tert-butyl methyl ether

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian cell study: DNA damage and/or repair

Remarks:

Type of genotoxicity: DNA damage and/or repair

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP-compliant near-guideline study, no restrictions, fully adequate for assessment.

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1994

Report date:

1994

Reference 2

Reference Type:

publication

Title:

Assessment of the in vivo mutagenic potential of methyl tertiary-butyl ether.

Author:

McKee RH, Vergnes JS, Galvin JB, Douglas JF, Kneiss JJ & Andrews LS

Year:

1997

Bibliographic source:

J Appl Toxicol, 17 Suppl 1, S31-6.

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 486 (Unscheduled DNA Synthesis (UDS) Test with Mammalian Liver Cells in vivo)

Principles of method if other than guideline:

Butterworth, B.E. et al. 1987. A protocol and guide for the in vivo rat hepatocyte DNA-repair assay. Mutational research 189: 123-133.

GLP compliance:

yes

Type of assay:

unscheduled DNA synthesis

Test material

Test material information

Constituent 1

Reference substance name:

tert-butyl methyl ether

EC Number:

216-653-1

EC Name:

tert-butyl methyl ether

Cas Number:

1634-04-4

Molecular formula:

C5H12O

IUPAC Name:

2-methoxy-2-methylpropane

Details on test material:

- Name of test material (as cited in study report): MTBE
- Physical state: colourless non-viscous liquid
- Analytical purity: 99.68 %
- Lot/batch No.: Lot 7D-52 / BRRC nr 56-183

Test animals

Species:

mouse

Strain:

CD-1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River
- Age at study initiation: 4-5 weeks
- Weight at study initiation:
- Housing: 2 cage , at exposure individual
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

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

Administration / exposure

Route of administration:

inhalation

Vehicle:

None

Details on exposure:

CD-1 mice (10 of each sex/dose) received by inhalation target MTBE vapour concentrations of 400, 3,000 and 8,000 ppm for 6 hours. The
hepatocytes from the positive control, N-nitrosodimethylamine (10mg/kg), were collected 2 hours after treatment.

TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure chamber: Young and Bertke, Cincinnati, OH (900 Liter)
- System of generating particulates/aerosols: vapour generation by metering through a piston pump (G-20 FMI) into a heated glass evaporator
- Temperature, humidity, pressure in air chamber: temperature and humidity were recorded by using a Fishrebrand dial type thermometer and
Airguide humidity indicator, a Dwyer Magnehelic pressure gauge was used to monitor pressure
- Air flow rate: 200 L/min
- Air change rate: 13-14 /hour

TEST ATMOSPHERE
- Brief description of analytical method used: by flame ionisation gas chromatography
- Samples taken from breathing zone: yes

Duration of treatment / exposure:

2 consecutive days

Frequency of treatment:

6 hours/day

Post exposure period:

16 hours

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
400, 3000 and 8000 ppm
Basis:
other: target concentration

Doses / concentrations 2

Remarks:

Doses / Concentrations:
415 (12.3), 3044 (81.5) and 8013 (101) ppm (SD in parentheses)
Basis:
analytical conc.

Doses / concentrations 3

Remarks:

Doses / Concentrations:
458, 3300 and 8516 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

10/sex/dose

Control animals:

yes

Positive control(s):

N-nitrosodimethylamine, 10 mg/kg

Examinations

Tissues and cell types examined:

liver hepatocytes

Details of tissue and slide preparation:

The liver was removed and hepatocytes selected, counted and seeded into culture dishes containing cover slips (18 hours after the second exposure). Cultures were incubated. Approximaltely 1.5-2 hours after incubation at 37 oC the cultures were rinsed once. Subsequently the cultures were incubated in serum free WME containing 10 µCi/ml 3H-methyl thymidine for 4 hours at 37 oC, after which they were rinsed and then incubated in WME containing 0.25 mM thymidine for 16 hours.

Following the chase period, the cultures were rinsed and then fixed in 3:1 ethanol:acetic acid solution. The cover slips were rinsed, air dried, and then mounted, cell side up, on glass slides whihc were dipped in Kodak NTB-2 emulsion and then exposed for 7-14 days. the slides were developed and stained with hematoxylin-eosin.

100 nuclei were evaluated for each animal. A background grain count was also made for a cytoplasmic area, similar in size to a nucleus and taken from a heavily labeled area of the slide. Net grain counts were determined by subtracting the cytoplasmic grain count from the nuclear grain count.

Evaluation criteria:

The number of cells in repair (net grain => 5) in air-only exposed animals must be less than 20%. The test results were considered positive if the mean net grain count for any treated group was greater than 0 and the percentage of cells in repair for that treated group was greater than 20%. The test results were considered negative if the mean net grain count for all treatment groups was less than 0 and the percentage of cells was in repaier was less than or equal to 20%. At least, 6 animals/sex/group (5 positive control animals/sex) must be suitable for evaluation.

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Toxicity:

yes

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

Toxicity
No mortalities. Clinical signs were observed during exposure to 8000 ppm and included hypoactivity, abdominal breathing, ataxia and prostration. Hypoactivity and a lack of startle response were also noted in animals from the 3000 ppm group during exposures.

Genotoxicity
The net nuclear grain counts were all less than zero for all concentrations and both sexes. The percentage of cells in repair was not increased; the percentages were less than 2% at all dose levels and in both sexes.