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Administrative data

Key value for chemical safety assessment

Effects on fertility

Description of key information

There are no reproductive toxicity data for n-propyl mercaptan, (1-propanethiol; CAS 107-03-9), therefore data were read-across from the structurally analogous substance tert-butyl mercaptan (2-methylpropane-2-thiol; CAS 75-66-1).

In a combined repeated dose/reproductive/developmental toxicity screening test, conducted according to OECD Test Guideline 422 and in compliance with GLP, 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 (MHLW, 2006).

Link to relevant study records
Reference
Endpoint:
one-generation reproductive toxicity
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
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.
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
Dose / conc.:
10 mg/kg bw/day (actual dose received)
Dose / conc.:
50 mg/kg bw/day (actual dose received)
Dose / conc.:
200 mg/kg bw/day (actual dose received)
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
Effect level:
>= 200 mg/kg bw/day
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No adverse effects observed
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:
other: Decreased pup body weights
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
Effect on fertility: via inhalation route
Endpoint conclusion:
no study available
Effect on fertility: via dermal route
Endpoint conclusion:
no study available
Additional information

There are no reproductive toxicity data for n-propyl mercaptan, (1-propanethiol; CAS 107-03-9), therefore data were read-across from the structurally analogous substance tert-butyl mercaptan (2-methylpropane-2-thiol; CAS 75-66-1). 1-Propanethiol and 2-methylpropane-2-thiol are characterised by an SH functional group with an aliphatic carbon chain. See attachment to Section 13 for justification of read-across.

In a combined repeated dose/reproductive/developmental toxicity screening test, conducted according to OECD Test Guideline 422 and in compliance with GLP (MHLW, 2006), 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.




Effects on developmental toxicity

Description of key information

There are no developmental toxicity data for n-propyl mercaptan, (1-propanethiol; CAS 107-03-9), therefore data were read-across from the structurally analogous substances tert-butyl mercaptan (2-methylpropane-2-thiol; CAS 75-66-1) and n-butyl mercaptan (1-butanethiol; CAS 109-79-5). 1-Propanethiol (NPM, target), 1-butanethiol (source) and 2-methylpropane-2-thiol (source) all contain a thiol (-SH) functional group with a branched or linear aliphatic carbon chain.

In a combined repeated dose/reproductive/developmental toxicity screening test, conducted according to OECD Test Guideline 422 and in compliance with GLP, treatment with 2-methylpropane-2-thiol 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 was considered to be 50 mg/kg bw/day (MHLW, 2006).

In a prenatal developmental toxicity study according to OECD Test Guideline 414 and in compliance with GLP, treatment with 2-methylpropane-2-thiol by whole-body inhalation did not produce any teratogenic effects in rat. Therefore, the maternal and developmental NOAEC was determined to ≥195 ppm (the highest concentration tested) (Ulrich, 1982b).

In a prenatal developmental toxicity study according to OECD Test Guideline 414 and in compliance with GLP, treatment with 2-methylpropane-2-thiol by whole-body inhalation did not produce any teratogenic effects in mouse. Therefore, the maternal and developmental NOAEC was determined to ≥195 ppm (the highest concentration tested) (Ulrich, 1982b).

In a developmental toxicity study in rats, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, whole body inhalation exposure to the vapour concentrations of 0, 10, 68, and 152 ppm 1-butanethiol (0, 38, 255, and 570 mg/m3) for 6 hours/day during gestation days 6 to 19, did not result in any treatment-related adverse systemic or developmental effects in maternal animals and their pups. The NOAEC for maternal and developmental toxicity was concluded to be ≥152 ppm (≥570 mg/m3) based on no treatment-related effects at the highest concentration tested (Ulrich, 1982b; Thomas, 1987).

In a developmental toxicity study in mice, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, mortality was observed at 1-butanethiol concentrations of 68 and 152 ppm (0.26 and 0.58 mg/L); however, no foetal toxicity was observed in surviving animals. The NOAEC for maternal toxicity was 10 ppm (38 mg/m3) and ≥68 ppm (≥255 mg/m3) for developmental toxicity (Ulrich, 1982b; Thomas, 1987).

Link to relevant study records

Referenceopen allclose all

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
2006
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
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.
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
Dose / conc.:
10 mg/kg bw/day (actual dose received)
Dose / conc.:
50 mg/kg bw/day (actual dose received)
Dose / conc.:
200 mg/kg bw/day (actual dose received)
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.
Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
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
Effect level:
>= 50 mg/kg bw/day
Based on:
test mat.
Basis for effect level:
other: Based on body weight reduction observed in female rats dosed at 200 mg/kg/day.
Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
Decreases in body weight of live pups on PND 4 were observed in both sexes at 200 mg/kg bw/day.
Dose descriptor:
NOAEL
Effect level:
>= 200 mg/kg bw/day (actual dose received)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No adverse effects observed
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.

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
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
Dose / conc.:
10 ppm
Remarks:
desired conc.
Dose / conc.:
100 ppm
Remarks:
desired conc.
Dose / conc.:
200 ppm
Remarks:
desired conc.
Dose / conc.:
11 ppm (analytical)
Dose / conc.:
99 ppm (analytical)
Dose / conc.:
195 ppm (analytical)
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 anomalies, 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. 

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
weight of evidence
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
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
Dose / conc.:
10 ppm
Remarks:
target conc.
Dose / conc.:
100 ppm
Remarks:
target conc.
Dose / conc.:
200 ppm
Remarks:
target conc.
Dose / conc.:
11 ppm (analytical)
Dose / conc.:
99 ppm (analytical)
Dose / conc.:
195 ppm (analytical)
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 behavior 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

-

-

7,4c

-

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.

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1982
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)
Deviations:
yes
Remarks:
limited information on animal husbandry and methods
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: vapour
Vehicle:
air
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 (97.5%) n-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
Dose / conc.:
10 ppm
Remarks:
36.9 mg/m³ air (analytical) (group 2)
Dose / conc.:
75 ppm
Remarks:
250.9 mg/m³ air (analytical) (group 3)
Dose / conc.:
150 ppm
Remarks:
560.7 mg/m³ air (analytical)
Dose / conc.:
10 ppm (analytical)
Dose / conc.:
68 ppm (analytical)
Dose / conc.:
152 ppm (analytical)
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
- Sacrifice on gestation day 17
- Organs examined: uterus, abdominal and thoracic cavities and organs of the dams
Ovaries and uterine content:
The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: No data
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:
Available in the report.
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
Emaciation, unkempt appearance, red or brown staining of the perivaginal region, lethargy, and/or staining of the hair was noted in mice at 68 and 152 ppm. These signs were exposure concentration related in respect of severity and/or incidence.
Dermal irritation (if dermal study):
not examined
Mortality:
mortality observed, treatment-related
Description (incidence):
Seventeen treated mice died, eight at 68 ppm (0.25 mg/L) and nine at 152 ppm (0.56 mg/L) between days 11 and 17. Parturition was in progress in one mouse at 68 ppm at the time of death on day 15. A presumptive cause of death was not established for any descendent. All control and 10-ppm (0.04 mg/L) exposed mice survived.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
A dose-related decrease in mean maternal body weight gain occurred during the treatment period (GD 6-17) and over the entire gestation period (GD 0-17) in all treatment groups when compared to the control. The adjusted mean maternal body weight gain over the entire gestation period was markedly reduced in group 4 when compared to the control group. The adjusted mean maternal body weight gain over the entire gestation period in groups 2 and 3 were slightly reduced when compared to the control group.
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
Description (incidence and severity):
In the treated groups, the mean relative kidney weights were slightly increased when compared to the control group. However, the mean absolute kidney weight in the treated groups was similar to the control group.
Gross pathological findings:
no effects observed
Description (incidence and severity):
No treatment-related trend in necropsy findings were observed. The kidneys were externally normal.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
not specified
Histopathological findings: neoplastic:
not specified
Other effects:
not specified
Number of abortions:
not specified
Pre- and post-implantation loss:
effects observed, treatment-related
Description (incidence and severity):
There was an increase in mean post-implantation loss in groups 3 and 4 when compared to the control group and the mean value in the historical control data. This increase was statistically significant in group 4.
There was no biologically meaningful or statistically significant differences in the mean post-implantation loss in the low dose group..
Total litter losses by resorption:
no effects observed
Description (incidence and severity):
Seven dams had resorptions only; one in group 3 and six in group 4.
Early or late resorptions:
effects observed, treatment-related
Description (incidence and severity):
There was no biologically meaningful or statistically significant differences in the number of early and late resorptions only in the low dose group..
Dead fetuses:
effects observed, treatment-related
Description (incidence and severity):
Due to the reduced sample size the mean number of viable fetuses in group 4 could not be validly compared to the control group. A reduction in the mean number of viable fetuses, corresponding to the increase in the mean post-implantation loss, occurred in group 3 when compared to the control group; however this value was within the historical control data range.
There was no biologically meaningful or statistically significant differences in the number of viable fetuses in the low dose group.
Changes in pregnancy duration:
no effects observed
Changes in number of pregnant:
effects observed, non-treatment-related
Description (incidence and severity):
In group 4, there was a decrease in the pregnancy rate and in mean number of total implantations when compared to the control group and the historical control data, but since ovulation and implantation in the mice in this study took place before the test material administration period, this decrease was not a treatment-related effect.
Other effects:
no effects observed
Description (incidence and severity):
There was no treatment-related trend in the mean number of corpora lutea in the treated groups when compared to the control group.
Dose descriptor:
NOAEC
Effect level:
>= 10 ppm (analytical)
Basis for effect level:
mortality
Remarks on result:
other: Equivalent to 36.9 mg/m³
Abnormalities:
not examined
Fetal body weight changes:
no effects observed
Description (incidence and severity):
There was no treatment-related trend in the mean fetal body weight in the treated groups when compared to the control group.
Reduction in number of live offspring:
effects observed, treatment-related
Description (incidence and severity):
Due to the reduced sample size the mean number of viable fetuses in group 4 could not be validly compared to the control group. A reduction in the mean number of viable fetuses, corresponding to the increase in the mean post-implantation loss, occurred in group 3 when compared to the control group; however this value was within the historical control data range.
There was no biologically meaningful or statistically significant differences in the number of viable fetuses in the low dose group.
Changes in sex ratio:
no effects observed
Description (incidence and severity):
There was no treatment-related trend in the mean fetal sex distribution in the treated groups when compared to the control group.
Changes in litter size and weights:
no effects observed
Changes in postnatal survival:
not examined
External malformations:
effects observed, non-treatment-related
Description (incidence and severity):
Cleft palate occurred in 8.3, 16.0 and 21.4% of the litters in groups 1 (control), 2 and 3, respectively. All of these values exceeded the range of the historical control data (0.0-5.6%). The malformations exencephaly, open eye and bend bones were noted in one fetus in one group 3 litter only; hydrocephaly was present in two fetuses in another litter in this group.
Skeletal malformations:
no effects observed
Description (incidence and severity):
There was no treatment related trend in the incidence of fetuses with the vertebral anomalies in litters in groups 2 and 3 when compared to the control.
Visceral malformations:
effects observed, non-treatment-related
Description (incidence and severity):
There was an increased incidence of litters with malformed fetuses in groups 2 and 3 when compared to the control group; however, the increase was not statistically significant.
Other effects:
no effects observed
Details on embryotoxic / teratogenic effects:
Because of the small sample size (only 30 fetuses from 3 litters) due to increased mortality, reduced pregnancy rate, and increased post-implantation loss, the incidence of malformations, genetic or developmental variations in treatment group 4 could not be validly compared to the control group. In this group a single instance of vertebral anomaly was the only malformation noted.
Cleft palate occurred in 8.3, 16.0 and 21.4% of the litters in groups 1 (control), 2 and 3, respectively. All of these values exceeded the range of the historical control data (0.0-5.6%). The malformations exencephaly, open eye and bend bones were noted in one fetus in one group 3 litter only; hydrocephaly was present in two fetuses in another litter in this group. There was no treatment related trend in the incidence of fetuses with the vertebral anomalies in litters in groups 2 and 3 when compared to the control. There was an increased incidence of litters with malformed fetuses in groups 2 and 3 when compared to the control group; however, the increase was not statistically significant.
The developmental or genetic variation noted in fetuses in the treatment groups did not occur in a treatment-related pattern and/or within the range of historical control data.
Dose descriptor:
NOAEC
Effect level:
>= 68 ppm (analytical)
Sex:
male/female
Basis for effect level:
other: No adverse effects observed
Remarks on result:
other: Equivalent to 250.9 mg/m³
Abnormalities:
no effects observed
Developmental effects observed:
no

Survival Data for Mice Dams and Fetuses

 

Control

10 ppm NBM

68 ppm NBM

152 ppm NBM

No. dams on study

25

25

25

25

No. dams dying on study

-

-

8

9

No. gravid dams dying on study

-

-

8

8

No. surviving dams

 

 

 

 

Nongravid

1

-

2

7

Gravid

24

25

15

9

Total corpora lutea

335

342

194

41

Corpora lutea/gravid dam

14.0

13.7

12.9

13.7

Total implants

290

303

180

90

Implants/gravid dam

12.1

12.1

12.0

10.0

Number with resportions only

0

0

1

6

Total viable fetuses

275

275

148

30

Viable fetuses/gravid dam

11.5

11.0

9.9

3.3a

Total early resorptions

5

11

25

59

Early resorptions/gravid dam

0.2

0.4

1.7*

6.6**

Postimplantation loss/gravid dam

0.6

1.1

2.1

6.7**

aSix dams showed early regressing resorption sites and no viable fetuses. 

*Significantly different from control p<0.05

**Significantly different from control p<0.01

Summary of the Incidence of Fetal External, soft tissue, and Skeletal Malformations

Malformations observed

Control

10 ppm NBM

68 ppm NBM

152 ppm NBM

 

No. fetuses

%

No. fetuses

%

No. fetuses

%

No. fetuses

%

External malformations

 

 

 

 

 

 

 

 

Cleft Palate

2

0.7

4

1.5

5

3.4

0

0

Open Eye

0

0

0

0

1

0.7

0

0

Exencephaly

0

0

0

0

1

0.7

0

0

Soft tissue malformations

 

 

 

 

 

 

 

 

Hydrocephaly

0

0

0

0

2

2.7

0

0

Skeletal malformations

 

 

 

 

 

 

 

 

Vertebral anomaly

5

3.6

7

5.1

5

6.8

1

6.3

Bent bones

0

0

0

0

1

1.4

0

0

Total fetuses/% with malformations

7

2.5

11

4.0

12*

8.1

1

3.3

* significantly different from control p</= 0.5

Conclusions:
In a developmental toxicity study in mice, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, mortality was observed at 1-butanethiol concentrations of 68 and 152 ppm (0.26 and 0.58 mg/L; measured); however, no fetal toxicity was observed in surviving animals. The NOAEC for maternal toxicity was 10 ppm (38 mg/m3) and ≥68 ppm (≥255 mg/m3) for developmental toxicity.
Executive summary:

In a developmental toxicity study, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP,  groups of 25 pregnant CD-1 mice were whole body exposed to actual concentrations of 0, 10, 68, and 152 ppm 1-butanethiol, CAS 109-79-5 (0, 38, 255, and 570 mg/m3), 6 hours/day, on gestational days 6 to 16. Caesarean sections were performed on all surviving mice on gestational day 17. Throughout the study period, 17 pregnant mice died: 8 in 68 ppm group and 9 in 152 ppm group. Increased maternal toxicity characterised by a thin appearance, unkempt haircoat, very little movement and/or red or brown matter (presumably blood) in the vaginal region and a decrease in mean maternal body weight gain, was present in treatment groups. An increased post-implantation loss and early resorption occurred in 68 and 152 ppm groups. Due to the reduced sample size no valid comparison of fetal morphological observations in 152 ppm group could be made. An increase in the incidence of cleft palate was observed in the control group and 10 ppm and 68 ppm groups when compared to the historical control data, which was attributed to maternal stress. There were no biologically meaningful or statistically significant differences in the total incidence of malformations in fetuses in litters when compared to the appropriate control group. 1-Butanethiol did not produce teratogenic effects at exposure levels of 68 ppm or less in mice. At the 152 ppm exposure level the sample size was insufficient to evaluate possible teratogenic effects; however, no effects were observed in the available litters.

Overall, in pregnant mice, mortality was observed at concentrations of 68 and 152 ppm (0.26 and 0.58 mg/L); however, no fetal toxicity was observed in surviving animals. The NOAEC for maternal toxicity was 10 ppm (38 mg/m3) and ≥68 ppm (≥255 mg/m3) for developmental toxicity.

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1982
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)
Deviations:
yes
Remarks:
limited information on animal husbandry and methods
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: vapour
Vehicle:
air
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 (97.5%) n-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
Dose / conc.:
10 ppm
Remarks:
36.9 mg/m³ air (analytical) (group 2)
Dose / conc.:
75 ppm
Remarks:
250.9 mg/m³ air (analytical) (group 3)
Dose / conc.:
150 ppm
Remarks:
560.7 mg/m³ air (analytical)
Dose / conc.:
10 ppm (analytical)
Dose / conc.:
68 ppm (analytical)
Dose / conc.:
152 ppm (analytical)
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 was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
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:
Available in the report.
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
A slight increase in the incidence of hair loss on the limbs was noted in group 4 when compared to the control group (group 1). Female #76523 and 76554 in groups 3 and 4 respectively, were dehydrated, Twenty-one rats had soft stool; 10, 8, 2 and 1 in the control, low (group 2), mid (group 3) and high (group 4) dose groups, respectively.
Dermal irritation (if dermal study):
not examined
Mortality:
no mortality observed
Description (incidence):
Survival was 100% in all groups.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
A very slight reduction in mean maternal body weight gain from gestation days 6-20 and over the entire gestation period (gestation days 0-20) was noted in the rats in the n-butyl Mercaptan treated groups 3 and 4 when compared to the control group. Similarly, the adjusted (dam weight on gestation day 20 minus gravid uterus weight) mean maternal body weight gain from gestation days 0-20 was reduced in these groups when compared to the control group. The mean maternal body weight gain during these intervals in group 2 was comparable to the control group. The adjusted mean maternal body weight gain from gestation days 0-20 was slightly reduced in this group when compared to the control group.
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
Description (incidence and severity):
Both the mean absolute and relative kidney weights in the treated groups were comparable to the control group.
Gross pathological findings:
effects observed, non-treatment-related
Description (incidence and severity):
In female #76548 in group 4 the spleen was mottled, pitted and adhered to the connective tissue. In female #76547 in group 4 the left kidney was pitted.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, non-treatment-related
Description (incidence and severity):
In female #76548 in group 4, moderate focal capsular fibrosis was noted in spleen at histopathological examination.
Histopathological findings: neoplastic:
not specified
Other effects:
not specified
Number of abortions:
no effects observed
Pre- and post-implantation loss:
no effects observed
Total litter losses by resorption:
no effects observed
Early or late resorptions:
no effects observed
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
Details on maternal toxic effects:
There were no biologically meaningful or statistically significant differences in the mean number of viable fetuses, postimplantation loss, total implantations, corpora lutea, or the fetal sex distribution in the treated groups when compared to the control group and the historical control data.
Dose descriptor:
NOAEC
Effect level:
>= 150 ppm (analytical)
Basis for effect level:
pre and post implantation loss
other: No adverse effects observed.
Remarks on result:
other: Equivalent to 560 mg/m³
Abnormalities:
effects observed, non-treatment-related
Fetal body weight changes:
effects observed, non-treatment-related
Description (incidence and severity):
A statistically significant (p<0.05) increase in mean fetal body weight was present in group 3. This increase 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:
no effects observed
Changes in postnatal survival:
not examined
External malformations:
no effects observed
Skeletal malformations:
no effects observed
Visceral malformations:
no effects observed
Other effects:
no effects observed
Details on embryotoxic / teratogenic effects:
Single instances of tail anomaly with associated small or no anal opening, scoliosis and/or pelvic anomaly were noted in one litter each in the groupa 3 and 4. The incidence of these malformations in the fetuses of groups 3 and 4 was within the range of occurrence in the historical control data and was not considered biologically meaningful.
There were no biologically meaningful trends in the occurrence of developmental and genetic variations in fetuses (or litters) in the treated groups when compared to the control group.
Dose descriptor:
NOAEC
Effect level:
>= 150 ppm (analytical)
Sex:
male/female
Basis for effect level:
other: No adverse effects observed
Remarks on result:
other: Equivalent to 560 mg/m³
Abnormalities:
no effects observed
Developmental effects observed:
not specified
Conclusions:
In a developmental toxicity study in rats, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, whole body inhalation exposure to the vapour concentrations of 0, 10, 68, and 152 ppm 1-butanethiol (0, 38, 255, and 570 mg/m3; measured) for 6 hours/day during gestation days 6 to 19, did not result in any treatment-related adverse systemic or developmental effects in maternal animals and their pups. The NOAEC for maternal and developmental toxicity was concluded to be ≥152 ppm (≥570 mg/m3) based on no treatment-related effects at the highest concentration tested.
Executive summary:

In a developmental toxicity study, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, pregnant female rats (COBS CD; 25/group) were exposed (inhalation, whole body) to 1-butanethiol (n-butyl mercaptan) at target concentrations of 0, 10, 75 and 150 ppm (0, 36.9, 250.9 and 560.7 mg/m3 analytical, respectively) for 6 hours/day during gestation days (GD) 6-19. All rats survived until study termination. During the in-life portion of the study, a very slight decrease in mean maternal body weight gain was noted in the two highest exposure groups (75 and 150 ppm), and females from the highest exposure group (150 ppm) showed a slight increase (2/25 females) in the incidence of hair loss around the limbs as compared to control females. There was a statistically significant increase in mean fetal body weights in the group exposed at 75 ppm; however, because the increase was within the range of the historical control data, the finding was not considered to be treatment-related. Of the noted fetal malformations, all were within the range of occurrence in the historical control data and not considered to be biologically significant. In conclusion, there were no developmental/teratogenic effects or maternal toxicity in rats when administeredn-butyl mercaptanby whole body inhalation at or below the 150 ppm, the NOAEC for both maternal and fetal toxicity was 150 ppm (560.7 mg/m3 analytical).

Effect on developmental toxicity: via oral route
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
200 mg/kg bw/day
Study duration:
subacute
Species:
rat
Effect on developmental toxicity: via inhalation route
Endpoint conclusion:
no adverse effect observed
Study duration:
subchronic
Species:
rat
Effect on developmental toxicity: via dermal route
Endpoint conclusion:
no study available
Additional information

There are no developmental toxicity data for n-propyl mercaptan, (1-propanethiol; CAS 107-03-9), therefore data were read-across from the structurally analogous substances tert-butyl mercaptan (2-methylpropane-2-thiol; CAS 75-66-1) and n-butyl mercaptan (1-butanethiol; CAS 109-79-5). 1-Propanethiol (NPM, target), 1-butanethiol (source) and 2-methylpropane-2-thiol (source) all contain a thiol (-SH) functional group with a branched or linear aliphatic carbon chain. See attachment to Section 13 for justification of read-across.

In a combined repeated dose/reproductive/developmental toxicity screening test, conducted according to OECD Test Guideline 422 and in compliance with GLP, 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.

In a rat developmental toxicity / teratogenicity study (Ulrich, 1982b), conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, 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 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 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 ≥ 195 ppm, equivalent to 721 mg/m³.

In a similar key mouse developmental toxicity / teratogenicity study (Ulrich, 1982b), conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, 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. 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 treated fetuses 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 fetal NOAEC was ≥ 195 ppm, equivalent to 721 mg/m³.

In a developmental toxicity study, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP, pregnant female rats (COBS CD; 25/group) were exposed (inhalation, whole body) to 1-butanethiol at target concentrations of 0, 10, 75 and 150 ppm (0, 36.9, 250.9 and 560.7 mg/m3 analytical, respectively) for 6 hours/day during gestation days (GD) 6-19 (Ulrich, 1982b; Thomas, 1987). All rats survived until study termination. During the in-life portion of the study, a very slight decrease in mean maternal body weight gain was noted in the two highest exposure groups (75 and 150 ppm), and females from the highest exposure group (150 ppm) showed a slight increase (2/25 females) in the incidence of hair loss around the limbs as compared to control females. There was a statistically significant increase in mean fetal body weights in the group exposed at 75 ppm; however, because the increase was within the range of the historical control data, the finding was not considered to be treatment-related. Of the noted fetal malformations, all were within the range of occurrence in the historical control data and not considered to be biologically significant. In conclusion, there were no developmental/teratogenic effects or maternal toxicity in rats when administered n-butyl mercaptan by whole body inhalation at or below the 150 ppm, the NOAEC for both maternal and fetal toxicity was 150 ppm (560.7 mg/m3 analytical).

In a developmental toxicity study, conducted according to a protocol similar to OECD Test Guideline 414 and in compliance with GLP,  groups of 25 pregnant CD-1 mice were whole body exposed to actual concentrations of 0, 10, 68, and 152 ppm 1-butanethiol (0, 38, 255, and 570 mg/m3), 6 hours/day, on gestational days 6 to 16. Caesarean sections were performed on all surviving mice on gestational day 17 (Ulrich, 1982b; Thomas, 1987). Throughout the study period, 17 pregnant mice died: 8 in 68 ppm group and 9 in 152 ppm group. Increased maternal toxicity characterised by a thin appearance, unkempt haircoat, very little movement and/or red or brown matter (presumably blood) in the vaginal region and a decrease in mean maternal body weight gain, was present in treatment groups. An increased post-implantation loss and early resorption occurred in 68 and 152 ppm groups. Due to the reduced sample size no valid comparison of fetal morphological observations in 152 ppm group could be made. An increase in the incidence of cleft palate was observed in the control group and 10 ppm and 68 ppm groups when compared to the historical control data, which was attributed to maternal stress. There were no biologically meaningful or statistically significant differences in the total incidence of malformations in fetuses in litters when compared to the appropriate control group. 1-Butanethiol did not produce teratogenic effects at exposure levels of 68 ppm or less in mice. At the 152 ppm exposure level the sample size was insufficient to evaluate possible teratogenic effects; however, no effects were observed in the available litters. Overall, in pregnant mice, mortality was observed at concentrations of 68 and 152 ppm (0.26 and 0.58 mg/L); however, no fetal toxicity was observed in surviving animals. The NOAEC for maternal toxicity was 10 ppm (38 mg/m3) and ≥68 ppm (≥255 mg/m3) for developmental toxicity.

Justification for classification or non-classification

Based on the available read-across data for tert-butyl mercaptan (2-methylpropane-2-thiol; CAS 75-66-1) and n-butyl mercaptan (1-butanethiol; CAS 109-79-5), no classification for reproductive or developmental toxicity is required for the registered substance, n-propyl mercaptan, (propane-1-thiol; CAS 107-03-9), according to Regulation (EC) No 1272/2008.

Additional information