2-methylbut-2-ene

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other: GLP compliant, guideline study, available as unpublished report, no restrictions, fully adequate for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2004

Report date:

2004

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: OECD 422

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-methylbut-2-ene

EC Number:

208-156-3

EC Name:

2-methylbut-2-ene

Cas Number:

513-35-9

Molecular formula:

C5H10

IUPAC Name:

2-methylbut-2-ene

Details on test material:

- Name of test material (as cited in study report): 2-methyl-2-butene
- Physical state: Clear, colourless liquid
- Volatile liquid with boiling point of between 35 and 38°C
- Analytical purity: >98%
- Lot/batch No.: A0153320
- Expiration date of the lot/batch: no data
- Stability under test conditions: stable for the duration of the study
- Storage condition of test material: In a cool, dry, well-ventilated area

Test animals

Species:

rat

Strain:

other: Crl:CD®(SD)IGS BR

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Ltd., Margate, Kent, UK
- Age at study initiation: Approximately 8-9 weeks
- Weight at study initiation: 252-314 g (males), 175-240 g (females)
- Housing: 1 male:1 female during pairing; individually (females, reproductive phase)
- Diet: Pelleted UAR VRF1 certified diet ad libitum except during exposure
- Water: ad libitum
- Acclimation period: 16 days

ENVIRONMENTAL CONDITIONS
- Temperature: 19-25°C
- Humidity: 40-70%
- Air changes (per hr): Each animal room was kept at positive pressure with respect to the outside by its own supply of filtered fresh air, which was passed to atmosphere and not re-circulated
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 28 September 2001 To: 18 April 2002 (pathology completed)

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel and glass construction and consisted of a cuboidal body fitted with a pyramidal base and top. The internal volume of each chamber was approximately 0.75 m. At the apex of the upper pyramidal figure was the tangentially mounted air duct. Immediately below this was a perforated canister, which ensured equal distribution of the test atmosphere within the chamber.
- Method of holding animals in test chamber: Exposure cages constructed of stainless steel mesh were suspended on a framework arranged on 4 levels. Each level was able to hold four cages, with each cage capable of housing 4 rats individually.
- Source and rate of air: For all groups exposed to 2-methyl-2-butene, the vapour/air mixture produced in the vapour generators was passed into the base of the secondary dilution vessel. A further supply of clean and dry air was supplied to Groups 2 and 3 to ensure a total chamber airflow of approximately 150 L/minute. The air supply for Group 4 was provided solely by the vapour generation system. The control group was exposed using a similar system to that used for the test groups, but received compressed air only at a rate of approximately 150 L/minute.
- System of generating particulates/aerosols: The vapour generation system for each of the test groups was supplied from individual reservoirs of liquid 2-methyl-2-butene maintained at pressure. The top of each reservoir was fitted with a central, "0" - ring sealed filler cap, a system to allow pressurisation and release of the helium head pressure and a safety pressure release valve set to operate at above the study operating pressure. Except during the filling procedure, 2-methyl-2-butene in the reservoirs was maintained under a helium pressure of 10 psi.
- Temperature, humidity, pressure in air chamber: Wet and dry bulb temperatures and relative humidity were recorded at approximately 30-minute intervals throughout each exposure.
- Air flow rate: The volume flow of air to the exposure chambers was measured using calibrated flow meters and also checked approximately every 30 minutes
- Treatment of exhaust air: The chamber air extract was vented to atmosphere via an exhaust stack.

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography
- Chamber atmosphere was sampled in sequence from each of the four exposure chambers (Chambers 4 - 1 sampled sequentially) and from one point within each chamber. Air from each chamber was continually drawn through a transfer line, which was therefore equilibrated with the mean concentration from each chamber. When not being sampled, these transfer lines were pumped to waste.
Every six minutes, air from the transfer lines was switched to the injection loop of the gas chromatograph for automated analysis and data processing.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The study mean analysed concentrations of 2-methyl-2-butene over the duration of the study were 584, 2026 and 7097 ppm. These levels were in good agreement with the target exposure levels.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Proof of pregnancy: sperm in vaginal smear, referred to as day 0 of pregnancy
- After successful mating each pregnant female was caged individually in solid polypropylene cage with bedding material

Duration of treatment / exposure:

6 hours/day , daily

Frequency of treatment:

Over a 2-week pre-mating period, throughout mating and through to Day 19 of gestation.

Duration of test:

The females were allowed to litter and rear their offspring to Day 4 of lactation.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 580, 2000 or 7000 ppm
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0, 1665, 5740 or 20090 mg/m3
Basis:
nominal conc.

Doses / concentrations 3

Remarks:

Doses / Concentrations:
0, 584, 2026 or 7097 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

12 females

Control animals:

yes, concurrent no treatment

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed observations were made daily, on the days of exposure, as follows:
Pre exposure observations; Observations during exposure; Observations within ½ to 1 hour of return to home cage.
During the daily exposure, obvious signs were recorded as a group response. Due to the type of exposure system used, the ability to observe individual animals during the exposures was severely restricted.
A more detailed weekly physical examination was performed on each animal to monitor general health.

BODY WEIGHT: Yes
- Time schedule for examinations: The weight of each rat was recorded on the day that treatment commenced (Week 0), then weekly to Week 2, and then on Days 0, 7, 14 and 20 after mating, and Days 1 and 4 of lactation.
During the exposure period, bodyweights were recorded before the daily exposure.

FOOD CONSUMPTION:
- Food consumption was recorded weekly to Week 2, then between Days 0-6, 7-13, and 14-19 of gestation, and Days 1 and 4 of lactation.

Ovaries and uterine content:

Not applicable

Fetal examinations:

Not applicable

Statistics:

All statistical analyses were carried out separately for males and females.
Data relating to food consumption was analysed on a cage basis. For all other parameters, the analyses were carried out using the individual animal as the basic experimental unit. Significant differences between control and treated groups were expressed at the 5% (p<0.05) or 1% (p<0.01) level.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
- There were no unscheduled deaths. Half closed eyes were seen on Day 1 of exposure in Inter dose and High dose animals. High dose animals were seen to be less responsive to outside stimuli on Days 1 and 14 of exposure.
- There was a dose-related reduction in bodyweight gain in treated females over the 2 weeks prior to pairing with significance being attained for Intermediate and High dose females. Bodyweight gain of females during gestation and lactation was unaffected by treatment.

Effect levels (maternal animals)

Dose descriptor:

NOAEC

Effect level:

7 000 ppm

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no data

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

It was concluded that the no effect level of 2-methyl-2-butene, for reproductive/developmental toxicity in this screening study, to rats for 4 weeks by inhalation administration, was 7000 ppm.

Executive summary:

The reproduction/developmental toxic potential of the test substance, 2-methyl-2-butene (an industrial chemical) to Crl:CD®(SD)IGS BR rats by inhalation administration was assessed. Three groups of twelve female rats were exposed over a 2-week pre-mating period, throughout mating and through to Day 19 of gestation. The females were allowed to litter and rear their offspring to Day 4 of lactation. All animals received 2-methyl-2-butene by whole body inhalation exposure at concentrations of 580, 2000 or 7000 ppm. A similarly constituted control group received air alone.

During the study, clinical condition, bodyweight, food consumption, oestrus cycles, mating performance, litter data, organ weights and macroscopic pathology were undertaken.

The study mean analysed concentrations of 2-methyl-2-butene over the duration of the study were 584, 2026 and 7097 ppm. These levels were in good agreement with the target exposure levels.

It was concluded that the no effect level of 2-methyl-2-butene, for reproductive/developmental toxicity in this screening study, to rats for 4 weeks by inhalation administration, was 7000 ppm.