Ethanethiol

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Remarks:

other: Combined repeat dose study with reproduction/developmental toxicity screening

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Study period:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: 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

Remarks:

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

No. of animals per sex per dose:

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

Control animals:

yes, concurrent vehicle

Parental animals: Observations and examinations:

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

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

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

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

WATER CONSUMPTION : No

Oestrous cyclicity (parental animals):

yes

Sperm parameters (parental animals):

No

Litter observations:

STANDARDISATION OF LITTERS
Performed on day 4 postpartum: no

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

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

Postmortem examinations (parental animals):

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

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

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

Postmortem examinations (offspring):

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

Statistics:

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

Reproductive indices:

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

Offspring viability indices:

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

Clinical signs:

no effects observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Other effects:

not examined

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

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

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

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

Dose descriptor:

NOAEL

Remarks:

General toxicity

Effect level:

>= 200 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse effects.

Dose descriptor:

NOAEL

Remarks:

reproductive toxicity

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.

Critical effects observed:

no

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 (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

Critical effects observed:

no

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:

In a combined repeated dose/reproductive/developmental toxicity screening test (OECD 422), conducted in compliance with GLP, the test substance had no effects on any reproductive parameters, including fertility (MHLW, 2006). Therefore the NOAEL for reproductive toxicity was considered to be ≥ 200 mg/kg bw/day. The NOAEL for parental toxicity was also ≥ 200 mg/kg bw/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 (MHLW, 2006). 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. Therefore the NOAEL for parental and reproductive performance was ≥ 200 mg/kg bw/day.

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

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

200 mg/kg bw/day

Study duration:

subacute

Species:

rat

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

No data regarding reproductive toxicity are available for ethanethiol. However, a key read across study from 2-methylpropane-2-thiol was identified to evaluate the reproductive toxicity potential of ethanethiol.

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

There were no treatment-related effects at any dose on reproductive 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 at 200 mg/kg bw/day. All reproductive organs from adult animals were normal during gross pathology and microscopic evaluations. The NOAEL for maternal and reproductive toxicity was ≥ 200 mg/kg bw/day as no adverse effects were observed for these endpoints.

Read-Across Justification

To reduce animal testing REACH recommends to make use of a read-across approach where appropriate based on the high accordance in properties relevant for the specific endpoint.

There are no data on the reproductive toxicity for ethanethiol, therefore a good quality study on the related substance

has been read-across to assess the potential for ethanethiol to cause reproductive toxicity.

The low molecular weight aliphatic alkylthiols are volatile organic liquids of moderate aqueous solubility and low n-octanol-water partition coefficient. The substances all contain a single thiol (-SH) functional group. The acid dissociation constant (pKa) of the thiol group is approximately 10 therefore the substances can be considered as weak acids which will not be significantly ionised at physiologically relevant pH.There are oral and inhalation data for repeated dose toxicity available for read-across substances butane-1-thiol, butane-2-thiol and 2-methylpropane-2-thiol. In repeated dose toxicity studies there was a consistent pattern of adaptive liver hypertrophy and species-specific alpha2u-globulin nephropathy. There were also slight and inconsistent signs of respiratory irritation in the repeated dose inhalation studies. None of the findings in the repeated dose studies were considered adverse and the NOAEL/NOAECs were the highest doses tested. Based on the similar pattern of metabolism expected for these substances, once absorbed the distribution to tissues and excretion is expected to be similar. Since the structures of the read across substances and ethanethiol are very similar, it is acceptable to assume that the systemic effects of ethanethiol following repeated oral and inhalation will be the same as those for the read across substances. These similarities are expected to extend to reproductive toxicity, as the substances would distribute to, and interact with, reproductive organs in a similar manner. Therefore ethanethiol is not likely to behave differently to 2-methylpropane-2-thiol.

Short description of key information:
No data regarding reproductive toxicity are available for ethanethiol. However, a key read across study was identified from a related substance, 2-methylpropane-2-thiol (MHLW, 2006). In an OECD Test Guideline 422 study, the NOAEL for maternal and reproductive toxicity was ≥ 200 mg/kg bw/day as no adverse effects were observed for these endpoints.

Justification for selection of Effect on fertility via oral route:
The key study was conducted to OECD test guideline 422 and in compliance with GLP.

Effects on developmental toxicity

Description of key information

No developmental toxicity / teratogenicity data were available for ethanethiol. However, five good quality read across studies were identified from the related substances 2-methylpropane-2-thiol and butane-1-thiol. 
In the key developmental toxicity/teratogeniticy studies in mice and rats (OECD 414), treatment with 2-methylpropane-2-thiol by whole-body inhalation did not produce developmental effects and the maternal and developmental NOAEC was ≥195 ppm in mice and rats (Ulrich, 1982). 
In the other key developmental toxicity/teratogeniticy study (OECD 414), rats exposed to butane-1-thiol by whole-body inhalation showed no treatment related developmental effects and the NOAEC was ≥0.56 mg/L (560 mg/m3 or 152 ppm). In mice exposed to butane-1-thiol, implantation loss and statistically significant decreases in the number of viable fetuses per dam were seen at the 0.56 mg/L exposure concentration. The developmental toxicity NOAEC was determined to be 0.28 mg/L (280 mg/m3 or 68 ppm) (Ulrich, 1982).
In an oral combined repeat-dose/reproductive/developmental toxicity study, decreases in body weights of live pups on PND 4 were observed at 200 mg/kg bw/daywere observed. Therefore the NOAEL for developmental toxicity was determined to be 50 mg/kg bw/day (MHLW, 2006). 

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

supporting study

Study period:

No data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: 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

Remarks:

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

No. of animals per sex per dose:

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

Control animals:

yes, concurrent vehicle

Maternal examinations:

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

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

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

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

WATER CONSUMPTION : No

Ovaries and uterine content:

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

Fetal examinations:

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

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

Statistics:

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

Indices:

Off-spring indices:

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

Reproductive indices:

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

Details on maternal toxic effects:

Maternal toxic effects:no effects

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:

ca. 50 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: other:

Dose descriptor:

NOAEL

Effect level:

>= 200 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

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 at 200 mg/kg bw/day.

Abnormalities:

not specified

Developmental effects observed:

not specified

Conclusions:

In a combined repeated dose/reproductive/developmental toxicity screening test (OECD 422) the test substance had no effects on maternal animals but there were decreases in live pup body weight on postnatal day 4. Therefore the NOAELs for maternal and developmental toxicity were >= 200 and 50 mg/kg bw/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. Therefore the NOAELs for maternal and developmental toxicity were >= 200 and 50 mg/kg bw/day.

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

Effect on developmental toxicity: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

50 mg/kg bw/day

Study duration:

subacute

Species:

rat

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

495.5 mg/m³

Study duration:

subacute

Species:

rat

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

No studies evaluating the developmental toxicity / teratogenicity were identified for ethanethiol. Good quality read across prenatal developmental toxicity studies were identified for 2-methylpropane-2-thiol and butane-1-thiol.

In a key read across rat developmental toxicity / teratogenicity study (Ulrich, 1982b, OECD 414; Klimisch Score =2), pregnant female Sprague-Dawley rats (COBS CD; 25/concentration) were exposed to analytical concentrations of 0, 11, 99, and 195 ppm (nominal concentrations of 0, 10, 100 and 200 ppm) of 2-methylpropane-2-thiol (CAS # 75-66-1) via whole-body inhalation 6 hrs/day during gestational days 6-19.  All rats survived until study termination. During the in-life portion of the study, there was an increase in the number of rats with hair loss in the treated groups when compared to the control group; however, there were no other signs of maternal toxicity. At necropsy, there were no biologically relevant or statistically significant differences in the mean number of viable foetuses, total implantations, corpora lutea, or foetal sex distribution in the exposed groups as compared to controls. Foetal evaluations did not reveal biologically relevant or statistically significant differences in malformations among the dosed animals as compared to the controls. There were no signs of maternal toxicity or biologically relevant adverse developmental effects when 2-methylpropane-2-thiol was administered by whole-body inhalation at or below the 195 ppm actual exposure; therefore, the maternal and developmental NOAEC was ≥ 195 ppm (495.5 mg/m³).

In a similar key read across mouse developmental toxicity / teratogenicity study (Ulrich, 1982b, OECD 414; Klimisch Score = 2), pregnant female mice (CD-1; 25/group) were exposed to analytical concentrations of 0, 11, 99, and 195 ppm (nominal concentrations of 0, 10, 100 and 200 ppm) of 2-methylpropane-2-thiol via whole-body inhalation 6 hrs/day during gestational days 6-16. All animals survived to scheduled termination. There were no statistically significant differences between the dosed animals and controls with respect to maternal endpoints. Foetal malformations were observed in mice exposed to 99 ppm (litter incidence, 47.8 %) and 195 ppm (litter incidence, 28.6%) when compared to the control group (litter incidence, 16.7%). The particular malformation noted (i. e., vertebral anomaly), however, did not increase in a dose-related pattern and was in the range of historical control data. There were no additional statistically significant differences in treated foetuses when compared to controls. There were no signs of maternal toxicity or biologically relevant developmental effects when 2-methylpropane-2-thiol was administered by whole-body inhalation at or below the 195 ppm actual exposure; therefore, the maternal and developmental NOAEC was ≥ 195 ppm (495.5 mg/m³). 

In a key developmental toxicity study (Ulrich, 1982; Klimisch score = 2), pregnant female rats (COBS CD; 25/group) were exposed (inhalation, whole body) to butane-1-thiol at 0, 9, 70, and 150 ppm (0, 0.033, 0.26, 0.55 mg/L; nominal concentrations of 0, 11, 86 and 187 ppm) for 6 hours/day during gestation days (GD) 6-19. The study design was similar to EPA Test Guideline OPPTS 870.3700 and OECD TG 414. 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 (70 and 150 ppm; 0.26 and 0.55 mg/L), and females from the highest exposure group (150 ppm; 0.55 mg/L) 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 68 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 butane-1-thiol by whole body inhalation at or below the 150 ppm (measured exposure level); therefore, the NOAEC for both maternal and developmental toxicity was ≥150 ppm (553 mg/m³).

In a similar key developmental toxicity study (Ulrich, 1982; Klimisch score = 2), pregnant female mice (CD-1; 25/group) were exposed (inhalation, whole body) to butane-1-thiol for 6 hrs/day during GD 6-16 at measured concentrations of 0, 9, 70, and 150 ppm (0, 0.033, 0.26, 0.55 mg/L; nominal concentrations of 0, 11, 86 and 187 ppm). The study design was similar to EPA Test Guideline OPPTS 870.3700 and OECD TG No. 414. During the in-life portion of the study, 8 mice died in the 70 ppm dose group and 9 died from the 150 ppm (0.55 mg/L) dose group; one death occurred during delivery (70 ppm; 0.26 mg/L). No cause of death was determined for the remaining females. At examination, all intact fetuses from these dams were externally normal. There were no unscheduled deaths in the control or low-dose groups (9 ppm; 0.033 mg/L). The following clinical observations appeared to be dose-related: thin appearance, unkempt hair-coat, little movement, and/or red or brown matter (presumably blood) in the vaginal region. One female at 152 ppm was observed with paralyzed limbs and spasmodic breathing prior to her unscheduled death. Decreases in maternal body weight among the exposed females were not statistically significantly different from controls. No treatment-related trends in necropsy findings were observed. At 150 ppm (0.55 mg/L), there were statistically significant increases in implantation loss and statistically significant decreases in the number of viable fetuses per dam. An insufficient number of animals were available for statistical evaluation of fetal morphological observations at the high test concentration, due to the unscheduled deaths of 9 dams. There were no biologically meaningful or statistically significant differences in the total incidence of malformations in fetuses from exposed dams at the low and mid concentrations when compared to controls. The NOAEC for developmental toxicity was 70 ppm (0.26 mg/L). Based on maternal mortality, the NOAEC for maternal toxicity was 9 ppm (0.033 mg/L). Due to the presence of severe maternal toxicity it is possible that the developmental effects were a secondary effect.

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

Read-Across Justification

To reduce animal testing REACH recommends to make use of a read-across approach where appropriate based on the high accordance in properties relevant for the specific endpoint.

There are no data on the developmental toxicity for ethanethiol, therefore good quality studies on the related substances

2-methylpropane-2-thiol and butane-1 -thiol have

been read-across to assess the potential for ethanethiol to cause developmental toxicity.

The low molecular weight aliphatic alkylthiols are volatile organic liquids of moderate aqueous solubility and low n-octanol-water partition coefficient. The substances all contain a single thiol (-SH) functional group. The acid dissociation constant (pKa) of the thiol group is approximately 10 therefore the substances can be considered as weak acids which will not be significantly ionised at physiologically relevant pH.There are oral and inhalation data for repeated dose toxicity available for read-across substances butane-1-thiol, butane-2-thiol and 2-methylpropane-2-thiol. In repeated dose toxicity studies there was a consistent pattern of adaptive liver hypertrophy and species-specific alpha2u-globulin nephropathy. There were also slight and inconsistent signs of respiratory irritation in the repeated dose inhalation studies. None of the findings in the repeated dose studies were considered adverse and the NOAEL/NOAECs were the highest doses tested. Based on the similar pattern of metabolism expected for these substances, once absorbed the distribution to tissues and excretion is expected to be similar. Since the structures of the read across substances and ethanethiol are very similar, it is acceptable to assume that the systemic effects of ethanethiol following repeated oral and inhalation will be the same as those for the read across substances. These similarities are expected to extend to developmental toxicity, as the substances would distribute to, and interact with, reproductive organs and the fetus in a similar manner. Therefore ethanethiol is not likely to behave differently to 2-methylpropane-2 thiol and butane-1-thiol.

Justification for selection of Effect on developmental toxicity: via oral route:
The key study was conducted to OECD test guideline 422 and in compliance with GLP.

Justification for selection of Effect on developmental toxicity: via inhalation route:
The key study was conducted using a study protocol equivalent to OECD test guideline 414 and in compliance with GLP.

Justification for classification or non-classification

One read across screening reproductive/developmental toxicity study and four read across teratogenicity studies are available for ethanethiol. These studies showed that exposure to substances related to ethanethiol had no effects on reproductive parameters or development at the highest dose tested. Ethanethiol is therefore not classified for reproductive or developmental toxicity according to Regulation (EC) No 1272/2008.