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Acute Toxicity: inhalation

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acute toxicity: inhalation
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comparable to guideline (OECD 403) with acceptable restriction (limited reporting: analytical purity of the test substance not reported, validity of the analytical methods used not reported)

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
equivalent or similar to guideline
OECD Guideline 403 (Acute Inhalation Toxicity)
(limited reporting: analytical purity of the test substance not reported, validity of the analytical methods used not reported)
GLP compliance:
Test type:
standard acute method
Limit test:

Test material

Constituent 1
Reference substance name:
Reference substance 001
Cas Number:
Constituent 2
Reference substance name:
Reference substance 002
Cas Number:
Molecular formula:
Details on test material:
- Name of test material (as cited in study report): polymeric MDI (Desmodur 44 V 20)
- Supplier: Bayer AG, Leverkusen
- Physical state: very viscous, dark, brown liquid
- Analytical purity: not reported
- Composition of test material, percentage of components: NCO-content 30±2%; hydrolysable chlorine ≤ 0.3%; total chlorine: ≤ 0.8%; chlorobenzenes: ≤ 0.015%; phenylisocyanate: ≤ 0.005%; monomeric MDI: 52± 3%; sediment: ≤ 0.01%
- Other: Oil red (0.5%; w/w) was added to the test substance to facilitate the spectrophotometric determination of the concentration of the test material in the exposure chamber.

Test animals

Details on test animals or test system and environmental conditions:
- Source: Central Institute for the Breeding of Laboratory Animals TNO, Zeist, NL.
- Age: not reported (young adults)
- Weight at study initiation: mean body weight of males: 167 g and that of the females: 139 g.
- Diet: ad libitum
- Water: tap water ad libitum

- Temperature (°C): 21 ± 1
- Humidity (%): 50 - 60

Administration / exposure

Route of administration:
Type of inhalation exposure:
whole body
other: unchanged (no vehicle)
Details on inhalation exposure:
- Exposure apparatus: A stainless steel exposure chamber having a capacity of 1.5 m3 was used. The front door of the exposure chamber is provided with a glass window for observation of the animals and with several holes for the collection of air samples from different locations in the chamber.

- A polymeric MDI aerosol was generated from a stainless steel/glass air nebuliser. The nebuliser was thermostated at about 45 °C. A cyclone was placed behind the air nebuliser to remove large particles. Upon entering the exposure chamber, additional air was mixed with the aerosol resulting in a total air flow of 30-60 m3/hour .

- Brief description of analytical method used:
1.) spectrophotometrical oil-red determination of samples taken by cascade impactor.
2.) spectrophotometrical oil-red determination of samples taken by a special sampling device.
3.) HPLC analysis of samples taken by a special sampling device.
Large differences were found between the individual and mean data obtained by the different methods, in particular between HPLC and the others where HPLC concentrations were systematically lower (see free text).

- Particle size distribution: 95% of the particles were < 5 µm

Analytical verification of test atmosphere concentrations:
Duration of exposure:
4 h
0.348, 0.418, 0.500 and 0.523 mg/l
No. of animals per sex per dose:
Control animals:
Details on study design:
- Five groups of rats each composed of 10 males and 10 females were treated by inhalation. Each group was sub-divided into sub-groups containing 5 rats per sex. Each group was exposed (whole body) to a different concentration of the test substance (TS).
- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: Deaths and clinical signs were recorded during the exposure and thereafter on a daily basis. Body weights were recorded at days 0, 1, 2, 4, 7 and 14.
- Necropsy of survivors performed: yes. Immediately after the exposure the survivors of one subgroup of rats were sacrificed, while the survivors of the second subgroup were sacrificed after 14 days.
- Other examinations performed: Lungs with trachea and larynx and the nose were preserved in a 4 % neutral aqueous phosphate-buffered formaldehyde solution.
Method of calculation: probit analysis: Finney, DJ., Probit analysis (3rd ed) London, Cambridge University Press, 1971.

Results and discussion

Effect levels
Dose descriptor:
Effect level:
0.49 mg/L air (analytical)
95% CL:
0.376 - 0.638
Exp. duration:
4 h
see free text
Clinical signs:
other: During exposure: laboured respiration and mouth breathing especially at the highest two levels.
Body weight:
Both males and females lost b.w. during the first two to four days of the observation period. Around day 4, the animals gained b.w. again.
Gross pathology:
Some haemorrhages in the lungs and a haemorrhagic fluid around the nares of animals killed directly after the exposure to the three highest concentrations. Most lungs of animals exposed to 0.523 mg/l air were grayish and too wet. A few animals that died during or were killed at the end of the observation period showed some haemorrhages in the lungs. This finding was most frequently observed in animals exposed to 0.418 mg/l air.
Other findings:
Lungs, trachea and larynx and nose (potential target organs) were preserved in buffered formaldehyde solution but no histological findings were reported. No sex differences with regard to clinical signs and pathological findings were reported.

Any other information on results incl. tables

Treatment group

Dose level (mg/l)

Mortalities (male/female) at day





























* Day 0 is day of exposure

LC50: 0.490 mg/l (95% confidence limits: 0.376 and 0.638 mg/l); with the HPLC analysis the values are 0.456 mg/l (0.054 and 3.822 mg/l).

Results of the test group B was rejected because the values were completely out of range (zero mortality) and the exposure appeared too low (mean: 167 mg/m3).

On analysis the hair of the animals, the results were: the amount of non-extractable pMDI components with free NCO groups ranged from 170 to 340 µg per g hair (or from 250 to 426 µg per animal). The amount of monomeric MDI on the hair ranged from 12 to 34 µg per g hair or from 16 to 50 µg per animal). No MDA could be detected in any hair samples (detection limit: 5 µg MDA per g hair). No grooming activity was observed in any of the rats. The mean body weight, measured in a group of 5 animals, was reduced by about 30 % after 4 exposure. No death occurred, but the animals showed serious clinical signs especially after the 2nd exposure period laboured respiration that did not disappear during the non-exposure period but worsened during the following exposures. At the end of the 5th exposure the animals showed mouth breathing and were in very bad conditions. The animals did not eat or drink during the last 2 days of the study. Results: only very small amounts of pMDI components could be recovered from the fur of the animals. Ingestion (via grooming) was not expected to contribute significantly to the effects seen in this and aforementioned inhalation study.

Applicant's summary and conclusion

Interpretation of results:
Migrated information Criteria used for interpretation of results: expert judgment
The International Isocyanate Institute Inc. (III) developed the technique to create reproducible atmospheres of respirable aerosols of PMDI for inhalation tests; the derived aerosol comprised > 95% respirable fraction. The particle size distribution of 2.1μm MMAD (mass mean aerodynamic diameter), having a GSD of 1.6 (geometric standard deviation), meets the internationally recognised criteria for acute inhalation studies on rats. The technique took some 2 years to develop and to achieve this continuous respirable atmosphere extremely high energy levels were required and a separation cyclone had to be used.

This acute inhalation LC50 study conducted by the III, as part of a full range of inhalation work, used the continuous respirable aerosol, described above, as the test atmosphere. Polymeric MDI was chosen as the study compound as it represents a significant product in use. This study resulted in acute inhalation LC50 (4 hr, rat) value of 0.490 mg/l as reported in this record.

Both the aerosol developed for the III tests and the conditions required to achieve it are artificial and not experienced in normal handling and use of MDI.

There is virtually no overlapping in the respirable region of the aerosols generated for the LC50 test to those generated in the workplace. Furthermore, due to the physical properties of these aerosols and the high settling velocity of particles generated under real life conditions, there is no potential for exposure to acutely toxic doses (dose = concentration x time). This finding is supported by the industrial exposure data.

When evaluating and extrapolating the effects of a particular exposure it is also important to consider the physico-chemical characteristics of the inhaled substances. The data show that the vapour pressure of monomeric and polymeric MDI is very low; this means that the concentrations likely to evoke acute pneumo-toxicity are impossible to achieve in real-use conditions.

The data was considered by EU experts and their conclusion that MDI be classified as harmful (Xn, R20) is reported in the 25th Adaptation to Technical Progress (ATP) to the Dangerous Substances Directive (67/548/EEC). This was endorsed in the 28th ATP and MDI remains as harmful in the 30th ATP published 2008.

The EU Risk Assessment of MDI (Directive 793/93/EEC, 3rd Priority List) published in 12/2005 notes that considering “the exposure assessment, it is reasonable to consider MDI as harmful only and to apply the risk management phrase ‘harmful by inhalation’.

This classification was also endorsed by the Scientific Committee on Toxicity, Ecotoxicity and the Environment (CSTEE, now SCHER) in giving their opinion on the Risk Assessment.

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