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Diss Factsheets

Administrative data

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

The weight of evidence suggests that CaTG is not genotoxic.

Link to relevant study records

Referenceopen allclose all

Endpoint:
in vitro gene mutation study in bacteria
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Justification for type of information:
The read-across is a category approach based on the hypothesis that compounds in this category are transformed to a common compound. This approach serves to use existing data on genotoxicity, repeated-dose toxicity, and reproductive toxicity endpoints for substances in this category.
There are no relevant variations in properties among source substances and the same potency is predicted for all target substances. This is Scenario 5 of the RAAF . Substances ATG, MEATG, KTG, CaTG, and NaTG are different inorganic salts of a common acid, thioglycolic acid (TGA; synonym: 2- mercaptoacetic acid). They dissociate rapidly in aqueous media, e.g., the test organism, to the common thioglycolate anion and to their different counter ions. The water solubility of all category members is high, except for CaTG which is only moderately soluble in water.
In the repeated-dose toxicity studies with NaTG, specific toxicity is exerted via the well-investigated inhibition of mitochondrial fatty acid beta-oxidation by the thioglycolate (2-mercaptoacetate) anion 2,3,4. Inhibition of beta-oxidation leads to increased triglycerides and decreased acetyl-CoA in liver, and subsequently reduced gluconeogenesis. The latter presents as hypoglycaemia in NaTGtreated rats, which is aggravated by fasting (Grosdidier, 2011; Report No. 37043 TSR). This mode of action (MoA) is thought to mediate the acute oral toxicity in fasted rats observed with all category members.
It can be predicted with high confidence that the target substances will display the same MoA and lead to the same effects seen with NaTG.

For more detailed information please refer to part 13.2.
Reason / purpose for cross-reference:
read-across: supporting information
Target gene:
Histidine reversion
Key result
Species / strain:
S. typhimurium TA 98
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
btw. 1000 - 5000µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 100
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
1000 - 5000µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 102
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
1000 - 5000µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1535
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
1000 - 5000µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Key result
Species / strain:
S. typhimurium TA 1537
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
cytotoxicity
Remarks:
1000 - 5000 µg/plate
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Conclusions:
In analogy to ATG and NaTG, CaTG is considered non-mutagenic in bacteria.
Endpoint:
in vitro gene mutation study in mammalian cells
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Justification for type of information:
The read-across is a category approach based on the hypothesis that compounds in this category are transformed to a common compound. This approach serves to use existing data on genotoxicity, repeated-dose toxicity, and reproductive toxicity endpoints for substances in this category.
There are no relevant variations in properties among source substances and the same potency is predicted for all target substances. This is Scenario 5 of the RAAF . Substances ATG, MEATG, KTG, CaTG, and NaTG are different inorganic salts of a common acid, thioglycolic acid (TGA; synonym: 2- mercaptoacetic acid). They dissociate rapidly in aqueous media, e.g., the test organism, to the common thioglycolate anion and to their different counter ions. The water solubility of all category members is high, except for CaTG which is only moderately soluble in water.
In the repeated-dose toxicity studies with NaTG, specific toxicity is exerted via the well-investigated inhibition of mitochondrial fatty acid beta-oxidation by the thioglycolate (2-mercaptoacetate) anion 2,3,4. Inhibition of beta-oxidation leads to increased triglycerides and decreased acetyl-CoA in liver, and subsequently reduced gluconeogenesis. The latter presents as hypoglycaemia in NaTGtreated rats, which is aggravated by fasting (Grosdidier, 2011; Report No. 37043 TSR). This mode of action (MoA) is thought to mediate the acute oral toxicity in fasted rats observed with all category members.
It can be predicted with high confidence that the target substances will display the same MoA and lead to the same effects seen with NaTG.

For more detailed information please refer to part 13.2.
Reason / purpose for cross-reference:
read-across: supporting information
Qualifier:
according to guideline
Guideline:
EU Method B.17 (Mutagenicity - In Vitro Mammalian Cell Gene Mutation Test)
Version / remarks:
Cited as Directive 2000/32/EC, B.17
Species / strain / cell type:
mouse lymphoma L5178Y cells
Details on mammalian cell type (if applicable):
- Type and identity of media: the medium used was RPMI 1640 (complete medium) with 3 or 15 % horse serum.
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes
- Periodically "cleansed" against high spontaneous background: yes
Additional strain / cell type characteristics:
not specified
Untreated negative controls:
yes
Negative solvent / vehicle controls:
yes
True negative controls:
no
Positive controls:
yes
Positive control substance:
cyclophosphamide
methylmethanesulfonate
Key result
Species / strain:
mouse lymphoma L5178Y cells
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
other: 4-h experiment (+/-S9): > 1600 µg/ml / 24-h experiment (-S9): >= 800 µg/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Remarks on result:
other: all strains/cell types tested
Remarks:
Migrated from field 'Test system'.
Conclusions:
By analogy to ATG, CaTG is considered non-mutagenic in mammalian cells.
Endpoint:
in vitro cytogenicity / chromosome aberration study in mammalian cells
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Justification for type of information:
The read-across is a category approach based on the hypothesis that compounds in this category are transformed to a common compound. This approach serves to use existing data on genotoxicity, repeated-dose toxicity, and reproductive toxicity endpoints for substances in this category.
There are no relevant variations in properties among source substances and the same potency is predicted for all target substances. This is Scenario 5 of the RAAF . Substances ATG, MEATG, KTG, CaTG, and NaTG are different inorganic salts of a common acid, thioglycolic acid (TGA; synonym: 2- mercaptoacetic acid). They dissociate rapidly in aqueous media, e.g., the test organism, to the common thioglycolate anion and to their different counter ions. The water solubility of all category members is high, except for CaTG which is only moderately soluble in water.
In the repeated-dose toxicity studies with NaTG, specific toxicity is exerted via the well-investigated inhibition of mitochondrial fatty acid beta-oxidation by the thioglycolate (2-mercaptoacetate) anion 2,3,4. Inhibition of beta-oxidation leads to increased triglycerides and decreased acetyl-CoA in liver, and subsequently reduced gluconeogenesis. The latter presents as hypoglycaemia in NaTGtreated rats, which is aggravated by fasting (Grosdidier, 2011; Report No. 37043 TSR). This mode of action (MoA) is thought to mediate the acute oral toxicity in fasted rats observed with all category members.
It can be predicted with high confidence that the target substances will display the same MoA and lead to the same effects seen with NaTG.

For more detailed information please refer to part 13.2.
Reason / purpose for cross-reference:
read-across: supporting information
Key result
Species / strain:
lymphocytes: human
Metabolic activation:
with and without
Genotoxicity:
negative
Cytotoxicity / choice of top concentrations:
other: With S9 : 1000 µg/ml. Without S9 : 300 µg/ml
Vehicle controls validity:
valid
Untreated negative controls validity:
not examined
Positive controls validity:
valid
Remarks on result:
other: strain/cell type: Human lymphocytes
Remarks:
Migrated from field 'Test system'.
Conclusions:
By analogy to TGA, CaTG is considered non-clastogenic in mammalian cells.

Genetic toxicity in vivo

Description of key information

The weight of evidence suggests that CaTG is not genotoxic.

Link to relevant study records
Reference
Endpoint:
in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
The read-across is a category approach based on the hypothesis that compounds in this category are transformed to a common compound. This approach serves to use existing data on genotoxicity, repeated-dose toxicity, and reproductive toxicity endpoints for substances in this category.
There are no relevant variations in properties among source substances and the same potency is predicted for all target substances. This is Scenario 5 of the RAAF . Substances ATG, MEATG, KTG, CaTG, and NaTG are different inorganic salts of a common acid, thioglycolic acid (TGA; synonym: 2- mercaptoacetic acid). They dissociate rapidly in aqueous media, e.g., the test organism, to the common thioglycolate anion and to their different counter ions. The water solubility of all category members is high, except for CaTG which is only moderately soluble in water.
In the repeated-dose toxicity studies with NaTG, specific toxicity is exerted via the well-investigated inhibition of mitochondrial fatty acid beta-oxidation by the thioglycolate (2-mercaptoacetate) anion 2,3,4. Inhibition of beta-oxidation leads to increased triglycerides and decreased acetyl-CoA in liver, and subsequently reduced gluconeogenesis. The latter presents as hypoglycaemia in NaTGtreated rats, which is aggravated by fasting (Grosdidier, 2011; Report No. 37043 TSR). This mode of action (MoA) is thought to mediate the acute oral toxicity in fasted rats observed with all category members.
It can be predicted with high confidence that the target substances will display the same MoA and lead to the same effects seen with NaTG.

For more detailed information please refer to part 13.2.
Reason / purpose for cross-reference:
read-across: supporting information
Key result
Sex:
male/female
Genotoxicity:
negative
Toxicity:
yes
Remarks:
clinical signs
Vehicle controls validity:
valid
Negative controls validity:
not examined
Positive controls validity:
valid
Conclusions:
By analogy to NaTG, CaTG is considered non-mutagenic in vivo.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (negative)

Additional information

Additional information from genetic toxicity in vivo:

Several in vitro and in vivo genotoxicity studies were performed with thioglycolic acid and its salts. The conducted genotoxicity studies on thioglycolic acid or its salts described in this chapter can be bridged to each other, because in aquous solutions only the organic thioglycolate anion may have the potential to cause genotoxic effects in vitro or in vivo. All genotoxicity studies conducted to date have either negative results or are of douptful significance. Therefore, the weight of evidence suggests that thioglycolic acid and its salts are non-genotoxic.

Justification for classification or non-classification

Conclusive, but not sufficient for classification.