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Diss Factsheets

Administrative data

Description of key information

Based on two OECD 406 studies with the structural analogue 2-mercaptoethanol, it can be concluded that sodium 2-mercaptoethanolate is a skin sensitiser.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records
Reference
Endpoint:
skin sensitisation: in vivo (non-LLNA)
Type of information:
experimental study
Adequacy of study:
other information
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 406 (Skin Sensitisation)
Deviations:
yes
Remarks:
historical data not presented in report
GLP compliance:
yes
Type of study:
guinea pig maximisation test
Justification for non-LLNA method:
Currently no LLNA study is available for assessment. The Guinea Pig Maximization Test (GPMT) has been carried out as an animal test to predict human sensitization for over a decade and is recommended by international test guidelines such as OECD.
Species:
guinea pig
Strain:
Dunkin-Hartley
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Viga, Sulzfeld, FRG.
- Age at study initiation: approximately 2 months
- Weight at study initiation: 358 to 456 g
- Housing: 2 animals per cage, metal cages with wire-mesh floors
- Diet: Standard guinea pig diet, including ascorbic acid (Hope Farms, Voerden (LC 23-B, pellet diameter 4 mm))
- Water: Tap water, ad libitum
- Acclimation period: 12 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-23
- Humidity (%): 55-75
- Photoperiod (hrs dark / hrs light): 12/12
Route:
intradermal
Vehicle:
physiological saline
Concentration / amount:
0.1 mL test substance (0.1% w/w in physiological saline)
Day(s)/duration:
Day 0
Route:
intradermal
Vehicle:
water
Concentration / amount:
0.1 mL FCA, emulsified with an equal volume of distilled water
Day(s)/duration:
Day 0
Route:
intradermal
Vehicle:
physiological saline
Concentration / amount:
0.1 mL test substance (0.2% w/w in physiological saline), emulsified with an equal volume of FCA.
Day(s)/duration:
Day 0
Route:
epicutaneous, occlusive
Vehicle:
water
Concentration / amount:
0.5 mL of 25% (w/w) test substance
Day(s)/duration:
Day 7 / 48 hours
No.:
#1
Route:
epicutaneous, occlusive
Vehicle:
water
Concentration / amount:
0.05 mL of 10%, 2.5%, 1.0% and 0% (w/w) test substance
Day(s)/duration:
Day 21 / 24 hours
No. of animals per dose:
- Control group: 10 animals
- Test group: 20 animals
Details on study design:
RANGE FINDING TESTS:
Primary irritation experiments included intracutaneous injections and epicutaneous applications of several concentrations of the test substance diluted in Milli-RO water {Millipore Corp., Bedford, Hass,. USA). Four animals received an epicutaneous application of the test substance at 100%, 50%, 25% and 5% (w/w) in an amount of 0.05 mL using Square chambers {v.d. Bend, Brielle, The Netberlands).

MAIN STUDY
Day 0 (intradermal injection)
The fur from an area approximately 4 cm x 6 cm between the shoulders was removed by clipping. Three pairs of intradermal injections were made in such a way that the three injections forwed a row on each side of the midline. The six injections were made within the boundaries of the 2 cm x 4 cm area, over which a patch was applied one week later, the injections consisted of:
A.0.1 mL of the test substance (0.1% w/w in physiological saline).
B.0.1 mL of FCA, emulsified with an equal volume of distilled water.
C.0.1 mL of the test substance (0.2% w/w in physiological saline), emulsified with an equal volume of FCA.

Day 7 (Topical application)
The same area in the shoulder region was clipped. A patch of Metalline (Lohmann, Neuwied FRG) (2 cm x 4 cm), moistened with approximately 0.5 mL of the 25% (w/w) test substance concentration was fixed onto a strip of Mierepore-tape (3M Co., St.Paul, USA) which was applied to the shoulder skin over the injection sites and secured by an elastic bandage (Coban, 3M Co., St.Paul, USA). The dressing was left in place for 48 hours.

Day 21 (Challenge procedure)
The challenge was carried out on day 21. The left flank was shaved. The test substance, diluted in Milli-RO water, was applied in an amount of 0.05 mL on Square chambers (v.d. Bend, Brielle, The Netherlands}, mounted on Micropore-tape. Each animal received 4 different concentrations of test substance; all animals were treated similarly. The concentrations tested were: 10%, 2.5%, 1.0% and 0% (w/w). The elastic bandage (Coban) was kept in place for 24 hours. Twenty-four and fourty-eight hours after removal of the dressings the readings were made. For proper evaluation of the skin reactions, the treated side was closely shaved on day 23 after the first reading.

Day 23 & 24
- Evaluation of response
Challenge controls:
Treatment of the control group with the test substance formulation
Positive control substance(s):
yes
Remarks:
Formaldehyde solution, historical data
Positive control results:
A sensitisation rate of 100%t was obtained to the 5%, 3% and 0.5% concentrations.
Reading:
1st reading
Hours after challenge:
24
Group:
negative control
Dose level:
10%, 2,5%, 1%, 0%
No. with + reactions:
0
Total no. in group:
10
Reading:
2nd reading
Hours after challenge:
48
Group:
negative control
Dose level:
10%, 2.5%, 1%, 0%
No. with + reactions:
0
Total no. in group:
10
Reading:
1st reading
Hours after challenge:
24
Group:
test chemical
Dose level:
10%
No. with + reactions:
16
Total no. in group:
20
Reading:
2nd reading
Hours after challenge:
48
Group:
test chemical
Dose level:
10%
No. with + reactions:
13
Total no. in group:
20
Reading:
1st reading
Hours after challenge:
24
Group:
test chemical
Dose level:
2.5%
No. with + reactions:
13
Total no. in group:
20
Reading:
2nd reading
Hours after challenge:
48
Group:
test chemical
Dose level:
2.5%
No. with + reactions:
12
Total no. in group:
20
Reading:
1st reading
Hours after challenge:
24
Group:
test chemical
Dose level:
1%
No. with + reactions:
12
Total no. in group:
20
Reading:
2nd reading
Hours after challenge:
48
Group:
test chemical
Dose level:
1%
No. with + reactions:
8
Total no. in group:
20
Reading:
1st reading
Hours after challenge:
24
Group:
test chemical
Dose level:
0%
No. with + reactions:
0
Total no. in group:
20
Reading:
2nd reading
Hours after challenge:
48
Group:
test chemical
Dose level:
0%
No. with + reactions:
0
Total no. in group:
20

Primary irritation experiments:

No signs of systemic toxicity were observed in these four treated animals. One animal, which received 4 x 0.1 mL intracutaneous injections of 5% (w/w) test substance and 0.5 mL undiluted test substance epicutaneously applied, died within 24 hours. One extra animal was treated in a similar manner to the first, but with the concentrations for intracutaneous injections of 1% (w/w) and for the epicutaneous application of 50% (w/w). This animal also died within 24 hours.Two of the four other animals (earlier used for epicutaneous applications with several test substance concentrations to determine possible skin irritancy) were treated in a similar manner to the first animal, but with one animal intracutaneously and one animal epicutaneously and with lower test substance concentrations. The intracutaneous injections with 0.1% (w/w) test substance caused red spots and the epicutaneous application with 25% test substance caused a very small crust formation on the edge of the treated site.

Main study:

The challenge treatment produced positive skin reactions (grade 2 or more) in sixteen experimental animals in reaction to the 10% test substance concentration, in thirteen animals in reaction to the 2.5% concentration and in twelve animals in reaction to the 1% concentration. These reactions were characterized with moderate, diffuse redness, in some animals with oedema and scaliness. No skin reactions were observed in the control animals to any of the application sites, except in one animal. This animal showed red spots in reaction to the 10% test substance concentration. No consistent signs of systemic toxicity were observed in any of the animals during the study. These results lead to a sensitization rate of 80 percent, which indicates that the test compound has strong sensitizing properties

Interpretation of results:
Category 1A (indication of significant skin sensitising potential) based on GHS criteria
Endpoint conclusion
Endpoint conclusion:
adverse effect observed (sensitising)
Additional information:

Read across: 2 -Mercaptoethanol

No studies regarding the skin sensitizing properties of sodium 2 -mercaptoethanolate were available. However, in accordance with column 2 of Annex VII of legislation EC1907/2006, these studies do not have to be conducted since the substance is classified as corrosive to the skin. Nonetheless, for classification purposes, data on the structural analogue 2 -mercaptoethanol (CAS: 60 -24 -2) have been used.

In a guinea pig maximization test (RCC NOTOX, 1988) performed according to OECD TG 406 and following GLP, a test group of 20 female guinea pigs (Dunkin-Hartley strain) received 0.1% 2-mercaptoethanol in vehicle (physiological saline) and Freund's adjuvant for intradermal induction, followed by epicutaneous induction with 25% 2-mercaptoethanol in vehicle under occlusive dressing for 48 hours. For challenge, 0.05 mL of a 10, 2.5, 1% solution in vehicle (max . non-irritant concentration, determined in the pretest) was applied to the intact skin for 24 hours (occlusive). The challenge resulted in a sensitisation response in treated animals (80%).

In a second guinea pig maximization test (CIT, 1994) performed according to OECD TG 406 and following GLP, a test group of 20 animals received 0.1% 2-mercaptoethanol in physiological saline and Freund's adjuvant for intradermal induction, followed by percutaneous induction with 10% 2-mercaptoethanol in vehicle under occlusive dressing for 48 hours. For challenge, 0.5 ml of a 25% solution in vehicle (max . non-irritant concentration, determined in the pretest) was applied to the intact skin for 24 hours (occlusive). The challenge resulted in a sensitisation response in 8 treated animals (40%).

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

Based on guinea pig maximization tests according to OECD TG 406 the substance is classified Skin sens. 1A, H317: May cause an allergic skin reaction, in accordance with EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.