Gasoline, pyrolysis, hydrogenated

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:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP status unknown, near guideline study, published in peer reviewed literature, adequate for assessment.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Chronic inhalation oncogenicity study of isoprene in B6C3F1 mice

Author:

Placke M, Griffis L, Bird M, Bus J, Persing R and Cox L Jr.

Year:

1996

Bibliographic source:

Toxicology, Vol. 113, pp. 253-262

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

not specified

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Isoprene

EC Number:

201-143-3

EC Name:

Isoprene

Cas Number:

78-79-5

Molecular formula:

C5H8

IUPAC Name:

isoprene

Details on test material:

- Name of test material (as cited in study report): isoprene
- Source: Goodyear Tire & Rubber Company, Beaumont, Texas, USA
- Analytical purity: >99%
- The test material contained less than one percent limonene (a degradation product)
- Tert-butyl catechol (TBC) was added by the supplier as a stabilizer at a target concentration of 50 ppm. TBC in each cylinder was measured and did not exceed 100 ppm for the initial cylinder analyses, with a measured range of between 4.1-95.3 ppm.

Test animals

Species:

mouse

Strain:

B6C3F1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River's Portage Laboratory
- Age at study initiation: no older than 10 weeks
- Housing: individually housed in stainless steel wire-mesh inhalation cages that fitted into the exposure chambers
- Diet: Certified Purina Rodent Chow in pellet form ad libitum except during exposure
- Water: ad libitum except during exposure
- Acclimation period: 25 days
- Prior to the study, sera were collected from at least 5 mice/sex and were found free of antibody titers to common murine pathogens.

ENVIRONMENTAL CONDITIONS
- Temperature: 22±2°C (chamber)
- Humidity: 40-70% (chamber)
- Air changes (per hr): no data
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: no data

Administration / exposure

Route of administration:

inhalation

Vehicle:

air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: exposure chambers (Hazelton H1000 or H2000, 1000 or 2000 L in volume)
- Method of holding animals in test chamber: stainless steel wire-mesh cages
- Test atmospheres were generated from the liquid as an aerosol by ultrasonic nebulization followed by evaporation in a stainless steel aging plenum
- Filtered compressed air was supplied to the ultrasonic spray nozzle. Isoprene was fed to the spray nozzle from the storage cylinder which was pressurized with N2 at 5 psig.
- Room air was drawn into the aging plenum through charcoal and high efficiency particulate air (HEPA) filters and carried isoprene vapour to the exposure chambers through a common distribution manifold with subsequent dilution at each chamber to the target concentrations.
- Temperature: 22±2°C (range:22.1 to 22.7°C); humidity 40-70% (range: 52.3 to 55.0%)
- Chamber flow was a nominal 15 air changes per h
- Chamber pressure and flowrate were monitored continuously during exposures.

TEST ATMOSPHERE
- Brief description of analytical method used: A Miran-980 infrared spectrometer (IR) was used to measure isoprene concentrations in the chambers and exposure room.
- An hourly sampling sequence was used to minimize the step change in concentration among chambers.
- Some chamber samples were also analyzed with a gas chromatograph with a Flame Ionization Detector, primarily to determine the concentrations of limonene (isoprene dimer).
- Uniformity within the exposure chambers was verified by measuring the isoprene concentration at the front, middle, and back of each chamber level.
- Samples taken from breathing zone: yes

Duration of treatment / exposure:

20, 40 or 80 weeks

Frequency of treatment:

4 or 8 hrs/day

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 10, 70, 140, 280, 700, 2200 ppm/ 4 or 8 hours/day, 5
Basis:

No. of animals per sex per dose:

10

Control animals:

yes, sham-exposed

Positive control(s):

none

Examinations

Tissues and cell types examined:

Micronucleated polychromatophilic or orthochromophilic erythrocytes

Details of tissue and slide preparation:

TREATMENT AND SAMPLING TIMES:
- Evaluations of peripheral blood were performed on 10 animals per exposure group using samples obtained the day after the last exposure for those groups ending exposure after 40 and 80 weeks.
- Ten controls were also sampled when an exposed group was.

DETAILS OF SLIDE PREPARATION:
- A slightly modified method (micronucleated polychromatophilic or orthoch-romophilic erythrocytes were counted) as de-scribed by Miller (1973) was used.
- A total of 2000 erythrocytes from each animal were evaluated.

Statistics:

Results from the micronucleus evaluation were analyzed using one way analysis of variance or a nonparametric test (Kruskal-Wallis and Dunn's summed rank).

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

positive

Toxicity:

no effects

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

not applicable

Any other information on results incl. tables

After 40 weeks of exposure, controls, 70 ppm and 140 ppm groups had similar group mean values. 2200 ppm animals had micronucleus counts that were significantly increased (147%) compared to controls. After 80 weeks of exposure, controls, 10 ppm and 70 ppm animals had similar values. All mice exposed to higher concentrations of isoprene (≥280 ppm) had significantly greater micronuclei values compared to controls. 280 ppm, 700 ppm, 2200 ppm/4 h and 2200 ppm animals were 92, 133, 167, and 125% higher, respectively, than the controls.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): positive
Exposure to isoprene resulted in genotoxic effects with the mean incidence of micronuclei in peripheral blood significantly (p≤0.05) greater at 700 ppm or higher after 80 weeks.

Executive summary:

The mean incidence of micronuclei in peripheral blood was significantly increased at 700 ppm and higher after 80 weeks. Similar effects were observed after 40 weeks, although only the 2200 ppm animals had significant elevations of micronuclei compared to the control, 70 and 140 ppm groups. (The 280 and 700 ppm groups were not sampled at 40 weeks). There was no apparent relationship to exposure duration or cumulative exposure on the incidence of micronuclei.