Ethylcyclohexane

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

Oral gavage of ethylcyclohexane at 0 (control: olive oil), 40, 200 and 1000 mg/kg per day were given to 12 each of male and female Crl: CD(SD) rats per group: total 42 days including periods before mating, mating period and after mating for male rats and before mating, mating and gestation, as well as for the period until day 3 of post-parturition (i.e. for 40 to 53 days) female rats in order to investigate the gonadal function, mating behavior and reproductive toxicities possibly affecting the fertility and parturition.

The no-observed-effect level (NOEL) and no observed adverse effect level (NOAEL) of ethylcyclohexane in parental animals in this study were considered 200 mg/kg per day for both male and female animals, given the changes related to the test substance observed in male and female animals of the 1000 mg/kg group including changes in general conditions, trends of low body weight and feed consumption at the initial phase of dosing, yellowish white discoloration of the kidneys in male animals, and the presence of eosinophilic bodies in the proximal tubular epithelia.

Although only viability index and body weight of pups on day 4 of lactation were tended to be decreased, these weak changes were not statistically significant. The NOAEL for reproductive/developmental toxicity of ethylcyclohexane is considered to be 1000 mg/kg bw/day.

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2013-07-29 - 2014-03-17

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

other: Methods of Testing New Chemical Substances (PFBS Notification No. 0331-7 dated March 31, 2011; MIB Notification No. 5 dated March 29, 2011; PPD/EHD Notification No. 110331009

Deviations:

not specified

GLP compliance:

yes

Limit test:

no

Specific details on test material used for the study:

Name: Ethylcyclohexane
CAS No.: 1678-91-7
Molecular weight: 112.22
Lot No.: TOKTA
Purity: 99.9%

Species:

rat

Strain:

other: Crl:CD (SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source:Atsugi Breeding Center, Charles River Laboratories Japan, Inc.
- Age at study initiation: 10 weeks of age for male and female rats
- Weight at study initiation: 354–418 g for male animals; 232–284 g for female animals
- Fasting period before study: no
- Housing:Two animals during quarantine and acclimation, one animal after allocation, one male and one female animal during cohabitation, 1 animal during pregnancy, and offspring per litter were housed.
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period:Quarantine period included days from the date of receipt (day 1 of quarantine) to day 6 of quarantine. Acclimation period included the quarantine period and days until the allocation day.
ENVIRONMENTAL CONDITIONS
- Temperature (°C):22°C ± 3°C
- Humidity (%):50% ± 20%
- Air changes (per hr):10-15 times/hour
- Photoperiod (hrs dark / hrs light):Artificial lighting was provided for 12 hours (8:00-20:00)
I

Route of administration:

oral: gavage

Vehicle:

olive oil

Details on exposure:

Preparation method: The test substance was precisely weighed and added to the control substance as a vehicle to give solutions at the specified concentration and dissolved using a stirrer.
Frequency of preparation: Once per 2-7 days
Storage location and period: Stored in a refrigerator in the test substance storage room; between August 7, 2013 (initial preparation) and October 5, 2013 (final administration)
Storage conditions: Refrigerated (actual measurement range is 2.8°C to 8.5°C), protected from the light and sealed.
Stability of dosing solution: After preparation, the stability of dosing solutions at concentrations of 0.2 and 20 w/v% (2 and 200 mg/mL) was confirmed under refrigerated conditions for seven days and under room temperature condition for one day.

Details on mating procedure:

Method: One pair each of male and female animals within the study group were housed together from the evening of the day of starting mating until copulation was observed.

Method for confirming successful copulation: This was checked by the presence of a vaginal plug inside the vagina or fallen on the base plate, or checked by the presence of sperm by vagina smear sampling. The day when successful copulation was confirmed was determined as the day of successful copulation (day 0 of gestation).

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Confirmation of the concentration of dosing solution: The concentration of the test substance in dosing solutions at all concentrations was confirmed by using dosing solutions initially administered and finally administered to male rats. The dosing solutions were prepared in the facility, the concentration of dosing solutions was analyzed by Nisso Chemical Analysis Service Co., Ltd., and the analysis result was obtained (Study No. : 13-144) The result showed that the content rate of the test substance was 93.1%, 97.3%, and 98.0% in initially administered dosing solutions at doses of 8, 40, and 200 mg/mL, respectively, while 91.3%, 96.0%, and 95.5% in finally administered dosing solutions at the same doses, respectively. The coefficient of variation was within the range between 0.0% and 0.9%. The result confirmed that the concentration met the acceptance criteria that the content rate was 85% to 115% and the coefficient of variation was below 10%.

Duration of treatment / exposure:

Male: For 14 days before mating and a subsequent 28 days, a total of 42 days
Female: For 14 days before mating and mating period until successful copulation, plus during the gestation until day 3 of lactation in animals with successful copulation and until day 25 of gestation in animals with delayed parturition.

Frequency of treatment:

Once daily

Dose / conc.:

0 mg/kg bw/day (nominal)

Dose / conc.:

40 mg/kg bw/day (nominal)

Dose / conc.:

200 mg/kg bw/day (nominal)

Dose / conc.:

1 000 mg/kg bw/day (nominal)

No. of animals per sex per dose:

12 male and 12 female rats per group

Control animals:

yes, concurrent vehicle

Details on study design:

In a 28-day repeated oral dose toxicity study (dose amount: 40, 200, 1000 mg/kg per day) salivation was observed in male and female animals given 1000 mg/kg per day immediately after dosing, and increases in liver weight and centrilobular hepatocytic hypertrophy were identified. However, no impacts of dosing were identified in body weight, feed consumption, reproductive organ weight measurement, or histopathological tests. Accordingly, a simple reproductive and developmental toxicity study used 1000 mg/kg per day as the high dose with dose levels of 200 and 40 mg/kg per day decided as in the 28-day repeated oral dose toxicity study.

Positive control:

no

Parental animals: Observations and examinations:

Clinical signs:
Twice every day, pre-dose and post-dose time points, excepting only once in the morning on the day of necropsy.

Body weight measurement:
Males: On days 1, 3, and 7 of dosing, and subsequently pre-dose every 7 days, the final day of dosing, and the day of necropsy.
Females: Pre-dose on days 1, 3, 7, and 14 of dosing, pre-dose on days 0, 7, 14, and 20 of gestation, pre-dose on day 0 of lactation and day 4 of lactation. Except, on day 26 of gestation (the day of necropsy) for infertile animals.

Food consumption measurement:
On the same day as the body weight measurement

Oestrous cyclicity (parental animals):

Period: From the day of starting dosing until the day of successful copulation.
Method: Vaginal smear samples by Giemsa staining were prepared and examined under optical microscope for determining the sexual cycle stage.

Litter observations:

Observation of general conditions in neonates:
Once per day, from day 0 of birth to day 4 of birth
Viability index for neonate: The neonate viability index on day 0 of birth and day 4 of birth was calculated.
Body weight measurement of neonates:
All the live litters were weighed on days 0 and 4 of post-parturition.

Observation on the delivered litters: Survival/death and sex were checked for the delivered litters on day 0 of birth, and the external surface was observed. The live litter count and deaths were separately counted for litter, and the total of those counts was used as the count of delivered litters and then the following formula was used to calculate the birth index by litter, the incidence of external abnormalities in the live litter and sex ratio of litters by group.
Birth index (%)=Live litters on day 0 of birth/Implantation sites ×100
Sex ratio of litters(%)=Male live litters/Male live litters+Female live litters×100
Incidence of external abnormalities in litters (%) = (litters with external abnormalities/delivered litter) ×100
Frequency of litters with external abnormalities by litter = litters with external abnormalities /delivered litters

Postmortem examinations (parental animals):

Autopsy:
Males:
Number of animals: all
Timing:The necropsy was performed on deaths immediately after the discovery and on surviving animals the day following day 42 of dosing (i.e. day 43).
Name of organs/tissues: Testis, epididymis, prostate, seminal vesicle (including coagulating gland) and macroscopically abnormal sites (including the margin adjacent to the normal tissue).
Females:
Number of animals: all
Timing: Day 4 of lactation
Name of organs/tissues: Ovary, uterus, vagina, and mammary gland.

Organ weight measurement:
Males:
Number of animals: All animals except deaths
Timing: Upon necropsy
Name of organ: Testis, epididymis and seminal vesicle
Females:
Number of animals: All animals
Timing: Autopsy
Name of organ: Ovary

Histopathological examinations:
Males:
Number of animals: all animals
Name of organs/tissues: Testis, epididymis, prostate and seminal vesicle (including coagulating gland), as well as testis, epididymis, prostate, seminal vesicle (including coagulating gland) of one male animal from the 40 mg/kg group (death, Animal No. 10203), testis and epididymis from one male animal in the 40 mg/kg group (Animal No. 10202) and the kidneys isolated from three male animals from 1000 mg/kg group (Animal Nos. 10401, 10402, and 10405).

Females:
Number of animals: Same as male animal
Name of organs/tissues: Ovary, uterus, and vagina

Postmortem examinations (offspring):

Autopsy on neonates:
The necropsy was performed on all the animals on day 4 of birth. The external surface of the body (including inside the oral cavity) was observed, the animals were overdosed with sodium pentobarbitone for euthanasia, and the organs/tissues all over the body were macroscopically observed.

Statistics:

Computer system (MiTOX, Mitsui Zosen Systems Research) was used for the analyses. The results were used to calculate the group mean and standard deviation for the body weight, body weight increase, feed consumption, organ absolute weight and relative weight, estrus interval, frequency of having estrus, days required for copulation, the count of gravid corpus lutea, number of implantation sites and implantation index, count of delivered litters, live and mortal litters upon delivery, birth index, gestation period, viability index on day 4 of birth and litters with external abnormalities, and Bartlett test was performed to analyze homoscedasticity. In case of homoscedasticity (p ≥ 0.05), one-way analysis of variance was performed and in case of heteroscedasticity (p < 0.05), Kruskal-Wallis’s test was performed for analyses. When one-way analysis of variance revealed a significant difference (p < 0.1), then Dunnett’s test was used to compare with the control group. When Kruskal-Wallis’s test revealed a significant difference (p < 0.1) and then Steel’s test was performed to compare the control group. Viability index on day 0 of birth was separately analyzed with statistical analysis system (Sanken System Co.,Ltd) for performing the same tests as already described above. Fisher's exact test was used for the abnormal incidence of sexual cycle, mating index, fertility index, gestation index, sex ratio of litters, and the frequency of litters with external abnormalities per litter as well as histopathological tests. In the comparative tests with the control group, the level of significance was given at 5%.

Reproductive indices:

Fertility: The gestation was confirmed by the presence of parturition and the count of the number of implantation sites in the uterus upon necropsy.
Fertility index (%)=Fertile animals/Animals with successful copulation ×100

Observation on parturition and lactation status:
All female animals confirmed to have had copulation were allowed spontaneous parturition. The status of parturition was observed between days 21 and 25 of gestation at least 3 times
Gestation index (%)=Female with normal delivery/Gestated female animals ×100
Calculation of gestation period: Days were counted from day 0 of gestation to day 0 of lactation.
Calculation of implantation index: The count of gravid corpus luteum in the ovary was counted for individual females upon the necropsy. The following formula was used to calculate implantation index per litter.
Implantation index (%)=Implantation sites/ Corpora lutea count×100

Offspring viability indices:

The neonate viability index on day 0 of birth and day 4 of birth was calculated.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

In 1000 mg/kg group, three animals had stained fur around the urethral opening found on days 3 to 4 of dosing. Moreover, one animal had salivation on days 19 to 31 and day 35 of dosing, and the same event was observed in one another animal on day 41 of dosing. The salivation was observed immediately after dosing lasting for about one hour.
In female animals, none of the animals in 40 and 200 mg/kg groups had abnormalities during the dosing period. In the 1000 mg/kg group, no abnormalities were identified before mating and mating period, while post-dose salivation was observed on gestation and thereafter in one or two animals in gestation and one in lactation period. The salivation was observed immediately after dosing lasting for about one hour.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One animal died in the 40 mg/kg group post-dose on day 8 of dosing (afternoon). The necropsy on this animal revealed no abnormalities, and thus the cause of death was not identified.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

In the 1000 mg/kg group, a trend of low body weight was observed on day 3 of dosing in the initial phase of dosing start. No significant differences were found when compared with the control group for the rest of the periods. In female animals, no significant differences were found in any of the groups on the test substance when compared with the control group.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

In male animals, significantly high level of feed consumption was noted on day 3 of dosing in the 40 mg/kg group compared with the control group that was considered as incidental findings since no significant differences were found in the 200 mg/kg group.In the 1000 mg/kg group, significant decrease in the feed consumption was noted on day 3 of dosing compared with the control group whereas significantly high level of food consumption was found on day 7 of dosing and thereafter throughout the dosing period when compared with the control group.
In female animals, no significant differences were found in the 40 and 200 mg/kg group vs. the control group during the dosing period.
In the 1000 mg/kg group, a trend of low body weight was observed on day 3 of dosing. No significant differences were found compared with the control group during the other periods.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In survived animals, necropsy on males in the 40 mg/kg group revealed severe atrophy of seminiferous tubule in the testis and severe sperm decrease and mild intraductal cellular debris in the epididymis associated with the miniaturization of testis and epididymis. Moreover, in male animals of the 1000 mg/kg group, the necropsy identified moderate, α2u-globulin antibody immunostaining-positive eosinophilic bodies in the proximal tubular epithelia associated with yellowish white discoloration of kidneys, and two among those animals additionally presented with tubular basification (mild and moderate). In infertile male animals of the 1000 mg/kg group, no abnormal findings were reported. Other findings in male animals of the control group included mild atrophy of seminiferous tubule in the testis, mild intraductal cellular debris in the epididymis, mild sperm granuloma (one animal each) and mild inflammation in the prostate (five animals). In the 1000 mg/kg group, one animal was found with mild cyst in the kidneys and three animals with mild inflammation in the prostate. In female animals of control group and animals including infertile animals of the 1000 mg/kg group, no abnormal findings were reported.

Histopathological findings: neoplastic:

not examined

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

No changes associated with the test substance at doses of up to 1,000 mg/kg in female estrus cycle, mating index, fertility index, the number of days until mating, the number of corpus luteum of pregnancy, the number of implantations, implantation index, gestation period, delivery index, the number of births, the number of live offspring and dead offspring, birth index, and sex ratio of offspring were found. In terms of the development and growth of the offspring, the 4-day survival rate of neonates and body weight of male and female rats tended to decrease in the 1,000 mg/kg group. This change may be caused by the rearing status of maternal animals.

Key result

Dose descriptor:

NOAEL

Effect level:

200 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Clinical signs:

no effects observed

Description (incidence and severity):

No milk band was found in four neonates of the 40 mg/kg group on day 0 of birth while no abnormalities were identified in either maternal animals, or in the higher dose group. Deaths during the lactation period were found in three male animals and one female (including those with unknown causes) in the control group, 3 male and 10 female animals in the 40 mg/kg group, 4 female animals in the 200 mg/kg group, and 5 male and 15 female animals plus 2 animals of unknown sex in the 1000 mg/kg group. For viability rate on day 0 of birth, no significant differences were found among any of the test substance groups compared with the control group. The viability rate on day 4 of birth had no significant difference in the 1000 mg/kg group with a trend of low viability.

Mortality / viability:

mortality observed, non-treatment-related

Description (incidence and severity):

Deaths during the lactation period were found in three male animals and one female (including those with unknown causes) in the control group, 3 male and 10 female animals in the 40 mg/kg group, 4 female animals in the 200 mg/kg group, and 5 male and 15 female animals plus 2 animals of unknown sex in the 1000 mg/kg group. For viability rate on day 0 of birth, no significant differences were found among any of the test substance groups compared with the control group. The viability rate on day 4 of birth had no significant difference in the 1000 mg/kg group with a trend of low viability.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

In the 1000 mg/kg group, a trend of low weights was found in both male and female animals on day 4 of birth.

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

In the necropsy on live litters on day 4 of birth, no abnormalities were identified in any of the study groups including the control group study group. In the mortal litters found on day 0 of birth, abdominal trauma was found in only one animal in the 1000 mg/kg group. No other abnormalities were found in mortal litters.

Key result

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

1 000 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no statistically significant effects observed

Key result

Reproductive effects observed:

no

Conclusions:

Oral gavage of ethylcyclohexane at 0 (control: olive oil), 40, 200 and 1000 mg/kg per day were given to 12 each of male and female Crl: CD(SD) rats per group: total 42 days including periods before mating, mating period and after mating for male rats and before mating, mating and gestation, as well as for the period until day 3 of post-parturition (i.e. for 40 to 53 days) female rats in order to investigate the gonadal function, mating behavior and reproductive toxicities possibly affecting the fertility and parturition.
The no-observed-effect level (NOEL) and no observed adverse effect level (NOAEL) of ethylcyclohexane in parental animals in this study were considered 200 mg/kg per day for both male and female animals, given the changes related to the test substance observed in male and female animals of the 1000 mg/kg group including changes in general conditions, trends of low body weight and feed consumption at the initial phase of dosing, yellowish white discoloration of the kidneys in male animals, and the presence of eosinophilic bodies in the proximal tubular epithelia.
Although only viability index and body weight of pups on day 4 of lactation were tended to be decreased, these weak changes were not statistically significant. The NOAEL for reproductive/developmental toxicity of ethylcyclohexane is considered to be 1000 mg/kg bw/day.

Executive summary:

Oral gavage of ethylcyclohexane at 0 (control: olive oil), 40, 200 and 1000 mg/kg per day were given to 12 each of male and female Crl: CD(SD) rats per group: total 42 days including periods before mating, mating period and after mating for male rats and before mating, mating and gestation, as well as for the period until day 3 of post-parturition (i.e. for 40 to 53 days) female rats in order to investigate the gonadal function, mating behavior and reproductive toxicities possibly affecting the fertility and parturition.

Parental animals:

In the 40 and 200 mg/kg groups, no changes possibly affected by the test substance were identified in general conditions, body weight, feed consumption, necropsy or histopathological tests. In male and female animals of the 1000 mg/kg group, changes in the general conditions were observed including salivation or stained fur around the urethral opening, as well as a trend of low body weight or feed consumption at the initial phase of dosing. Moreover, significantly high levels of feed consumption were noted in male animals on day 7 of dosing and thereafter throughout the study period in relation to the control group, while the body weight remained unchanged, indicating the reduced food efficiency. These changes were attributed to the test substance. In addition, the necropsy identified yellowish white discoloration of the kidneys in three male animals in the same group; the histopathological test revealed moderate presence of eosinophilic bodies in the proximal tubular epithelia, and these changes were attributed to the test substance. Immunostaining by α2u-globulin antibody was positive for the presence of eosinophilic body in the proximal tubular epithelia, indicated α2u-globulin nephropathy. α2u-globulin nephropathy is a change specific to male rats and thus not extrapolatable to humans,5 and hence the changes were not considered toxic changes. For the weight of reproductive organs, no changes attributed to the test substance were found up to the 1000 mg/kg group in both male and female animals. One mortal male animal was reported

from the 40 mg/kg group with unknown cause of death. Still, no mortality was reported in the higher dose group, and thus the death was considered unrelated to the test substance.

Reproduction of male and female animals and genesis of neonates:

For fertility in parental animals, no changes attributed to the test substance were found in females for sexual cycle, mating index, fertility index, days required for copulation, the count of gravid corpus lutea, number of implantation sites and implantation index, gestation period, gestation index, count of delivered litters, live and mortal litters upon delivery, birth index, and sex ratio of delivered litters up to the 1000 mg/kg group. For the genesis and development of offspring, trends were found for low viability rate and body weight on day 4 of birth in neonates in the 1000 mg/kg group. These changes suggested a possible influence on the lactation status of maternal animals and thus were considered related to the test substance.

In conclusion, no-observed-effect level (NOEL) and no observed adverse effect level (NOAEL) of ethylcyclohexane in parental animals in this study were considered 200 mg/kg per day for both male and female animals, given the changes related to the test substance observed in male and female animals of the 1000 mg/kg group including changes in general conditions, trends of low body weight and feed consumption at the initial phase of dosing, yellowish white discoloration of the kidneys in male animals, and the presence of eosinophilic bodies in the proximal tubular epithelia.

Although only viability index and body weight of pups on day 4 of lactation were tended to be decreased, these weak changes were not statistically significant. The NOAEL for reproductive/developmental toxicity of ethylcyclohexane is considered to be 1000 mg/kg bw/day.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Effects on developmental toxicity

Description of key information

Oral gavage of ethylcyclohexane at 0 (control: olive oil), 40, 200 and 1000 mg/kg per day were given to 12 each of male and female Crl: CD(SD) rats per group: total 42 days including periods before mating, mating period and after mating for male rats and before mating, mating and gestation, as well as for the period until day 3 of post-parturition (i.e. for 40 to 53 days) female rats in order to investigate the gonadal function, mating behavior and reproductive toxicities possibly affecting the fertility and parturition.

The no-observed-effect level (NOEL) and no observed adverse effect level (NOAEL) of ethylcyclohexane in parental animals in this study were considered 200 mg/kg per day for both male and female animals, given the changes related to the test substance observed in male and female animals of the 1000 mg/kg group including changes in general conditions, trends of low body weight and feed consumption at the initial phase of dosing, yellowish white discoloration of the kidneys in male animals, and the presence of eosinophilic bodies in the proximal tubular epithelia.

Although only viability index and body weight of pups on day 4 of lactation were tended to be decreased, these weak changes were not statistically significant. The NOAEL for reproductive/developmental toxicity of ethylcyclohexane is considered to be 1000 mg/kg bw/day.

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

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Justification for classification or non-classification

No classification for developmental or reproductive toxicity for the substance ethylcyclohexane is required.

In a reproduction/developmental toxicity screening test (similar to TG 421), rats (12 animals/sex/dose) were treated with ethylcyclohexane by gavage at 0, 40, 200 and 1000 mg/kg bw/day. Male rats were dosed for 42 days, and female rats were dosed for 40-53 days (including 14 day pre-mating, mating, and gestation periods and days until day 3 of lactation). Reproductive parameters were not affected up to 1000 mg/kg bw/day. Although only viability index and body weight of pups on day 4 of lactation were tended to be decreased, these weak changes were not statistically significant. The NOAEL for reproductive/developmental toxicity of ethylcyclohexane is considered to be 1000 mg/kg bw/day.