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Toxicological information

Genetic toxicity: in vivo

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Administrative data

in vivo mammalian cell study: DNA damage and/or repair
Type of genotoxicity: DNA damage and/or repair
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Fully reported study meeting generally accepted standards

Data source

Reference Type:
study report
Report date:

Materials and methods

Principles of method if other than guideline:
Ashby et al. (1985) Method for UDS adapted for a single exposure by inhalation.
GLP compliance:
Type of assay:
unscheduled DNA synthesis

Test material

Constituent 1
Chemical structure
Reference substance name:
m-tolylidene diisocyanate
EC Number:
EC Name:
m-tolylidene diisocyanate
Cas Number:
Molecular formula:
C9 H6 N2 O2
m-tolylidene diisocyanate
Details on test material:
This study was carried out using mixed isomers of TDI. As mixed isomers of TDI contains generally 65% or 80% of the 2,4-TDI isomer, (the remainder being 2,6-TDI), this study can also be considered to be a valid test of 2,4-TDI. No claim is made as to the contribution or otherwise of the 2,6-TDI isomer in this assay.

Test animals

Fischer 344
Details on test animals or test system and environmental conditions:
All animals were checked for signs of illness or poor condition on arrival and during the pre-exposure period.

Administration / exposure

Route of administration:
Details on exposure:
Rats were exposed via inhalation for 4 hours. Animals were observed during the exposure period for clinical signs. Immediately after exposure, animals were removed from the chambers and allowed to recover overnight. Autopsies were then performed on 3 rats/group.
Duration of treatment / exposure:
4 hours
Doses / concentrations
Doses / Concentrations:
0, 0.077, 0.40, 1.49 ppm, 4 rats/group.

No. of animals per sex per dose:


Details of tissue and slide preparation:
Sections of the livers and lungs were removed and hepatocyte and lung explant cultures were then prepared immediately. Sections of lung, trachea, nasal turbinates, liver and kidney were removed and fixed in 10% neutral buffered formalin. The hepatocyte cultures were then incubated for 2 hours and then medium removed and labeled thymidine in serum free medium was added to each plate and dishes incubated for 3 to 4 hours. The labeled medium was then washed out with fresh unlabeled medium and the cultures were incubated overnight. Cells were then fixed and slides prepared. The results of the test were quantified by determining the production of net nuclear grains. The nuclear grain counts and the highest grain count from an equivalent area of cytoplasm were scored on each of 50 randomly selected cells. For the lung explant cultures, 4 pieces of lung from each animal (3 mm3) were cut and placed in petri dishes. Medium containing labeled thymidine was added and cultures were incubated in a CO2 chamber for 4 hours. Cultures were then washed, transferred to 10% formalin and then embedded into paraffin and cut into sections for slide preparation. All slides were autoradiographed and then stained with hematoxylin and eosin. Only explants with normal histology were analyzed. The net number of grains per nucleus was determined in 50 cells in healthy alveolar regions of each slide. Evidence of unscheduled DNA synthesis was examined in cultured hepatocytes and lung explant samples.
Mean net nuclear counts ± S.E.M. were determined for each of the triplicate slides per animal and the mean ± S.D. of net nuclear counts and percentage of cells in repair for each rat was then calculated. From these values, the mean ± S.D. for each dose group was determined. The test compound is considered positive if the mean net nuclear grain count of the treated animals is statistically greater than that of controls and equal to or greater than 2 grains/nucleus (the upper limit of control values).

Results and discussion

Test results

Any other information on results incl. tables

TDI did not induce UDS at any of the administered doses in lung cultures from any of the treated animals.

Histopathology of the preserved upper respiratory tract sections from each animal, evidence of lung infection (pneumonitis or bronchopneumonia) was observed in controls and consisted of inflammatory cell infiltrate in the interstitial space and alveoli in the lungs and nasal region. Clear dose-related effects were observed in the upper respiratory tract in rats exposed to TDI by inhalation. At the lowest dose, only 1 animal was affected by hyperplasia in the epithelium covering the turbinates and nasal septum. Hyperplasia and metaplasia in these areas increased with increase in dose and at the highest dose, one animal had minute but clearly definable ulceration. The trachea and main bronchi were affected in 1 animal at this dose level. There were no lesions in liver or kidneys from any animals exposed to TDI by inhalation.

Applicant's summary and conclusion

TDI administered to rats via inhalation did not induce unscheduled DNA synthesis in hepatocytes or lung explant cultures although it did cause signs of severe upper respiratory tract irritation.