Methanethiol

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Remarks:

Type of genotoxicity: gene mutation

Type of information:

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

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:

1992

Report date:

1992

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Test material

Test material information

Constituent 1

Reference substance name:

Sodium methanethiolate

EC Number:

225-969-9

EC Name:

Sodium methanethiolate

Cas Number:

5188-07-8

IUPAC Name:

sodium methanethiolate

Details on test material:

Test article name : Sodium methylmercaptide
CAS RN°: 5188-07-8
Origin: Elf Atochem, Rotterdam
Batch: 462

Method

Target gene:

Histidine operon

Species / strain

Species / strain / cell type:

S. typhimurium, other: TA 1535, TA 1537, TA 102, TA 98, TA 100

Additional strain / cell type characteristics:

other: test organisms were properly maintained and were checked for appropriate genetic markers (rfa mutation, R factor)

Metabolic activation:

with and without

Metabolic activation system:

S9 derived from male Sprague-Dawley rats induced with a single intraperitoneal injection of Aroclor 1254 (500 mg/kg)

Test concentrations with justification for top dose:

Plate incorporation assay: 
0, 312.5, 625, 1250, 2500 or 5000 µg/plate for all test strains with and without metabolic activation. 
Pre-incubation assay: 
0, 312.5, 625, 1250, 2500 or 5000 µg/plate for TA1535, TA1537 and TA100 or 0, 125, 250, 500, 1000 or 2000 µg/plate for TA 102 and TA 98, without metabolic activation. 
0, 312.5, 625, 1250, 2500 or 5000 µg/plate for TA1535, TA1537, TA100 and TA102 or 0, 312.5, 625, 1250, 2500 or 4000 µg/plate for TA 102, with metabolic activation.

Vehicle / solvent:

Distilled water

Controls

Untreated negative controls:

yes

Remarks:

culture medium

Negative solvent / vehicle controls:

yes

Remarks:

distilled water (50 mg/mL)

True negative controls:

no

Positive controls:

yes

Remarks:

All positive controls were diluted in dimethyl sulfoxide.

Positive control substance:

other: With S9:  2-anthramine 2.0 µg/plate (TA98-TA100-TA1535-TA1537 ), Danthron 30 µg/plate ( TA102 ). Without S9: 2-nitrofluorene 0.5 µg/plate(TA98 ), Sodium azide 1 µg/plate (TA100-TA1535), 9-aminoacridine 50 µg/plate (TA1537), Mitomycin 0.5 µg/plate (TA102)

Details on test system and experimental conditions:

PRELIMINARY TOXICITY ASSAY
The preliminary toxicity assay was used to establish the dose range over which the test article would be assayed. 

MUTAGENICITY ASSAY
Five dose levels of test article along with appropriate vehicle control and positive controls were plated with overnight cultures of TA98, TA100, TA1535, TA1537 and TA102 on selective agar in the presence and absence of Aroclor induced rat liver S9. All dose levels of test article, vehicle control and positive controls were plated in triplicate.

TEST PROCEDURE
Plate incorporation method:
One half (0.5) milliliter of S9 or Sham mix, 100 µL of tester strain and 100 µL of vehicle or test article dilution were added to 2.0 mL of molten selective top agar at 45°C. After vortexing, the mixture was overlaid onto the surface of minimal bottom agar. 
Preincubation method:
One-half (0.5) milliliter of S9 or sham mix, 100 µL of  tester strain and 100 µL of vehicle or test article dilution were added to glass culture tubes. Alter vortexing, these mixtures were incubated with shaking for 60 minutes at 37°C. Following the preincubation, 2.0 mL of selective top agar was added to each tube and the mixture was vortexed and overlaid onto the surface of minimal bottom agar.  When plating the positive controls, the test article aliquot was replaced by the of appropriate positive control. After the overlay had solidified, the plates were inverted and incubated for approximately 48 to 72 hours at 37°C.  Revertant colonies for a given tester strain and activation condition were counted by automated colony counter.

Evaluation criteria:

Data sets for a tester strain was judged positive if the increase in mean revertants at one or more of the tested concentrations is equal to or greater than 2.0-times the mean vehicle control value.

Results and discussion

Test results

Species / strain:

S. typhimurium, other: TA 1535, TA 1537, TA 102, TA 98, TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

Without S9: >= 1000 µg/plate. With S9: >= 2500 µg/plate

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

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

The negative and solvent control results were equivalent to those usually obtained in the Laboratory. The number of revertants induced by the positive controls was higher than the spontaneous one, which demonstrated the sensitivity of
this test and the efficacy of the S9 mix throughout this study.

The test substance SODIUM METHYL MERCAPTIDE did not induce any significant increase in the revertant number with or
without S9 mix in any of the 5 strains.

Mean Number of Revertants Per Plate

Activation:  None

Dose (µg/plate)	TA98	TA100	TA102	TA1535	TA1537
Ctrl	2	7	370*	14	15
312.5	5	5	478	16	16
625	3	7	400	13	17
1250	18(+++)	5	388	16	16
2500	5(++)	5	347(+++)	19	13
5000	18 (+++)	5	229(+++)	20(+)	15
Positive Control	103	43	1996	490	348

*Spontaneous revertants rather than solvent control, study error

Dose (µg/plate)	TA100	TA1535	TA1537
Ctrl	102	16	12
312.5	93	24	18
625	97	21	14
1250	94(+)	19	9
2500	90(++)	20	17
5000	64(+++)	18(+)	8
Positive Control	658	461	180

Dose (µg/plate)	TA98	TA102
Ctrl	32	284
125	43	294
250	34	320
500	27	362
1000	34(++)	325(++)
2000	13(++)	242(+++)
Positive Control	1173	1335

Activation:  S9, Direct plate incorporation

Dose (µg/plate)	TA98	TA100	TA102	TA1535	TA1537
Ctrl	33	122	505	14	14
312.5	28	139	607	20	20
625	35	128	551	21	19
1250	41	139	457	16	20
2500	36	131	578	16	16
5000	35	120	446	16	15
Positive Control	1211	1765	984	263	115

Activation:  S9, Plate - preincubation

Dose (µg/plate)	TA98	TA100	TA102	TA1535	TA1537
Ctrl	42	113	375	23	15
312.5	48	94	431	21	24
625	38	97	489	21	20
1250	47	99(+)	513	27	24
2500	47(++)	94(++)	530	26	21
5000	0(+++)	0(+++)	409(+)	0(+++)	0(+++)
Positive Control	952	1217	1040	338	148

 ( ) Parentheses denote degree of toxicity noted at these concentration: +, ++ , +++

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information):
negative

Executive summary:

A Salmonella typhimurium reverse mutation assay was performed with sodium methanethiolate according to OECD Guideline 471. S. typhimuriumstrains, TA98, TA100, TA102, TA1535 and TA1537, were exposed to five concentrations of sodium methanethiolate in the presence and absence of a metabolic activation system using the plate incorporation and the preincubation methods. All doses of sodium methanethiolate, vehicle control and positive controls were plated in triplicate and incubated for 48-72 hours at 37 ºC. The positive controls gave expected responses. Sodium methanethiolate was cytotoxic at ≥1000 and ≥2500 µg/plate, in the absence and presence of a metabolic activation system, respectively. Treatment of the S. typhimurium strains with sodium methanethiolate in the presence or absence of metabolic activation did not induce any significant increases in the revertant numbers.