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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 from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant, guideline study, published in peer reviewed literature, fully adequate for assessment
Cross-referenceopen allclose all
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1987
Report Date:
1987

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
EU Method B.31 (Prenatal Developmental Toxicity Study)
Deviations:
not specified
Principles of method if other than guideline:
not applicable
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): 1,3-butadiene
- Physical state: gas
- Analytical purity: 99.88% (by gas chromatography)
- Lot/batch No.: F-909
- Storage condition of test material: Constant temperature of 72°F
- Other: To prevent the appearance of high concentrations of dimer in the 1,3-butadiene atmospheres used for the exposures, cylinder usage was limited to 80% of the net contents, and the acceptable dimer concentration in material sampled from the headspace was specified to be <500 ppm .

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River laboratory, Portage, MI, USA
- Age at delivery: 7-8 weeks
- Weight at delivery: 200-225 g (males), 170-175 g (females)
- Housing: 5/sex/cage during the acclimatisation period; 2 females:1 male during pairing; females housed individually during gestation and lactation.
- Diet: NIH-07 open formula diet ad libitum except during exposure
- Water: ad libitum
- Acclimation period: 19 days

ENVIRONMENTAL CONDITIONS
- Temperature: 72±3°F
- Humidity: 50±15%
- Air changes (per hr): no data
- Photoperiod: no data

IN-LIFE DATES: From: 18 November 1985 To: 13 December 1985

Administration / exposure

Route of administration:
inhalation: gas
Type of inhalation exposure (if applicable):
whole body
Vehicle:
other: air
Details on exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Stainless-steel chambers. The total volume of the chamber was 2 .3 M3, and the active mixing volume was 1 .7 M3.
- Method of holding animals in test chamber: There were three levels of caging in each chamber; each level was split into two tiers, which were offset from each other and from the chamber walls. Drawer-like stainless steel cage units, consisting of individual animal cages, were suspended in the space above each tier.
- System of generating particulates/aerosols: For generation of chamber atmospheres, 1,3-butadiene was withdrawn directly from the gas cylinder through a solenoid valve and, subsequently, through a check-valve filter-flow-limit switch and a flow meter, which accurately metered gas to a distribution manifold, where it was initially diluted with filtered air. An air-driven vacuum pump delivered the butadiene-air mixture to the exposure chamber inlet for final dilution to the desired concentration .
- Temperature and humidity, in air chamber: Temperature range 70-75°F; Humidity range 43-68%

TEST ATMOSPHERE
- Brief description of analytical method used: Chamber monitoring of 1,3-butadiene concentrations was performed using an HIP 5840 gas chromatograph equipped with an FID, a Valco (1-ml loop) sampling valve and a Valco stream-select valve capable of sampling eight different sites.
- Samples taken from breathing zone: yes
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Eight sites were sampled every 16 minutes: four exposure chambers, two "holding" chambers, the exposure room and the GC standard . Data from the monitor were accumulated by the HIP 85B computer and compared with limit values for the specific sampling location. When the value exceeded the control limits, the HP 85B computer transmitted the information to the executive computer, which initiated an appropriate action to correct the concentration .
Details on mating procedure:
- Impregnation procedure: cohoused
- M/F ratio per cage: 1:2
- Length of cohabitation: 5 successive nights
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: sperm in vaginal smear, referred to as day 0 of pregnancy
Duration of treatment / exposure:
Daily, for 6 hours/day
Frequency of treatment:
From 6 through 15 day.
Duration of test:
Until gestation day 20
Doses / concentrations
Remarks:
Doses / Concentrations:
40, 200 and 1000 ppm
Basis:
nominal conc.
No. of animals per sex per dose:
30 sperm-positive females per group
Control animals:
yes, concurrent no treatment
Details on study design:
Females were mated with unexposed males.
Three days prior to the initiation of exposure, the animals were housed in the exposure chambers in the exposure room.
From 16 day until sacrifice at 20 day, all animals were housed in exposure chambers with filtered-air atmospheres. The 5 days of mating resulted in staged starts and cessations of exposures. Accordingly, "filler" animals (excess males and females) were used to maintain a constant animal load in the exposure chambers.

Examinations

Maternal examinations:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily

BODY WEIGHT: Yes
- Time schedule for examinations: During the week prior to mating, and on days 0, 6, 11, 16 and 20 of gestation

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

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20 (following euthanasia with CO2)
- Examined for gross abnormalities: yes
Ovaries and uterine content:
The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: No data
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other: Placentas were examined and weighed
Fetal examinations:
- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: all per litter
- Skeletal examinations: Yes: all per litter
- Head examinations: Yes: approximately half per litter
- Other: Examinations for foetal lens opacities were conducted by removing the eyelid and examining the eye in situ. In addition, the eyeballs were removed for observation under the dissecting microscope.
Statistics:
Analysis of variance (ANOVA; Steel and Torrie, 1980) was used to analyze weight data and, if the result of the analysis was significant, Duncan's multiple range test (Duncan, 1955 ; Kramer, 1956) was used for further statistical analyses. Response proportions, such as the number of resorptions, implants, live, dead, or affected foetuses/litter, were also analyzed by ANOVA following arcsin transformation of the response proportion. An orthogonal contrast (Winer, 1971) was used to test trends for dose dependency. In the case of maternal weights, which were repeated over time, analyses for differences among growth curves employed a randomization test (Zerbe, 1979). Binary-response variables between groups were compared, using chi-square or Fischer's exact test (Siegel, 1956). These variables included numbers of pregnant females/number inseminated.
Indices:
Not given
Historical control data:
Not given

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
No deaths occurred in any of the four exposure groups during the study interval. No significant effects of treatment were observed for maternal body weight gains of rats exposed to 1,3-butadiene levels of 40 or 200 ppm, but weight gains of animals of the 1000 ppm group were significantly decreased for the first 5 days of exposure. Extragestational weight gains in the rats exposed to this highest concentration tended to be lower than values for control and 40 ppm groups and were significantly less than gains of animals exposed to 200 ppm. Weights of gravid uteri and values for extragestational body weights for exposed animals were not significantly different from control values.

Effect levels (maternal animals)

open allclose all
Dose descriptor:
NOEC
Effect level:
1 000 other: ppm (2212 mg/m3)
Basis for effect level:
other: developmental toxicity
Dose descriptor:
NOAEC
Effect level:
200 other: ppm (442 mg/m3)
Basis for effect level:
other: maternal toxicity

Results (fetuses)

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

Details on embryotoxic / teratogenic effects:
One foetus in each of three litters in the 40 ppm exposure group was hydrocephalic. Two foetuses from one litter in the 1000 ppm group each had a meningoencephalocele; in addition, one of these foetuses also had microphthalmia accompanied by aphakia and retinal dysgenesis. Another litter in the 1000 ppm group had one foetus with a dilation between the meninges and the skull. No major malformations of the head were found in foetuses from the control or the 200 ppm exposure groups. No significant treatment-related differences or trends were noted in the incidence of malformations.
The incidence of reduced ossification of sternebrae numbers 1 through 4 was higher in foetuses of the 200 ppm treatment group than in control foetuses, but values for foetuses from the 40 and 1000 ppm groups were not different from control values. In contrast, the number of foetuses with reduced ossification of thoracic vertebrae in the 200 and in the 1000 ppm groups was significantly lower than the number with this variation in the control group.
When reduced ossifications at all anatomical sites were combined and the incidences compared on a litter basis, there were no effect of treatment on the mean percent of Iitters affected.

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Any other information on results incl. tables

Summary of exposure chamber concentrations

Observation

Chamber concentrations (ppm)

 

40

200

1000

Mean chamber concentration ± SD

40.1 ± 0.62

199.8 ± 2.61

1005 ± 11.9

Mean of target concentration (%)

100

100

101

 

Summary of changes in maternal bodyweight (g)

Gestation day

Chamber concentrations (ppm)

 

0 (number=28)

40 (number=24)

200 (number=26)

1000 (number=28)

0 – 6

21.4

21.1

22.9

20.1

6 - 11

25.5

23.6

26.6

17.5 *

11 – 16

29.2

30.9

31.7

31.2

16 - 20

44.5

36.7

43.6

43.2

E.wt gain

47.6

42.7

50.9

39.9*

*statistically significant from control (p≤0.05)

E.wt gain: extragestational weight minus bodyweight on day 0 of gestation

 

Summary of numbers of foetal examinations

Numbers

Chamber concentrations (ppm)

examined

0

40

200

1000

Litters

28

24

26

27

Foetuses

389

321

372

382

Foetal heads

196

161

185

191

#

2/2

6/4

3/3

4/2

Total incidence of foetuses with malformations (foetuses/litters)

Applicant's summary and conclusion

Conclusions:
There was no evidence for a teratogenic response in rats exposure to 1,3-butadiene exposure at concentrations up to 1000 ppm (2212 mg/m3).
Executive summary:

Pregnant rats were exposed to 1,3-butadiene 6h/day, from days 6-15 of gestation at concentrations of 40, 200 or 1000 ppm (88, 442, 2212 mg/m3) in a pre-natal developmental toxicity study. Exposure to 1,3-butadiene had no effects on developmental parameters at any dose and the NOAEL for developmental toxicity was 1000 ppm (2,212 mg/m3). The NOAEC for maternal toxicity was 200 ppm (422 mg/m3) based on reduced body weights.