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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 based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: no restrictions, fully adequate for assessment

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2000

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Deviations:
yes
Remarks:
Because the study examined the inhalation affects related to exposure of cyclohexane, test animals received whole body exposure to the cyclohexane vapour. Test animals failed to be weighed daily but rather were weighed weekly.
GLP compliance:
yes

Test material

Constituent 1
Reference substance name:
Cyclohexane
EC Number:
203-806-2
EC Name:
Cyclohexane
Cas Number:
110-82-7
IUPAC Name:
cyclohexane
Details on test material:
This substance is very similar in structure to the substance being registered.

Purity: 99.99%

Test animals

Species:
rabbit
Strain:
other: Hra:(NZW)SPF
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Age at study initiation: Approximately 6 months
- Housing: Animals were housed individually in suspended, wire-mesh, stainless steel cages.
- Diet: Approximately 150 g/day of Purina Certified Rabbit Diet HF #5325 except during exposure.
- Water: tap water ad libitumexcept during exposure.

ENVIRONMENTAL CONDITIONS
- Temperature: 20+/- 1°C
- Humidity: 50+/- 10%
- Photoperiod: 12 hrs dark / 12 hrs light

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Vehicle:
unchanged (no vehicle)
Details on exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: All exposure chambers were constructed of stainless steel and glass and had a nominal internal volume of 1.4 m3. The chamber volume was chosen so that the total body volume of the test animals did not exceed 5% of the chamber volume. A tangential feed at the chamber inlet promoted gas mixing and uniform chamber distribution of vapour
- Atmospheres of cyclohexane were generated by metering the liquid test substance into a heated glass Instatherm flask with a Fluid Metering Inc. pump. Nitrogen, introduced into the flask, swept the cyclohexane vapour into the inhalation chamber air supply. The chamber concentration of cyclohexane was controlled by varying the amount of the metered liquid evaporated in the chamber air stream. Nitrogen and air were passed through the control chamber at approximately the same flow rates as those used in the exposure chambers.

TEST ATMOSPHERE-The atmospheric concentration of cyclohexane was determined by gas chromatography at approximately 15-minute intervals during each 6-hour exposure.
Chamber-atmosphere samples were drawn by vacuum pump from representative areas of the chamber where animals were exposed and were directly injected into a Hewlett Packard model 5880 Gas Chromatograph equipped with a flame ionization. All samples were chromatographed isothermally at 70°C on an HP-20M Carbowax column. The chamber distribution of cyclohexane vapour was determined prior to animal exposures in the high-concentration exposure chamber and while the study was underway with animals in the low- and high-concentration chambers.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
The atmospheric concentration of cyclohexane was determined by gas chromatography at approximately 15 minute intervals during each 6-hour exposure. The results of these determinations indicated the distribution of cyclohexane vapour was sufficiently homogeneous (less than 2% difference in chamber concentration from position to position)
Duration of treatment / exposure:
Assumed-pregnant rabbits were exposed on days 6-18 of gestation (6-18G). The day that copulation was confirmed was designated as day 0.
Frequency of treatment:
daily
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0 (air), 500, 2000 or 7000 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
0 (air), 500, 2000 or 7000 ppm
Basis:
other: overall mean measured
No. of animals per sex per dose:
20 per concentration level
Control animals:
yes, concurrent vehicle

Examinations

Maternal examinations:
During the exposure period, the animals were weighed daily and clinical signs were recorded before and after exposure. During the pre- and post- exposure periods, rabbits were weighed twice weekly and clinical signs were recorded once per day. Near the end of gestation (29 days), the maternal animals were euthanized and the organs of the thoracic and abdominal cavities were examined grossly. The method of euthanasia was by intravenous injection of sodium pentobarbital.
Ovaries and uterine content:
The uterus of each animal was removed and opened. The types of implants (live and dead foetuses, and resorptions) were counted and their relative positions were recorded.
Fetal examinations:
Foetuses were euthanized by an oral or intraperitoneal injection of sodium pentobarbital. They were weighed, sexed and examined for external, visceral and skeletal alterations.
Statistics:
Sequential trend testing was applied to the data of each parameter. Adult body weight and food consumption data were analyzed by pair-wise comparisons. Parametric analyses were used to compare continuous data. Linear contrast of means from One-way Analysis of Variance (ANOVA) was the method of analysis followed by Dunnett's test. Litter-related continuous data were analyzed by a nonparametric method Jonckheere's trend test. For litter parameters, the litter mean was used as the experimental unit for statistical evaluation. Where the data were tied, exact p values were calculated using permutation methodology. Pup weight data were analyzed by an Analysis of Covariance (covariates: litter size, sex ratio) followed with a linear contrast of the least square means. Discrete data were evaluated by the Cochran-Armitage test for trend. Microscopic observations were analyzed by the Fisher's exact test.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:no effects

Details on maternal toxic effects:
There were no treatment-related effects on maternal bodyweight or body weight gain, food consumption, clinical condition or alerting response. There were no post-mortem findings suggestive of compound-related effects.

Effect levels (maternal animals)

Dose descriptor:
NOAEC
Effect level:
7 000 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:
No compound-related effect on the incidence of foetal malformations or variations was observed.

Effect levels (fetuses)

Dose descriptor:
NOAEC
Effect level:
7 000 ppm
Basis for effect level:
other: teratogenicity

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
Cyclohexane was not a developmental toxin in female rabbits after exposure to 7000 ppm (24,080 mg/m3) during pregnancy.
Executive summary:

Therefore the maternal NOAEC for rabbits was 7000 ppm. No compound-related evidence of developmental toxicity was observed at any test concentration.

Therefore the developmental NOAEC for rabbits was 7000 ppm (24,080 mg/m3), the highest concentration tested and the highest concentration permissible under national fire protection association standards.