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Toxicological information

Carcinogenicity

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Description of key information

No data is available on the carcinogenic potential of mercaptoacetic acid and its salts by the oral and inhalation routes. In a non-standard study by dermal route, sodium mercaptoacetate was administered to mice as 0, 1.0 and 2.0% solutions, until all animals died. Differences in the life span and the incidence of neoplasms between experimental and negative control mice were not statistically significant.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records
Reference
Endpoint:
carcinogenicity: dermal
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted scientific principles, acceptable for assessment
Reference:
Composition 0
Qualifier:
no guideline followed
GLP compliance:
no
Test material information:
Composition 1
Species:
mouse
Strain:
Swiss
Sex:
female
Details on test animals and environmental conditions:
-Animals:
Source: the Eppley colony
Age: 7 weeks old
Housing: 10 per cage plastic cage
Diet: Wayne diet (Allied Mills, Chicago, IL) ad libitum
Water: ad libitum
Route of administration:
dermal
Vehicle:
acetone
Details on exposure:
The chemicals were applied in a volume of 0.02 ml twice weekly to a 1-cm  diameter regularly-shaved area of intrascapular skin of the mice.
Analytical verification of doses or concentrations:
no
Duration of treatment / exposure:
life-time
Frequency of treatment:
twice weekly
Remarks:
Doses / Concentrations:
1 and 2% in acetone solution
Basis:

No. of animals per sex per dose:
50 per treated group, n=100 for control group, n=40 for positive  control group
Control animals:
yes, concurrent vehicle
Details on study design:
Post-exposure period: none
Positive control:
7,12-Dimethylbenz[a]anthracene
Supplier: Aldrich Chemical Co.
Purity: no data
Observations and examinations performed and frequency:
Animals were checked weekly and all lesions and tumours were recorded.
Sacrifice and pathology:
Complete autopsy was performed on all animals and skin samples, grossly  observed tumours and lesions of lungs, kidneys and other tissues were  studies histologically. Formalin-fixed paraffin embedded specimens were  cut and stained with haematoxylin and eosin, and with other stains as  appropriate. 
Statistics:
The statistical significance of the results was evaluated using the  method of Armitage (1971).
Clinical signs:
no effects observed
Mortality:
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Water consumption and compound intake (if drinking water study):
not examined
Histopathological findings: neoplastic:
no effects observed
Details on results:
The average lifespan of the animals were not affected by the  treatment.None of the experimental or control mice survived beyond week  120 of treatment. Infectious diseases, such as pneumonia and hepatitis,  occurred in a small number of animals, resulting in an increased number  of deaths.  

The behaviour of mice in test groups was normal and there were no marked  differences between groups with respect to the body weight changes and  food intake. No local changes occurred in treated mice and no treatment related  epidermal hyperplasia, ulceration or dermatitis was observed.

No significant difference was seen in the incidence or tissue location of  neoplasms or in the numbers of mice with neoplasms, following the  application of 0.02 ml of 1% and 2% solutions of sodium thioglycolate in  acetone to the shaved backs of 49 and 45 female Swiss mice, twice weekly  for up to 120 weeks. No epidermal tumours were  reported. One each of the following tumours was found in the treated mice  but not in controls; subcutaneous haemangioma, mammary adenoma, liver  leiomyosarcoma, uterine leiomyosarcoma. Of 49 and 45 mice treated with 1  and 2% solutions respectively, 19 (39%) and 22 (49%) had tumours,  compared to 39 (42%) of 93 mice, which were apparently untreated. The  total number of tumours in each case was 22 and 24 compared to 46 in the  untreated controls.
Relevance of carcinogenic effects / potential:
In a non-standard study by dermal route, sodium thioglycolate was administered to mice as a 0%, 1.0% and 2.0% solution, until all animals died. Differences in the life span and the incidence of neoplasms between experimental and negative control mice were statistically not significant.
Dose descriptor:
conc. level: 1.0 and 2.0 %
Sex:
female
Basis for effect level:
other: Differences in the life span and the incidence of neoplasms between experimental and negative control mice were not statistically significant.
Remarks on result:
other: Effect type: carcinogenicity (migrated information)

Frequencies of neoplams in mice

Conc. applied (%)

Total # of rats

# of rats with tumours (%)

Total # of tumours

Lym-phoma

Lung adenoma

Liver haeman-gioma

Ovarian

Sub-cutaneous fibroma

Others

Negative control

-

93

39 (42)

46

25

16

1

3

1

-

Sodium thioglycolate

1.0

49

19 (39)

22

14

3

1

0

1

Sc. haemangioma (1)
Mammary adenoma (1)

2.0

45

22 (49)

24

13

7

2

0

0

Liver and uterine leiomyosarcomas (1)

DMBA (+ control)

0.1

40

38 (95)

67

5

0

0

0

0

Keratoacenthomas (14)

Squamuous-cell carcinomas (10)

Conclusions:
Under the experimental conditions, NaTG was shown to be not carciongenic.
Executive summary:

The carcinogenicity of sodium thioglycolate (NaTG) was evaluated using 94 Swiss female mice (7 weeks old) from the Eppley colony. 0.02 ml of a 1.0 and 2.0 % solutions of sodium thioglycolate in acetone (equivalent to dose levels of 6.6 and 13.3 mg/kg bw) were applied twice per week to the shaved skin (interscapular region) of each of the 49 or 45 mice, respectively. Ninety-three mice served as negative controls. Positive control groups, 40 mice, were treated with 7,12-dimethylbenz-[a]-anthracene. None of the experimental or control mice survived beyond week 120 of treatment. Infectious diseases, such as pneumonia and hepatitis, occurred in a small number of animals, resulting in an increased number of deaths. Large numbers of neoplasms were observed in treated and negative control mice: lymphomas, pulmonary adenomas, hepatic hemangiomas, ovarian neoplasms, and dermal fibromas. Epidermal neoplasms were not observed. Differences in the incidence of neoplasms between experimental and negative control mice were not statistically significant. No significant decrease in the life span of mice in experimental groups was observed.

It can be concluded, that NaTG was not carcinogenic under this experimental condition.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Carcinogenicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Carcinogenicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

No carcinogenicity data is available on mercaptoacetic acid and its salts by the inhalation or oral routes. The information on the carcinogenicity potential of mercaptoacetic acid and its salts is limited to a study in mice by chronic cutaneous application of sodium mercaptoacetate.

The carcinogenicity of sodium mercaptoacetate was evaluated using 94 Swiss female mice (7 weeks old) from the Eppley colony. 0.02 ml of a 1.0 and 2.0 % solutions of sodium mercaptoacetate in acetone (equivalent to dose levels of 6.6 and 13.3 mg/kg bw) were applied twice per week to the shaved skin (interscapular region) of each of the 49 or 45 mice, respectively. Ninety-three mice served as negative controls. Positive control groups, 40 mice, were treated with 7,12-dimethylbenz-[a]-anthracene. None of the experimental or control mice survived beyond week 120 of treatment. Infectious diseases, such as pneumonia and hepatitis, occurred in a small number of animals, resulting in an increased number of deaths. Large numbers of neoplasms were observed in treated and negative control mice: lymphomas, pulmonary adenomas, hepatic hemangiomas, ovarian neoplasms, and dermal fibromas. Epidermal neoplasms were not observed. Differences in the incidence of neoplasms between experimental and negative control mice were not statistically significant. No significant decrease in the life span of mice in experimental groups was observed. The authors concluded that sodium mercaptoacetate was not carcinogenic (Stenback et al., 1977).

Justification for classification or non-classification

According to REGULATION (EC) No 1272/2008 of 16 December 2008 and the available carcinogenicity data, no classification is warranted for mercaptoacetic acid and its salts. Conclusive but not sufficient for classification.