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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Equivalent or similar to OECD Guideline 414 GLP study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1988
Report date:
1988

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Deviations:
not specified
GLP compliance:
yes

Test material

Constituent 1
Chemical structure
Reference substance name:
m-tolylidene diisocyanate
EC Number:
247-722-4
EC Name:
m-tolylidene diisocyanate
Cas Number:
26471-62-5
Molecular formula:
C9 H6 N2 O2
IUPAC Name:
m-tolylidene diisocyanate
Details on test material:
80:20 mixture of the 2,4- and 2,6-TDI.

Data on physical and chemical properties, eco-toxicity and toxicity can be used for read-across from 2,4-TDI to 2,6-TDI and mixed TDI isomers (i.e. 80/20, 65/35, 2,4/2,6 ratios). 2,4 TDI is the major component of the TDI mixed isomers and so has the major influence on their properties and effects. The reactivity of the 2,6-TDI isomer is somewhat less than that of 2,4-TDI but is of the same order of magnitude. It may therefore be concluded that the effects of 2,6-TDI will be similar to those of 2,4-TDI. This is in fact observed where there are overlapping data.

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals or test system and environmental conditions:
Animals during acclimation were housed separately by sex, two-three per cage in stainless-steel wire-mesh cages. Food and water were available ad libitum except during exposures. Paperboard was placed beneath the cages, light phase, temperature and relative humidity were recorded continuously.

25 Timed-pregnant Sprague-Dawley rats were assigned to each experimental group on gestational day 0 by stratified randomisation procedures based on body weight.

Rats were mated 1:1 (on male: one female) in stainless steel wire mesh cages and the paperboard beneath the cages was checked twice daily for dropped copulation plugs. The date a copulation plug was found was designated gestational day 0.
Plug-positive females were individually housed for the duration of the study (except during exposure). For exposures, plug-positive females were transferred to stainless steel wire-mesh exposure cage. Food and water were withheld during exposures.

Maternal clinical signs were taken daily and body weights were measured on gestation day 0, 6, 9, 12, 16, and 21. Food and water consumption were measured every 3 days.

All live fetuses were anesthetized by hypothermia, and were weighed, sexed and examined for external malformations including cleft palate, and variations. Approximately half of the live fetuses in each litter were examined for thoracic and abdominal visceral abnormalities. The fetuses examined viscerally were decapitated and their heads fixed in Bouin's solution for examination of craniofacial structures. Intact fetuses in each litter were eviscerated, fixed in ethanol, and then processed for skeletal staining and examined for skeletal malformations and variations.

Maternal body cavities were opened by midline thoracolaparotomy. The gravid uterus, ovaries (including corpora lutea), cervix, vagina, and abdominal and thoracic cavities were examined grossly. Ovarian corpora lutea of pregnancy were counted. Maternal liver and uterine weights were determined. Sections of maternal liver, kidneys and upper and lower respiratory tract (including nasal turbinates) were retained in fixative for possible subsequent histological examination. The uteri were immediately ligated at their cervical end to prevent the expulsion of conceptuses by myometrial perstalsis, externally examined for signs of hemorrhage, removed from the peritoneal cavity, and dissected longitudinally to expose their contents. All live and dead fetuses and resorption sites (early and late) were noted and recorded. Uteri from females that appeared nongravid were placed in a 10% ammonium sulfide solution for detection of early resorptions.

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Details on exposure:
25 Pregnant females rats/group (56 days of age) were exposed to TDI vapour in 4320 litre chambers at 0.00, 0.02, 0.10 or 0.5 ppm. Exposures were for 6 hours/day, gestation day 6-15.

See below "Details on analytical verification of doses or concentrations"
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Generation of atmospheres: Liquid toluene diisocyanate was metered from a syringe pump into a heated glass evaporator. The temperature in the evaporator was monitored and maintained at the lowest level sufficient to vaporise the liquid (46 - 60°C). The resultant vapour was carried into the chamber (4320 liter chambers) by dilution air stream. Each chamber atmosphere was analysed for toluene diisocyanate approximately six times during each 6-hour exposure. Daily nominal concentrations and chamber airflow during the exposure period were calculated for each chamber. Chamber concentrations were monitored via Autostep Portable Monitors. In addition, chamber atmosphere samples were drawn through midget impingers and samples measured via UV.

Using a standard EPA conversion factor of 10.83 liters/hour of air breathed by 350 g rat, actual doses are roughly estimated at: 0.02 ppm = 3.71 mg/kg, 0.1 ppm = 18.57 mg/kg, and 0.2 0.5 ppm = 92.83 mg/kg.
Details on mating procedure:
Rats were mated 1:1 (on male: one female) in stainless steel wire mesh cages and the paperboard beneath the cages was checked twice daily for dropped copulation plugs. The date a copulation plug was found was designated gestational day 0.
Duration of treatment / exposure:
Exposures were for 6 hours/day, gestation day 6-15.
Frequency of treatment:
6 hours per day
Duration of test:
21 days (days 0-21 of gestation)
Doses / concentrations
Remarks:
Doses / Concentrations:
0.0, 0.02, 0.10, 0.50 ppm
Basis:
no data
No. of animals per sex per dose:
25 Pregnant females rats/group/dose level
Control animals:
yes, sham-exposed

Examinations

Maternal examinations:
Maternal clinical signs were taken daily and body weights were measured on gestation day 0, 6, 9, 12, 16, and 21. Food and water consumption were measured every 3 days.
Ovaries and uterine content:
Maternal body cavities were opened by midline thoracolaparotomy. The gravid uterus, ovaries (including corpora lutea), cervix, vagina, and abdominal and thoracic cavities were examined grossly. Ovarian corpora lutea of pregnancy were counted. Maternal uterine weights were determined. The uteri were immediately ligated at their cervical end to prevent the expulsion of conceptuses by myometrial perstalsis, externally examined for signs of hemorrhage, removed from the peritoneal cavity, and dissected longitudinally to expose their contents. Uteri from females that appeared nongravid were placed in a 10% ammonium sulfide solution for detection of early resorptions.
Fetal examinations:
All live fetuses were anesthetised by hypothermia, and were weighed, sexed and examined for external malformations including cleft palate, and variations. Approximately ½ of the live fetuses in each litter were examined for thoracic and abdominal visceral abnormalities. The fetuses examined viscerally were decapitated and their heads fixed in Bouin's solution for examination of craniofacial structures. Intact fetuses in each litter were eviscerated, fixed in ethanol, and then processed for skeletal staining and examined for skeletal malformations and variations.
Statistics:
Quantitative continuous variables were intercompared via Levene's test, ANOVA, and T-tests with Bonferroni probabilities. Nonparametric data were analyzed using the Kruskal-Wallis test followed by the Mann-Whitney U test. Incidence data were compared using Fisher's Exact Test. The fiducial limit of 0.05 (two-tailed) was used as the criterion for significance.
Indices:
Not applicable.
Historical control data:
Not applicable.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
Maternal weight gain was significantly depressed over the exposure period for 0.5 ppm group. Significant body weight reduction, significant body weight gain reduction and significantly reduced food consumption.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOAEC
Effect level:
0.1 ppm
Basis for effect level:
other: maternal toxicity
Dose descriptor:
LOAEC
Effect level:
0.5 ppm
Basis for effect level:
other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
Not applicable.

Effect levels (fetuses)

open allclose all
Dose descriptor:
NOAEC
Effect level:
0.1 ppm
Basis for effect level:
other: teratogenicity
Dose descriptor:
LOAEC
Effect level:
0.5 ppm
Basis for effect level:
other: fetotoxicity

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Any other information on results incl. tables

No deaths in dams. No significant differences in the number pregnant/dose level, number of dams aborting, pre- and post-implantation loss, number of corpora lutea, and number of resorptions. Number of total implants/litter and number of viable implants reduced at 0.02 ppm.

Maternal weight gain was significantly depressed over the exposure period for 0.5 ppm group. Maternal weight gain was significantly reduced early in the exposure period, gd 6-9, at 0.02, 0.1. Maternal food consumption was reduced at the high dose from exposure day 9 onward. In addition, food consumption was reduced at 0.02 ppm for gd 18-21 due to the dam with one fully resorbed litter eating at a nonpregnant rate in this group.

Treatment-related clinical sings of toxicity were limited to audible respiration in dams at 0.5 ppm and red nasal discharge at 0.02, 0.1, and 0.5 ppm.

No differences in maternal gross observations at necropsy. No differences gravid uterine weights, or body weight change was observed among the groups. Hydronephrosis, a typical finding in CD® rats was observed in 2 dams at 0.1 and 1 dam at 0.5 ppm.

No significant differences in litter size and weights, number of viable fetuses, or sex ratio. Increased incidence of poorly ossified cervical centrum 5 at 0.5 ppm indicating minimal fetotoxicity. No effect level for maternal and developmental toxicity is 0.1 ppm.

Applicant's summary and conclusion

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