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Toxicological information

Acute Toxicity: inhalation

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Administrative data

acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
27 April 2010 - 31 May 2010
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guidelineopen allclose all
according to guideline
EPA OPPTS 870.1300 (Acute inhalation toxicity)
according to guideline
OECD Guideline 436 (Acute Inhalation Toxicity: Acute Toxic Class Method)
GLP compliance:
Test type:
acute toxic class method
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
Zirconium dioxide
EC Number:
EC Name:
Zirconium dioxide
Cas Number:
Molecular formula:
Test material form:
solid: particulate/powder
Details on test material:
- Name of test material (as cited in study report): zirconium dioxide
- Substance type: off-white powder (8.40% < 1 micron)
- Physical state: solid
- Analytical purity: 98.87% ZrO2 + HfO2
- Impurities (identity and concentrations): 0.50% SiO2, 0.16% Na2O, 0.02% CaO, <0.01% MgO, 0.03% Fe2O3, 0.07% TiO2, 0.13% Al2O3, 0.08% H2O
- Composition of test material, percentage of components: no data
- Purity test date: 3 May 2010
- Lot/batch No.: 10 01 002
- Expiration date of the lot/batch: 1 March 2015
- Stability under test conditions: responsibility of the sponsor and on file at WIL Research Laboratories, LLC (WIL)
- Storage condition of test material: the test substance was stored at room temperature protected from light
- Other: a reserve sample of the test substance (approximately 3 g) was collected on 7 May 2010, and stored in the WIL Archives.

Test animals

other: Crl:CD(SD)
Details on test animals or test system and environmental conditions:
- Source: Charles River Laboratories, Raleigh, NC; animals were received on 20 April 2010
- Age at study initiation: approximately 11 weeks
- Weight at study initiation: body weight values ranged from 316 g to 357 g for males and from 220 g to 238 g for females. Individual body weights at assignment were within ± 20% of the mean for each sex.
- Fasting period before study: during acclimation to restraint and during the exposure period
- Housing: Upon arrival, all animals were housed in individual suspended wire-mesh cages. The animals were maintained by the WIL Animal Husbandry staff in accordance with WIL standard operating procedures (SOPs). On the day of exposure, the animals were placed in nose-only exposure holding tubes in the animal room, transported to the exposure room, exposed for the requisite duration and then returned to their home cages.
- Diet (e.g. ad libitum): The basal diet used in this study, PMI Nutrition International, LLC, Certified Rodent LabDiet 5002, is a certified feed with appropriate analyses performed by the manufacturer and provided to WIL.
- Water (e.g. ad libitum): Municipal water supplying the facility is analyzed for contaminants according to WIL SOP
- No contaminants were present in animal feed or water at concentrations sufficient to interfere with the objectives of this study. The basal diet and municipal water, delivered by an automatic watering system, were provided ad libitum, except during acclimation to restraint and the exposure period.
- Acclimation period: 5 days, the animals were observed twice daily for mortality and moribundity. The animals were subjected to restraint in the nose-only exposure holding tubes for 1 hour on 27 April 2010 prior to the start of exposure. Animals were held in restraint tubes for 35 minutes prior to initiation of exposure.

- Temperature (°C): The room temperature control was set to maintain environmental conditions of 71°F ± 5°F (22°C ± 3°C) and 50% ± 20% relative humidity. Room temperature was monitored using the Metasys DDC Electronic Environmental control system and schedule for data collection was on an hourly basis. Actual mean daily temperature ranged from 70.3°F to 72.1°F (21.3°C to 22.3°C).
- Humidity (%): The humidity control was set to maintain environmental conditions of 50% ± 20% relative humidity. Relative humidity was monitored using the Metasys DDC Electronic Environmental control system and as scheduled for data collection on an hourly basis. Mean daily relative humidity ranged from 49.2% to 55.9% during the study.
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12 hours light/12 hours dark

IN-LIFE DATES: no data

Administration / exposure

Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
other: air (for compressed air system) and deionized water (for humidified air system)
Details on inhalation exposure:
- Exposure apparatus: the test substance was delivered using an auger-type feeder (Schenck AccuRate, INc., Whitewater, WI) which fed test substance at a constant rate to a jet mill air micronizer (model 00, Jet-O-Mizer, Fluid Energy Aljet, Hatfield, PA) operating as a particle size reduction and dispersion device.
- Exposure chamber volume: 7.9 L convential nose-only exposure system (designed and fabricated by WIL)
- Method of holding animals in test chamber: Animals were restrained in nose-only exposure holding tubes during exposure
- Source and rate of air: Using 2 regulators, dry compressed air was supplied to the micronizing and inlet ports of the jet mill. The resulting aerosol from the jet mill was delivered to the nose-only exposure system through 22-mm respiratory tubing. A glass cyclone was placed in-line after the jet mill to reduce particle size. A tee fitting was placed at the inlet of the exposure system to provide humidified air. Humidified air was added using a Coilhose Pneumatics regulator and controlled using a rotameter-type flowmeter. Dry compressed air passed through a muffler-type bubbler submerged in a 2-L Erlenmeyer flask filled with deionized water to produce humidified air. The airflows used for the animal exposure is as follows: inlet airflow rate = 28.5-29.2 L/minute, micronizing airflow rate is 18.6L/minute, humidified airflow rate is 7.6 L/minute and total airflow rate is 54.7-55.4 L/minute
- Method of conditioning air: see above (source and rate of air)
- System of generating particulates/aerosols: see above (source and rate of air)
- Method of particle size determination: Three aerosol particle size determinations were conducted for this exposure using a 7-stage stainless steel cascade impactor (model 02-140, In-Tox Products, Moriarty, NM). Pre-weighed, 23-mm stainless steel discs were used as the collection substrates. Samples were collected at approximately 1.8 L/minute for 0.25 minutes. The filters were re-weighed and the particle size calculated based on the impactor stage-cut-offs. The aerosol size was expressed as the mass median aerodynamic diameter (MMAD) and the geometric standard deviation (GSD).
- Treatment of exhaust air: Exhaust atmosphere was filtered using a Solberg filter (Solberg Manufacturing, Inc., Itasca, IL) prior to entering the in-house exhaust system with activated charcoal and HEPA-filtration.
- Temperature, humidity, pressure in air chamber: The room temperature and humidity controls were set to maintain environmental conditions of 71°F±5°F (22°C ± 3°C) and 50%±20% relative humidity. Room temperature and relative humidity were monitored using the Metasys DDC Electronic Environmental control system and were scheduled for data collection on an hourly basis. Actual mean daily temperature ranged from 70.3°F to 72.1°F (21.3°C to 22.3°C) and mean daily relative humidity ranged from 49.2% to 55.9% during the study

- Actual exposure concentrations: Actual exposure concentrations were determined using standard gravimetric methods. Samples were collected on pre-weighed, 25-mm glass-fiber filters (type A/E, PALL Corporation, Ann Arbor, MI) held in an open-faced filter holder positioned in the animal breathing zone within the nose-only exposure system. Following sample collection, the filters were re-weighed and the concentration calculated as the filter weight difference divided by the sample volume. Samples were collected at approximately 2 L/minute for 0.5 mintues.

- Composition of vehicle (if applicable): not applicable
- Concentration of test material in vehicle (if applicable): not applicable
- Justification of choice of vehicle: not applicable
- Lot/batch no. (if required): not applicable
- Purity: not applicable

TEST ATMOSPHERE (if not tabulated)
- Particle size distribution: Effective cut-off diameter: 5.27 µm for stage 1, 4.22 µm for stage 2, 3.20 µm for stage 3, 1.90 µm for stage 4, 1.07 µm for stage 5, 0.41 µm for stage 6 and 0.27 µm for stage 7
- MMAD (Mass median aerodynamic diameter) / GSD (Geometric st. dev.): 2.00 µm (mean MMAD) and 1.75 (Mean GSD)

CLASS METHOD (if applicable)
- Rationale for the selection of the starting concentration: The target exposure concentration was based on toxicity data from similar compounds as outlined in the product MSDS. Under the generation and exposure conditions of this study and requirements for a particle size of 1 to 4 microns and maintenance of a stable concentration for the 4-hour exposure period, it was determined that the maximum obtainable concentration of zirconium dioxide as a dust aerosol was approximately 4.3 mg/L. Since no animals died following exposure to the maximum obtainable concentration of the test substance, additional exposure levels were not required.
Analytical verification of test atmosphere concentrations:
Duration of exposure:
4 h
Actual exposure concentration: 4.3 mg/L (SD 1.39 mg/L), this is the maximum obtainable mean concentration for a 4-hour exposure. The nominal exposure concentration was 41.4 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 and weighing:
Body weights were obtained immediately prior to exposure on study day 0 and on post-exposure days 1, 3, 7, and 14.
Mortality: each animal was observed for mortality at the approximate midpoint of exposure, immediately following exposure on study day 0, and twice daily thereafter for 14 days.
Clinical observations: each animal was observed immediately following exposure on study day 0 and once daily thereafter for 14 days.
- Necropsy of survivors performed: yes; animals at the scheduled necropsy were euthanized by isoflurane anesthesia followed by exsanguination. The major organ systems of the cranial, thoracic, and abdominal cavities were examined for all animals.
no data

Results and discussion

Effect levels
Key result
Dose descriptor:
Effect level:
> 4.3 other: mg/L (actual exposure concentration: maximum technically achievable concentration)
Based on:
test mat.
Exp. duration:
4 h
None of the animals died during exposure or during the 14-day post-exposure observation period. Based on the data obtained, the LC50 of zirconium dioxide was found to be greater than 4.3 mg/L, the maximum obtainable mean concentration.
Clinical signs:
other: There were no toxicologically significant clinical signs immediately following exposure. Several animals were noted with clear material on the neck, forelimb(s), trunk, and urogenital area, red material around the nose and mouth, and/or yellow material ar
Body weight:
All animals lost weight (10 g to 39 g) from study day 0 to 1. One male lost weight (9 g) from study day 1 to 3. All animals surpassed their initial (study day 0) body weight by study day 14 and were considered normal.
Gross pathology:
There were no macroscopic findings for any animal at the scheduled necropsy.

Applicant's summary and conclusion

Interpretation of results:
GHS criteria not met
Based on the results of this study, the LC50 of zirconium dioxide was greater than 4.3 mg/L, the maximum obtainable mean concentration, when male and female albino rats were exposed to a dust aerosol of the test substance as a single, 4-hour, nose-only exposure.