Propane-2-thiol

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

No studies were identified for the registered substance, propane-1 -thiol and propane-2-thiol. In an OECD Test Guideline 422 study with 2-methylpropane-2-thiol, a structural analogue substance, the NOAEL for reproductive performance and developmental toxicity was 200 mg/kg bw/day, and the NOAEL for parental and neonatal toxicity was 50 mg/kg bw/day.

 

In an OECD Test Guideline 422 study (MLHW, 2006), groups of male and female Sprague-Dawley rats (12-17/sex/dose) were administered 0, 10, 50 or 200 mg/kg bw/day of a structural analogue, 2-methylpropane-2-thiol, by gavage in corn oil 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 grossly and microscopically. The NOAEL for reproductive performance and developmental toxicity is 200 mg/kg bw/day, and the NOAEL for neonatal toxicity is 50 mg/kg bw/day.

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Reason / purpose for cross-reference:

reference to same study

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:

parental toxicity

Effect level:

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

Sex:

male/female

Basis for effect level:

other: decreased body weight gain at 200 mg/kg/day

Dose descriptor:

NOAEL

Remarks:

reproductive performance and developmental toxicity

Effect level:

>= 200 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: no effect

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

Remarks:

neonatal toxicity

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 parental and neonatal toxicity is considered to be 50 mg/kg/day.

Executive summary:

The OECD Test Guideline 422 study conducted for t-butyl mercaptan is described in Section 3.1.5. In this study, groups of male and female Sprague-Dawley rats (12-17/sex/dose) were administered 0, 10, 50 or 200 mg/kg bw/day of t-butyl mercaptan by gavage in corn oil 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 grossly and microscopically. The NOAEL for reproductive performance and developmental toxicity was 200 mg/kg bw/day and the NOAEL for parental and neonatal toxicity was considered to be 50 mg/kg bw/day.

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

Quality of whole database:

Read across to 2-Methylpropane-2-thiol

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Effects on developmental toxicity

Description of key information

No studies were identified for the registered substance, propane-1-thiol and propane-2-thiol. Treatment with butyl-1-thiol and 2-methylpropane-2-thiol, structural analogue substances to propane-1-thiol and propane-2-thiol, by whole body inhalation to rats did not produce teratogenic or other developmental effects at an actual exposure level of 560.7 and 719.4 mg/m3 or less.

 

Pregnant female rats (COBS CD; 25/group) were exposed (inhalation, whole body) to butyl-1-thiol (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 (Ulrich, 1982). 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 (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.

 

Pregnant female rats (COBS CD; 25/group) were repeatedly exposed (inhalation, whole body) to 2-methylpropane-2-thiol (t-butyl mercaptan) for 6 hrs/day during gestational days (GD) 6-19 (Ulrich, 1982). Exposure conditions consisted of target concentrations of 0, 10, 100 and 200 ppm (0, 40.6, 365.2 and 719.4 mg/m3 analytical). The control group was exposed to filtered air only on a comparable regimen. Cesarean 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 200 ppm; therefore, the maternal and fetal NOAEC was equal or higher than 200 ppm (719.4 mg/m3 analytical).

Link to relevant study records

Reference

Reference 1

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1982

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: This study was classified as reliable without restriction because it follow sound scientific guidelines.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

concentrations were administered by inhalation instead of orally; limited information on animal husbandry and methods

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

- 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

Type of inhalation exposure (if applicable):

whole body

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 humidities 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 liquïd.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%) 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:

6 hrs/day

Frequency of treatment:

Gestation days 6 through 19

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)

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.

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.

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 materna! 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 materna! body weight gain from gestation days 0-20 was slightly reduced in this group when compared to the control group.

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 groupa 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.

Description (incidence and severity):

In female #76548 in group 4, moderate focal capsular fibrosis was noted in spleen at histopathological examination.

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 number of pregnant:

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:

>= 560.7 mg/m³ air (analytical)

Remarks on result:

not determinable due to absence of adverse toxic effects

Abnormalities:

effects observed, non-treatment-related

Fetal body weight changes:

no effects observed

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

External malformations:

no effects observed

Skeletal malformations:

no effects observed

Visceral malformations:

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:

>= 560.7 mg/m³ air (analytical)

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Abnormalities:

no effects observed

Developmental effects observed:

no

Conclusions:

No teratogenic effects occurred in rats when n-butyl Mercaptan was administered by whole body inhalation at the 560 mg/m3 actual exposure level.

Executive summary:

Pregnant female rats (COBS CD; 25/group) were exposed (inhalation, whole body) to 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. 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 (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).

Reference 2

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

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

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

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

Animal Exposure Methods:
Exposures were conducted in one cubic meter glass and stainless steel exposure chambers. Air for the chamber ventilation was supplied from a HVAC system separate from the general laboratory systems. This air was particulate filtered (99.9% + 0.3 µ) and controlled for temperature and humidity. Chamber airflow rate varied between 200 and 260 L/min depending on desired exposure concentrations.
Exposure chamber temperatures and relative humidities 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 liquïd. 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:

40.6 mg/m³ air (analytical) (group 5)

Dose / conc.:

100 ppm

Remarks:

365.2 mg/m³ air (analytical) (group 6)

Dose / conc.:

200 ppm

Remarks:

719.4 mg/m³ air (analytical) (group 5)

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:

See the attached file

Clinical signs:

effects observed, non-treatment-related

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Details on results:

During the study no rats died. 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.
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. In addition, the adjusted (dam weight on gestation day 20 minus the gravid uterus weight) mean maternal body weight change from gestation days 0-20 in the treated groups in this study segment was comparable to the control group (Table 4).
There was no treatment-related differences in necropsy observations and organs weight (Table 6) between the treated and control group.

Number of abortions:

no effects observed

Pre- and post-implantation loss:

effects observed, non-treatment-related

Total litter losses by resorption:

effects observed, non-treatment-related

Early or late resorptions:

effects observed, non-treatment-related

Dead fetuses:

no effects observed

Changes in number of pregnant:

no effects observed

Details on maternal toxic effects:

An increased post-implantation loss occurred in rats in the 200 ppm exposure group (Table 5) 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. There was no biologically meaningful or statistically significant difference in the mean number of viable fetuses, total implantation, corpora lutea, or the fetal sex distribution in the TBM treated group rats when compared to the control group (Table 5).

Dose descriptor:

NOAEC

Effect level:

>= 719.4 mg/m³ air (analytical)

Remarks on result:

not determinable due to absence of adverse toxic effects

Abnormalities:

effects observed, non-treatment-related

Fetal body weight changes:

effects observed, non-treatment-related

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

no effects observed

External malformations:

effects observed, non-treatment-related

Skeletal malformations:

no effects observed

Visceral malformations:

no effects observed

Details on embryotoxic / teratogenic effects:

A statistically significant increase in mean fetal body weight was noted in the group exposed to 10 ppm when compared to the control group (Table 5); however, the value was within the range of the historical control data and was considered due to random occurrence. Mean fetal body weights at the two highest dose groups exceeded the control value.
Five fetuses in one litter in the 200 ppm dose group exhibited the external malformation of dwarfism (Table 7). As dwarfism has been observed in several fetuses in a single litter in the historical control data (attached file) this effect is believed to be of genetic origin in the testing laboratory and not considered treatment-related (Table 7). There was no biologically meaningful trend in the incidence of fetuses with genetic or developmental variations in litters in the treated groups when compared to the control group (Table 7).

Dose descriptor:

NOAEC

Effect level:

>= 719.4 mg/m³ air (analytical)

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Abnormalities:

no effects observed

Developmental effects observed:

no

TABLE 4: Summary of Group Mean Maternal Body Weights

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

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

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

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

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

Total No. Corpora Lutea

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

                                                                Total No. Implantations

^cValue does not include dams with regressing corpora lutea

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

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

- Not applicable

S.D.- Standard deviation

 

Table 6: Individual Maternal Organ Weight

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

 

Conclusions:

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

Executive summary:

Pregnant female rats (COBS CD; 25/group) were repeatedly exposed (inhalation, whole body) to 2 -methylpropane-2-thiol for 6 hrs/day during gestational days (GD) 6-19. Exposure conditions consisted of target concentrations of 0, 10, 100 and 200 ppm (0, 40.6, 365.2 and 719.4 mg/m3 analytical). The control group was exposed to filtered air only on a comparable regimen. Cesarean 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 200 ppm; therefore, the maternal and fetal NOAEC was equal or higher than 200 ppm (719.4 mg/m3 analytical).

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

560.7 mg/m³

Study duration:

subacute

Species:

rat

Quality of whole database:

Read across to butyl-1-thiol and 2-Methylpropane-2-thiol.

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Justification for classification or non-classification

No classification is warranted according to CLP criteria.