Registration Dossier

Diss Factsheets

Toxicological information

Developmental toxicity / teratogenicity

Currently viewing:

Some information in this page has been claimed confidential.

Administrative data

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: This study is classified as reliable without restrictions because it is well documented and follows OECD Guideline 414.
Cross-reference
Reason / purpose for cross-reference:
read-across: supporting information
Reference
Endpoint:
developmental toxicity
Type of 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: This study is classified as reliable without restrictions because it is well documented and follows OECD Guideline 414.
Justification for type of information:
A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
Overall mean body weight gain for the exposure period (GD 6-16) was statistically significantly reduced for female rats exposed to 7000 ppm cyclohexane (approximately 69% of control). Mean body weight gain for the exposure and post-exposure period (GD 6-21) calculated using the adjusted final body weight (GD 21 body weight minus Gravid Uterine Weight), was also statistically significantly decreased (approximately 75% of control) for female rats in the 7000 ppm group.
Key result
Dose descriptor:
NOAEC
Effect level:
ca. 2 000 ppm
Based on:
test mat.
Basis for effect level:
other: maternal toxicity
Key result
Dose descriptor:
NOAEC
Effect level:
> 7 000 ppm
Based on:
test mat.
Basis for effect level:
other: developmental toxicity
Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
There were no dead rat fetuses. There were no statistically significant differences between control and treatment groups in early, late, or total resorptions. There were no statistically significant differences between control and treatment groups in mean fetal weight. No compound-related effect on the incidence of fetal malformations or variations was observed.
Key result
Dose descriptor:
NOAEC
Effect level:
> 7 000 ppm
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No developmental effects observed at the highest concentration tested.
Abnormalities:
not specified
Developmental effects observed:
not specified
Conclusions:
In rats, the maternal NOAEC was 2000 ppm (6000 mg/m3), and the maternal LOAEC was 7000 ppm (21000 mg/m3) based on reduced body weight gain. The developmental NOAEC 7000 ppm (21000 mg/m3) in rats.
Executive summary:

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

The purpose of this study was to examine the developmental toxicity of cyclohexane in rats. Groups of 25 pregnant female rats were exposed to concentrations of 0, 500, 2000, or 7000 ppm for 6 hrs/day during gestational days 6 -15. The animals were then sacrificed on GD 21. During the study, the animals were examined for clinical signs, mortality, food and water consumption, and body weights taken. After sacrifice, the internal organs were examined, and the uterus was examined for viable fetuses, number of resorptions, and number of corpora lutea. Fetuses were examined for malformations. Maternal effects were restricted to changes in maternal body weight gain and associated with decreased food consumption. No fetal effects were reported. Maternal NOAEC was determined to be 2000 ppm (6000 mg/m3) while the fetal NOAEC was greater than the highest concentration tested.

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)
GLP compliance:
yes

Test material

Constituent 1
Details on test material:
Cyclohexane was supplied as a liquid in a 55-gallon stainless steel drum by Phillips Petroleum Company, Sweeney Refinery, Sweeney, Texas.

Test animals

Species:
rat
Strain:
Crj: CD(SD)
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Age at study initiation: 8 weeks (males) and 11 weeks (females)
- Housing: individually in stainless steel wire mesh cages
- Diet (e.g. ad libitum): Purina Certified Rodent Checkers, ad libitum
- Water (e.g. ad libitum): tap water, ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 +/- 2 deg C
- Humidity (%): 50% +/- 10%
- Photoperiod (hrs dark / hrs light): 12 hrs light/12 hrs dark

Administration / exposure

Route of administration:
inhalation: vapour
Details on exposure:
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 vapor 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.
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. 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 vapor 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. The results of these determinations indicated the distribution of cyclohexane vapor was sufficiently homogeneous (less than 2% difference in chamber concentration from position to position) for inhalation toxicology testing.
Details on mating procedure:
- Impregnation procedure: cohoused in breeding pairs (M/F ratio per cage - 1/1)
- Proof of pregnancy: vaginal plug referred to as day 0
Duration of treatment / exposure:
Assumed pregnant rats were exposed on gestation days (GD) 6-15
Frequency of treatment:
6 hrs/day
Duration of test:
GD 21
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0, 500, 2000, 7000 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
Basis:

No. of animals per sex per dose:
25 pregnant females per exposure group
Control animals:
yes

Examinations

Maternal examinations:
During the exposure period, 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 recorded once per day. On GD 21, dams were euthanized and organs of the thoracic and abdominal cavities examined grossly.
Ovaries and uterine content:
The uterus of each animal was removed and opened. The types of implants (live and dead fetuses, and resorptions) were counted and their relative positions were recorded.
Fetal examinations:
Live fetuses were weighed, sexed, and examined for external, visceral, and skeletal alterations.
Statistics:
In general, sequential trend testing was applied to the data of each parameter. If a significant dose-response was detected, data from the top dose group was excluded and the test repeated until no significant trend was detected. Due to limitations of the data collection and reporting system, in the reproductive toxicity study, adult body weight and food consumption data were analyzed by pair-wise comparisons. The level of significance selected for all analyses was p <= 0.05. Parametric analyses were used to compare continuous data such as adult body weight and food consumption data among study groups. Linear contrast of means from One-way Analysis of Variance (ANOVA) was the method of analysis in the developmental toxicity studies; in the reproductive toxicity study, Dunnett's test followed the ANOVA. Litterrelated continuous data were analyzed by a nonparametric method, Jonckheere's trend test. For litter parameters, the proportion of affected fetuses per litter or 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. Fetal and pup weight data were analyzed by an Analysis of Covariance (co variates: litter size, sex ratio) followed with a linear contrast of the least square means. Discrete data, such as the incidences of clinical observations and reproductive indices, were evaluated by the Cochran-Armitage test for trend. Since tissues or
organs were not microscopically evaluated in all groups, the incidences of 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:
Overall mean body weight gain for the exposure period (GD 6-16) was statistically significantly reduced for female rats exposed to 7000 ppm cyclohexane (approximately 69% of control). Mean body weight gain for the exposure and post-exposure period (GD 6-21) calculated using the adjusted final body weight (GD 21 body weight minus Gravid Uterine Weight), was also statistically significantly decreased (approximately 75% of control) for female rats in the 7000 ppm group.

Effect levels (maternal animals)

open allclose all
Key result
Dose descriptor:
NOAEC
Effect level:
ca. 2 000 ppm
Based on:
test mat.
Basis for effect level:
other: maternal toxicity
Key result
Dose descriptor:
NOAEC
Effect level:
> 7 000 ppm
Based on:
test mat.
Basis for effect level:
other: developmental toxicity

Results (fetuses)

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

Details on embryotoxic / teratogenic effects:
There were no dead rat fetuses. There were no statistically significant differences between control and treatment groups in early, late, or total resorptions. There were no statistically significant differences between control and treatment groups in mean fetal weight. No compound-related effect on the incidence of fetal malformations or variations was observed.

Effect levels (fetuses)

Key result
Dose descriptor:
NOAEC
Effect level:
> 7 000 ppm
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No developmental effects observed at the highest concentration tested.

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
In rats, the maternal NOAEC was 2000 ppm (6000 mg/m3), and the maternal LOAEC was 7000 ppm (21000 mg/m3) based on reduced body weight gain. The developmental NOAEC 7000 ppm (21000 mg/m3) in rats.
Executive summary:

The purpose of this study was to examine the developmental toxicity of cyclohexane in rats. Groups of 25 pregnant female rats were exposed to concentrations of 0, 500, 2000, or 7000 ppm for 6 hrs/day during gestational days 6 -15. The animals were then sacrificed on GD 21. During the study, the animals were examined for clinical signs, mortality, food and water consumption, and body weights taken. After sacrifice, the internal organs were examined, and the uterus was examined for viable fetuses, number of resorptions, and number of corpora lutea. Fetuses were examined for malformations. Maternal effects were restricted to changes in maternal body weight gain and associated with decreased food consumption. No fetal effects were reported. Maternal NOAEC was determined to be 2000 ppm (6000 mg/m3) while the fetal NOAEC was greater than the highest concentration tested.

Categories Display