Thioacetic acid

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

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1996

Report date:

1996

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

no

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

Thioacetic acid

EC Number:

208-063-8

EC Name:

Thioacetic acid

Cas Number:

507-09-5

Molecular formula:

C2H4OS

IUPAC Name:

ethanethioic S-acid

Test material form:

other: liquid

Details on test material:

- Name of test material (as cited in study report): Thioacetic acid
- batch 94-000607,
- purity 99.83%.

Method

Target gene:

Histidine operon

Species / strain

Species / strain / cell type:

other: Strains: TA 1535, TA 1537, TA 98, TA 100 and TA 102

Metabolic activation:

with and without

Metabolic activation system:

liver microsomal fraction (S9 fraction) of rats induced with Aroclor 1254.

Test concentrations with justification for top dose:

The selected treatment-levels were for the first experiment: 3, 10, 30, 100, 300 µg/plate.
As no toxicity was observed at 300 µg/plate, the dose-levels were increased for the second experiment: 62.5, 125, 250, 500, 1000 µg/plate.

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: DMSO
- Justification for choice of solvent/vehicle: solubility

Controls

Untreated negative controls:

no

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Remarks:

see below

Details on test system and experimental conditions:

A preliminary toxicity test was performed to define the dose-levels of THIOACETIC ACID to be used for the mutagenicity study. THIOACETIC ACID was then tested in three independent experiments, with or without a metabolic activation system, the S9 mix, prepared from a liver microsomal fraction (S9 fraction) of rats induced with Aroclor 1254.
The experiments were performed according to the direct plate incorporation method except the second and the third experiments with S9 mix, which were performed according to the preincubation method (60 minutes, 37°C).
Five strains of bacteria Salmonelle typhimurium: TA 1535, TA 1537, TA 98, TA 100 and TA 102 were used. Each strain was exposed to five dose-levels of the test substance (three plates/dose-level). After 48 to 72 hours of incubation at 37°C, the revertant colonies were scored.
The dose-levels of the positive controls were as follows:
without S9 mix:
. 1 µg/plate of sodium azide (NaN3): TA 1535 and TA 100 strains,
. 50 µg/plate of 9-Aminoacridine (9AA): TA 1537 strain,
. 0.5 µg/plate of 2-Nitrofluorene (2NF): TA 98 strain,
. 2 µg/plate of N-ethyl-N-nitro-nitrosoguanidine (ENNG): WP2uvrA strain,
. 0.5 µg/plate of Mitomycin C (MMC): TA 102 strain.

with S9 mix:
. 2 µg/plate of 2-Anthramine (2AM): TA 1535, TA 1537, TA 98 and TA 100 strains,
. 10 µg/plate of 2-Anthramine (2AM): TA 102 strain.

Evaluation criteria:

Acceptance criteria
This study was considered valid since the following criteria were fully met:
. the number of revertants in the vehicle controls was within the range of the historical data,
. the number of revertants in the positive controls was higher than that of the vehicle controls and was within the range of our historical data.

Evaluation criteria
A reproducible two-fold increase in the number of revertants compared with the vehicle controls, in any strain at any dose-level and/or evidence a dose-relationship was considered as a positive result. Reference to historical data, or other considerations of biological relevance may also be taken into account in the evaluation of the data obtained.

Results and discussion

Test results

Species / strain:

S. typhimurium TA 1535, TA 1537, TA 98, TA 100 and TA 102

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

see below

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

Positive controls validity:

valid

Additional information on results:

The number of revertants of the vehicle and positive controls was as specified in the acceptance criteria and within the range of our historical data.

Since the test substance was toxic, the highest dose-level was based on the level of toxicity, according to the criteria specified in the international regulations: reduction in the number of revertants and/or clearing of the bacterial lawn.

Moderate to important toxicity was noted without S9 mix in the five strains at dose-levels higher than 125 µg/plate and with S9 mix in the TA 1535, TA 1537 and TA 100 at dose-levels higher than 250 µg/plate. In the TA 98 and TA 102 strains with S9 mix, only slight toxicity was noted.

Therefore as only 3/5 dose-levels were available, a third experiment was performed with the same treatment-levels as in the first experiment. Slight (TA 102) or severe (the four other strains) toxicity was observed at 300 µg/plate without S9 mix. No toxicity was observed with S9 mix in TA 1535, TA 1537 and TA 100 strains.

Remarks on result:

other: all strains/cell types tested

Remarks:

Migrated from field 'Test system'.

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information):
negative

Thioacetic acid did not induce any significant increase in the number of revertants, with or without S9 mix, in any of the five strains.

Executive summary:

The potential of THIOACETIC ACID to induce reverse mutation was evaluated inSalmonella typhimurium.

A preliminary toxicity test was performed to define the dose-levels of THIOACETIC ACID to be used for the mutagenicity study. THIOACETIC ACID was then tested in three independent experiments, with or without a metabolic activation system, the S9 mix, prepared from a liver microsomal fraction (S9 fraction) of rats induced with Aroclor 1254. The experiments were performed according to the direct plate incorporation method except the second and the third experiments with S9 mix, which were performed according to the preincubation method (60 minutes, 37°C). Five strains of bacteriaSalmonella typhimurium:TA 1535, TA 1537, TA 98, TA 100 and TA 102 were used. Each strain was exposed to five dose-levels of the test substance (three plates/dose-level). After 48 to 72 hours of incubation at 37°C, the revertant colonies were scored. THIOACETIC ACID was dissolved in dimethylsulfoxide (DMSO).

The number of revertants of the vehicle and positive controls was as specified in the acceptance criteria and within the range of the historical data. Since the test substance was toxic, the highest dose-level was based on the level of toxicity, according to the criteria specified in the international regulations: reduction in the number of revertants and/or clearing of the bacterial lawn. The selected treatment-levels were for the first experiment: 3, 10, 30, 100, 300 µg/plate. As no toxicity was observed at 300 µg/plate, the dose-levels were increased for the second experiment: 62.5, 125, 250, 500, 1000 µg/plate. Moderate to important toxicity was noted without S9 mix in the five strains at dose-levels higher than 125 µg/plate and with S9 mix in the TA 1535, TA 1537 and TA 100 at dose-levels higher than 250 µg/plate. In the TA 98 and TA 102 strains with S9 mix, only slight toxicity was noted. Therefore as only 3/5 dose-levels were available, a third experiment was performed with the same treatment-levels as in the first experiment. Slight (TA 102) or severe (the four other strains) toxicity was observed at 300 µg/plate without S9 mix. No toxicity was observed with S9 mix in TA 1535, TA 1537 and TA 100 strains. The test substance did not induce any significant increase in the number of revertants, with or without S9 mix, in any of the five strains.

THIOACETIC ACID did not show mutagenic activity in this bacterial reverse mutation test onSalmonella typhimurium.