Pentane

Toxicity to reproduction

Administrative data

Endpoint:

one-generation reproductive toxicity

Remarks:

based on test type

Type of information:

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

Adequacy of study:

key study

Study period:

2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Conducted according to OECD TG 415. GLP.

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Cross-reference

Reason / purpose for cross-reference:

read-across: supporting information

Reference

Endpoint:

one-generation reproductive toxicity

Remarks:

based on test type

Type of information:

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

Adequacy of study:

key study

Study period:

2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Conducted according to OECD TG 415. GLP.

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

Species:

rat

Clinical signs:

no effects observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Other effects:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)

Post-dosing salivation was noted in the dosed groups and was observed only immediately after treatment. This is likely due to the irritating effects of the test article rather than an indication of toxicity. Other clinical signs found in the treatment groups, such as loss of fur, scratch wounds, and scabs, were not considered to be related to treatment of 2-methylbutane since they occurred at a very low incidence and did not exhibit a dose-response relationship.

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)

A statistical significant suppression of body weight gain observed in the male 1000 mg/kg group which was attributed to the administration to the test chemical, which is consistent with the slightly decreased food consumption observed in the group during the study period. this change did not exhibit a dose-response relationship and was not accompanied by changes in body weight; therefore, it was not considered to be a treatment related effect.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)

Treatment with 2-methylbutane did not affect any of the fertility and reproductive performance parameters evaluated.

ORGAN WEIGHTS (PARENTAL ANIMALS)

In males, absolute heart weight in the 1000 mg/kg group was significantly decreased in comparison to that of the control group. The relative weight of adrenal glands was significantly increased without a dose-response relationship in comparison to the control group. Relative weights of brain, liver, kidneys, and testes in the 1000 mg/kg group were also significantly increased in comparison to the control group.

2-methylbutane to rats caused a statistically significant suppression in body weight gain in the male 1000 mg/
kg group. The suppressed body weight affected the weights of the heart, brain, liver, and testes in the high dose group. However, the weight changes in these organs were within the limits of normal biological variations and there were no corresponding pathological changes. Previous studies have demonstrated that the function and weight of adrenal glands are adversely affected by various stressful factors. Therefore, these changes are not considered toxicologically significant.

GROSS PATHOLOGY (PARENTAL ANIMALS)
No abnormal gross pathological findings were observed

HISTOPATHOLOGY (PARENTAL ANIMALS)
Renal tubular degeneration/regeneration was observed in 13, 10, 11, and 18 males at 0, 100, 300, and 1000 mg/kg, respectively. These effects were the only treatment related finding and are related to the male rat specific a2u-globulin nephropathy. This finding is not relevant to human health.

Key result

Dose descriptor:

NOAEL

Remarks:

reproductive toxicity

Effect level:

>= 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: highest dose given

Key result

Dose descriptor:

NOAEL

Remarks:

systemic toxicity

Effect level:

>= 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: highest dose given

Key result

Dose descriptor:

NOAEL

Remarks:

systemic toxicity

Effect level:

300 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: a2u-globulin nephropathy observed in male rats. This effect is not relevant to human health.

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

Litter size and sex, number of live and stillborn at birth and pup mortality from PND 1 to weaning were comparable among all groups. No significant differences in clinical observations or body weight changes were noted for both dams and pups during the lactation period. Macroscopic examination of pups did not reveal gross malformations or findings that would indicate abnormal development.

Key result

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

>= 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: pup development

Reproductive effects observed:

not specified

Conclusions:

The reproductive and developmental NOAEL >= 1000 mg/kg/day, the highest dose tested. The systemic NOAEL for male rats the NOAEL = 300 mg/kg/day based on the a2u-globulin nephropathy observed that is not relevant to human health. The systemic NOAEL for female rats was NOAEL >= 1000 mg/kg/day, the highest dose tested.

Executive summary:

This data is being read across from the source study that tested 2-methylbutane based on analogue read across.

A one-generation reproductive toxicity study using Sprague-Dawley rats was conducted using the test material 2-methylbutane. Male and female rats (24 per treatment group) were treated by oral gavage with 2-methylbutane at 0, 100, 300, and 1000 mg/kg/day. Males were dosed for 10 weeks prior to mating and during mating and females were dosed from 2 weeks before mating to day 21 of lactation.

 

No treatment-related effects of 2-methylbutane were found in relation to the reproductive capacity of parental animals or the pre- and post-natal development of the F1 generation.

 

At 1000 mg/kg/day, a2u-globulin nephropathy observed in male rats. This effect is not relevant to human health. While several organs had altered weights, the changes were within the normal biological range and were considered to be not toxicologically relevant.

 

Therefore, the reproductive and developmental NOAEL >= 1000 mg/kg/day, the highest dose tested. The systemic NOAEL for male rats the NOAEL = 300 mg/kg/day based on the a2u-globulin nephropathy observed that is not relevant to human health. The systemic NOAEL for female rats was NOAEL >= 1000 mg/kg/day, the highest dose tested.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2011

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 415 [One-Generation Reproduction Toxicity Study (before 9 October 2017)]

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

2-methylbutane

EC Number:

201-142-8

EC Name:

2-methylbutane

Cas Number:

78-78-4

Molecular formula:

C5H12

IUPAC Name:

2-methylbutane

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

Male and female 5-week-old Sprague - Dawley rats were maintained in an animal room at 22 +/- 3 deg C with a relative humidity of 30-70% under a 12 h light/dark cycle. Rats were housed 2 per cage in stainless wire caging during the premating (2 males or 2 females), mating (1 male and 1 female), and post-mating periods (2 males). Mated females were housed individually during the gestation period. Lactating animals with suckling pups were housed in the same cages. The animals were provided sterilized water, ad libitum.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

0, 100, 300, and 1000 mg/kg/day. Males were dosed for 10 weeks prior to mating and during mating. Females were dosed from 2 weeks before mating to day 21 of lactation.

Details on mating procedure:

After the 70-day premating exposure period was completed, the F0 animals were mated one male to one female, selected randomly within each dose group for 14 days. The observation of a vaginal plug or sperm in a vaginal smear was considered evidence of successful mating. The day a vaginal plug and/or sperm in a vaginal smear were observed was designated as day 0 of pregnancy. Once the vaginal plug or sperm were observed, the animals were separated and housed individually in cages. A female was re-mated with a male of proven fertility within the same experimental group if mating was not confirmed in 2 weeks. Any female that did not show evidence of successful mating after cohabitation was individually housed and euthanized on day 21 after separation. Females were examined daily during the mating period and from GD 20, females were checked two times daily for evidence of onset, progress, and completion of parturition.

All animals were allowed to litter naturally (F1 generation), and rear their own offspring until LD 21. Dams were examined daily for evidence of normal maternal behavior.

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

Males were dosed for 10 weeks prior to mating and during mating. Females were dosed from 2 weeks before mating to day 21 of lactation.

Frequency of treatment:

once per day

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 100, 300, and 1000 mg/kg/day
Basis:
nominal conc.

No. of animals per sex per dose:

24 rats/sex/dose

Control animals:

yes, concurrent vehicle

Examinations

Parental animals: Observations and examinations:

All animals were observed daily for clinical signs when treated with the test chemical, and abnormal signs were recorded individually by type, observation day/time, and duration. Body weight of each male was measured twice weekly until euthanized. Female rats were weighed twice weekly during the premating period and on gestation days (GD) 0, 3, 6, 9, 12, 15, 18, and 20, as well as on lactation days (LD) 1, 4, 7, 14, and 21. In mated females that produced no litters, body weights were measured up to day 21 of the presumed gestation period. The individual amount of food consumed was recorded once a week during the premating period and on GD 0, 3, 6, 9, 12, 15, 18, and 20, as well as on lactation days (LD) 1, 4, 7, 14, and 20. Food consumption was not measured during the mating period.

Litter observations:

Pups were examined as soon as possible on the day of birth to determine the number alive and stillborn in each litter. All live pups were individually counted, sexed, weighed, and examined externally. The number of live and dead pups was noted on PND 4, 7, 14, and 21. The body weights of F1 offspring were measured by randomly selecting one pup of each sex from each litter on PND 1, 7, 14 and 21.

Postmortem examinations (parental animals):

Males were euthanized at the end of the 14-day mating period; females that delivered were euthanized on day 22 after parturition. All adult animals were subjected to a full and detailed gross necropsy, which included a careful examination of the external surface of the body, the cranial, thoracic, abdominal cavities, and their contents. Special attention was paid to the reproductive organs. At necropsy the following organs were obtained and weighed from all animals: brain, pituitary gland, thymus, heart, lung, liver, kidneys, adrenal glands, spleen, testes, epididymides, prostates, seminal vesicles, ovaries, uterus and abnormal lesions. Testes and epididymides were preserved in Bouin’s fixative. Other tissues were fixed with a 10% neutral buffered formalin solution. The tissues were routinely processed, embedded in paraffin and sectioned at 3-5 um. These sections were stained with hematoxylin-eosin (H&E) for microscopic examination. All tissues taken from the control and high dose groups, and testis and epididymis from the low and middle dose groups were examined microscopically.

Postmortem examinations (offspring):

Culled pups and dead pups found during the study were examined macroscopically for structural abnormalities or pathological changes. On PND 22, one male and one female per litter were euthanized and subjected to external and internal macroscopic examination.

Statistics:

The data are expressed as mean ± standard deviation (SD). Parametric data were subjected to one-way analysis of variance (ANOVA). Other data were analyzed using Kruskal-Wallis nonparametric ANOVA. If either test showed statistical significance, the data were analyzed using the Dunnett multiple comparison procedure.

Precoital time, duration of gestation, and the numbers of live and dead pups were statistically evaluated using the
Kruskal–Wallis nonparametric ANOVA, followed by the Mann- Whitney U-test when appropriate. Incidence data (e.g. clinical signs and histopathological findings) were compared using Fisher’s exact probability test.

Reproductive indices:

copulation index, fecundity index, fertility index, delivery index, precoital time, and duration of gestation

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

no effects observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Other effects:

no effects observed

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Details on results (P0)

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)

Post-dosing salivation was noted in the dosed groups and was observed only immediately after treatment. This is likely due to the irritating effects of the test article rather than an indication of toxicity. Other clinical signs found in the treatment groups, such as loss of fur, scratch wounds, and scabs, were not considered to be related to treatment of 2-methylbutane since they occurred at a very low incidence and did not exhibit a dose-response relationship.

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)

A statistical significant suppression of body weight gain observed in the male 1000 mg/kg group which was attributed to the administration to the test chemical, which is consistent with the slightly decreased food consumption observed in the group during the study period. this change did not exhibit a dose-response relationship and was not accompanied by changes in body weight; therefore, it was not considered to be a treatment related effect.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)

Treatment with 2-methylbutane did not affect any of the fertility and reproductive performance parameters evaluated.

ORGAN WEIGHTS (PARENTAL ANIMALS)

In males, absolute heart weight in the 1000 mg/kg group was significantly decreased in comparison to that of the control group. The relative weight of adrenal glands was significantly increased without a dose-response relationship in comparison to the control group. Relative weights of brain, liver, kidneys, and testes in the 1000 mg/kg group were also significantly increased in comparison to the control group.

2-methylbutane to rats caused a statistically significant suppression in body weight gain in the male 1000 mg/
kg group. The suppressed body weight affected the weights of the heart, brain, liver, and testes in the high dose group. However, the weight changes in these organs were within the limits of normal biological variations and there were no corresponding pathological changes. Previous studies have demonstrated that the function and weight of adrenal glands are adversely affected by various stressful factors. Therefore, these changes are not considered toxicologically significant.

GROSS PATHOLOGY (PARENTAL ANIMALS)
No abnormal gross pathological findings were observed

HISTOPATHOLOGY (PARENTAL ANIMALS)
Renal tubular degeneration/regeneration was observed in 13, 10, 11, and 18 males at 0, 100, 300, and 1000 mg/kg, respectively. These effects were the only treatment related finding and are related to the male rat specific a2u-globulin nephropathy. This finding is not relevant to human health.

Effect levels (P0)

1

Key result

Dose descriptor:

NOAEL

Remarks:

systemic toxicity

Effect level:

300 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: a2u-globulin nephropathy observed in male rats. This effect is not relevant to human health.

2

Key result

Dose descriptor:

NOAEL

Remarks:

systemic toxicity

Effect level:

>= 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: highest dose given

3

Key result

Dose descriptor:

NOAEL

Remarks:

reproductive toxicity

Effect level:

>= 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: highest dose given

Results: F1 generation

General toxicity (F1)

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

Details on results (F1)

Litter size and sex, number of live and stillborn at birth and pup mortality from PND 1 to weaning were comparable among all groups. No significant differences in clinical observations or body weight changes were noted for both dams and pups during the lactation period. Macroscopic examination of pups did not reveal gross malformations or findings that would indicate abnormal development.

Effect levels (F1)

Key result

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

>= 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: pup development

Overall reproductive toxicity

Key result

Reproductive effects observed:

no

Applicant's summary and conclusion

Conclusions:

The reproductive and developmental NOAEL >= 1000 mg/kg/day, the highest dose tested. The systemic NOAEL for male rats the NOAEL = 300 mg/kg/day based on the a2u-globulin nephropathy observed that is not relevant to human health. The systemic NOAEL for female rats was NOAEL >= 1000 mg/kg/day, the highest dose tested.

Executive summary:

A one-generation reproductive toxicity study using Sprague-Dawley rats was conducted using the test material 2-methylbutane. Male and female rats (24 per treatment group) were treated by oral gavage with 2-methylbutane at 0, 100, 300, and 1000 mg/kg/day. Males were dosed for 10 weeks prior to mating and during mating and females were dosed from 2 weeks before mating to day 21 of lactation.

 

No treatment-related effects of 2-methylbutane were found in relation to the reproductive capacity of parental animals or the pre- and post-natal development of the F1 generation.

 

At 1000 mg/kg/day, a2u-globulin nephropathy observed in male rats. This effect is not relevant to human health. While several organs had altered weights, they changes were within the normal biological range and were considered to be not toxicologically relevant.

 

Therefore, the reproductive and developmental NOAEL >= 1000 mg/kg/day, the highest dose tested. The systemic NOAEL for male rats the NOAEL = 300 mg/kg/day based on the a2u-globulin nephropathy observed that is not relevant to human health. The systemic NOAEL for female rats was NOAEL >= 1000 mg/kg/day, the highest dose tested.