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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
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 the results are obtained by valid read-across. The read-across study was conducted according to similar or equvalent to OECD TG 414 guideline.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1982
Report Date:
1982

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
TS: t-butyl mercaptan product TBM (2-methylpropane-2-thiol)
Source: NGO Chemical, Baytown, Texas
Batch: ODB
Purity: > 99.0%

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals 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

Administration / exposure

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
No. of animals per sex per dose:
25
Control animals:
yes, sham-exposed

Examinations

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.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:no effects

Details on maternal toxic effects:
Maternal Observations:
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 change 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.
There was no treatment-related differences in necropsy observations between the treated and control group.

Cesarean Section Observations:
An increased post-implantation loss occurred in rats in the 195 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. 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. Mean fetal body weights at the two highest dose groups exceeded the control value. 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.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOAEC
Effect level:
>= 195 ppm (analytical)
Based on:
test mat.
Basis for effect level:
other: maternal toxicity
Dose descriptor:
NOAEC
Effect level:
>= 195 ppm (analytical)
Based on:
test mat.
Basis for effect level:
other: developmental toxicity

Maternal abnormalities

Abnormalities:
no effects observed

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
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. 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.

Effect levels (fetuses)

Dose descriptor:
NOAEC
Effect level:
>= 195 ppm
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No adverse effects observed

Fetal abnormalities

Abnormalities:
no effects observed

Overall developmental toxicity

Developmental effects observed:
no

Any other information on results incl. tables

Measured Concentration of t-Butyl Mercaptan

Group Number
Desired
Conc. (ppm)
Nominal Conc (ppm)
Actual Conc (ppm)
Mean
S.D.
Mean
S.D.
5
10
10
0.7
11
0.9
6
100
104
4.9
99
5.9
7
200
226
15.0
195
8.3

Conc = Concentration
S.D. = Standard Deviation

Applicant's summary and conclusion

Conclusions:
No adverse effects on development occurred in rats when administered 2-methylpropane-2-thiol by whole body inhalation at or below the 195 ppm (495.5 mg/m3) actual exposure level (Ulrich, 1982).
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 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 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 equal or higher than 195 ppm (495.5 mg/m3) (Ulrich, 1982). 

This study was classified as reliable with restriction because the results are obtained by valid read-across. The read-across study was conducted according to similar or equvalent to OECD TG 414 guideline.