2-methylbutane

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

There is no data available for 2-methylbutane. However, data is available for a structural analogue, cyclohexane and presented in the dossier. This data is read across to 2-methylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

Cyclohexane:

 

NOAEC for reproductive toxicity in rats = 7000 ppm (24080 mg/m³)

Link to relevant study records

Reference

Endpoint:

two-generation reproductive toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restriction because this study was performed in accordance with GLP and appeared to closely followed OECD 416.

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 416 (Two-Generation Reproduction Toxicity Study)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crl:CDBR

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: (P males) 8 weeks; (P females) 8 weeks
- Housing: Individually housed except during cohabitation periods in wire mesh cages. Assumed-pregnant females and those without evidence of copulation were individually housed in polycarbonate pans with bedding. During lactation, adult females were housed with their litters in polycarbonate pans with bedding
- Diet (e.g. ad libitum): Ad libitum, Purina Certified Rodent Checkers
- Water (e.g. ad libitum): Ad libitum

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

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 vapor
- 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.

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 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).

Details on mating procedure:

No data reported.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Achieved concentrations were determined by gas chromatography at approximately 15-minute intervals during each 6-hour exposure. Chamber distribution of cyclohexane was determined prior to animal exposures in the high-concentration exposure chamber. Results showed that the distribution of cyclohexane vapour was sufficiently homogeneous (less than 2% difference in chamber concentration from position to position).

Duration of treatment / exposure:

Males and females were exposed prior to mating (at least 10 weeks for the P generation and 11 weeks for the F1 generation). Pregnant females were exposed daily during gestation days 0 through 20; exposure ceased from gestation day 21 until lactation day 4. Exposure resumed on lactation day 5 until litters were weaned. Males continued to be exposed 5 days/week until sacrificed. Neonates were not exposed during lactation.

Frequency of treatment:

6 hours/day, 5 days/week, including holidays

Details on study schedule:

P animals were mated after approximately 10 weeks after exposure. Dams were allowed to deliver and rear pups until weaning (postpartum day 25). After at least 11 weeks after weaning, F1 animals were bread to produce F2 litters. Pups were culled on lactation day 4.

Remarks:

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

No. of animals per sex per dose:

P generation: 30 animals/sex/dose
F1 generation: 30 animals/sex/dose

Control animals:

yes, concurrent vehicle

Details on study design:

The high concentration was selected to be 60% of the Lower Explosive Limit; the low concentration was selected because it exceeds the threshold limit for human exposure and was not expected to cause toxicological effects. The mid dose was selected to provide approximately equal spacing between and high and low doses on a log scale.

Positive control:

No positive control was used.

Parental animals: Observations and examinations:

DETAILED CLINICAL OBSERVATIONS: Yes; Prior to the initiation of each exposure, during exposure, and during the time required to clear the chambers of test substance, the groups of animals within exposure levels were observed for a normal, diminished, or hyper-responsive alerting behavior in response to a standardized auditory stimulus.

BODY WEIGHT: Yes
- Time schedule for examinations: P and F1 rats were weighed weekly during the premating, gestation, and lactation periods.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

Oestrous cyclicity (parental animals):

No data reported.

Sperm parameters (parental animals):

No data reported.

Litter observations:

F1 and F2 pup weights and clinical observations were recorded on postpartum days 0, 4, 7, 14, 21, and 25.

Postmortem examinations (parental animals):

After litter production, all P and F1 parental animals were euthanized by carbon dioxide and exsanguinated. Reproductive organs and pituitary gland were collected from each animal. Tissues from the high-dose and control animals for both generations were examined microscopically.

Postmortem examinations (offspring):

Pups were euthanized by carbon dioxide and exsanguinated.

Statistics:

In general, sequential trend testing was applied to the data of each parameter. If a result was significant, data from the high-dose group was excluded; the test was repeated in until no significant trend was detected. 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.

Among study groups, parametric analyses were used to compare continuous data. Linear contrast was performed by conducting a Dunnett's test followed by ANOVA. Litter-related continuous data were analyzed by Jonckheere's test. Foetal and pup weights were analyzed by an Analysis of Covariance followed with a linear contrast of the least square means. Discrete data were evaluated by the Cochran-Armitage test for trend. The incidence of microscopic observations were analyzed by the Fisher's exact test.

Reproductive indices:

Mating index, fertility index, and mean gestation length were calculated.

Offspring viability indices:

The sex ratio, implantation efficiency, gestation index, day 0-4 viability, lactation index, and litter survival were calculated.

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)
At 2000 and 700 ppm, animals exhibited treatment-related transient diminished or absent response to sound stimulus during each exposure session, being at exposures 16 and 15, respectively. Males (P and F1) treated with 2000 and 7000 ppm and 7000-ppm females from both generations were showed significantly increased incidence fur staining and wetness presumably related to salivation. These clinical signs were not considered treatment-related.

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
P males showed no treatment-related body weight changes in any dose group. High-dose F1 males were generally statistically significantly reduced throughout the study. This decrease was considered by the result of pre-existing body weight differences established as pups during the lactation period.

High-dose P females showed a significant decrease in mean body weight and body weight gain by the end of the premating period. High-dose females showed lower body weight and body weight gain, but to a lesser magnitude. Food consumption was similar between control and treated rats for both generations; however, food efficiency was reduced for both generations at the high dose.

During gestation, mean body weight and body weight gain was not affected by treatment. Food consumption for 7000-ppm P females was less than control females during gestation days 0 through 7; no differences were observed for F1 females. During lactation, 2000- and 7000-ppm P females were greater than the control group; these differences were not observed in the F1 generation. There were no differences in food consumption during lactation for either generation; however, 7000-ppm females had better food efficiency than the control group, which was attributable to the difference in body weight gains between the two groups.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
There were no statistically significant treatment-related differences in mating, fertility, or gestation indices, implantation efficiency or gestation length in either generations.

GROSS PATHOLOGY (PARENTAL ANIMALS)
There were no treatment-related effects with regard to gross observations in rats of any generation.

HISTOPATHOLOGY (PARENTAL ANIMALS)
There were no treatment-related effects with regard to microscopic findings in rats of any generation. An increased incidence of prostatic inflammation in high-dose males in both generations was observed. The severity of this lesion was only in four P and F1 control animals and four high-dose males, and was considered incidental due to its lack of severity and common occurrence in this species.

Key result

Dose descriptor:

other: Parental NOAEC

Effect level:

500 ppm (nominal)

Sex:

male/female

Basis for effect level:

other: 1720 mg/m3

Remarks on result:

other: Generation: P and F1 (migrated information)

Key result

Dose descriptor:

other: Parental LOAEC

Effect level:

2 000 ppm (nominal)

Sex:

male/female

Basis for effect level:

other: 6880 mg/m3; based on transient treatment-related sedative effect on the rats' alerting response to sound stimulus

Remarks on result:

other: Generation: P and F1 (migrated information)

Key result

Dose descriptor:

other: Reproductive NOAEC

Effect level:

7 000 ppm (nominal)

Sex:

male/female

Basis for effect level:

other: 24,080 mg/m3; there were no adverse compound-related effects on reproductive function.

Remarks on result:

other: Generation: P and F1 (migrated information)

Clinical signs:

no effects observed

Mortality / viability:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

VIABILITY (OFFSPRING)
There was a significant decrease in the mean percent born alive in high-dose F1 pups; however, this decrease was considered incidental since it was not observed in the F2 pups. There were no other changes observed in viability for F1 or F2 pups at any dose level.

CLINICAL SIGNS (OFFSPRING)
There were no treatment-related effects observed for either F1 and F2 pups.

BODY WEIGHT (OFFSPRING)
Mean pup weight was statistically significantly reduced from postpartum day 7 throughout the remainder of the 25-day lactation period for 7000-ppm F1 and F2 litters (see Table 1 below).

Key result

Dose descriptor:

NOAEC

Generation:

F1

Effect level:

ca. 2 000 ppm (nominal)

Sex:

male/female

Basis for effect level:

other: 6880 mg/m3

Key result

Dose descriptor:

LOAEC

Generation:

F1

Effect level:

ca. 7 000 ppm (nominal)

Sex:

male/female

Basis for effect level:

other: 24,080 mg/m3; decreased mean pup weight from lactation days 7 through 25

Key result

Dose descriptor:

NOAEC

Generation:

F2

Effect level:

ca. 2 000 ppm (nominal)

Sex:

male/female

Basis for effect level:

other: 6880 mg/m3

Key result

Dose descriptor:

LOAEC

Generation:

F2

Effect level:

ca. 7 000 ppm (nominal)

Sex:

male/female

Basis for effect level:

other: 24,080 mg/m3; decreased mean pup weight from lactation days 7 through 25

Key result

Reproductive effects observed:

no

Table 1: Mean Pup Weights (g)

Concentration (ppm)	0	500	2000	7000	0	500	2000	7000
	F1 generation				F2 generation
Day 0	6.7	6.7	6.7	6.6	6.4	6.6	6.3	6.3
Day 4 preculling	11.0	11.0	11.2	10.6	10.8	10.8	10.1	10.2
Day 4 postculling	11.0	11.0	11.3	10.6	10.9	10.8	10.1	10.1
Day 7	16.2	16.2	16.3	15.1*	16.3	16.0	15.3	14.3*
Day 14	30.0	29.9	29.7	26.5*	31.0	30.2	28.9	26.2*
Day 21	48.5	48.5	48.3	43.1*	50.0	48.3	46.4	42.8*
Day 25	67.5	67.8	68.3	62.2*	69.3	67.1	65.6	61.3*

* Statistically significant difference from control (p ≤0.05) by Analysis of Covariance with litter and sex ration as covariates.

Conclusions:

Decreased sound stimulus observed in 2000- and 7000-ppm animals (both sexes in both generations) was considered to be the most sensitive indicator of parental toxicity. This effect was an expected outcome of overexposure. Additional parental effects include decreased mean body weight and mean body weight gain in 7000 -ppm P and F1 rats. Mean pup weight was statistically significantly reduced from postpartum day 7 throughout the remainder of the 25-day lactation period for 7000-ppm F1 and F2 litters. There were no adverse treatment regarding reproductive function.
 

Executive summary:

In a 2-generation inhalation reproduction study, cyclohexane was administered to 30 Crl:CD BR rats /sex/dose at dose levels of 0, 500, 2000, or 7000 ppm. Whole body exposures were conducted, and animals were exposed 6 hours/day, 5 days/week including holidays. For both generations, animals were exposed prior to mating, and pregnant females were exposed daily during gestation days 0 through 20; exposure cessed from gestation day 21 until lactation day 4. Exposure resumed on lactation day 5 until litters were weaned. Males continued to be exposed 5 days/week until sacrificed. Neonates were not exposed during lactation. Pups were culled on lactation day 4; however, there were no additional details provided on the culling procedure. ECD 416. This study will influence the DNEL.

 

Decreased sound stimulus observed in 2000- and 7000 -ppm animals (both sexes in both generations) was considered to be the most sensitive indicator of parental toxicity. This effect was an expected outcome of overexposure. Additional parental effects include decreased mean body weight and mean body weight gain in 7000 -ppm P and F1 rats. Decreased male body weights observed at 7000 ppm were considered to be an artefact of body-weight deficits established as pups. Although not established by the study authors, the parental systemic LOAEC appears to be 2000 ppm (6880 mg/m3) in males and females, based on decreased sound stimulus. The parental systemic NOAEC appears to be 500 ppm (1720 mg/m3) in males and females.

 

Mean pup weight was statistically significantly reduced from postpartum day 7 throughout the remainder of the 25-day lactation period for 7000-ppm F1 and F2 litters. The offspring LOAEC is 7000 ppm (24,080 mg/m3) based on decreased litter weights. The offspring NOAEC is 2000 ppm (6880 mg/m3).

There were no adverse treatment regarding reproductive function. Consequently, the reproductive NOAEC appears to be 7000 ppm (24,080 mg/m3).

 

This study received a Klimisch score of 1 and is classified as reliable without restriction because this study was performed in accordance with GLP and appeared to closely followed OECD 416. This study will influence the DNEL.

Effect on fertility: via oral route

Endpoint conclusion:

no study available

Effect on fertility: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

24 080 mg/m³

Study duration:

subacute

Experimental exposure time per week (hours/week):

30

Species:

rat

Quality of whole database:

One key read across study from a structural analogue available for assessment.

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

There is no data available for 2-methylbutane. However, data is available for a structural analogue, cyclohexane and presented in the dossier. Cyclohexane is oxidized to cyclohexanol, and excretion and conjugation of cyclohexanol is identical to 2-methylbutane. Therefore, data on the toxicokinetics and reproductive toxicity of cyclohexane can be used to fill data gaps for 2 -methylbutane when relevant data for this chemical is missing. This data is read across to 2-methylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

 

Cyclohexane

 

In a 2-generation inhalation reproduction study (Kreckmann et al. 2000), cyclohexane was administered to 30 Crl:CD BR rats /sex/dose at dose levels of 0, 500, 2000, or 7000 ppm. Whole body exposures were conducted, and animals were exposed 6 hours/day, 5 days/week including holidays. For both generations, animals were exposed prior to mating, and pregnant females were exposed daily during gestation days 0 through 20; exposure cessed from gestation day 21 until lactation day 4. Exposure resumed on lactation day 5 until litters were weaned. Males continued to be exposed 5 days/week until sacrificed. Neonates were not exposed during lactation. Pups were culled on lactation day 4; however, there were no additional details provided on the culling procedure.

 

Decreased sound stimulus observed in 2000- and 7000 -ppm animals (both sexes in both generations) was considered to be the most sensitive indicator of parental toxicity. This effect was an expected outcome of overexposure. Additional parental effects include decreased mean body weight and mean body weight gain in 7000 -ppm P and F1 rats. Decreased male body weights observed at 7000 ppm were considered to be an artefact of body-weight deficits established as pups. Although not established by the study authors, the parental systemic LOAEC appears to be 2000 ppm (6880 mg/m3) in males and females, based on decreased sound stimulus. The parental systemic NOAEC appears to be 500 ppm (1720 mg/m3) in males and females.

 

Mean pup weight was statistically significantly reduced from postpartum day 7 throughout the remainder of the 25-day lactation period for 7000-ppm F1 and F2 litters. The offspring LOAEC is 7000 ppm (24,080 mg/m3) based on decreased litter weights. The offspring NOAEC is 2000 ppm (6880 mg/m3).

 

There were no adverse treatment regarding reproductive function. Consequently, the reproductive NOAEC appears to be 7000 ppm (24,080 mg/m3).

 

This study received a Klimisch score of 1 and is classified as reliable without restriction because this study was performed in accordance with GLP and appeared to closely followed OECD 416.

.

Effects on developmental toxicity

Description of key information

There is no data available for 2-methylbutane. However, data is available for structural analogues, pentane and cyclohexane and presented in the dossier. This data is read across to 2-methylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

 

Cyclohexane:

 

NOAEC for developmental toxicity (Rat): 7000 ppm (24080 mg/m³)

NOAEC for developmental toxicity (Rabbit): 7000 ppm (24080 mg/m³)

 

Pentane:

 

NOAEL for developmental toxicity: 1000 mg/Kg bw/day

Link to relevant study records

Reference

Reference 1

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: supporting information

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

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

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

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:

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.

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.

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:

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).

Reference 2

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: supporting information

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

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

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

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

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.

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.

Key result

Dose descriptor:

NOAEC

Effect level:

7 000 ppm

Basis for effect level:

other: maternal toxicity

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.

Key result

Dose descriptor:

NOAEC

Effect level:

7 000 ppm

Basis for effect level:

other: teratogenicity

Abnormalities:

not specified

Developmental effects observed:

not specified

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.

Reference 3

Endpoint:

developmental toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

1996-07-25 to 1997-04-11

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restriction because it is was performed according to GLPs and in compliance with OECD principles 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: supporting information

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.31 (Prenatal Developmental Toxicity Study)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crl:CD BR VAF/Plus

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc., Portage, Michigan
- Age at study initiation: 14 to 16 weeks (females)
- Weight at study initiation: 243 to 316 grams (females)
- Fasting period before study: no
- Housing: individually-housed except during mating in suspended stainless-steel, wire mesh cages
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 20 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 to 24
- Humidity (%): 40 to 70
- Air changes (per hr): not reported
- Photoperiod (hrs dark / hrs light): 12 hours light and 12 hours dark

- IN-LIFE DATES: From: 1996-10-07 To: 1996-11-08

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Test material formulations were prepared weekly by mixing appropriate amounts of test material with vehicle; test-material formulations were divided into individual samples for each day and stored in a refrigerator until needed.

VEHICLE
- Justification for use and choice of vehicle (if other than water): test material was soluble in carrier
- Concentration in vehicle: not reported
- Amount of vehicle (if gavage): not reported
- Lot/batch no. (if required): not reported
- Purity: not reported

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Test material formulations were evaluated for stability, homogeneity, and achieved concentration. Stability and homogeneity were evaluated prior to the start of the study as part of the dose-range finding study (Study no. 157533; achieved concentration was evaluated on the first and third dosing mixture preparations. Results from the dose-range finding study indicate that the test material formulations were stable for at least 7 days at 2% and 20% w/v and homogenous (with the relative standard deviation being 1% for both sample sets). Test material formulations were found to be within 16% of the nominal concentration.

Details on mating procedure:

- Impregnation procedure: [artificial insemination / purchased timed pregnant / cohoused]: cohoused
- If cohoused:
- M/F ratio per cage: 1:1
- Length of cohabitation: not reported
- Females were placed in cage with male. After confirmation of mating, each female was returned to its own cage. New females were then placed in the males' cages until the required number of mated females was obtained by continuous cohabitation in consideration of lab scheduling.
- Further matings after two unsuccessful attempts: not reported
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: vaginal plug and/or sperm in vaginal rinse referred to as day 0 of pregnancy

Duration of treatment / exposure:

gestation day (gd) 6 though 15

Frequency of treatment:

daily

Duration of test:

IN-LIFE DATES: From: 1996-10-07 To: 1996-11-08

Remarks:

Doses / Concentrations:
0, 100, 500, or 1000 mg/kg/day
Basis:
nominal conc.
Dosing volumes were 5 mL/kg and based on the most recent individual body weights

No. of animals per sex per dose:

25 dams per group

Control animals:

yes

Details on study design:

- Dose selection rationale: A dose-range finding study (Study no. 157533), in which rats were dosed with n-pentane via gavage at levels of 0, 250, 500, 750, and 1000 mg/kg. Maternal signs of toxicity were observed at 1000 mg/kg and included decreased body weight gain and food consumption over the treatment period and overall gestation interval; no other signs of toxicity were observed in dams or fetuses.
- Rationale for animal assignment (if not random): Mated females were assigned to dose groups in the order of mating.

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least twice daily during treatment and at least once daily at other times during the study

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Daily during gestation

BODY WEIGHT: Yes
- Time schedule for examinations: gd 0, 6, 9, 12, 15, 18, and 21

FOOD CONSUMPTION: Yes
- Time schedule for examinations: gd 0, 6, 9, 12, 15, 18, and 21

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # 21
- Organs examined: Ovaries

OTHER: Surviving dams and those that delivered prior to scheduled necropsy were scarified by carbon dioxide asphyxiation and exsanguination. Dams that delivered prior to scheduled necropsy were examined for gross lesions, and the number of implantation sites or concepti in each horn was counted. Surviving dams were necropsied, and uterine weight with ovaries attached was recorded. Uteri of all non-pregnant females were stained with ammonium sulfide to confirm pregnancy status.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: yes
Examinations included:
- Gravid uterus weight: yes
- Number of corpora lutea: yes
- Number of implantations: yes
- Number of early resorptions: yes
- Number of late resorptions: yes
- Other: location of implantations

Fetal examinations:

- External examinations: yes: all per litter (number of live and dead fetuses was counted; fetuses were weighed, sexed, and examined for gross malformations)
- Soft tissue examinations: yes: half per litter
- Skeletal examinations: yes: half per litter
- Head examinations: yes: half per litter

Statistics:

Statistical methods used are presented in the table below. Statistical evaluation of equality of means was conducted by a one-way analysis of variance and a test for ordered response in dose groups. Equal variances were evaluated by Bartlett's test. Equal variances were then tested using parametric methods, otherwise nonparametric techniques were used. Percentages, where appropriate, were calculated and transformed by Cochran's transformation, followed by the arc sine transformation. Both raw and transformed percentages were tested for statistical significance. The Bartlett's test was conducted at the 1% level of significance; all other tests were conducted at the 5% and 1% level of significance.

Indices:

preimplantation loss
postimplantation loss

Historical control data:

not provided

Details on maternal toxic effects:

Maternal toxic effects:no effects

Details on maternal toxic effects:
There were no treatment-related changes in mean body weight, body weight gain, uterine weight, corrected body weight, food consumption, or uterine implantation data. There were no treatment-related mortalities or clinical signs of toxicity.

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

Basis for effect level:

other: maternal toxicity

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

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 treatment-related changes in growth or increased fetal death. There were no changes in total malformations or variations.

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: Developmental Toxicity

Abnormalities:

not specified

Key result

Developmental effects observed:

no

^a Data obtained from pages 28 -29 in the study report.

Cesarean section observations^a
Observation	Dose (mg/kg bw/day)
	0	100	500	1000
No. Animals assigned (mated)	25	25	25	25
No. Animals pregnant	24	25	23	25
Pregnancy rate (%)	96	100	92	100
No. Nonpregnant	1	0	2	0
Maternal wastage
No. died	0	0	0	0
No. Died pregnant	0	0	0	0
No. Died nonpregnant	0	0	0	0
No. Aborted	0	0	0	0
No. Premature delivery	1	1	0	0
Corpora lutea/Dam	15.26±1.63	15.88±1.68	15.43±1.78	15.68±2.21
Implantations/Dam	14.52±1.70	14.88±2.33	14.83±1.83	15.16±2.32
Total No. litters	23	24	23	25
Total number of live fetuses Live fetuses/Dam	310 13.48±1.78	346 14.42±2.26	318 13.83±2.19	359 14.36±2.29
Total number of dead fetuses Dead fetuses/Dam	0 0.0±0.0	0 0.0±0.0	0 0.0±0.0	0 0.0±0.0
Total No. resorptions	24	11	23	19
Early	22	11	23	18
Late	2	0	0	1
Resorptions/Dam	1.04±0.98	0.46±0.59	1.00±0.95	0.76±0.83
Early	0.96±0.98	0.46±0.59	1.00±0.95	0.72±0.84
Late	0.09±0.29	0.0±0.0	0.0±0.0	0.04±0.20
Litters with total resorptions	0	0	0	0
Mean fetal weight (g)	0	0	0	0
Males	5.34±0.38	5.45±5.40	5.40±0.44	5.42±0.46
Females	5.13±0.40	5.12±0.37	5.21±0.37	5.14±0.55
Sex ratio (% male)	49	49	47	50
Preimplantation loss (%)	4.6±7.8	6.3±12.5	4.0±5.3	3.5±4.7
Postimplantation loss (%)	7.1±6.5	3.0±3.7	7.0±7.0	5.3±5.6

^a Data obtained from pages 32 -34 and 73 -167 in the study report.

 

External examinations^a
Observations^b	Dose (mg/kg bw/day)
	0	100	500	1000
No. Fetuses (litters) examined	309 (23)	346 (24)	318 (23)	359 (25)
No. Fetuses (litters) affected with variations	0 (0)	0 (0)	0 (0)	0 (0)
No. Fetuses (litters) affected with malformations	0 (0)	0 (0)	1 (1)	1 (1)

^a Data obtained from pages 35 in the study report.

^b Some observations may be grouped together.

^c Fetal (litter) incidence

 

Visceral examinations^a
Observations^b	Dose (mg/kg bw/day)
	0	100	500	1000
No. Fetuses (litters) examined	156 (23)	172 (24)	161 (23)	178 (25)
No. Fetuses (litters) affected with variations	0 (0)	3 (2)	2 (2)	1 (1)
No. Fetuses (litters) affected with malformations	4 (3)	7 (4)	2 (2)	9 (6)

^a Data obtained from page 35 in the study report.

^b Some observations may be grouped together.

^c Fetal (litter) incidence

 

Skeletal examinations^a
Observations^b	Dose (mg/kg bw/day)
	0	100	500	1000
No. Fetuses (litters) examined	154 (23)	174 (24)	157 (23)	181 (25)
No. Fetuses (litters) affected with variations	27 (14)	31 (13)	25 (13)	44 (17)
No. Fetuses (litters) affected with malformations	0 (0)	0 (0)	1 (1)	0 (0)

^aData obtained from page 35 in the study report.

^bSome observations may be grouped together.

^cFetal (litter) incidence

 

 

Conclusions:

There were no signs of maternal toxicity at any dose level. There were no treatment-related changes in mean body weight, body weight gain, uterine weight, corrected body weight, food consumption, or uterine implantation data. There were no treatment-related mortalities or clinical signs of toxicity. The maternal NOAEL is 1000 mg/kg/day.

There were no signs of developmental toxicity at any dose level. There were no treatment-related changes in growth or increased fetal death. There were no changes in total malformations or variations. The developmental NOAEL is 1000 mg/kg/day.

Executive summary:

In a developmental toxicity study, n-pentane was orally administered via gavage to 25 Crl:CD BR VAF rats per dose at dose levels of 0, 100, 500, or 1000 mg/kg bw/day from days 6 through 15 of gestation.  There were no signs of maternal toxicity at any dose level.  There were no treatment-related changes in mean body weight, body weight gain, uterine weight, corrected body weight, food consumption, or uterine implantation data.  There were no treatment-related mortalities or clinical signs of toxicity.  A maternotoxic dose was not used.  However, the highest dose tested was 1000 mg/kg/day, and no adverse effects were observed.  In general, the highest dose tested does not need to exceed 1000 mg/kg/day unless potential human exposure data indicate the need for higher doses.  Therefore, the study reported a maternal NOAEL of 1000 mg/kg/day.  

 

There were no signs of developmental toxicity at any dose level. There were no treatment-related changes in growth or increased fetal death. There were no changes in total malformations or variations. The developmental NOAEL is 1000 mg/kg/day.

 

This study received a Klimisch score of 1 and is classified as reliable without restriction because it was performed according to GLPs and in compliance with OECD principles 414.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

One key oral read across study from a stuctural analogue available for assessment.

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

24 080 mg/m³

Study duration:

subacute

Experimental exposure time per week (hours/week):

30

Species:

other: Rat and Rabbit

Quality of whole database:

One key rodent and one key non-rodent read across inhalation study from a stuctural analogue available for assessment.

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

There is no data available for 2-methylbutane. However, data is available for structural analogues, pentane and cyclohexane and presented in the dossier. Cyclohexane is oxidized to cyclohexanol, and excretion and conjugation of cyclohexanol is identical to 2-methylbutane. Therefore, data on the toxicokinetics and reproductive toxicity of cyclohexane can be used to fill data gaps for 2-methylbutane when relevant data for these chemicals are missing. This data is read across to 2-methylbutane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

Cyclohexane

 

In a key study (Kreckmann et al., 2000), 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 500 ppm (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).

 

In a second key study (Kreckmann et al., 2000), the developmental toxicity of cyclohexane was assessed in rabbits. No compound-related evidence of maternal or developmental toxicity was observed at any test concentration. Therefore the maternal NOAEC for rabbits was 7000 ppm and the developmental NOAEC for rabbits was also 7000 ppm (24,080 mg/m³), the highest concentration tested and the highest concentration permissible under national fire protection association standards.

 

Pentane

 

In a developmental toxicity study (ExxonMobil, 1997), the test material (n-pentane) was orally administered via gavage to 25 Crl:CD BR VAF rats per dose at dose levels of 0, 100, 500, or 1000 mg/Kg bw/day from days 6 through 15 of gestation. There were no signs of maternal toxicity at any dose level. There were no treatment-related changes in mean body weight, body weight gain, uterine weight, corrected body weight, food consumption, or uterine implantation data. There were no treatment-related mortalities or clinical signs of toxicity. A maternotoxic dose was not used. However, the highest dose tested was 1000 mg/Kg/day, and no adverse effects were observed. In general, the highest dose tested does not need to exceed 1000 mg/Kg/day unless potential human exposure data indicate the need for higher doses. Therefore, the study reported a maternal NOAEL of 1000 mg/Kg/day.  

 

There were no signs of developmental toxicity at any dose level. There were no treatment-related changes in growth or increased fetal death. There were no changes in total malformations or variations. The developmental NOAEL is 1000 mg/Kg/day.

 

This study received a Klimisch score of 1 and is classified as reliable without restriction because it was performed according to GLPs and in compliance with OECD principles 414.

 

Justification for classification or non-classification

Based on available read across data from structural analogues, 2-methylbutane does not warrant the classification as a reproductive or developmental toxicant under the new Regulation (EC) 1272/2008 on classification, labeling and packaging of substances and mixtures (CLP).