Tetrahydrothiophene

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

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

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1988

Report date:

1988

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Tetrahydrothiophene

EC Number:

203-728-9

EC Name:

Tetrahydrothiophene

Cas Number:

110-01-0

Molecular formula:

C4H8S

IUPAC Name:

tetrahydrothiophene

Details on test material:

Source: Pennwalt Corporation
Batch No.: Lot 271.
Purity: 99.0% minimum.

Test animals

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River UK Limited
- Age at study initiation: 8-10 weeks old
- Weight at study initiation: 200-220 g
- Housing: five to a cage in suspended polypropylene cages
- Diet (e.g. ad libitum): Labsure Laboratory Animal Diey no. 1
- Water (e.g. ad libitum): tap water
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 16.5-22
- Humidity (%): 40-74
- 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:

Vapour generation:
The vapour generation system, contained in a separate, sealed exposure chamber metered the liquid from a pressurised reservoir to a glass sinter, contained in a glass vessel through which air was passed. The vapour produced passed out of this vessel and into each chamber via an inlet duct. By varying the feed rate to each vapour generator it was possible to obtain the desired chamber concentrations.

Exposure chambers:
The exposure chambers were constructed of stainless steel and glass and were approximately 0.675 m3 in volume. The vapour from each generator entered the top of the chamber and was exhausted via a perforated plenum located in the base of each chamber. The exhaust from all chamber was drawn through an activated charcoal scrubbing system (Ventsorb R, Chemviron Ltd., Uppermill, Lancs.) by an extractor fan, before being vented to atmosphere. Extract flow was adjusted using gate valves downstream of the chamber to maintain a chamber internal pressure of 10 mm H20) below ambient, as indicated by magnehelic gauges connected to each chamber.
The rats were held during exposure in compartmented stainless steel mesh cages. A wet and dry bulb hygrometer was positioned in the chamber to monitor chamber temperature and relative humidity during exposure. Ports, fitted with removeable bungs, were present in the walls of each chamber to permit removal of chamber air samples for analysis. Routinely a port mid-centre of the chamber side wall was used.

Exposure chamber conditions:
- Measurement of chamber concentration of THT
The concentration of THT present at each level of exposure was determined at least 4 times during each exposure, typically at 1, 2, 4 and 5 hours into exposure.
- Air flow
The air flow into each chamber was monitored continuously using tapered-tube rotameters and recorded at 30-minute intervals throughout each exposure.
- Temperature
The air temperature in each chamber was monitored continuously with a mercury bulb thermometer and recorded at approximately hourly intervals throughout each exposure.
- Pressure
The air pressure in each exposure chamber, relative to that in the exposure room, was monitored using a magnehelic gauge and recorded at 30-minute intervals throughout exposure.
- Relative humidity
The humidity in each exposure chamber was monitored continuously with a wet and dry bulb hygrometer and recorded at hourly intervals throughout each exposure.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples of chamber air were withdrawn through glass tubes 10 cm in length, nominal bore 2 mm, packed for 2 - 3 cm of their length at one end only with chromosorb 102, 60 - 80 mesh. The vapour was adsorbed on this medium. The samples were thermally desorbed into a gas chromatograph and the amounts of THT collected determined by using external standards.

Details on mating procedure:

Sexually mature female brats time-mated to identified males of the same strain, were ordered from Charles River UK Limited. The day of mating, as judged by the appearance of sperm in the vaginal smear or by the presence of a vaginal plug was considered as Day 0 of pregnancy.

Duration of treatment / exposure:

Day 6 to day 15 of the gestation

Frequency of treatment:

6 h/day

Duration of test:

Sacrifice on GD 20

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

234 ppm (analytical)

Remarks:

844 mg/m3

Doses / concentrations 2

Dose / conc.:

782 ppm (analytical)

Remarks:

2822 mg/m3

Doses / concentrations 3

Dose / conc.:

1 910 ppm (analytical)

Remarks:

6888 mg/m3

No. of animals per sex per dose:

25

Control animals:

yes, concurrent vehicle

Details on study design:

Sex: female
Duration of test: Sacrifice on day 20 of gestation

Examinations

Maternal examinations:

The following observations were made during the study:
(a) Signs
All animals were regularly handled and observed daily for obvious changes or signs of reaction to treatment.
(b) Food and water consumption
Food consumption was measured from weighday to weighday. Water consumption was measured daily throughout the study.
(c) Bodyweights
All animals were weighed initially (=Day 1 of pregnancy) and on Days 3, 6, 8, 10, 14, 18 and 20.

Ovaries and uterine content:

On Day 20 of pregnancy the animals were killed by CO2 asphyxiation, dissected and examined for congenital abnormalities and macroscopic pathological changes in maternal organs; the ovaries and uteri were examined immediately to determine:
(a) number of corpora lutea
(b) number and distribution of live young
(c) number and distribution of embryofoetal deaths
(d) individual foetal weight from which the litter weight is calculated
(e) foetal abnormalities.
Embryofoetal deaths were classified as:
Early: only placenta visible at termination.
Late: both placental and embryonic remnants visible at termination.

Uteri or individual uterine horns without visible implantations were immersed in a 10% solution of ammonium sulphide to reveal evidence of embryonic death at very early stages of implantation.

Fetal examinations:

Live young were examined externally and weighed. Half the foetuses in each litter were preserved in Bouin's solution for subsequent free-hand sectioning to discover visceral abnormalities (Wilson technique); the remainder were fixed in 74 OP industrial methylated spirit for subsequent macroscopic examination, evisceration, clearing and alizarin staining (modified Dawson technique) for skeletal examination. Young showing suspected abnormalities were processed by the more appropriate technique for clarification of initial observations.

All foetuses were sexed by gonadal inspection following preservation.

Structural changes are presented as:
Malformations: rare and/or probably lethal, e.g. exencephaly, anury.
Anomalies: minor differences from 'normal' that are detected relatively frequently either by free-hand sectioning, e.g. increased renal pelvic dilatation, or at skeletal examination, e.g. bipartite centrum.
Variants: alternative structures occurring regularly in the control population are classified as variants. These may be permanent structures, e.g. an extra pair of ribs, or they may be transient stages of development, e.g. unossified sternebra(e).

Statistics:

Statistical analyses were performed on the litter data. The basic sample unit was the litter and due to the preponderance of non-normal distributions, non-parametric analyses have generally proved more consistent. Significance tests were generally two-tailed.

Mean values of litter size, pre- and post implantation loss, litter weights, mean foetal weight and the incidence of skeletal anomalies and variants were analysed by the Kruskal-Wallis and Jonckheere tests. Intergroup comparisons were made using the non-parametric equivalent of the 't' test and were only reported if supported by the Kruskal-Wallis or Jonckheere tests.
Where 75% of the values for a given parameter consisted of one value a Fisher's exact testz was used.

Indices:

Assessment of results:
Individual litter values
In assessing litter parameters, pre-implantation loss was calculated as a percentage from the formula:

(No. of corpora lutea-no. of implantations) x 100/No. of corpora lutea

Post implantation loss was similarly calculated from the formula:
(No. of implantations-no. of live young) x 100/No. of implantations

Litter weight and mean foetal weight were calculated from individual foetal weight.
In the absence of any litter losses, group mean values were calculated to include all animals with live young at termination.

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Signs associated with treatment were only observed during actual exposure to tetrahydrothiophene. There was a clear association of exposure level and the type of signs observed. At 250 ppm, lachrymation and licking of inside of mouth were observed; at 750 ppm the same signs were observed as well as rubbing of chin and paws on the cage floor and partial/total closure of eyes. All the signs observed at the lower dosages were observed at 2000 ppm with the addition of salivation. In addition, during the last two days of exposure, extreme agitation was also observed at this dosage.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Following initial exposure, there was a dosage-related retardation in bodyweight gain with no weight gain apparent at 2000 ppm. From Day 8, weight gain at 250 ppm was comparable to control values; at higher exposures, weight gain although showing a slight recovery, was still retarded relative to controls. Weight gain at 750 and 2000 ppm attained parity with controls from Day 10 and remained comparable with controls thereafter.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

At 2000 ppm, there was an initial reduction in food intake from the initiation of treatment with a gradual recovery to control levels as the treatment period progressed. At lower dosages, intake was generally comparable with controls throughout.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

There was a dosage-related increase in water consumption from the initiation of treatment at 750 and 2000 ppm. At both dosages, intake tended to increase as treatment progressed with the effect being particularly marked at 2000 ppm. After treatment had ceased, mean water intake in these two groups, although still high when compared with controls, showed evidence of returning to pre-exposure levels.

Gross pathological findings:

no effects observed

Description (incidence and severity):

Findings at autopsy were occasional and not obviously related to treatment.

Maternal developmental toxicity

Number of abortions:

no effects observed

Pre- and post-implantation loss:

no effects observed

Description (incidence and severity):

Post implantation losses were generally comparable amongst the groups.

Total litter losses by resorption:

no effects observed

Early or late resorptions:

no effects observed

Dead fetuses:

no effects observed

Changes in pregnancy duration:

not examined

Description (incidence and severity):

Migrated Data from removed field(s)
Field "Effects on pregnancy duration" (Path: ENDPOINT_STUDY_RECORD.DevelopmentalToxicityTeratogenicity.ResultsAndDiscussion.ResultsMaternalAnimals.MaternalDevelopmentalToxicity.EffectsOnPregnancyDuration): not examined

Changes in number of pregnant:

no effects observed

Effect levels (maternal animals)

Dose descriptor:

NOAEC

Effect level:

782 ppm (analytical)

Based on:

test mat.

Basis for effect level:

body weight and weight gain

clinical signs

other: 2822 mg/m3

Maternal abnormalities

Abnormalities:

no effects observed

Results (fetuses)

Fetal body weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

Although slight variations in litter and mean foetal weights were observed, they were associated with differences in litter size. There was no indication of an effect of treatment.

Reduction in number of live offspring:

effects observed, non-treatment-related

Description (incidence and severity):

Although litter size at 250 ppm was significantly lower relative to controls, this was attributed to differences in ovulation rate which would have been established prior to the initiation of treatment. Litter sizes at higher concentrations were comparable with controls.

Changes in sex ratio:

no effects observed

Description (incidence and severity):

Sex ratios were generally comparable amongst the groups.

Changes in litter size and weights:

effects observed, non-treatment-related

External malformations:

no effects observed

Skeletal malformations:

no effects observed

Visceral malformations:

no effects observed

Effect levels (fetuses)

Dose descriptor:

NOAEC

Effect level:

> 1 910 ppm (analytical)

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Fetal abnormalities

Abnormalities:

no effects observed

Overall developmental toxicity

Developmental effects observed:

no

Applicant's summary and conclusion

Conclusions:

There was no evidence of an effect of treatment with THT on foetal development as assessed by litter parameters and visceral and skeletal examinations.

Executive summary:

In an OECD 414 study performed following GLP, pregnant SD rats were exposed by inhalation for a period of 6 hours per day from Day 6 to Day 15 of pregnancy to analytical concentrations of 0 (Control), 234, 782 and 1910 ppm (equivalent to 844, 2822 and 6888 mg/m3) THT. On Day 20, dams were sacrificed, litter values determined and foetuses subsequently examined for visceral or skeletal anomalies. Exposure to THT was characterised by signs of reaction during exposure, which included lachrymation, licking of mouth, rubbing of chin and paws on cage floor, partial/total closure of eyes, salivation and extreme agitation. The occurrence was related to the level of exposure with all the signs being observed only at 1910 ppm. 1910 ppm was also associated with reduced food consumption, increased water consumption and retarded weight gain. At 782 ppm, maternal reaction included increased water consumption and retarded weight gain. At 234 ppm, other than clinical signs during exposure and a transient retardation in weight gain during the first few days of exposure, there was no clear effect of treatment. There was no evidence of an effect of treatment on foetal development as assessed by litter parameters and visceral and skeletal examinations.