Gas oils (petroleum), straight-run, high-boiling

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Remarks:

Type of genotoxicity: gene mutation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1989-06-13 to 1989-07-13

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restriction because the study was conducted according or similar to OECD 471 with modifications.

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1991

Report date:

1991

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

yes

Remarks:

modified Ames assay

GLP compliance:

not specified

Type of assay:

other: modified Ames assay

Test material

Test material information

Constituent 1

Reference substance name:

Straight run gas oils (CAS# 64741-44-2 and 68814-87-9)

IUPAC Name:

Straight run gas oils (CAS# 64741-44-2 and 68814-87-9)

Details on test material:

Straight-run gas oils
Sample Number 1 (in study report): MD 57324, North Africa crude, no desulphurisation
Total Polyaromatic hydrocarbons: <27.64 mg/kg,
3 to 7 Ring Polyaromatic carbons (%): 0.7

Sample Number 2 (in study report): MD 57380, North Sea crude, no desulphurisation
Total Polyaromatic hydrocarbons: < 8.38 mg/kg
3 to 7 Ring Polyaromatic carbons (%): 0.8

Two millilitres of test article were mixed with three millilitres of cyclohexane to homogeneity. Ten millilitres of dimethylsulphoxide was then added and mixed thoroughly. The mixture was vortexed every 5 minutes for a total of 30 minutes. Afterwards, the mixture was centrifuged at 200xg for 5 minutes at 22°C, and the DMSO layer was extracted and stored in an amber bottle at 4°C until ready for assay.

Method

Species / strain

Species / strain / cell type:

S. typhimurium TA 98

Additional strain / cell type characteristics:

not specified

Metabolic activation:

with

Metabolic activation system:

Aroclor 1254-induced male hamster S9

Test concentrations with justification for top dose:

DMSO extracts of middle distillates were delivered at doses of 60 μl, 50 μl/60 μl, 40 μl/60 μl, 30 μl/60 μl, 20 μl/60 μl, 15 μl/60 μl, 10 μl/60 μl, or 5 μl/60 μl.

Vehicle / solvent:

Dimethylsulphoxide

Controls

Untreated negative controls:

not specified

Negative solvent / vehicle controls:

yes

True negative controls:

not specified

Positive controls:

yes

Positive control substance:

other: 2-Aminoanthracene, benzo(a)pyrene, 2-nitrofluorene

Details on test system and experimental conditions:

Modified Ames (1975) procedure included preliminary solubilisation of the oil in cyclohexane followed by single extraction of dimethylsulphoxide. Additionally, S9 fraction from hamster liver was used instead of rat S9, and the concentration of NADP was increased from 4 to 8 millimolar.

The extracted oil, tester bacteria (TA98), and metabolic activation system (hamster S9) were combined in suspension, incubated for 20 minutes at 37°C were poured into a petri dish, incubated for 48 hours overnight at 37°C, and subsequently counted for revertant colonies.

Evaluation criteria:

The assay is considered acceptable under the following conditions: (1) the spontaneous and solvent control reversion rates are between 30 and 55 revertants per plate, and (2) the single dose of Stock 642-100” CNN at 50 microlitres reversion rate is between 100 and 200 revertants per plate.

Statistics:

The mean number of revertants per plate for each dose was calculated. The Student-Newman Keuls Test (SAS) was performed to determine if dose-related doubling relative to the mean was statistically significant. If doubling was reached, triplicate revertant values at all doses were plotted versus dose on an arithmetic scale. Nonlinear regression was used to determine the slope of the dose-response curve, and this value is the mutagenicity index of the test material.

Results and discussion

Test results

Test results 1

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with

Genotoxicity:

positive

Remarks:

Marginally genotoxic for straight run components (CAS# 64741-44-2) )

Cytotoxicity / choice of top concentrations:

not specified

Vehicle controls validity:

valid

Untreated negative controls validity:

not specified

Positive controls validity:

valid

Test results 2

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with

Genotoxicity:

negative

Remarks:

CAS# 68814-87-9

Cytotoxicity / choice of top concentrations:

not specified

Vehicle controls validity:

valid

Untreated negative controls validity:

not specified

Positive controls validity:

valid

Remarks on result:

other: all strains/cell types tested

Remarks:

Migrated from field 'Test system'.

Any other information on results incl. tables

Sample Number	Sample Code	Mutagenicity index
1	MD 57324	0.8
2	MD 57380	1.3

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information):
positive with metabolic activation marginally mutagenic

The two straight-run gas oils, CAS# 68814-87-9 and CAS# 64741-44-2, were marginally mutagenic with metabolic activation and had mutagenicity indices of 0.8 and 1.3, respectively.

Executive summary:

In a reverse gene mutation assay in bacteria, S. typhimurium strain TA98 was exposed to straight run gas oil (CAS# 68814-87-9 or CAS# 64741-44-2) at concentrations of 0, 5, 10, 15, 20, 30, 40, 50, or 60 μl/plate in the presence of mammalian metabolic activation (Aroclor 1254-induced hamster liver S9) using the pre-incubation method.

 

CAS# 68814-87-9 and CAS# 64741-44-2 were tested up to concentrations that were completely soluble.  The positive controls induced the appropriate response.  There was marginal evidence of induced mutant colonies over background, with the straight-run gas oils producing mutagenicity indices of 0.8 and 1.3, respectively.

This study received a Klimisch score of 1 and is classified as reliable without restriction because the study was conducted according or similar to OECD 471 with modifications.