2-methylpropane-2-thiol

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

A key screening for reproductive / developmental toxicity study, conducted according to OECD 422 and in compliance with GLP, reported a NOAEL for reproductive performance and developmental toxicity to be ≥ 200 mg/kg bw/day (MHLW, 2006). The NOAEL for maternal toxicity was 50 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

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Deviations:

yes

Remarks:

The histopathological examination of the reproductive organs was only performed on 5 animals/sex of the control and top dose.

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: 272.2-325.1 g for males, 188.1-235-9 g for females
- Housing:no data
- Diet (e.g. ad libitum): no data
- Water (e.g. ad libitum):no data
- Acclimation period:no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-27
- Humidity (%): 35-75
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12-12

Route of administration:

oral: gavage

Vehicle:

corn oil

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

no details available

Duration of treatment / exposure:

Exposure period: Males: 42 days; Females: 42-53 days from 14 days before mating to day 4 of lactation
Premating exposure period (males): 2 weeks
Premating exposure period (females): 2 weeks
Duration of test: 10, 50, 200 mg/kg bw/day

Frequency of treatment:

Once daily

Remarks:

Doses / Concentrations:
10, 50, 200 mg/kg bw/day
Basis:

No. of animals per sex per dose:

Males: 12
Females: 17 for control and top dose, 12 for low and mid doses

Control animals:

yes, concurrent vehicle

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
General condition was observed 2 or 3 times a day throughout the administration period

DETAILED CLINICAL OBSERVATIONS: Yes
Detailed clinical observation was carried out once a week in all animals throughout the administration period. In pregnant females, it was carried out on days 7, 14, and 20 of gestation and on day 4 of lactation. Sensory reaction test, grip strength, and motor activity were examined at 6 weeks of administration in males and on day 4 of lactation in pregnant females.

BODY WEIGHT: Yes
Body weights were measured on days 1 (before dosing), 4, 8, 11, 15, 18, 22, 25, 30, 32, 36, 39, and 42 of administration for males, For females, body weight was measured on days 1 (before dosing), 4, 8, 11, 15, 18, 22, 25, 30, 32, 36, 39, and 42 of administration, except for pregnant females for whom it was measured on days 0, 7, 14, and 20 of gestation and days 0 and 4 of lactation. Further, it was measured at necropsy in both sexes.

FOOD CONSUMPTION :
Food consumption was measured on days 1 (before dosing), 4, 8, 11, 15, 30, 32, 36, 39, and 42 of administration for males. For females, food consumption was measured on days 1 (before dosing), 4, 8, 11, 15, 30, 32, 36, 39, and 42 of administration, except for pregnant females for whom it was measured on days 1, 7, 14, and 20 of gestation and days 1 and 4 of lactation

WATER CONSUMPTION : No

Oestrous cyclicity (parental animals):

yes

Sperm parameters (parental animals):

No

Litter observations:

STANDARDISATION OF LITTERS
Performed on day 4 postpartum: no

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring:
number and sex of pups, stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain

GROSS EXAMINATION OF DEAD PUPS:
yes, for external and internal abnormalities; possible cause of death was not determined for pups born or found dead.

Postmortem examinations (parental animals):

SACRIFICE
Necropsy was carried out at the day following the end of the administration and recovery periods

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.
- The testis and epididymis of all males were weighed.

HISTOPATHOLOGY / ORGAN WEIGHTS
The testis, epididymis, prostate, and seminal vesicles of 5 males at 0 and 200 mg/kg bw/day were microscopically examined at the end of the administration period. Further, the ovary, uterus, and vagina of 5 females at 0 and 200 mg/kg bw/day were microscopically examined at the end of the administration period.

Postmortem examinations (offspring):

SACRIFICE
- The F1 offspring were sacrificed at 5 days of age.
- These animals were subjected to postmortem macroscopic examination for gross abnormalities.

Statistics:

Statistical methods: X2 test was used for mating index, males and females fertility indices, gestation index, and delivery index were used. Wilcoxon Rank Sum Test Method for implantation index, death birth index, live birth index, and viability index on day 4 were used.

Reproductive indices:

Estrous cycle, number of copulated, number of pregnant females, mating length, mating index (# of pairs with successful copulation/# of pairs mating × 100), males or females fertility indices (# of pregnant animals/#of animals with successful mating×100), number of females with live pups, gestational length, number of corpora lutea, number of implantations, number of pups delivered, number of live pups delivered, gestation index (# of females with live pups/# of pregnant females × 100), implantation index (# of implants/# of corpora lutea × 100), delivery index (# of pups born/# of implants × 100), death birth index (number of stillborns/number of litter × 100), were determined.

Offspring viability indices:

Sex ratio, live birth index (# of live pups born/# of pups born × 100), and viability index on day 4 (# of live pups on postnatal day (PND) 4 /# of live pups born × 100) were determined.

Clinical signs:

no effects observed

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:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Other effects:

not examined

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
A low body weight value was observed in both sexes at 200 mg/kg bw/day throughout the administration period. During the recovery period, a lower body weight was observed in females, but their body weight gains throughout the recovery period were similar to those of the control group.

A low food consumption value or a tendency toward a low value was observed in males at 200 mg/kg bw/day on days 4 and 15 of administration and in females at 200 mg/kg bw/day throughout the administration period. During the recovery period, females exhibited lower food consumption on day 1 of the recovery period, but food consumption after day 4 of the recovery period was similar to the control group. A decrease in food consumption was observed in females at 10mg/kg on day 15 of the administration period. However, it was not observed at 50mg/kg and not considered to be a dose-related effect.

ORGAN WEIGHTS (PARENTAL ANIMALS)
There were increases in relative weights of the testes and epididymides in males at 200 mg/kg. However, absolute weights of these organs were not changed, and no histopathological changes were observed in these organs. These changes were considered to be due to decreases in body weights.
Increases in absolute and relative weights of the epididymides were observed at 50mg/kg, but these changes were not considered to be dose related effects because these effects were not observed at 200 mg/kg bw/day.

Dose descriptor:

NOAEL

Remarks:

maternal toxicity

Effect level:

50 mg/kg bw/day

Sex:

female

Basis for effect level:

body weight and weight gain

food consumption and compound intake

organ weights and organ / body weight ratios

Dose descriptor:

NOAEL

Remarks:

reproductive toxicity

Effect level:

>= 200 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: No effects on reproductive parameters

Clinical signs:

not examined

Mortality / viability:

no mortality observed

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:

not specified

Histopathological findings:

not examined

BODY WEIGHT (OFFSPRING)
Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day.

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

50 mg/kg bw/day

Sex:

male/female

Basis for effect level:

body weight and weight gain

Remarks on result:

other:

Remarks:

Neonatal toxicity

Reproductive effects observed:

not specified

Reproductive performance of rats

Dose (mg/kg bw/day)	0	10	50	200
Number of females eximaned	12	12	12	12
Count of estrus	3.67(0.78)	3.92(0.29)	3.83(0.58)	3.83(0.39)
Estrus cycle	3.97(0.10)	4.00(0.00)	4.03(0.10)	4.00(0.00)
No. of pairs mating	12	12	12	12
No. of pairs with successful mating	12	12	12	12
No. of pregnant females	12	12	12	11
Duration of mating	2.75(1.42)	3.33(2.84)	3.58(3.18)	3.36(1.80)
Fertility index (%)	100	100	100	91.67

Terminal delivery of F0 dams

Dose (mg/kg bw/day)	0	10	50	200
No. of females with live pups	12	12	12	11
Gestational length (day)	22.08(0.29)	22.50(0.52)	22.33(0.65)	22.18(0.40)
# of corpora lutea	15.08(2.11)	14.58(2.61)	15.67(2.15)	15.36(1.96)
# of implantation sites	14.25(1.76)	13.42(3.00)	14.92(2.75)	14.45(3.00)
# of pups delivered	13.75(1.82)	13.08(3.34)	14.08(3.20)	13.64(2.77)
Sex ratio (male/female)	0.83	1.20	0.92	0.88
# of live pups on day 4	13.75(1.82)	13.00(3.28)	13.75(3.11)	13.64(2.77)
Viability index on day 4	98.79	98.08	96.97	99.33
Body weight of live newborns (g)
Male Day 0	6.4(0.5)	6.9(0.6)	6.7(0.7)	6.2(0.2)
Male Day 4	10.3(0.8)	10.3(2.2)	10.0(2.4)	8.6(0.9)**
Female Day 0	6.1(0.6)	6.4(0.6)	6.3(0.6)	5.9(0.2)
Female Day 4	9.8(0.9)	9.8(2.0)	9.5(2.4)	8.2(0.9)**
Number with external anomalies	0	0	0	1 (exencephaly open eyelid protruding tongue)

**: P<0.01

Conclusions:

The test substance had no effects on any reproductive or developmental parameter. The NOAEL for reproductive and developmental toxicity was considered to be >= 200 mg/kg bw/day and the NOAEL for neonatal toxicity is considered to be 50 mg/kg/day.

Executive summary:

In a combined repeated dose/reproductive/developmental toxicity screening test (OECD 422), groups of male and female Sprague-Dawley rats (12-17/sex/dose) were administered 2 -methylpropane-2 -thiol in corn oil by gavage at 0, 10, 50 or 200 mg/kg bw/day daily for 42-53 days. The animals were dosed daily for 2 weeks prior to mating, during mating and gestation, and the females were dosed for 4 days post-partum after which the adult females and their pups were terminated. 

There were no treatment-related effects at any dose on reproductive and developmental parameters including mating index, fertility index, duration of gestation, gestation index, total number of pups born, live birth index, number of pups alive and viability index on day 4 of lactation or sex ratio. Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day. All reproductive organs from adult animals were normal during gross pathology and microscopic evaluations. The NOAEL for reproductive performance and developmental toxicity was 200 mg/kg bw/day and the NOAEL for neonatal toxicity was considered to be 50 mg/kg bw/day.

This study was classified as reliable with restriction because although it is a GLP guideline study, a study report in English was not available for data verification. However, this study is peer reviewed and considered sufficient for this endpoint.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

200 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Reliable with restrictions (Klimisch score = 2)

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

In a combined repeated dose reproductive and developmental toxicity screening test (OECD 422), groups of male and female Sprague-Dawley rats (12-17/sex/dose) were administered 2-methylpropane-2-thiol in corn oil by gavage at 0, 10, 50 or 200 mg/kg bw/day daily for 42-53 days. The animals were dosed daily for 2 weeks prior to mating, during mating and gestation, and the females were dosed for 4 days post-partum after which the adult females and their pups were terminated (MHLW, 2006).

 

There were no treatment-related effects at any dose on reproductive and developmental parameters including mating index, fertility index, duration of gestation, gestation index, total number of pups born, live birth index, number of pups alive and viability index on day 4 of lactation or sex ratio. Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day. All reproductive organs from adult animals were normal during gross pathology and microscopic evaluations. The NOAEL for reproductive performance and developmental toxicity was 200 mg/kg bw/day and the NOAEL for neonatal toxicity was considered to be 50 mg/kg bw/day. A NOAEL for neonatal toxicity of 50 mg/kg bw/day was observed.

Effects on developmental toxicity

Description of key information

In a key prenatal developmental toxicity study according to OECD TG 414 and in compliance with GLP, treatment with 2-methylpropane-2-thiol by whole-body inhalation did not produce any teratogenic effects in neither rat nor mouse. Therefore, the maternal and developmental NOAEC was determined to ≥195 ppm (Ulrich, 1982, Klimisch score = 1).

A combined repeated dose toxicity study with the reproduction/developmental toxicity screening test occurring by oral gavage, conducted according to OECD TG 422 and in compliance with GLP, did not observe any treatment-related effects on developmental parameters in rat. The NOAEL for developmental toxicity was determined to be 200 mg/kg bw/day (MHLW, 2006, Klimisch score = 2). A NOAEL for neonatal toxicity of 50 mg/kg bw/day was observed.

Link to relevant study records

Reference

Reference 1

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes

Limit test:

no

Species:

mouse

Strain:

CD-1

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: The Charles River Breeding Laboratories Inc., Portage, Michigan, USA
- Age at study initiation: approximately 12 weeks old
- Weight at study initiation: 25-36 grams at the time of mating
- Housing: individually housed, except during mating, in suspended wire-mesh cages
- Diet (e.g. ad libitum): Purina® Certified Rodent Chow #5002
- Water (e.g. ad libitum): tap water
- Acclimation period: 26 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): no data
- Humidity (%): no data
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

Animal Exposure Methods:
Exposures were conducted in one cubic meter glass and stainless steel exposure chambers. Air for the chamber ventilation was supplied from a HVAC system separate from the general laboratory systems. This air was particulate filtered (99.9% + 0.3 µ) and controlled for temperature and humidity. Chamber airflow rate varied between 200 and 260 L/min depending on desired exposure concentrations.
Exposure chamber temperatures and relative humidity were recorded each day alter three and six hours of exposure. Table 1 presents the minimum and maximum and the mean temperature and relative humidity at the six hour measurement time for each group over the course of the study.

Exposure Atmosphere Generation Methods:
A vapor atmosphere of the test material was generated utilizing a counter-current vaporization system. This system operated as follows: The test material was pumped at a known and constant rate to the top of the bead column by a FMI® fluid metering pump or Sagee syringe drive.
Dry-compressed air passed up the bead column in a countercurrent manner relative to the liquid. Vaporization occurred on the bead column. The concentrated vapors were piped to the exposure chamber air inlet where dilution with chamber ventilation air reduced the concentration to the desired level. Table 2 summarizes the vapor generation system operating conditions.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Nominal exposure concentrations were calculated for all exposures. Actual exposure concentrations were measured by non-dispersive Infrared spectrophotometry utilizing a Wilks (MIRAN®) lA analyzer. The analyzer was calibrated by volumetric dilution of pure (99%) t-Butyl Mercaptan in saran gas bags. The calibration was checked once daily.

Details on mating procedure:

One female and one male animal of the same species and strain were placed together for mating. The occurrence of copulation was determined by daily inspection for a copulatory plug. The day evidence of mating was detected was designated day 0 of gestation and the female was returned to an individual cage.

Duration of treatment / exposure:

gestation days 6 - 16

Frequency of treatment:

6 hour/day

Duration of test:

until GD17

Remarks:

Doses / Concentrations:
10, 100 and 200 ppm
Basis:
other: desired conc.

Remarks:

Doses / Concentrations:
11, 99 and 195 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

25

Control animals:

yes, sham-exposed

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
Prior to initiation of the treatment period all animals were observed twice daily for mortality and overt changes in appearance and behavior. All animals were observed daily for mortality and clinical signs of toxicity from gestation day 6 through sacrifice.

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
Individual maternal body weights were recorded on gestation days 0, 6, 9, 12, 15 and 17 .

FOOD CONSUMPTION: No

WATER CONSUMPTION : No

POST-MORTEM EXAMINATIONS: Yes
On gestation day 17, all surviving dams were sacrificed by carbon dioxide inhalation. The abdominal and thoracic cavities and organs of the dams were examined for grossly evident morphological changes and the carcasses discarded. Uteri from females that appeared nongravid were placed in 10% ammonium sulfide solution for confirmation of pregnancy.

Ovaries and uterine content:

The ovaries and uterine content were 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

Fetal examinations:

- External examinations: Yes
All fetuses were individually weighed and examined for external malformations and variations, including the palate and eyes. Each fetus was externally sexed and individually numbered and tagged for identification

- Soft tissue examinations: Yes
Approximately one-half of the fetuses were placed in Bouin's fixative for subsequent visceral examination by razor-blade sectioning as described by Wilson.

- Skeletal examinations: Yes
The remaining one-half of the fetuses were fixed in alcohol, macerated in potassium hydroxide and stained with Alizarin Red S by a method similar to that described by Dawson2 for subsequent skeletal examination

- Head examinations: No

Statistics:

The male to female fetal sex distribution and the numbers of fetuses and litters with malformations were compared using the X2 test criterion with Yate's correction for 2X2 contingency tables and/or Fisher's exact probability test. The numbers of early and late resorptions, nonviable fetuses, and postimplantation loss were compared by the Mann-Whitney U test. The mean numbers of viable fetuses, total implantations, and corpora lutea, and mean fetal body weights were compared by analysis of variance (one way classification). Bartlett's test for homogeneity of variances, and the appropriate t test using Dunnett's multiple comparison tables were used to judge significance of differences. All statistical analyses compared the treatment group to the control group with the level of significance at p<0.05.

Historical control data:

See the attached file

Clinical signs:

no effects observed

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not specified

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

not examined

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

The livers of all female mice, preserved in 10% formalin as specified in the protocol, were externally normal. At 100 and 200 ppm, the mean absolute and relative liver weights were increased when compared to the control group (Table 6), but were not statistically significant and likely an adaptive response. The values et 10 ppm were comparable to the control group.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Other effects:

no effects observed

Number of abortions:

not specified

Pre- and post-implantation loss:

no effects observed

Total litter losses by resorption:

not specified

Early or late resorptions:

not specified

Dead fetuses:

no effects observed

Changes in pregnancy duration:

not specified

Changes in number of pregnant:

not specified

Other effects:

no effects observed

Description (incidence and severity):

corpora lutea

Details on maternal toxic effects:

Maternal toxic effects:no effects

Details on maternal toxic effects:
Maternal Observations:
Survival was 100% in all groups. The mice in the treated groups were similar in appearance and behavior to the control group mice. No treatment-related trend in necropsy findings was observed. The livers of all female mice, preserved in 10% formalin as specified in the protocol, were externally normal. At 100 and 200 ppm, the mean absolute and relative liver weights were increased when compared to the control group (Table 6), but were not statistically significant and likely an adaptive response. The values et 10 ppm were comparable to the control group.
There were no biologically meaningful differences in mean maternal body weight (Table 4) during the treatment period (gestation days 6-17) or over the entire gestation period (gestation day 0-17) in the t-butyl Mercaptan treated mice when compared to the control group mice. In addition, the adjusted (dam weight on gestation day 17 minus the gravid uterus weight) mean maternal body weight change (Table 4) from gestation days 0-17 in the treated groups in this study segment was comparable to the control group.

Caesarean Section Observations:
There were no biologically meaningful or statistically significant differences in the mean number of viable fetuses, postimplantation loss, total implantations, corpora lutea, fetal body weight or the fetal sex distribution in the treated groups when compared to the control group (Table 5) and the historical control data.

Dose descriptor:

NOAEC

Effect level:

>= 195 ppm (analytical)

Basis for effect level:

other: no observed effects

Remarks on result:

other:

Remarks:

Equivalent to 721 mg/m³

Fetal body weight changes:

no effects observed

Reduction in number of live offspring:

not specified

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

no effects observed

Changes in postnatal survival:

not specified

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

An increase in the total litters with malformations, due primarily to the increased incidence of the malformation vertebral anomaly, was noted in the t-butyl Mercaptan treated groups when compared to the control group. However, this incidence did not occur in a dose-related pattern (47.8% and 28.6% of the litters in the 100 and 200 ppm groups, respectively, had malformed fetuses) and was not statistically significant (p>0.05).

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Vertebral anomalies were present in 16.7% of the litters in both the control group and the 10 ppm group, in 43.5% of the litters in the group 100 ppm and in 23.8% of the litters in the 200 ppm. The only other malformation present in the 200 ppm group was a single instance of rib anomalies. In the 10 and 100 ppm groups, the remaining malformations did not occur in a dose-related pattern and/or were within the range of the historical control data.

Visceral malformations:

effects observed, non-treatment-related

Description (incidence and severity):

An increase in the percent of fetuses per group with the variations misaligned sternebrae and/or 14th rudimentary ribs was noted in the treated groups when compared to the control group. The incidence of misaligned sternebrae in the control and treated groups was greater than the highest value in the historical control data, while the occurrence of 14th rudimentary ribs in the control and treated groups was within the range of the historical control data. There were no other trends in the incidence of genetic or developmental variations in the treated groups when compared to the control group.

Dose descriptor:

NOAEC

Effect level:

>= 195 ppm (analytical)

Sex:

male/female

Basis for effect level:

other: no observed effects

Remarks on result:

other: Equivalent to 721 mg/m³

Abnormalities:

not specified

Developmental effects observed:

not specified

TABLE 4: Summary of Group Mean Maternal Body Weights

	Control	10 ppm	100 ppm	200 ppm
Day of gestation	Mean±S.D.	Mean±S.D.	Mean±S.D.	Mean±S.D.
0	29±2.39	29±2.1	29±2.6	29±2.0
6	31±2.6	31±2.3	32±2.7	30±4.0
9	33±2.6	33±2.7	34±2.6	33±3.2
12	38±3.0	38±2.9	39±3.6	38±3.0
15	44±3.5	45±3.3	46±4.4	46±3.4
17	51±4.0	51±3.6	52±5.6	52±4.2
17 (adjusted)^a	35±3.9	35±2.4	35±3.7	36±2.4

^aDam body weight on gestation day 17 minus gravid uterus weight

TABLE 5: Summary of Group Mean Maternal and Fetal Observations at Cesarean Section

Group	Control			10 ppm			100 ppm			200 ppm
	No.	%	S.D.	No.	%	S.D.	No.	%	S.D.	No.	%	S.D
Animals on study:	25	-	-	24	-	-	25	-	-	25	-	-
Animals that were gravid:	24	96.0	-	24	96.0	-	23	92.0	-	21	84.0	-
Animals that died:	0	0.0	-	0	0.0	-	0	0.0	-	0	0.0	-
Nongravid:	-	-	-	-	-	-	-	-	-	-	-	-
Gravid:	-	-	-	-	-	-	-	-	-	-	-	-
Animals that aborted/delivered:	0	0.0	-	0	0.0	-	0	0.0	-	0	0.0	-
Animals examined at Cesarean section:	25	100.0	-	25	100.0	-	25	100.0	-	25	100.0	-
Nongravid:	1	4.0	-	1	4.0	-	2	8.0	-	4	16.0	-
Gravid:	24	96.0	-	24	96.0	-	23	92.0	-	21	84.0	-
Dams with resorptions only:	0	0.0	-	0	0.0	-	0	0.0	-	0	0.0	-
Dams with viable fetuses:	24	100.0	-	24	100.0	-	23	100.0	-	21	100.0	-
Viable fetuses/dam:	11.5	-	2.34	11.1	-	1.65	11.4	-	2.19	11.3	-	1.65
Postimplantation loss/dam:	0.6	-	0.88	0.9	-	1.08	0.7	-	0.76	0.7	-	1.15
Total implantations/dam:	12.1	-	1.04	12.0	-	2.00	12.1	-	2.02	12.0	-	1.80
Corpora lutea/dam:	14.0	-	2.10	13.9	-	2.46	14.5	-	3.51	14.6	-	3.44
Fetal sex distribution                       Male:	130	47.3	-	128	47.9	-	135	51.5	-	110	46.2	-
Female	145	52.7	-	139	52.1	-	127	48.5	-	128	53.8	-
Mean fetal body weight (grams)	0.88	-	0.079	0.92	-	0.094	0.92	-	0.112	0.94	-	0.092
Group mean preimplantation (%)	-	13.4	-	-	13.5	-	-	16.5	-	-	17.3	-
Group mean postimplantation loss (%)^b:	-	5.2	-	-	7.3	-	-	5.8	-	-	5.9	-

^aGroup mean preimplantation loss (%) =Total No. Corpora Lutea - Total No. Implantationsx 100

Total No. Corpora Lutea

^bGroup mean postimplantation loss (%) =Total No. Implantations-Total No. Viable Fetuses x 100

                                                                    Total No. Implantations

^cValue does not include dams with regressing corpora lutea

*Significantly different from control group mean, p<0.05.

**Significantly different from control group mean, p<0.01.

- Not applicable

S.D.- Standard deviation

Table 6: Individual Maternal Liver Weight

Group	Terminal bw (g)	Liver weight (g)	Relative liver weight (%)
Control	51±4.0	2.89±0.287	5.7±0.48
10 ppm	51±3.6	2.97±0.249	5.9±0.46
100 ppm	52±5.6	3.22±0.466	6.2±0.70
200 ppm	52±4.2	3.58±0.385	6.9±0.57

Conclusions:

No teratogenic effects occurred in mice when administered 2-methylpropane-2-thiol by whole body inhalation at or below the 195 ppm actual exposure level.

Executive summary:

Pregnant female mice (CD-1; 25/group) were repeatedly exposed (inhalation, whole body) to 2-methylpropane-2-thiol for 6 hrs/day during GD 6-16. Exposure conditions consisted of measured concentrations of 0, 11, 99, and 195 ppm (nominal concentrations of 0, 10, 100 and 200 ppm). The study design was similar to OECD Test Guideline No. 414. All animals survived to scheduled termination. there were no statistically significant differences between the dosed animals and controls with respect to maternal endpoints. Fetal malformations were observed in mice exposed to 99 ppm (litter incidence, 47.8 %) and 195 ppm (litter incidence, 28.6%) when compared to the control group (litter incidence, 16.7%). The particular malformation noted (i.e., vertebral anomaly), however, did not increase in a dose-related pattern and was in the range of historical control data. There were no additional statistically significant differences in fetuses exposed to 2 -methylpropane-2-thiol when compared to controls. There were no signs of maternal toxicity or biologically relevant teratogenic effects when t-butyl mercaptan was administered by whole body inhalation at or below the 195 ppm actual exposure; therefore, the maternal and fetal NOAEC was equal or higher than 195 ppm. 

Reference 2

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: The Charles River Breeding Laboratories Inc., Portage, Michigan, USA
- Age at study initiation: approximately 14 weeks old
- Weight at study initiation: 221-303 grams at the time of mating
- Housing: individually housed, except during mating, in suspended wire-mesh cages
- Diet (e.g. ad libitum): Purina® Certified Rodent Chow #5002
- Water (e.g. ad libitum): tap water
- Acclimation period: 26 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): no data
- Humidity (%): no data
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

Animal Exposure Methods:
Exposures were conducted in one cubic meter glass and stainless steel exposure chambers. Air for the chamber ventilation was supplied from a HVAC system separate from the general laboratory systems. This air was particulate filtered (99.9% + 0.3 µ) and controlled for temperature and humidity. Chamber airflow rate varied between 200 and 260 L/min depending on desired exposure concentrations.
Exposure chamber temperatures and relative humidity were recorded each day alter three and six hours of exposure. Table 1 presents the minimum and maximum and the mean temperature and relative humidity at the six hour measurement time for each group over the course of the study.

Exposure Atmosphere Generation Methods:
A vapor atmosphere of the test material was generated utilizing a counter-current vaporization system. This system operated as follows: The test material was pumped at a known and constant rate to the top of the bead column by a FMI® fluid metering pump or Sagee syringe drive.
Dry-compressed air passed up the bead column in a countercurrent manner relative to the liquid. Vaporization occurred on the bead column. The concentrated vapors were piped to the exposure chamber air inlet where dilution with chamber ventilation air reduced the concentration to the desired level. Table 2 summarizes the vapor generation system operating conditions.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Nominal exposure concentrations were calculated for all exposures. Actual exposure concentrations were measured by non-dispersive Infrared spectrophotometry utilizing a Wilks (MIRAN®) lA analyzer. The analyzer was calibrated by volumetric dilution of pure (99%) t-Butyl Mercaptan in saran gas bags. The calibration was checked once daily.

Details on mating procedure:

One female and one male animal of the same species and strain were placed together for mating. The occurrence of copulation was determined by daily inspection for a copulatory plug. The day evidence of mating was detected was designated day 0 of gestation and the female was returned to an individual cage.

Duration of treatment / exposure:

gestation days 6 - 19

Frequency of treatment:

6 hour/day

Duration of test:

until GD20

Remarks:

Doses / Concentrations:
10, 100 and 200 ppm
Basis:
other: target conc.

Remarks:

Doses / Concentrations:
11, 99 and 195 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

25

Control animals:

yes, sham-exposed

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
Prior to initiation of the treatment period all animals were observed twice daily for mortality and overt changes in appearance and behavior. All animals were observed daily for mortality and clinical signs of toxicity from gestation day 6 through sacrifice.

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
Individual maternal body weights were recorded on gestation days 0, 6, 9, 12, 16 and 20.

FOOD CONSUMPTION: No

WATER CONSUMPTION : No

POST-MORTEM EXAMINATIONS: Yes
On gestation day 20, all surviving dams were sacrificed by carbon dioxide inhalation. The abdominal and thoracic cavities and organs of the dams were examined for grossly evident morphological changes and the carcasses discarded. Uteri from females that appeared nongravid were placed in 10% ammonium sulfide solution for confirmation of pregnancy.

Ovaries and uterine content:

The ovaries and uterine content were 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

Fetal examinations:

- External examinations: Yes
All fetuses were individually weighed and examined for external malformations and variations, including the palate and eyes. Each fetus was externally sexed and individually numbered and tagged for identification

- Soft tissue examinations: Yes
Approximately one-half of the fetuses were placed in Bouin's fixative for subsequent visceral examination by razor-blade sectioning as described by Wilson.

- Skeletal examinations: Yes
The remaining one-half of the fetuses were fixed in alcohol, macerated in potassium hydroxide and stained with Alizarin Red S by a method similar to that described by Dawson2 for subsequent skeletal examination

- Head examinations: No

Statistics:

The male to female fetal sex distribution and the numbers of fetuses and litters with malformations were compared using the X2 test criterion with Yate's correction for 2X2 contingency tables and/or Fisher's exact probability test. The numbers of early and late resorptions, nonviable fetuses, and postimplantation loss were compared by the Mann-Whitney U test. The mean numbers of viable fetuses, total implantations, and corpora lutea, and mean fetal body weights were compared by analysis of variance (one way classification). Bartlett's test for homogeneity of variances, and the appropriate t test using Dunnett's multiple comparison tables were used to judge significance of differences. All statistical analyses compared the treatment group to the control group with the level of significance at p<0.05.

Historical control data:

See the attached file

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

An increase in the number of rats with hair loss on the limbs was noted in the treated groups when compared to the control group. Soft stool was observed in 10, 8, 9 and 8 rats in the 0, 10, 100 and 200 ppm groups. There were no other biologically meaningful differences in the appearance or behaviour of rats between the treated and control groups.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Description (incidence and severity):

There were no biologically meaningful differences in mean maternal body weight (Table 4) during the treatment period (gestation days 6-20) or over the entire gestation period (gestation days 0-20) in the t-butyl Mercaptan treated rats when compared to the control group rats.

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

not examined

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

not specified

Other effects:

not specified

Number of abortions:

no effects observed

Pre- and post-implantation loss:

effects observed, non-treatment-related

Description (incidence and severity):

An increased post-implantation loss occurred in rats in the 200 ppm exposure group when compared to the control and mean values in the historical control data. These data may have been skewed by one animal having 14 (100%) postimplantation losses.

Total litter losses by resorption:

no effects observed

Early or late resorptions:

not specified

Dead fetuses:

no effects observed

Changes in pregnancy duration:

no effects observed

Changes in number of pregnant:

no effects observed

Other effects:

no effects observed

Dose descriptor:

NOAEC

Effect level:

>= 195 ppm (analytical)

Basis for effect level:

clinical signs

pre and post implantation loss

Remarks on result:

other:

Remarks:

Equivalent to 721 mg/m³

Fetal body weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

A statistically significant increase in mean fetal body weight was noted in the group exposed to 10 ppm when compared to the control group; however, the value was within the range of the historical control data and was considered due to random occurrence.

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

effects observed, treatment-related

Description (incidence and severity):

Mean foetal body weights at the two highest dose groups exceeded the control value.

Changes in postnatal survival:

no effects observed

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Five fetuses in one litter in the 200 ppm dose group exhibited the external malformation of dwarfism. As dwarfism has been observed in several fetuses in a single litter in the historical control data this effect is believed to be of genetic origin in the testing laboratory and not considered treatment-related.

Skeletal malformations:

no effects observed

Visceral malformations:

no effects observed

Other effects:

no effects observed

Description (incidence and severity):

No relevant or statistically significant differences in the mean number of corpora lutea.

Dose descriptor:

NOAEC

Effect level:

>= 195 ppm (analytical)

Sex:

male/female

Basis for effect level:

fetal/pup body weight changes

Remarks on result:

other:

Remarks:

Equivalent to 721 mg/m³

Abnormalities:

not specified

Developmental effects observed:

not specified

TABLE 4: Summary of Group Mean Maternal Body Weights

Group	Control	10 ppm	100 ppm	200 ppm
Day of gestation	Mean±S.D.	Mean±S.D.	Mean±S.D.	Mean±S.D.
0	257±11.9	258±21.1	255±17.0	254±14.2
6	285±13.2	285±20.7	282±17.0	278±20.2
9	288±15.0	289±21.3	284±16.3	275±25.2
12	299±14.8	302±21.7	300±13.8	294±20.8
16	322±16.0	327±20.6	323±20.9	317±22.7
20	371±21.5	376±24.7	370±24.8	366±29.8
20 (adjusted)^a	298±16.6	300±18.5	294±15.2	295±18.4

^aDam body weight on gestation day 20 minus gravid uterus weight

TABLE 5: Summary of Group Mean Maternal and Fetal Observations at Cesarean Section

Group	Control			10 ppm			100 ppm			200 ppm
	No.	%	S.D.	No.	%	S.D.	No.	%	S.D.	No.	%	S.D
Animals on study:	25			25	-		25		-	25
Animals that were gravid:	23	92.0		24	96.0	-	23	92.0		23	92.0
Animals that died:	0	0.0		0	0.0		0	0.0		0	0.0
Nongravid:	-	-	-	-	-	-	-	-		-	-
Gravid:	-	-	-	-	-	-	-	-		-	-
Animals that aborted/delivered:	0	0.0		0	0.0	-	0	0.0	-	0	0.0	-
Animals examined at Cesarean section:	25	100.0		25	100.0	-	25	100.0	-	25	100.0	-
Nongravid:	2	8.0		1	4.0	-	2	8.0	-	2	8.0	-
Gravid:	23	92.0		24	96.0	-	23	92.0	-	23	92.0	‑
Dams with resorptions only:	0	0.0		0	0.0	-	0	0.0	-	1	4.4	‑
Dams with viable fetuses:	23	100.0		24	100.0	-	23	100.0	-	22	95.7	‑
Viable fetuses/dam:	14.0	-	2.31	14.3	-	1.81	14.1	-	3.21	13.3	-	3.66
Postimplantation loss/dam:	0.6	-	0.95	0.4	-	0.50	0.5	-	0.73	1.3	-	2.95
Total implantations/dam:	14.5	-	1.88	14.8	-	1.75	14.6	-	3.37	14.7	-	1.80
Corpora lutea/dam:	16.4	-	2.44	15.8	-	1.80	16.5	-	2.71	15.9	-	1.17
Fetal sex distribution - Male:	153	47.7	-	167	48.5	-	162	49.8	-	140	45.6	‑
Female	168	52.3	-	177	51.5	-	163	50.2	-	167	54.4	-
Mean fetal body weight (grams)	3.3	-	0.23	3.4*	-	0.21	3.5	-	0.41	3.4	-	0.22
Group mean preimplantation (%)	-	11.4	-	-	6.3	-	-	11.6	-	-	7,4^c	-
Group mean postimplantation loss (%)^b:	-	3.9	-	-	2.8	-	-	3.3	-	-	8.9	-

^aGroup mean preimplantation loss (%) =Total No. Corpora Lutea - Total No. Implantationsx 100

Total No. Corpora Lutea

^bGroup mean postimplantation loss (%) =Total No. Implantations-Total No. Viable Fetuses x 100

                                                                Total No. Implantations

^cValue does not include dams with regressing corpora lutea

*Significantly different from control group mean, p<0.05.

**Significantly different from control group mean, p<0.01.

- Not applicable

S.D.- Standard deviation

 

Table 6: Individual Maternal Organ Weight

Group	Terminal bw (g)	Kidney weight (g)	Liver weight (g)	Relative kidney weight (%)	Relative liver weight (%)
Control	371±21.5	2.02±0.312	15.43±1.167	0.6±0.09	4.2±0.23
10 ppm	376±24.7	2.02±0.349	15.45±1.612	0.5±0.08	4.1±0.34
100 ppm	370±24.8	2.24±0.472	14.83±2.846	0.6±0.15	3.9±0.72
200 ppm	366±29.8	2.08±0.152	15.4±1.67	0.6±0.12	4.2±0.27

 

Conclusions:

No teratogenic effects occurred in rats when administered 2-methylpropane-2-thiol by whole body inhalation at or below the 195 ppm actual exposure level.

Executive summary:

Pregnant female rats (COBS CD; 25/group) were repeatedly exposed (inhalation, whole body) to 2-methylpropane-2-thiol for 6 hrs/day during gestational days (GD) 6-19. Exposure conditions consisted of measured concentrations of 0, 11, 99, and 195 ppm (nominal concentrations of 0, 10, 100 and 200 ppm). The control group was exposed to filtered air only on a comparable regimen. Caesarean sections were performed on all surviving rats on gestation day 20. The study design was similar to OECD Test Guideline No. 414. All rats survived until study termination. During the in-life portion of the study, there was an increase in the number of rats with hair loss in the treated groups when compared to the control group; however, there were no other signs of maternal toxicity. At necropsy, there were no biologically relevant or statistically significant differences in the mean number of viable fetuses, total implantations, corpora lutea, or fetal sex distribution in the exposed groups as compared to controls. Fetal evaluations did not reveal biologically relevant or statistically significant differences in malformations among the dosed animals as compared to the controls. There were no signs of maternal toxicity or biologically relevant teratogenic effects when 2-methylpropane-2-thiol was administered by whole body inhalation at or below the 195 ppm actual exposure; therefore, the maternal and fetal NOAEC was equal or higher than 195 ppm.

Reference 3

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2006

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

other: OECD 422

Deviations:

yes

Remarks:

The histopathological examination of the reproductive organs was only performed on 5 animals/sex of the control and top dose.

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: 272.2-325.1 g for males, 188.1-235-9 g for females
- Housing:no data
- Diet (e.g. ad libitum): no data
- Water (e.g. ad libitum):no data
- Acclimation period:no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-27
- Humidity (%): 35-75
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12-12

Route of administration:

oral: gavage

Vehicle:

corn oil

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

no data

Details on mating procedure:

Exposure period: Males: 42 days; Females: 42-53 days from 14 days before mating to day 4 of lactation

Premating exposure period (males): 2 weeks
Premating exposure period (females): 2 weeks

Duration of treatment / exposure:

Exposure period: Males: 42 days; Females: 42-53 days from 14 days before mating to day 4 of lactation

Frequency of treatment:

once daily

Remarks:

Doses / Concentrations:
10, 50, 200 mg/kg bw/day
Basis:

No. of animals per sex per dose:

Males: 12
Females: 17 for control and top dose, 12 for low and mid doses

Control animals:

yes, concurrent vehicle

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
General condition was observed 2 or 3 times a day throughout the administration period

DETAILED CLINICAL OBSERVATIONS: Yes
Detailed clinical observation was carried out once a week in all animals throughout the administration period. In pregnant females, it was carried out on days 7, 14, and 20 of gestation and on day 4 of lactation. Sensory reaction test, grip strength, and motor activity were examined at 6 weeks of administration in males and on day 4 of lactation in pregnant females.

BODY WEIGHT: Yes
Body weights were measured on days 1 (before dosing), 4, 8, 11, 15, 18, 22, 25, 30, 32, 36, 39, and 42 of administration for males, For females, body weight was measured on days 1 (before dosing), 4, 8, 11, 15, 18, 22, 25, 30, 32, 36, 39, and 42 of administration, except for pregnant females for whom it was measured on days 0, 7, 14, and 20 of gestation and days 0 and 4 of lactation. Further, it was measured at necropsy in both sexes.

FOOD CONSUMPTION :
Food consumption was measured on days 1 (before dosing), 4, 8, 11, 15, 30, 32, 36, 39, and 42 of administration for males. For females, food consumption was measured on days 1 (before dosing), 4, 8, 11, 15, 30, 32, 36, 39, and 42 of administration, except for pregnant females for whom it was measured on days 1, 7, 14, and 20 of gestation and days 1 and 4 of lactation

WATER CONSUMPTION : No

Ovaries and uterine content:

Examinations included:
- Gravid uterus weight: Yes / No / No data
- Number of corpora lutea: Yes
- Number of implantations: Yes

Fetal examinations:

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring:
number and sex of pups, stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain

GROSS EXAMINATION OF DEAD PUPS:
yes, for external and internal abnormalities; possible cause of death was not determined for pups born or found dead.

Statistics:

Statistical methods: X2 test was used for mating index, males and females fertility indices, gestation index, and delivery index were used. Wilcoxon Rank Sum Test Method for implantation index, death birth index, live birth index, and viability index on day 4 were used.

Indices:

Off-spring indices:

Sex ratio, live birth index (# of live pups born/# of pups born × 100), and viability index on day 4 (# of live pups on postnatal day (PND) 4 /# of live pups born × 100) were determined.

Reproductive indices:

Estrous cycle, number of copulated, number of pregnant females, mating length, mating index (# of pairs with successful copulation/# of pairs mating × 100), males or females fertility indices (# of pregnant animals/#of animals with successful mating×100), number of females with live pups, gestational length, number of corpora lutea, number of implantations, number of pups delivered, number of live pups delivered, gestation index (# of females with live pups/# of pregnant females × 100), implantation index (# of implants/# of corpora lutea × 100), delivery index (# of pups born/# of implants × 100), death birth index (number of stillborns/number of litter × 100), were determined.

Clinical signs:

no effects observed

Dermal irritation (if dermal study):

not examined

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

A low body weight value was observed in both sexes at 200 mg/kg bw/day throughout the administration period. During the recovery period, a lower body weight was observed in females, but their body weight gains throughout the recovery period were similar to those of the control group.

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

A low food consumption value or a tendency toward a low value was observed in males at 200 mg/kg bw/day on days 4 and 15 of administration and in females at 200 mg/kg bw/day throughout the administration period. During the recovery period, females exhibited lower food consumption on day 1 of the recovery period, but food consumption after day 4 of the recovery period was similar to the control group. A decrease in food consumption was observed in females at 10mg/kg on day 15 of the administration period. However, it was not observed at 50mg/kg and not considered to be a dose-related effect.

Food efficiency:

effects observed, treatment-related

Description (incidence and severity):

A low food consumption value or a tendency toward a low value was observed in males at 200 mg/kg bw/day on days 4 and 15 of administration and in females at 200 mg/kg bw/day throughout the administration period. During the recovery period, females exhibited lower food consumption on day 1 of the recovery period, but food consumption after day 4 of the recovery period was similar to the control group.

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

not examined

Haematological findings:

effects observed, non-treatment-related

Clinical biochemistry findings:

effects observed, non-treatment-related

Urinalysis findings:

no effects observed

Behaviour (functional findings):

no effects observed

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Description (incidence and severity):

There were increases in relative weights of the testes and epididymides in males at 200 mg/kg. However, absolute weights of these organs were not changed, and no histopathological changes were observed in these organs. These changes were considered to be due to decreases in body weights.
Increases in absolute and relative weights of the epididymides were observed at 50mg/kg, but these changes were not considered to be dose related effects because these effects were not observed at 200 mg/kg bw/day.

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, non-treatment-related

Histopathological findings: neoplastic:

no effects observed

Other effects:

not specified

Number of abortions:

not specified

Pre- and post-implantation loss:

no effects observed

Total litter losses by resorption:

not specified

Early or late resorptions:

not specified

Dead fetuses:

no effects observed

Changes in pregnancy duration:

not examined

Changes in number of pregnant:

no effects observed

Other effects:

not specified

Dose descriptor:

NOAEL

Effect level:

>= 200 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

body weight and weight gain

food efficiency

Fetal body weight changes:

effects observed, treatment-related

Description (incidence and severity):

Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day.

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

not specified

Changes in postnatal survival:

not specified

External malformations:

no effects observed

Skeletal malformations:

not specified

Visceral malformations:

not specified

Other effects:

not specified

Dose descriptor:

NOAEL

Effect level:

200 mg/kg bw/day

Sex:

male/female

Basis for effect level:

fetal/pup body weight changes

Abnormalities:

not specified

Developmental effects observed:

not specified

Conclusions:

The test substance had no effects on any developmental parameter. The NOAEL for developmental toxicity was considered to be >= 200 mg/kg bw/day and the NOAEL for neonatal toxicity is considered to be 50 mg/kg/day.

Executive summary:

In a combined repeated dose/reproductive/developmental toxicity screening test (OECD 422), groups of male and female Sprague-Dawley rats (12-17/sex/dose) were administered 2-methylpropane-2-thiol in corn oil by gavage at 0, 10, 50 or 200 mg/kg bw/day daily for 42-53 days. The animals were dosed daily for 2 weeks prior to mating, during mating and gestation, and the females were dosed for 4 days post-partum after which the adult females and their pups were terminated. 

There were no treatment-related effects at any dose on reproductive and developmental parameters including mating index, fertility index, duration of gestation, gestation index, total number of pups born, live birth index, number of pups alive and viability index on day 4 of lactation or sex ratio. Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day. All reproductive organs from adult animals were normal during gross pathology and microscopic evaluations. The NOAEL for reproductive performance and developmental toxicity was 200 mg/kg bw/day and the NOAEL for neonatal toxicity was considered to be 50 mg/kg bw/day.

This study was classified as reliable with restriction because although it is a GLP guideline study, a study report in English was not available for data verification. However, this study is peer reviewed and considered sufficient for this endpoint.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

200 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

721 mg/m³

Study duration:

subchronic

Species:

other: rat and mouse

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

In a key rat developmental toxicity / teratogenicity study (Ulrich, 1982b, OECD 414; Klimisch Score =1), pregnant female Sprague-Dawley rats (COBS CD; 25/concentration) were exposed to analytical concentrations of 0, 11, 99, and 195 ppm (nominal concentrations of 0, 10, 100 and 200 ppm) of 2-methylpropane-2-thiol (CAS # 75-66-1) via whole-body inhalation 6 hrs/day during gestational days 6-19. All rats survived until study termination. During the in-life portion of the study, there was an increase in the number of rats with hair loss in the treated groups when compared to the control group; however, there were no other signs of maternal toxicity. At necropsy, there were no biologically relevant or statistically significant differences in the mean number of viable foetuses, total implantations, corpora lutea, or foetal sex distribution in the exposed groups as compared to controls. Foetal evaluations did not reveal biologically relevant or statistically significant differences in malformations among the dosed animals as compared to the controls. There were no signs of maternal toxicity or biologically relevant teratogenic effects when 2-methylpropane-2-thiol was administered by whole-body inhalation at or below the 195 ppm actual exposure; therefore, the maternal and foetal NOAEC was ≥ 195 ppm, equivalent to 721 mg/m³.

 

In a similar key mouse developmental toxicity / teratogenicity study (Ulrich, 1982b, OECD 414; Klimisch Score = 1), pregnant female mice (CD-1; 25/group) were exposed to analytical concentrations of 0, 11, 99, and 195 ppm (nominal concentrations of 0, 10, 100 and 200 ppm) of 2-methylpropane-2-thiol via whole-body inhalation 6 hrs/day during gestational days 6-16. All animals survived to scheduled termination. There were no statistically significant differences between the dosed animals and controls with respect to maternal endpoints. Foetal malformations were observed in mice exposed to 99 ppm (litter incidence, 47.8 %) and 195 ppm (litter incidence, 28.6%) when compared to the control group (litter incidence, 16.7%). The particular malformation noted (i. e., vertebral anomaly), however, did not increase in a dose-related pattern and was in the range of historical control data. There were no additional statistically significant differences in treated foetuses when compared to controls. There were no signs of maternal toxicity or biologically relevant teratogenic effects when 2-methylpropane-2-thiol was administered by whole-body inhalation at or below the 195 ppm actual exposure; therefore, the maternal and foetal NOAEC was ≥ 195 ppm, equivalent to 721 mg/m³. 

 

In a combined repeated dose/reproductive/developmental toxicity screening test (OECD 422; MHLW, 2006; Klimisch score = 2), groups of male and female Sprague-Dawley rats (12 -17/sex/dose) were administered 2 -methylpropane-2 -thiol in corn oil by gavage at 0, 10, 50 or 200 mg/kg bw/day daily for 42-53 days. The animals were dosed daily for 2 weeks prior to mating, during mating and gestation, and the females were dosed for 4 days post-partum after which the adult females and their pups were terminated. There were no treatment-related effects at any dose on reproductive and developmental parameters including mating index, fertility index, duration of gestation, gestation index, total number of pups born, live birth index, number of pups alive and viability index on day 4 of lactation or sex ratio. Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day. All reproductive organs from adult animals were normal during gross pathology and microscopic evaluations. The NOAEL for developmental toxicity was 200 mg/kg bw/day and the NOAEL for maternal and neonatal toxicity was considered to be 50 mg/kg bw/day.

Justification for classification or non-classification

One screening reproductive/developmental toxicity study and three teratogenicity studies are available for 2-methylpropane-2-thiol. These studies showed that exposure to 2-methylpropane-2-thiol had no effects on reproductive parameters or development at the highest dose tested. 2-methylpropane-2-thiol is therefore not classified for reproductive or developmental toxicity under the CLP Regulation (EC) No 1272/2008.