Registration Dossier

Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

Tert-dodecanethiol did not produce genetic changes in standard in vitro tests using animal cells (mouse lymphoma forward mutation assay and in vitro sister chromatid exchange assay) or bacterial cells (Ames Salmonella assay). A clastogenic activity was observed in a chromosomal aberrations assay in cultured Human lymphocytes in the conditions of a prolonged and cytotoxic treatment.

 

Gene mutation

In two reverse mutation assays, Salmonella typhimurium strains TA98, TA100, TA1535, TA1537, and/or TA1538 were exposed to at least five concentrations of tert-dodecanethiol in the presence and absence of a metabolic activation system using concentrations up to 10 mg/plate according to OECD TG 471. No increase in reversion rates occurred over the dose range tested, with or without S9 mix, in any of the four (Zeiger et al., 1992; NTP, 1988, 1990) or five (Pence, 1983) test strains.

In an in vitro Mammalian Cell Gene Mutation (mouse lymphoma) assay, L5178Y TK (+/-) mouse lymphoma cells were exposed to eight graded doses of tert-dodecanethiol (6.1-100 µg/mL) with and without metabolic activation according to OECD TG 476. A 2-fold increase in the induction of forward mutations at the T/K locus in L5178Y mouse lymphoma cells occurred only at the 13.5 µg/mL level with activation. The test is considered positive if the dose-related response at 2 or more test concentrations is at least 2- or 3-fold higher than the mutation frequency of solvent control. Therefore, tert-dodecanethiol was considered to be negative in this test system (Pence, 1983).

 

Chromosomal aberration

In a chromosomal aberration assay, human lymphocytes were exposed to tert-dodecanethiol concentrations up to 94 µg/mL, with and without metabolic activation. The study was conducted according to OECD TG 473. No effects were observed at the 20-hour sampling time. At 44 hours in the absence of S9, the number of cells with aberrations was significantly higher than in concurrent negative controls at all dose levels analyzed. The numbers of cells with aberrations observed exceeded the historical control range, but this effect was only seen in both replicates at the highest concentration tested (30.03 µg/mL) at which severe mitotic inhibition was apparent. It was concluded that tert-dodecanethiol induced chromosomal aberrations in cultured human peripheral blood lymphocytes; however, this effect was restricted to prolonged, cytotoxic treatment in the absence of S9, and is therefore, considered to be equivocal (Marshall, 1997).

 

DNA damage

In an in vitro Sister Chromatid Exchange (CHO cells) assay, CHO cells were exposed to five graded doses (0.5-75 µg/mL) of tert-dodecanethiol with and without metabolic activation according to OECD TG 479. There were no dose-dependent increases in the number of SCEs/chromosome. Therefore, tert-dodecanethiol was considered to be negative in this test system (Pence, 1984).

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP Guideline study
Qualifier:
according to
Guideline:
OECD Guideline 473 (In Vitro Mammalian Chromosome Aberration Test)
Deviations:
no
GLP compliance:
yes
Type of assay:
in vitro mammalian chromosome aberration test
Species / strain / cell type:
other: Human lymphocytes
Metabolic activation:
with and without
Metabolic activation system:
rat liver post-mitochondrial fraction (S-9) from Aroclor 1254 induced animals
Test concentrations with justification for top dose:
16.89, 22.53, 30.03 µg/ml (20-h treatment, -S9)
53.39, 71.19, 94.92 µg/ml (3-h treatment, -S9)
16.89, 22.53, 30.03 (44-h treatment, -S9)
94.92 µg/ml (3-h treatment, +S9)
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: 4-Nitroquinoline 1-oxide (-S9) and cyclophosphamide (+S9)
Details on test system and experimental conditions:
t-Dodecyl mercaptan was tested in an in vitro cytogenetics assay using duplicate human lymphocyte cultures from a male human donor. Treatments covering a broad range of doses, separated by narrow intervals, were performed both in the absence and presence of metabolic activation by a rat liver post-mitochondrial fraction (S-9) from Aroclor 1254 induced animals. The highest dose level used, 300 µg/mL was just in excess of the limit of solubility in culture medium.

Treatment in the absence of S-9 was continuous for 20 or 44 hours (20+0, 44+0). Treatment in the presence of S-9 was for 3 hours only followed by a 17 or 41 hour recovery period (3+17, 3+41). The test article dose levels for chromosome analysis were selected by evaluating the effect of t-dodecyl mercaptan on mitotic index. Following 20+0 hour treatments, -S-9 and 3+17 hour treatments, +S-9, chromosome aberrations were analysed at three consecutive dose levels. The highest concentrations chosen for analysis, 30.03 µg/mL and 94.92 µg/mL, induced approximately 48% and 70% mitotic inhibition (reduction in mitotic index) in the absence and presence of S-9 respectively.

The effects of these single concentrations only, (30.03 µg/mL, without and 94.92 µg/mL with S-9) were initially investigated at the delayed (44+0, 3+41) sampling time. Slides from cultures treated with 16.89 and 22.53 µg/mL in the absence of S-9 were subsequently examined to further investigate chromosome damage induced under these conditions.

Appropriate negative (solvent) control cultures and untreated cultures were included in the test system under each treatment condition.

SPINDLE INHIBITOR (cytogenetic assays): colchicine

STAIN (for cytogenetic assays): Giemsa

NUMBER OF REPLICATIONS: 2

NUMBER OF CELLS EVALUATED: Where possible, 100 metaphases from each code were analysed for chromosome aberrations.

DETERMINATION OF CYTOTOXICITY
Slides were examined, uncoded, for mitotic index (MI) or percentage of cells in mitosis. Slides from enough dose levels from each treatment regime were scored to determine if chemically induced mitotic inhibition had occurred. This is defined as a clear decrease in mitotic index compared with negative controls (based on at least 1000 cells counted), preferably dose-related.

OTHER EXAMINATIONS:
- Determination of polyploidy/ endoreplication: Only cells with 44-46 chromosomes were considered acceptable for analysis of structural aberrations. Any cell with more than 46 chromosomes, that is polyploid, endoreduplicated and hyperdiploid cells, observed during this search was noted and recorded separately.
Evaluation criteria:
The test article was to be considered as positive in this assay if:
1) a statistically significant increase in the proportion of cells with structural aberrations (excluding gaps) occurred at one or more concentrations, and
2) the proportion of cells with structural aberrations at such doses exceeded the normal range.
A positive result only at the delayed harvest was to be taken as evidence of clastogenicity provided criteria 1 and 2 were met. Increases in numbers of cells with gaps or increases in the proportions of cells with structural aberrations, not exceeding the normal range or occurring only at very high or very toxic concentrations, were likely to be concluded as "equivocal". Full assessment of the biological importance of such increases is likely only to be possible with reference to data from other test systems. Cells with exchange aberrations or cells with greater than one structural aberration were to be considered of particular biological significance.
Statistics:
Fisher's exact test. Probability values of p <0.05 were accepted as significant
Species / strain:
lymphocytes: human
Metabolic activation:
with and without
Genotoxicity:
ambiguous
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
30.03 µg/mL and 94.92 µg/mL, induced approximately 48% and 70% mitotic inhibition (reduction in mitotic index) in the absence and presence of S-9 respectively
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
Treatment of cultures with t-dodecyl mercaptan in the absence and presence of S-9 resulted, at the 20 hour sampling time, in frequencies of cells with aberrations which were similar to those seen in concurrent negative controls. Frequencies of cells with aberrations (excluding gaps) fell just outside historical negative control ranges in one culture at the highest dose level analysed after treatment both with and without S-9, but insofar as the effect was small and not seen in both replicates it was considered unlikely to be biologically significant. Treatment of cultures with t-dodecyl mercaptan for 44 hours in the absence of S-9 resulted in numbers of cells with aberrations which were significantly higher than in concurrent negative controls at all dose levels analysed. The numbers of cells with aberrations (excluding gaps) observed exceeded the historical negative control range, but this effect was only seen in both replicates at the highest concentration tested (30.03 µg/mL) at which severe mitotic inhibition was apparent. At both 16.89 and 22.53 µg/mL numbers of aberrant cells exceeded the normal range in only one of the two replicate cultures analysed. No increase in aberrant cells was seen at the delayed sampling time after treatment in the presence of S-9.

t-Dodecyl Mercaptan: cells with structural aberrations

TABLE 1

20 hour treatment -S-9, 0 hour recovery (20+0) Donor sex: male

Treatment

Replicate

Cells

Cells with

Cells with         Significance

Mitotic

(µg/mL)

scored

aberrations

including

gaps

aberrations              §

encluding gaps

index

(mean)

Solvent

A

100

4

2

4.7

B

100

4

4

4.1

Totals

200

8

6

(4.4)

16.89

A

100

6

3

3.9

B

100

7

3

4.3

Totals

200

13

6                      NS

(4.1)

22.53

A

100

7

3

3.4

B

100

6

3

4.3

Totals

200

13

6                      NS

(3.9)

30.03

A

100

3

1

2.1

B

100

10

6

2.5

Totals

200

13

7                      NS

(2.3)

NQO, 2.5

A

25

S

S

B

25

$

$

Totals

50

16

16               p 0.001

TABLE 2

3 hour treatment +S-9, 17 hour recovery (3+17) Donor sex: male

Treatment

Replicate

Cells

Cells with

Cells with         Significance

Mitotic

(µg/mL)

scored

aberrations

including

gaps

aberrations               §

excluding gaps

index

(mean)

Solvent

A

100

1

1

5.5

B

100

2

1

5.0

Totals

200

3

2

(5.3)

53.39

A

100

5

3

3.2

B

100

3

0

5.2

Totals

200

8

3                      NS

(4.2)

71.19

A

100

$

4

4.3

B

100

3

2

2.9

Totals

200

11

6                      NS

(3.6)

94.92

A

100

0

0.7

B

100

6

4

2.5

Totals

200

16

11                  p <0.01

(1.6)

CPA, 12.5

A

25

19

i

B

25

13

_

Totals

50

32

25                 p <0.001

TABLE 3

44 hour treatment -S-9, 0 hour recovery (44+0) Donor sex: male

Treatment

Replicate

Cells

Cells with

Cells with        Significance

Mitotic

(µg/mL)

scored

aberrations

including

gaps

aberrations               §

encluding gaps

index

(mean)

Solvent

A

100

1

0

2.8

B

100

3

2

4.3

Totals

200

4

2

(3.6)

16.89

A

100

9

2

3.3

B

100

11

3.2

Totals

200

20

8                  p <0.05

(3.3)

22.53

A

100

5

3

2.8

B

100

9

7

2.8

Totals

200

14

10                 p < 0.05

(2.8)

30.03

A

56

9

7

0.6

B

100

24

14

0.7

_

Totals

156              _

33

21                 p <0.001

(0.7)

TABLE 4

3 hour treatment +S-9, 41 hour recovery (3+41) Donor sex: male

Treatment

Replicate

Cells

Cells with

Cells with        Significance

Mitotic

(µg/mL)

scored

aberrations

including

gaps

aberrations              §

excluding gaps

index

(mean)

Solvent

A

100

2

1

4.3

B

100

2

2

3.6

Totals

200

4

3

(4.0)

94.92

A

100

5

4

3.3

B

100

4

2

1.8

Totals

200

9

6                      NS

(2.6)

§ Statistical significance (Appendix 5b) NS = not significant

Conclusions:
Interpretation of results (migrated information):
ambiguous without metabolic activation at cytotoxic concentrations
negative with metabolic activation

It is concluded that t-dodecyl mercaptan induced chromosome aberrations in cultured human peripheral blood lymphocytes. The effect, however, was restricted to prolonged, cytotoxic treatment in the absence of S-9.
Executive summary:

In a chromosomal aberration assay performed according to OECD guideline #473, human lymphocytes were exposed to t-dodecyl concentrations up to 94 µg/ml, with and without metabolic activation. No effects were observed at the 20-hour sampling time. At 44 hours in the absence of S9, the number of cells with aberrations was significantly higher than in concurrent negative controls at all dose levels analyzed. The numbers of cells with aberrations observed exceeded the historical control range, but this effect was only seen in both replicates at the highest concentration tested (30.03 µg/mL) at which severe mitotic inhibition was apparent. It was concluded that t-dodecyl mercaptan induced chromosomal aberrations in cultured human peripheral blood lymphocytes; however, this effect was restricted to prolonged, cytotoxic treatment in the absence of S9, and is therefore, considered to be ambiguous.  

Endpoint:
in vitro gene mutation study in mammalian cells
Remarks:
Type of genotoxicity: gene mutation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)
Deviations:
yes
Remarks:
Study not duplicated
GLP compliance:
not specified
Type of assay:
mammalian cell gene mutation assay
Target gene:
Thymidine kinase locus
Species / strain / cell type:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Metabolic activation system:
Aroclor-induced rat liver microsomal fraction
Test concentrations with justification for top dose:
100, 67, 44.9, 30.1, 20.2, 13.5, 9.0, 6.1 µg/ml
Vehicle / solvent:
DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: EMS (-S9) and 3-MCA (+S9)
Details on test system and experimental conditions:
The assay was performed with the TK+/- phenotype of L5178Y mouse lymphoma cells from sub-line 3.7.2C using a minimum of eight test compound doses with and without metabolic activation by an Aroclor-induced rat liver microsomal fraction. Appropriate negative, solvent, and positive controls were included with each assay. 
The test compound dose levels were determined by a preliminary multidose-ranging study with the highest dose tested being selected to give approximately 50-90% inhibition of suspension cell growth depending on the solubility of the compound. Tertiary dodecyl mercaptan solubilized at approximately 100 µg/ml in dimethylsulfoxide. The maximum dose selected for the mutagenicity test was 100 µg/ml because it exhibited growth inhibition. 
Each test concentration was prepared to contain the test dose in 0.1 ml volumes. Six million precleansed TK+/- cells in 6 ml of F10 P were added to centrifuge tubes. An additional 4 of the S-9 mix were added to half of the tubes. Immediately thereafter, 0.1 ml of the 100x and 0.1 ml of the solvent were added to the appropriate tubes. Each tube was mixed, gassed with a mixture of carbon dioxide and air, and incubated at 37; 0.50 C on a revolving roller drum for 4 hours. Following this incubation the tubes were centrifuged and the treatment solutions decanted. The cells were washed twice with F10 P and resuspended in 20 ml F10 P after the second wash. The tube cultures were readjusted to 3.0 x 100,000 cells/ml as necessary. At the end of the expression period, a sample of each of the cultures was centrifuged and the cells resuspended at 500,000 viable cells/ml in F10 P. The concentrated cells were serially diluted and appropriate dilutions were plated in triplicate in cloning medium with and without TFT. Approximately 500,000 cells were plated on each of 3 selective medium plates containing 2 mg/ml TFT, and 100 cells were cloned on each of 3 non-selective plates for each test concentration and a control tube. The plates  were incubated for 12+/-2 days. The mutant colonies (TK-/-) were counted on the selective TFT containing plates and the survivors (TK+/- and TK-/-) were counted on the non-selective medium plates.
Evaluation criteria:
A chemical will be considered positive if a dose-related response is obtained in which the mutation frequencies at two or more test concentrations (in the absence of severe toxicity) are at least two to three-fold higher than the mutation frequency of the solvent control.
Statistics:
None
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
Acceptable growth inhibition observed at 100 µg/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
Cells were exposed to eight graded doses of the test material in the presence of and in the absence of metabolic activation. A two-fold increase in the induction of forward mutations at the T/K locus in L5178Y mouse lymphoma cells occurred only at the 13.5 µg/ml level with activation. Test considered positive if dose-related response at two or more test concentrations is at least two or three-fold higher than mutation frequency of solvent control. Therefore, tertiary dodecyl mercaptan is not considered to be mutagenic in this test system.

See the table of results in the attached document

Conclusions:
Interpretation of results (migrated information):
negative

t-dodecyl mercaptan was considered to be negative in this test system
Executive summary:

In an in vitro Mammalian Cell Gene Mutation (mouse lymphoma) assay, L5178Y TK (+/-) mouse lymphoma cells were exposed to eight graded doses of t-dodecyl mercaptan (6.1-100 µg/ml) with and without metabolic activation according to OECD Test Guideline 476. A 2-fold increase in the induction of forward mutations at the T/K locus in L5178Y mouse lymphoma cells occurred only at the 13.5 µg/mL level with activation. The test is considered positive if the dose-related response at 2 or more test concentrations is at least 2- or 3-fold higher than the mutation frequency of solvent control.  Therefore, t-dodecyl mercaptan was considered to be negative in this test system.  

Endpoint:
in vitro gene mutation study in bacteria
Remarks:
Type of genotoxicity: gene mutation
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study that meets generally accepted scientific standards, acceptable for assessment
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
yes
Remarks:
No duplication of the study
GLP compliance:
not specified
Type of assay:
bacterial reverse mutation assay
Target gene:
Histidine operon
Species / strain / cell type:
other: Strains TA 1535, TA 1537, TA 1538, TA 98, TA 100
Metabolic activation:
with and without
Metabolic activation system:
S-9 hepatic microsomes from Aroclor (1254)-induced adult male Sprague-Dawley rats.
Test concentrations with justification for top dose:
10,000, 3,333, 1,111, 370, 123.5 µg/plate. Highest dose of test substance used represented limit of solubility.
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: DMSO
- Justification for choice of solvent/vehicle: solubility of t-DM, 100 mg/ml
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: - S9: MNNG (TA 1535, TA 100), 9-AA (TA 1537), 2-NF (TA 1538, TA 98). + S9: 2-AA (all strains)
Details on test system and experimental conditions:
Exposure of auxotrophic bacteria was done dIrectly by the plate Incorporation assay. For the induction of reverse mutations, the chemicals was tested against the five bacterial strains with and without the metabolic activation systems. Each concentration of the compound and controls will be plated in triplicate.
Data derived from the toxicity studies wasutilized to establish test levels of the test compound. A minimum of five concentrations of the test compound was prepared to contain the test dose in 0.1 ml volumes for evaluation with and without metabolic activation. The highest dose tested was that level of the chemical exhibiting inhibition of the bacterial growth in toxicity studies, unless this is not possible due to limited solubility of the investigated agent.
To each of 2 ml of complete top agar, 0.1 ml of an overnight broth culture of each tester strain, 0.1 ml of the test compound or diluent, and 0.5 ml of the S-9 mix for the activated tests were added. The contents of the tube were mixed thoroughly and poured onto VBE minimal agar plates. Plates were gently rotated and tilted to assure untform distribution of the top agar, allaôwed to harder on an even surface for one hour, inverted and put in a dark 37 +/- 0.5°C incubator. After two days, the colonies in both test plates and controls will be counted using an electronic colony counter and the density of the background growth will be noted.
Evaluation criteria:
For a test to be considered valid, the following conditions are required:
1. Demonstration of toxicity of the chemical for the S. typhimurium strain(s), unless this is not possible due to limited solubility of the test compound.
2. The negative control responses are within the normal range of the laboratory data base.
3. Confirmation of sensitivity and responsiveness of the tester strains to mutagenic action as indicated by their responses to the positive controls.

If the above criteria are met, a chemical is considered to be mutagenic if it induces a positive response in a dose-related manner over three concentrations with the baseline increase in the number of histidine revertants equal to twice the solvent control level.
Species / strain:
other: Strains TA 1535, TA 1537, TA 1538, TA 98, TA 100
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
no cytotoxicity nor precipitates, but tested up to recommended limit concentrations
Remarks:
> 10,000 µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid

See tables of results in the attached document.

Conclusions:
Interpretation of results (migrated information):
negative

Exposure to five graded doses of the test material in the presence of and in the absence of metabolic activation did not increase the reversion to histidine prototrophy of S. typhimurium strains TA1535, TA1537, TA1538, TA98 or TA100. Therefore, tertiary dodecyl mercaptan is not considered to be mutagenic in this test system.
Executive summary:

Five Salmonella typhimurium tester strains, TA1535, TA1537, TA1538, TA98 and TA100, were utilized as the experimental organisms. Each strain was exposed to a minimum of five test compound doses both with and without metabolic activation by an Aroclor-induced rat liver microsomal fraction. The test compound dose levels were determined by a preliminary multidose-ranging study with optimal concentration allowing survival of about 50% of the cells. Tertiary dodecyl mercaptan solubilized at approximately 100 mg/ml in dimethyl sulfoxide. The maximum dose selected for the mutagenicity test was approximately 10,000 µg/plate because it represents the limits of solubility of the test material. The mutagenicity assay was done directly by the plate incorporation method. Each of 2 ml of complete top agar, 0.1 ml of an overnight broth culture of each tester strain, 0.1 ml of the test compound or diluent and 0.5 ml of the S-9 mix, for the activated tests only, were combined, mixed thoroughly, and poured onto VBE minimal agar plates. Each concentration of the compound and the positive and negative controls were plated in triplicate. Plates were gently rotated and tilted to assure uniform distribution of the top agar, allowed to harden to an even surface for 1 hour, inverted and put in a dark 37 +/- 0.50°C incubator. After 2 days, the colonies on both test and control plates were counted using an electronic colony counter and the density of the background growth was noted. Exposure to five graded doses of the test material in the presence of and in the absence of metabolic activation did not increase the reversion to histidine prototrophy of S. typhimurium strains TA1535, TA1537, TA1538, TA98 or TA100. Therefore, tertiary dodecyl mercaptan is not considered to be mutagenic in this test system.

Endpoint:
in vitro DNA damage and/or repair study
Remarks:
Type of genotoxicity: DNA damage and/or repair
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comparable to guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 479 (Genetic Toxicology: In Vitro Sister Chromatid Exchange Assay in Mammalian Cells)
GLP compliance:
not specified
Type of assay:
sister chromatid exchange assay in mammalian cells
Species / strain / cell type:
other: Chinese Hamster Ovary Cells, K-1, Number CCL61
Metabolic activation:
with and without
Metabolic activation system:
S-9 hepatic microsomes from Aroclor (1254)-induced adult male Sprague-Dawley rats
Test concentrations with justification for top dose:
75, 25, 7.5, 2.5, 0.5 µg/ml.
Vehicle / solvent:
DMSO
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: EMS (-S9) and Cyclophosphamide (+S9)
Details on test system and experimental conditions:
This assay was performed using Chinese Hamster Ovary Cells and a minimum of five test compound doses with and without metabolic activation by an Aroclor-induced rat liver microsomal fraction. Appropriate negative, solvent and positive controls were included with each assay. The test compound dose levels were determined by a preliminary multidose-range finding study with the highest concentration of the chemical tested depending upon its solubility. Tertiary dodecyl mercaptan achieved an apparent homogeneous suspension at approximately 200 mg/ml in dimethyl sulfoxide. The maximum dose selected for the mutagenicity test was approximately 75 ug/ml because it exhibited growth inhibition.  Cells were treated in an exponential stage of growth by setting up cultures with 2 to 5 x 100,000 cells per 25 cm² flask, 24 hours prior to treatment. Cells were exposed to the chemical for 2 hours, washed twice and then 5-bromodeoxyuridine (Brd U) was added to each culture. All cultures were sampled a minimum of 24 hours after addition of Brd U to ensure completion of two full cell cycles. Duplicate cultures were set up for each dose level and all controls.  Twenty-four hours after the above initiation of the cultures, the cells were treated with the test chemical in the presence of an S-9 rat liver activation system for 2 hours and washed twice in a balanced salt solution. The cells were then sampled and treated as described above. Two hours after, colcemid (0.2 mg/ml) was added to each tube and metaphases were collected by mitotic shake-off. The cells  were swollen in a 0.075M KCL hypotonic, and washed three times in an acetic alcohol fixative. Slides were prepared and stained. Fifty cells in the metaphase stage of mitosis were scored at each dose level for the number of sister chromatid exchanges (SCE).
Evaluation criteria:
Test considered positive if there is a statistically significant increase in SCE's per chromosome and a two-fold  increase in SCE's per chromosome compared with solvent  control
Statistics:
(1) comparison of mean SCE°s per cell among dose levels
(2) comparison of mean SCE°s per chromosome dose levels
Species / strain:
other: Chinese Hamster Ovary Cells, K-1, Number CCL61
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
75 µg/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
valid
Positive controls validity:
valid
Additional information on results:
A statistically significant increase in the number of SCE's per chromosome occurred at 7.5 ug/ml in the presence of metabolic activation.  However, the increase did not meet the additional criterion of a minimum two-fold increase in SCE's per chromosome required for a positive finding of mutagenicity. 
Conclusions:
Interpretation of results (migrated information):
negative
Executive summary:

In an in vitro Sister Chromatid Exchange (CHO cells) assay, CHO cells were exposed to five graded doses (0.5-75 µg/ml) of t-dodecyl mercaptan with and without metabolic activation according to OECD Test Guideline 479. There were no dose-dependent increases in the number of SCEs/chromosome. Therefore, t-dodecyl mercaptan was considered to be negative in this test system.

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: Guideline study
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 471 (Bacterial Reverse Mutation Assay)
Deviations:
no
GLP compliance:
not specified
Type of assay:
bacterial reverse mutation assay
Target gene:
Histidine operon
Species / strain / cell type:
other: TA97, TA98, TA100, TA1535
Metabolic activation:
with and without
Metabolic activation system:
S9 fractions of Aroclor 1254-induced male Sprague Dawley rats and male Syrian hamster livers
Test concentrations with justification for top dose:
0, 100, 333, 1000, 3333 and 10000 µg/plate (TA98, TA 100 & TA1535)
0, 0.1, 0.3, 1.0, 3.., 10.0, 33.0, 100.0, 333.0, 1000, 3333 and 10000 µg/plate (TA97)
Vehicle / solvent:
- Vehicle(s)/solvent(s) used: ethanol and DMSO
Untreated negative controls:
no
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
other: - Without S9: Sodium azide (TA 1535 and TA100), 9-aminoacridine or ICR-191 (TA 97 and TA1537), 4-nitro-o-phenylenediamine (TA98) - With S9: 2-aminoanthracene (all strains)
Details on test system and experimental conditions:
In the Salmonella assay, a test tube containing a suspension of one strain of Salmonella typhimurium plus S9 mix or plain buffer without S9, is incubated for 20 minutes at 37º C with the test chemical. Control cultures, with all the same ingredients except the test chemical, are also incubated. In addition, positive control cultures are also prepared; these contain the particular bacterial tester strain under investigation, the various culture ingredients, and a known potent mutagen. After 20 minutes, agar is added to the cultures and the contents of the tubes are thoroughly mixed and poured onto the surface of Petri dishes containing standard bacterial culture medium. The plates are incubated for 48 hours and then counted.

Initial testing was without metabolic activation, with 10% rat liver S-9, or with 10% hamster liver S-9. After a negative result was obtained, DMSO was retested without S-9 and with 30% S-9 from rat and hamster.

The positive control plates are counted, and the number of mutant colonies appearing on them must be significantly increased over the spontaneous control number for the test to be considered valid.
Evaluation criteria:
If no increase in mutant colonies is seen after testing several strains under several different culture conditions, the test chemical is considered to be non-mutagenic in the Salmonella test.
Species / strain:
other: TA97, TA98, TA100, TA1535
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
other: >= 3333 µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Additional information on results:
The positive control chemicals induced a significant increase of the revertant frequency in all tester strains, either with or without metabolic activation.
tert-Dodecyl mercaptan was negative, in the presence and absence of metabolic activation, in all tester strains.
Conclusions:
Interpretation of results (migrated information):
negative

Under these experimental conditions, tert-dodecanethiol is considered as non genotoxic.
Executive summary:

The potential of tert-dodecanethiol (TDM) to induce reverse mutation in Salmonella typhimurium (strains: TA97, TA98, TA100, TA1535) was evaluated according to a protocol comparable to the OECD guidelines 471. TDM was tested in two consecutive experiments, with and without a metabolic activation system, according to the preincubation method (20 min at 37°).

Concentrations of TDM (100, 333, 1000, 3333, and 10,000 µg), overnight culture of S. typhimurium (0.05-0.10 ml) and S-9 mix or buffer were incubated without shaking for 20 minutes. The top agar was added and the contents of the tubes were mixed and poured onto the surfaces of Petri dishes. His+ (histidine dependent) colonies arising on plates were machine-counted after two days incubation at 37°C.

Initial testing was without metabolic activation, with 10% rat liver S-9, or with 10% hamster liver S-9. After a negative result was obtained, TDM was retested without S-9 and with 30% S-9 from rat and hamster.

The positive control chemicals induced a significant increase of the revertant frequency in all tester strains, either with or without metabolic activation. TDM was negative, in the presence and absence of metabolic activation, in all tester strains.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Genetic toxicity in vivo

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Justification for classification or non-classification

No Classification for germ cell mutagenicity according to the available data and CLP/GHS criteria.