres/minute, measured at the generator outlet.
- Method of conditioning air: A neutralised diluent air supply, adjusted to give 10 litres/minute, was connected to the elutriator to provide a total air supply of 25 liters/minute. The neutralised air supply was also passed externally over the elutriator to aid the removal of any electrostatic charge. The test atmosphere was passed through a horizontal glass elutriator to reduce, by sedimentation, the amount of non-respirable particulate in the test atmosphere
- System of generating particulates/aerosols: a wright dust feed mechanism was used to produce the test atmosphere
- Method of particle size determination: two air samples were taken during the exposure at a sampling rate of 2 litres/minute using a Marple cascade impactor to determine particle size distribution. The samples were taken at 102 and 212 minutes into exposure- The volume of air sampled was measured using a wet-type gas meter. The amount of material collected on the stages of the sampler was determined gravimetrically. The particle size distribution of the test atmosphere was assessed using linear regression analysis
- Treatment of exhaust air: the exhaust airflow was calibrated and adjusted to produce a slightly negative pressure
- Temperature, humidity, air chamber: air temperature in the exposure chamber was measured using an alcohol-in-glass thermometer and the relative humidity was measured using a Casella type T6900 relative humidity meter. The temperature and relative humidity were recorded at the start of the exposure and then at 30 minutes intervals during the 4-hour exposure

TEST ATMOSPHERE
- Brief description of analytical method used: Seven samples of air were removed from the test chamber during exposure in order to determine the concentration of the test aerosol. Each air sample was withdrwam, at a rate of 2 litres/minute, through a pre-weighed glass fibre filter mounted in an open face filter holder. The volume of air sampled was measured using a wet-type gas meter. The filters were re-weighed following sampling for gravimetric analysis of the test aerosol
- Samples taken from breathing zone: no

TEST ATMOSPHERE (if not tabulated)
- MMAD: 3.3 µm, approximately 88% of the particulate were considered of respirable size (<7 µm in aerodynamic diameter)

Analytical verification of test atmosphere concentrations:

yes

Duration of exposure:

4 h

Concentrations:

Chamber concentration of Nb2O5:
The mean chamber concentration was 5.45 mg/L and was in good agreement with target (5 mg/L).

Nominal concentration
The nominal concentration was 26.1 mg/l. The mean chamber concentration was 20.9% of the nominal concentration and reflects losses of the test material due to impaction and deposition with the exposure system. When generating Niobium pentoxide static agglomeration was considered to be a significant factor in the particulate losses within the aerosol generation system. The use of a neutralized air supply, both to the WDF and diluents supply, was necessary to achieve the concentration attained. In addition, neutralized air was passed over the external surface of the elutriator to reduce electrostatic losses. The relatively low efficiency observed in this study is not unusual for the exposure system and test compound employed.

Particle size distribution
The mass median aerodynamic diameter (MMAD) of the test aerosol was 3.3m and was within the acceptable range (1m to 4 m) for an acute inhalation study. Approximately 88% of the particulate were considered of a respirable size (<7m in aerodynamic diameter).

No. of animals per sex per dose:

5

Control animals:

yes

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations:
Mortality: all cages were checked at least twice daily for dead or moribund animals
Clinical signs: animals were observed intermittently for signs of reaction during exposure and at least twice daily throughout the observation period
- Frequency of weighing: all animals were weighed at least twice during the week prior to exposure, prior to exposure (day 0), weekly during the observation period and on the day of death
- Terminal studies: at the end of the observation period the animals were killed by ip injection of pentabarbitone sodium followed by exanguination from the brachial blood vessels. All animals were subjected to detailed macroscopic examination. The lungs (including the larynx and trachea) were removed, dissected clear of surrounding tissue, weighed and the weights recorded. Lungs were discarded following necropsy.
- Other examinations performed: water consumption: a visual inspection of water bottles was conducted daily.

Statistics:

N.A.

Preliminary study:

not applicable

Sex:

male/female

Dose descriptor:

LC0

Effect level:

> 5 450 mg/m³ air

Based on:

test mat.

Exp. duration:

4 h

Mortality:

There were no unscheduled deaths.

Clinical signs:

other: During exposure: Exaggerated breathing was observed in most test rats from 1 hour, and all test rats from 2 hours into exposure. Observation period: Exaggerated breathing was observed in all test rats immediately post exposure, persisting to day 4 of the

Body weight:

A slightly reduced mean bodyweight gain was evident for male test rats during the first week following exposure. Thereafter, the mean bodyweight gain was similar to that of the control values. Bodyweight gain values of the female test rats were similar to that of the control values.

Gross pathology:

There were no treatment-related findings noted at necropsy

Other findings:

- Organ weights: no effects seen on lung weights
- Water consumption: no treatment-related effects were observed

Interpretation of results:

not classified

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

The LC0 (4-hour) for diniobium pentoxide is greater than 5.45 mg/L and therefore no classification is required according to CLP.

Executive summary:

In an acute inhalation toxicity study according to OECD Guideline 403, groups of young adult Sprague-Dawley rats (5/sex) were exposed via the inhalation route to niobium pentoxide (99.9% purity) as aerosol in air for 4 hours nose only at a concentration of 5.45 mg/L. Animals then were observed for 14 days. No death occurred. Exaggerated breathing was observed in most test animals from the 1st hour and in all test rats from the 2nd hour of exposure. Exaggerated breath persisted until day 4 post exposure. Based on the results a LC50 of greater than 5.45 mg/L can be considered for both sexes. Niobium pentoxide is not classified according to CLP. These results are used in a read-across approach in the assessment of niobium carbide.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LC50

Value:

5 450 mg/m³ air

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No data is available for niobium carbide (target substance). Thus, available data from niobium pentoxide (source substance) is used to assess the acute oral and inhalation toxicity potential of niobium carbide. Assuming that the niobium ion is the crucial component for the toxicity assessment, niobium pentoxide data are considered suitable due to comparable dissolution of both compounds. Details on the read-across rational are provided in section 13.

In an acute inhalation toxicity study according to OECD Guideline 403, groups of young adult Sprague-Dawley rats (5/sex) were exposed via the inhalation route to niobium pentoxide (99.9% purity) as aerosol in air for 4 hours nose only at a concentration of 5.45 mg/L. Animals then were observed for 14 days. No death occurred. Based on the results a LC50 of greater than 5.45 mg/L can be considered for both sexes. Supporting data is derived from two publications, in which LD50 values from acute oral toxicity studies were presented. The LD50 after acute oral treatment in mice with niobium pentoxide was established to be greater than 4000 mg/kg bw (Shalganova, 1967) and the LD50 in rats after treatment with niobium pentoxide was established to be greater than 10000 mg/kg bw (Davidova, 1991).

Justification for selection of acute toxicity – oral endpoint

Publication referring to a suitable analogue (niobium pentoxide)

Justification for selection of acute toxicity – inhalation endpoint

GLP guideline study with a suitable analogue (niobium pentoxide)

Justification for classification or non-classification

Based on the available data from the read across partner niobium pentoxide, the niobium carbide 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 5.45 mg/L.