Extract residues (coal), tar oil alk.

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 based on grouping of substances (category approach)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Not GLP, but key cytogenetic parameters measured comparable to guideline study.

Data source

Reference

Reference Type:

publication

Title:

Benzene-induced micronuclei in erythrocytes: an inhalation concentration-response study in B6C3F1 mice

Author:

Farris GM, Wong VA, Wong BA, Janszen DB and Shah RS

Year:

1996

Bibliographic source:

Mutagenesis 11, 455-462

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

yes

Remarks:

- no positive control.

Principles of method if other than guideline:

Mice were exposed to benzene vapour (up to 200 ppm; 640 mg/m3) for up to 8 weeks and blood and bone marrow samples evaluated for the presence of micronuclei within 2 hours of end of exposure

GLP compliance:

no

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Benzene

EC Number:

200-753-7

EC Name:

Benzene

Cas Number:

71-43-2

Molecular formula:

C6H6

IUPAC Name:

benzene

Details on test material:

- Name of test material (as cited in study report): High purity liquid chromatography grade benzene- Supplier: VWR Scientific, Marietta, GA, USA- Analytical purity: >99.9%

Test animals

Species:

mouse

Strain:

B6C3F1

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS- Source: Charles River Breeding Laboratories, Inc., Portage, Nil, USA- Age at study initiation: 12 weeks±2 days - Assigned to test groups randomly: yes, by weight- Housing: one per cage in 8 m3 stainless steel and glass inhalation chambers- Diet: NIH-07 rodent chow (Ziegler Bros., Gardener, PA, USA) ad libitum- Water: Filtered tap water ad libitum- Acclimation period: 10-17 days

Administration / exposure

Route of administration:

inhalation: vapour

Vehicle:

- Vehicle(s)/solvent(s) used: air

Details on exposure:

TYPE OF INHALATION EXPOSURE: whole bodyGENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION: Benzene exposures conducted in 8 m3 stainless steel and glass Hinners-style whole body inhalation chambers. Air was conditioned to 72°F and 50% humidity and maintained at a flow of 2000 L/min through the chambers. Temperature, relative humidity, airflow and static pressure continuously monitored. - System of generation: Atmospheres of 10, 100 and 200ppm benzene generated by vaporizing liquid benzene contained in a 10-gallon stainless steel pressure vessel. A controlled flow of nitrogen was bubbled through the liquid benzene and carried vapours out of the vessel into the chamber air inlet. The 1 ppm benzene atmosphere was also generated from liquid benzene, however, the pressure vessel was maintained at 10 p.s.i. gauge pressure with nitrogen. The flow of the benzene vapours and nitrogen into the chambers controlled by mass flow controllers placed on the outlet side of the pressure vessels.TEST ATMOSPHERE- Brief description of analytical method used: An infrared (IR) gas analyser used to monitor the 0, 10, 100 and 200 ppm benzene concentrations. The 1 ppm chamber was monitored by gas chromatography.

Duration of treatment / exposure:

1, 2, 4 and 8 weeks of exposure

Frequency of treatment:

6 h/day, 5 days/week

Post exposure period:

None. Blood and bone marrow samples collected within 2 h of end of final exposure.

Doses / concentrations

Remarks:

Doses / Concentrations:0, 1, 10, 100 or 200 ppmBasis:other: target concentrations

No. of animals per sex per dose:

7

Control animals:

yes, sham-exposed

Positive control(s):

none

Examinations

Tissues and cell types examined:

Micronucleated polychromatic erythrocytes (MPCE) in the bone marrow and blood and micronucleated normochromatic erythrocytes (MNCE) in the blood.

Statistics:

For each timepoint, the data from each benzene exposure group was compared to the controls using Dunnett's analysis of variance (ANOVA) with a 5% significance level. Linear and quadratic regression models were fit to the bone marrow NIPCE data. Evaluation of linear and quadratic curves with the data required a weighted analysis because of nonhomogeneous variability. A P value of <0.05 for lack of fit test meant that the curve was not appropriate for the data set.

Results and discussion

Test results

Sex:

male

Genotoxicity:

positive

Remarks:

at exposure concentrations of 100 and 200 ppm

Toxicity:

yes

Vehicle controls validity:

not applicable

Negative controls validity:

valid

Positive controls validity:

not applicable

Additional information on results:

Atmosphere analysis: The analytical concentrations of benzene within the individual chambers were stable during each exposure period and over the time course of the studies. The actual concentrations of benzene averaged 0.95±0.09, 9.9±1.2, 98.5±1.5 and 198.5±4.8 ppm.

Any other information on results incl. tables

100 and 200 ppm benzene induced a statistically significant increased frequency of micronucleated erythrocytes in the bone marrow and blood. No such increase was observed at levels of 1 or 10ppm benzene. The increase was seen at weeks 1, 2, 4 and 8 of exposure, and the frequency of MPCE plateaued at week 2 with 43/1000 (100 ppm) and 86/1000 (200 ppm) in the bone marrow as compared with 10/1000 for controls. The frequency of MNCE in the blood progressively increased to 13.4/1000 (100 ppm) and 32.5/1000 (200 ppm) at week 8 as compared with 1.8/1000 for controls. Cytotoxicity was seen at 100 and 200 ppm with decreases in both PCE and total erythrocyte counts.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): positive at exposure levels of 100 ppm and 200 ppmBenzene produced an increased frequency of micronuclei following inhalation exposure in mice and is considered to be an in vivo clastogen.

Executive summary:

The frequencies of micronucleated polychromatic erythrocytes (MPCE) in the bone marrow and blood and micronucleated normochromatic erythrocytes (MNCE) in the blood of male B6C3F1 mice were measured following inhalation of benzene at 0, 1, 10, 100 or 200 ppm for 1, 2, 4 or 8 weeks of exposure. 100 and 200 ppm benzene induced a statistically significant increased frequency of micronucleated polychromatic erythrocytes and/or micronucleated erythrocytes in the bone marrow and blood of exposed animals at all time points. It is concluded that benzene is an in vivo clastogen.