1,1-dimethylheptanethiol

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, well documented and acceptable for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1983

Report date:

1983

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

yes

Remarks:

only two concentration tested

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Tert-Dodecanethiol (CAS # 25103-58-6)

IUPAC Name:

Tert-Dodecanethiol (CAS # 25103-58-6)

Details on test material:

- Supplier: Phillips Petroleum Company
- Name of test material (as cited in study report): t-dodecyl mercaptan
- Physical state: pale yellow liquid
- Analytical purity: 96.8%
- Lot/batch No.: 444

Test animals

Species:

rat

Strain:

other: Charles River COBS CD strain

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Portage, Michigan
- Age at study initiation: 12 weeks old
- Weight at study initiation: 205 and 264 grams on gestation day 0
- Fasting period before study: no
- Housing: individually in hanging wire-mesh cages, nn gestation day 6 animals were transferred to stainless steel and glass exposure chambers
- Diet (ad libitum, except during the exposure period ): Purina® Certified Rodent Chow® #5002
- Water (ad libitum, except during the exposure period): tap water
- Acclimation period: 14 day

ENVIRONMENTAL CONDITIONS
- Temperature (°F): 76-85 (exposure chambers)
- Humidity (%): 35-41 (exposure chambers)
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel and glass exposure chambers with a volume of one cubic meter
- Method of holding animals in test chamber: individually in hanging wire-mesh cages
- System of generating vapor: Vapor atmospheres of t-dodecyl mercaptan (TDM) were generated by one of two methods. The first method was used to generate the 25 ppm group atmosphere. With this system a syringe-drive pump (Sage model 355) delivered the test materiai at a known, constant rate to the top of a 19.6 cm high column filled with 5 mm diameter glass beads. Air heated by a 400 watt cartridge heater passed up the bead column counter-current to the liquid flow. Vaporization occurred within the bead column. The vapors were then piped to the air inlet of the exposure chamber where dilution with chamber ventilation air (approximately 250 L/min) reduced the concentration to the desired level. Heat tape was wrapped around the trap to prevent condensation. The current supplied to both the cartridge heater and the heat tape was controlled individually by variable autotransformers.
The TDM concentration for the 100 ppm group was generated with a second method of vapor generation. With this system all of the chamber ventilation air was passed through an atomization chamber which had been charged with a known amount of test material. An FMI laboratory pump was then used to deliver the test material to an atomizer (Spraying Systems, No. 1650 liquid nozzle, No. 64 air nozzle). The atomization step served to greatly increase the surface area of the test material which increased, in turn, the vaporization rate to obtain a relatively high vapor concentration of test material. Glass wool was placed in the exit pipe of the atomization chamber to prevent aerosol from passing into the exposure chamber. To overcome the resistance of the glass wool filter, the exposure chamber was operated at a negative pressure of approximately 0.2 - 0.4 inches of vater.
- Temperature, humidity, pressure in air chamber: 76-85 °F, 35-41%
- Air flow rate: no data
- Air change rate: no data
- Method of particle size determination: Since the generation method for the 100 ppm group vapor level involved an atomization step, samples were collected to determine the amount of aerosol in the chamber atmosphere. Samples were collected on 25 mm glass fiber filters at a rate of 1 L/min for 30 minutes. The filters were placed in 2 ml of n-hexane to extract the collected TDM and 2 pl of the resultant solution were injected into the GC. Two injections were made of each of 4 filter samples. Three concurrent vapor samples were collected for each filter sample. During the experiment the vapor phase concentration averaged 53 ppm while the samples of recovered aerosol averaged 0.18 ppm. From these data we concluded that aerosol would not constitute an appreciable fraction of the total TDM concentration in the vapor exposure atmosphere.
- Treatment of exhaust air: no data

TEST ATMOSPHERE
- Brief description of analytical method used: The actual vapor concentration of TDM in the chamber atmosphere was determined by a gas chromatograph fitted with a gas sampling valve and sample loop. The GC was connected to a Hewlett-Packard Model 3388A integrator for data collection and reduction and was calibrated with liquid-phase standards of TDM in n-hexane.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

see above

Details on mating procedure:

At the end of the acclimation period, all animals were weighed and subjected to a detailed physical examination. At this time, animals considered suitable for study were cohabitated with stock males utilized exclusively for this purpose.
One female and one male animal of the same species, strain and source were placed together for mating. The occurrence of copulation was determined by daily inspection for a copulatory plug or vaginal smear for sperm. The day evidence of mating was detected was
designated day 0 of gestation and the female was returned to an individual cage, assigned a permanent animal number and properly identified by ear-tag.

Duration of treatment / exposure:

G6 to G19

Frequency of treatment:

6 hours/day

Duration of test:

up to gestation day 20

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
25 and 100 ppm
Basis:
other: Desired conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
22.7 ppm and 88.6 ppm
Basis:
analytical conc.

Doses / concentrations 3

Remarks:

Doses / Concentrations:
34 and 109 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

25

Control animals:

yes, sham-exposed

Details on study design:

- Dose selection rationale:
- Rationale for animal assignment (if not random): Mated females were consecutively assigned in a block design to one control group and two t-dodecyl mercaptan treated groups of 25 rats. The order in which the mated females were assigned corresponded to the day the copulatory plug was observed and the order in which the animal appeared on the breeding record. The first mated female on the breeding record was assigned to the first group. The second mated female was assigned to the next group. Animals were assigned in this manner until the required number of mated females had been placed into each group.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Prior to treatment, the females were observed twice daily for mortality and overt changes in appearance and behavior. They were observed twice daily for mortality and once daily for clinical signs of toxicity from gestation day 6 through sacrifice. Females not surviving to the scheduled sacrifice were necropsied in an attempt to determine the cause of death.

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
- Time schedule for examinations: gestation days 0, 6, 9, 12, 16 and 20

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): No

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: On gestation day 20 all surviving dams were sacrificed by carbon dioxine inhalation. The abdominal and thoracic cavities and organs of the dams were examined for grossly evident morphological changes and the carcasses discarded.

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
- Other: number and location of viable and nonviable fetuses

Fetal examinations:

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. Approximately one-third of the fetuses were placed in Bouin's fixative for subsequent visceral examination by razor-blade sectioning as described by Wilson. The remaining two-thirds 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 Dawson for subsequent skeletal examination.

Statistics:

The male to female fetal sex distribution and the number of litters with malformations were compared using the Chi-square test criterion with Yates' correction for 2 x 2 contingency tables and/or Fisher's exact probability test as described by Siegel to judge significance of differences.
The number of early and late resorptions, nonviable fetuses and postimplantation loss were compared by the Mann-Whitney U-test as described by Siegel and Weil to judge significance of differences.
The mean number of viable fetuses, total implantations, corpora lutes 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 (for equai or unequal variances) as described by Steel and Torrie using Dunnett's multiple comparison tables to judge significance ot differences.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
One rat in the 100 ppm group died on gestation day 14. Antemortem observations included thinness, an unkempt haircoat and reddened conjunctiva. Mottled kidneys were noted at necropsy; the cause of death could not be determined. The normally developing implants in this female were inadvertently not examined further. Survival was 100% in the control group and the 25 ppm group.
There were no biologically meaningful differences in the appearance and behavior of rats in the t-dodecyl mercaptan treated groups when compared to those of the rats in the control group. Incidental observations occurring in a few control and/or treated rats included hair loss, soft stool, reddened conjunctiva, wet red matter or red liquid in the vagins or toes red, swollen and/or scabbed. A circumscribed areas in the inguinal area was noted in a female in the 100 ppm group.
The occurrence of necropsy findings in the 25 ppm and 100 ppm groups was similar to that of the control group. Incidental observations included hydronephrosis, pitted kidneys, calculi in the kidneys, ureters and urinary bladder and distended ureters.

There was a dose-related decrease in mean maternal body weight gain of the rats in the treated groups when compared to the control value over the entire exposure period (gestation days 6-20) and the entire gestation period (gestation days 0-20).

There were no biologically meaningful or statistically significant differences in the mean number of postimplantation loss, total implantations and corpora lutea in the treated groups.

Effect levels (maternal animals)

1

Dose descriptor:

LOAEC

Effect level:

22.7 ppm (analytical)

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEC

Effect level:

>= 88.6 ppm (analytical)

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
A slight (less than 10%) but statistically significant increase in mean fetal body weight in comparison to the control value occurred in the 100 ppm group. The 100 ppm group mean fetal body weight was comparable to the mean value in the historical control data. The mean fetal body weight in the 25 ppm group was similar to that of the control group and the historical control data; no statistically significant differences from the control group were observed.
There were no biologically meaningful or statistically significant differences in the mean number of viable fetuses or the fetal sex distribution in the treated groups.

The incidence of fetal malformations in litters of the rats in the t-dodecyl mercaptan treated groups was comparable to that of the control group; no statistically significant differences were observed.
There were no biologically meaningful differences in the occurrence of genetic and developmental variations between the control and treated groups.

Effect levels (fetuses)

Dose descriptor:

NOAEC

Effect level:

>= 88.6 ppm (analytical)

Based on:

test mat.

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Treatment with tert-dodecanethiol by whole body inhalation at an actual exposure level of 88.6 ppm or less did not produce a teratogenic effect in rats.

Executive summary:

In a study comparable to OECD 414 guideline, pregnant Charles River COBS^®CD^®rats, randomly assigned to one control group and two tert-dodecanethiol treated groups of 25 animals, were used to determine the teratogenic potential of tert-dodecanethiol. Mean actual exposure levels of 22.7 and 88.6 ppm, which corresponded to desiredexposure levels of 25 and 100 ppm,were administered by whole body inhalation exposure on gestation days 6 through 19 on a 6-hour dailyexposure schedule. 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 and fetuses removed for teratologic evaluation.

 

One rat died at 100 ppm. The cause of death could not be determined. Survival was 100% in the control rats and the 25 ppm group. There were no biologically meaningful or relevant statistically significant differences in the mean number of total implantations, corpora lutes and fetal body weight or in the fetal sex distribution inall Cesarean section observationswhen compared to the control values. No adverse treatment-related or statistically significant differences in the incidence of fetal malformations when compared to those of the control group. Dose-related decreases in mean maternal body weight gain occurred in the tert-dodecanethiol treated rats. There were no meaningful differences in the appearance, behavior and necropsywhen compared to those of thecontrol group. Treatment with tert-dodecanethiol by whole body inhalation at anactual exposure level of 88.6 ppm or less did not produce a teratogeniceffect in rats. This study received a Klimisch score of 2 and is classified as reliable with restriction because it meets generally accepted scientific standards, is well documented, and acceptable for assessment.