2-methylbutane

Developmental toxicity / teratogenicity

Some information in this page has been claimed confidential.

Administrative data

Endpoint:

developmental toxicity

Type of 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: no restrictions, fully adequate for assessment

Cross-reference

Reason / purpose for cross-reference:

read-across: supporting information

Reference

Endpoint:

developmental toxicity

Type of 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: no restrictions, fully adequate for assessment

Reason / purpose for cross-reference:

read-across source

Species:

rat

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
There were no unscheduled deaths. Rats exposed to 2000 or 7000ppm exhibited a transient diminished or absent alerting response during each exposure session; this effect was not seen in rats exposed to 500ppm. Overall mean body weight gain for the exposure period (days 6-16) was statistically significantly reduced for rats exposed to 7000 ppm (69% of control) and mean daily food consumption was 89% of control. Mean body weight gain for the exposure and post-exposure period (Days 6-21) calculated using the final body weight minus the gravid uterine weight) was also statistically significantly reduced (75% of control). There was judged to be no effect of exposure to 2000 or 500ppm on maternal bodyweight.
A similar reduction in weight gain was seen in the pair-fed animals. There were no post-mortem findings that were considered indicative of a treatment-related effect

Key result

Dose descriptor:

NOAEC

Effect level:

500 - 2 000 ppm

Basis for effect level:

other: maternal toxicity

Details on embryotoxic / teratogenic effects:

Details on embryotoxic / teratogenic effects:
There were no treatment-related differences in pregancy rate, early delivery rate, abortion rate, total resoption rate, mean number of implantations per litter, the mean number of live foetuses per litter or sex ratio. There were no dead foetuses, nor was there any difference in the incidence of early, late or total resorptions. Foetal weight was unaffected by treatment. There were no effects on the incidence of foetal malformations or variations.

Key result

Dose descriptor:

NOAEC

Effect level:

7 000 ppm

Sex:

male/female

Basis for effect level:

other: teratogenicity

Abnormalities:

not specified

Developmental effects observed:

not specified

Mean maternal bodyweight gain (g) selected timepoints

	0	0#	500	2000	7000
0 to 6	18.7	22.4	22.3	24.6	22.1
6 to 16	64.2	32.1^†	60.1	57.2*	44.2*
6 to 21 (b)	49.6	12.5^†	43.0*	43.0*	37.1*

# - pair fed control b- ANOVA and Dunnets test

†- Significant difference from control (ANOVA and Dunnetts test); p< 0.05

* significant trend (linear contrast of means from ANOVA); p< 0.05

b- bwt gain on GD6-21 after correction for gravid uterus weight

Conclusions:

Cyclohexane was not a developmental toxin in female rats exposed during pregnancy. The foetal NOAEC was 7000 ppm, and the maternal NOAEC was 500 ppm (based upon transient sedation) or 2000 ppm (based upon significant reductions in absolute and adjusted body weight gain).

Executive summary:

This data is being read across from the source study that tested cyclohexane based on analogue read across.

The developmental toxicity of cyclohexane was assessed in Crl:CD BR rats. The animals were exposed whole-body to nominal atmospheric concentrations of 0, 500, 2000, or 7000 ppm cyclohexane vapour. For rats in the 7000 ppm group, statistically significant reductions were observed in overall and adjusted maternal body weight gain while a transient diminished or absent response to a sound stimulus was apparent at 2000 ppm. Therefore the maternal no-observed-adverse-effect concentration (NOAEC) was 500ppm (1,720 mg/m³) (based upon transient sedation) or 2000 ppm (6,880 mg/m³) (based upon significant reductions in overall and adjusted body weight gain).  No compound-related evidence of developmental toxicity was observed at any test concentration, equivalent to a NOAEC of 7000 ppm (24,080 mg/m³).

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

Test material information

Constituent 1

Constituent 2

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:

rat

Strain:

other: Crl:CD BR

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: Approximately 11 weeks
- Housing: Animals were housed individually in suspended, wire-mesh, stainless steel cages.
- Diet: Purina "Certified Rodent Checkers" was available ad libitum, except during exposures to all rats other than those in the pair-fed control group of the developmental toxicity study. Beginning with exposure, each animal in the pair-fed control group received an amount of Purina Certified Rodent Checkers approximately equal to the cumulative average amount of food consumed by the high-concentration group (7000 ppm) animals on the corresponding gestation day
- Water: tap water ad libitumexcept during exposures

ENVIRONMENTAL CONDITIONS
- Temperature: 23±2°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 rats (25/concentration level) were exposed on days 6-15 of gestation (6-15G). The day that copulation was confirmed was designated as day 0.

Frequency of treatment:

5 d/wk

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0 (air), 500, 2000 or 7000 ppm
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0 (air), 500, 2000 or 7000 ppm
Basis:
other: overall mean measured

No. of animals per sex per dose:

25 per concentration level

Control animals:

yes, concurrent vehicle

Details on study design:

A pair-fed control group was established for the 7000 ppm treatment group. Beginning with exposure, each animal in the pair-fed control group received an amount of Purina Certified Rodent Checkers approximately equal to the cumulative average amount of food consumed by the high-concentration group (7000 ppm) animals on the corresponding gestation day. Each rat received approximately 150 grams per day of Purina Certified Rat Diet HF #5325; feed was not available during exposure.

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, rats were weighed weekly and clinical signs were recorded once per day. Near the end of gestation (21 days), the maternal animals were sacrificed and the organs of the thoracic and abdominal cavities were examined grossly. The method of euthanasia was carbon dioxide asphyxiation.

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:

The foetuses were euthanatized by decapitation or by 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:yes

Details on maternal toxic effects:
There were no unscheduled deaths. Rats exposed to 2000 or 7000ppm exhibited a transient diminished or absent alerting response during each exposure session; this effect was not seen in rats exposed to 500ppm. Overall mean body weight gain for the exposure period (days 6-16) was statistically significantly reduced for rats exposed to 7000 ppm (69% of control) and mean daily food consumption was 89% of control. Mean body weight gain for the exposure and post-exposure period (Days 6-21) calculated using the final body weight minus the gravid uterine weight) was also statistically significantly reduced (75% of control). There was judged to be no effect of exposure to 2000 or 500ppm on maternal bodyweight.
A similar reduction in weight gain was seen in the pair-fed animals. There were no post-mortem findings that were considered indicative of a treatment-related effect

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEC

Effect level:

500 - 2 000 ppm

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Details on embryotoxic / teratogenic effects:
There were no treatment-related differences in pregancy rate, early delivery rate, abortion rate, total resoption rate, mean number of implantations per litter, the mean number of live foetuses per litter or sex ratio. There were no dead foetuses, nor was there any difference in the incidence of early, late or total resorptions. Foetal weight was unaffected by treatment. There were no effects on the incidence of foetal malformations or variations.

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEC

Effect level:

7 000 ppm

Sex:

male/female

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Mean maternal bodyweight gain (g) selected timepoints

	0	0#	500	2000	7000
0 to 6	18.7	22.4	22.3	24.6	22.1
6 to 16	64.2	32.1^†	60.1	57.2*	44.2*
6 to 21 (b)	49.6	12.5^†	43.0*	43.0*	37.1*

# - pair fed control b- ANOVA and Dunnets test

†- Significant difference from control (ANOVA and Dunnetts test); p< 0.05

* significant trend (linear contrast of means from ANOVA); p< 0.05

b- bwt gain on GD6-21 after correction for gravid uterus weight

Applicant's summary and conclusion

Conclusions:

Cyclohexane was not a developmental toxin in female rats exposed during pregnancy. The foetal NOAEC was 7000 ppm, and the maternal NOAEC was 500 ppm (based upon transient sedation) or 2000 ppm (based upon significant reductions in absolute and adjusted body weight gain).

Executive summary:

The developmental toxicity of cyclohexane was assessed in Crl:CD BR rats. The animals were exposed whole-body to nominal atmospheric concentrations of 0, 500, 2000, or 7000 ppm cyclohexane vapour. For rats in the 7000 ppm group, statistically significant reductions were observed in overall and adjusted maternal body weight gain while a transient diminished or absent response to a sound stimulus was apparent at 2000 ppm. Therefore the maternal no-observed-adverse-effect concentration (NOAEC) was 500ppm (1,720 mg/m³) (based upon transient sedation) or 2000 ppm (6,880 mg/m³) (based upon significant reductions in overall and adjusted body weight gain).  No compound-related evidence of developmental toxicity was observed at any test concentration, equivalent to a NOAEC of 7000 ppm (24,080 mg/m³).