2-ethoxy-2-methylpropane

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Remarks:

Type of genotoxicity: chromosome aberration

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, no restrictions, fully adequate for assessment.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

2-ethoxy-2-methylpropane

EC Number:

211-309-7

EC Name:

2-ethoxy-2-methylpropane

Cas Number:

637-92-3

Molecular formula:

C6H14O

IUPAC Name:

2-ethoxy-2-methylpropane

Details on test material:

ETBE, 98% pure based on gas chromatography, lot no. 11, liquid, stored at room temperature

Test animals

Species:

mouse

Strain:

CD-1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Chareles River
- Age at study initiation: 7-8 weeks
- Weight at study initiation: 25-28 gram
- Assigned to test groups randomly: yes
- Housing: 2/cage
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: appr. 3 weeks

ENVIRONMENTAL CONDITIONS
- Temperature : 66-77 °F
- Humidity (%): 40-70
- Air changes (per hr): 13
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation

Details on exposure:

Groups of 5 male (approx. 28g) and 5 female (approx. 25 g) CD-1 mice were exposed whole body to 0, 400, 2000 or 5000 ppm ETBE vapour (6 hr/d for 5d). The highest exposure represented one half of the lower explosive  limit for ETBE. Liquid ETBE was delivered by a metered piston pump into a heated glass evaporator and the resultant vapour delivered into a 900 l stainless steel  and glass exposure chamber. The air flow was approximately 200 L/min. The nominal vapour concentration in the  chambers was calculated from the volume of ETBE vapourised and the total airflow. The actual vapour concentration was determined using GC-FID (23-24 measurements during each 6 hr exposure period). Daily exposure concentrations (mean+/-SD) were 400+/-8.5, 1996+/-37 and 5053+/-80 ppm (limit of detection 10 ppm).

Duration of treatment / exposure:

5 days

Frequency of treatment:

6 hours/day

Post exposure period:

24 hours

Doses / concentrations

Remarks:

Doses / Concentrations:
400, 2000 or 5000 ppm
Basis:
other: target concentrations

No. of animals per sex per dose:

5 animals/sex/dose

Control animals:

yes

Positive control(s):

Cyclophosphamide (15 mg/kg bwt in distilled water; ip injection) was administered 24 hr prior to sacrifice. 

Examinations

Tissues and cell types examined:

Body weights were recorded before first exposure and at scheduled termination. Individual clinical observations were recorded before and after exposure, and on a group basis during exposures. 

Details of tissue and slide preparation:

Femoral bone marrow smears were prepared from each mouse 24 hr after the final exposure.

Evaluation criteria:

Bone marrow smears were prepared from femurs:
- 2000 PCEs scored for the presence of micronuclei;
- the ratio of PCE:NCE was quantified in 1000 erythrocytes. Toxicity was determined from the number of PCEs per 1000 erythrocytes.

Statistics:

Results were analysed using the Mann Whitney U test.

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Toxicity:

yes

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

CLINICAL SIGNS AND TOXICITY

All animals survived until study termination. Clinical signs included abnormal gait, hypoactivity, incoordination, abdominal breathing and lack of startle reflex in the 5000 ppm group and to a lesser extent in the 2000 ppm group. Hypoactivity was also present following 4.5 hr exposure or more hours of exposure on study days 1 and 3 to 400 ppm ETBE vapour. There were no differences in body weight (gains) between the groups.

MICRONUCLEUS TEST

No statistically significant increase in micronucleus frequency were seen in animals exposed to ETBE. A statistically significant increase (P<0.01) was observed in the positive control group. There was no significant change in proportion of PCEs to NCEs.