Buta-1,3-diene

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 with no restrictions, fully adequate for assessment

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1982

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Principles of method if other than guideline:

not applicable

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

1,3-Butadiene

Cas Number:

106-99-0

Molecular formula:

C4H6

IUPAC Name:

1,3-Butadiene

Details on test material:

- Name of test material (as cited in study report): 1,3-butadiene
- Supplied by: ICI Ltd., Wilton, Middlesborough, Cleveland, UK
- Physical state: colourless, flammable liquid
- Storage condition of test material: room temperature
No further details reported

Test animals

Species:

rat

Strain:

other: Sprague-Dawley CD

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Ltd., Margate, Kent, UK
- Age at study initiation: sexually mature, virgin females, sexually mature males
- Weight at study initiation: 220-266 g (females at mating)
- Housing: Stainless steel mesh cages. Prior to mating: 5 same sex/cage; during mating 1 male and 1 female/cage: following mating females housed individually
- Diet: Pelleted Rat and Mouse Expanded Breeder Diet No. 3, (BP Nutrition (UK) Ltd., Stepfield, Witham, Essex, UK) ad libitum (except during exposure)
- Water: Mains water ad libitum (except during exposure)
- Acclimation period: 14 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22±3°C (intended range)
- Humidity: 55±25% (intended range)
- Air changes (per hr): not reported
- Photoperiod: 12hrs dark / 12hrs light

IN-LIFE DATES: From: 8 January 1981 (animal arrival) To: 27 February 1981

Administration / exposure

Route of administration:

inhalation: gas

Vehicle:

other: air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Whole body stainless steel and glass exposure chambers
- Method of holding animals in test chamber: In stainless steel mesh cages
- Generation: 1000-1200L/min air drawn from room, through a filter, into chamber, passed into an expansion chamber where it was mixed with test material. The liquid 1,3-butadiene was volatilised in stainless steel coils in a heat exchanger prior to entry into the expansion chamber. The air/vapour mixture then passed into head of exposure chamber to provide an even distribution of butadiene.

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography using flame ionisation detector.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

With exception of the occasional deviation all values were within the following pre-set limits: 5, 180-220, 900-1100 and 7360-8640 ppm v/v for 0, 200, 1000 and 8000 ppm v/v exposure concentrations.

Details on mating procedure:

- M/F ratio per cage: 1:2
- Length of cohabitation: 10 days
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy. If sperm present, cytology of smear examined as only females in late pro-oestrus or oestrus phases of the cycle were used.

Duration of treatment / exposure:

Days 6-15 of gestation

Frequency of treatment:

6h/day

Duration of test:

Mated females killed on day 20 of gestation.

No. of animals per sex per dose:

24 mated females

Control animals:

yes, sham-exposed

other: positive controls - 250 mg/kg acetylsalicyclic acid orally by gavage

Details on study design:

Sex: female
Duration of test: no data
- Dose selection rationale: High dose was limited by safety requirements to be below the lower explosive limit of butadiene in air, intermediate dose matched the AGGIH reccomended levels for occupationally exposed personnel (as given at the date of the study). The low level represented upper range expected to occur in an industrial situation (as estimated at the date of the study).

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice/day

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily during gestation

BODY WEIGHT: Yes
- Time schedule for examinations: 0, 3, 6, 9, 12, 15, 18 and 20 of gestation

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: ovaries, uterus

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
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other:

Fetal examinations:

- Foetal weight: Yes: all per litter
_ Foetal length: Yes: all per litter
- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: [2/3rds per litter]
- Skeletal examinations: Yes: [2/3rds per litter]
- Head examinations: Yes: [1/3rds per litter]

Statistics:

Continuous or semi-continuous responses and some discrete responses: analysis of variance techniques followed by t-test. Kruskal-Wallis test, Wilcoxin rank sum test.
Discrete responses: Fisher's two-sum randomisation test with Monte Carlo simulation.

Indices:

not given

Historical control data:

none

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Dose-related decreased body weight gain during the initial part of the study (up to day 12). At 8000 ppm weight loss during days 1-3 and loss of body weight gain in the other groups. All weight was regained by the end of exposure. Post-implantation loss was slightly but not statistically significantly higher in all 1,3-butadiene exposed groups than in controls, considered to be a consequence of the maternal toxicity.

Effect levels (maternal animals)

Key result

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:yes

Details on embryotoxic / teratogenic effects:
There was no effect at any dose level on pregnancy index, implantation, pre-implantation loss, or on gravid uterus weight. Mean foetal weight and crown/rump length lower in 1,3-butadiene exposed groups (only stat. sig. at 8000 ppm). Higher incidence of minor foetal defects and variants, associated with the smaller foetal size, in the buta-1,3-diene groups. A dose-related increase in the number of major foetal defects, particularly wavy ribs, in the 1,3-butadiene groups, considered to be associated with the dose-related embryonic growth retardation. Other major skeletal defects - abnormalities of the skull, spine, sternum, long bones and ribs - occurred mainly at 8000 ppm and were considered to be due to exposure to 1,3-butadiene. There was no evidence of teratogenicity at dose levels of 200 or 1000 ppm.

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEC

Effect level:

1 000 other: ppm (2212 mg/m3)

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

The positive control study verified the susceptibility of the strain of rat used to a known teratogen.

Foetal defect data

 

Parameter	Control	Butadiene 200 ppm	Butadiene 1,000 ppm	Butadiene 8,000 ppm
EXTERNAL AND VISCERAL DEFECTS
Number of foetuses examined	450	265	308	294
Number showing minor defects only (% of foetuses examined)	76 (16.9)	63 (23.8)	75 (24.4*)	75 (25.5)
Number showing major defects (% of foetuses examined)	0 (0)	0 (0)	0 (0)	2 (0.7)
SKELETAL DEFECTS
Number of foetuses examined	311	182	215	204
Number showing minor defects only (% of foetuses examined)	72 (23.2)	49 (26.9*^1)	45 (20.9)	43 (21.1)
Number showing major defects (% of foetuses examined)	2 (0.6)	4 (2.2)	6 (2.8*)	12 (5.9**)
VARIANTS
Number of foetuses examined	311	182	215	204
Number showing variants (% of foetuses examined)	267 (85.9)	164 (90.1)	185 (86.0)	199 (97.5*^1)

** - Significantly higher than in the control group p<0.01: Fisher's randomisation test based on the frequencies of affected litters.

* - Significantly higher than in the control group p<0.05: Fisher's randomisation test based on the frequencies of affected litters.

**¹- Significantly higher than in the control group p<0.01: Wilcoxon's test

*¹- Significantly higher than in the control group p<0.05: Wilcoxon's test

Applicant's summary and conclusion

Conclusions:

Exposure of 1,3-butadiene (up to 8000 ppm, 17701 mg/m3) to rats during the period of major organogenesis elicited maternal toxicity and, as a result, embryonic growth retardation at all dose levels tested. There was no evidence of teratogenicity at the the lower exposure levels. (200 and 1000 ppm).

Executive summary:

Pregnant rats were exposed to 1,3-butadiene (200, 1000 and 8000 ppm; 442, 2212 and 17,701 mg/m3,) 6h/day to rats during the period of major organogenesis ( days 6-15 of gestation) in a pre-natal developmental toxicity study. Maternal toxicity and, as a result, embryonic growth retardation occurred at all dose levels tested. The magnitude of the effect was dose-related. At 8 000 ppm, increased incidences of major foetal defects occurred such as severe wavy ribs. These effects are considered to be indicative of delayed development. There was no evidence of teratogenicity at the lower exposure levels. The NOAEC for teratogenicity was 1000 ppm (2212 mg/m3).