Butyl 3-mercaptopropionate

Endpoint summary

Description of key information

According to the category approach based on structur similarity BuMP has to be classified as Skin Sens. 1B.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vivo (LLNA)

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Justification for type of information:

There are no relevant variations in qualitative properties among source substances and the same potency is predicted for all target substances. This is Scenario 4 of the RAAF1. Substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are different alkyl esters of a common acid, 3-mercaptopropionic acid (3-MPA).
This scenario covers the category approach for which the read-across hypothesis is based on the assumption, that toxicity of compounds in this category are driven by a common toxophore. This approach serves to use existing data on genotoxicity, acute toxicity, repeated-dose toxicity and reproductive toxicity endpoints for substances in this category. For the REACH information requirement under consideration, the property investigated in studies conducted with different source substances is used to predict the property that would be observed in a study with the target substance if it were to be conducted. Similar properties are observed for the different source substances; this may include absence of effects for every member of the category.
There are differences in strength of the effects forming a regular pattern. This corresponds to Scenario 4 of the RAAF. The substances MMP, BuMP, EHMP, iOMP, iC13MP, and ODMP are esters of a common acid, 3-mercaptopropionic acid (3-MPA). All category members share the same mercaptopropionic acid moiety with one free SH group per MPA unit. The MPA unit with free SH is a prerequisite for this category.

The observed differences in effect levels (higher effect levels with increasing carbon chain length were observed in the available acute oral toxicity studies) are assumed to be mainly due to differences in molecular weight (corrections will be made for these differences) and decreasing bioavailability with increasing carbon chain length (no corrections are made for this effect; a worst-case approach is applied here, since based on the available data no exact quantification for bioavailability differences is possible at the moment).

It can be predicted with high confidence that the substances within this category will lead to the same type of effects. The main driver for toxicity is the free SH group of the MPA moiety.
Beside structural similarities and the common toxophore, the MPA moiety, category members are also likely to have similar metabolites. As explained in the Toxicokinetics section, substances are predicted to be rapidly hydrolysed into 3-MPA and the respective alcohol after absorption. According to low toxicity of the corresponding alcohols (Table 8), this would support the role of the MPA moiety as toxophore, as well as propose scenario 3 of the RAAF as applicable for this category approach. However, no experimental toxicokinetic data to support this hypothesis are available by now. To proof this hypothesis, simulated gastric acid hydrolysis studies, as well as in-vitro metabolism studies using liver microsomes will be conducted. Based on the results of these studies, scenario selection will be revaluated.

Reason / purpose for cross-reference:

read-across: supporting information

Reason / purpose for cross-reference:

read-across source

Parameter:

SI

Value:

5.1

Variability:

±1.6

Test group / Remarks:

12.5%

Parameter:

SI

Value:

5.6

Variability:

±2.9

Test group / Remarks:

25%

Parameter:

SI

Value:

9.5

Variability:

±2.7

Test group / Remarks:

50%

Parameter:

EC3

Remarks on result:

other: linear extrapolation

Interpretation of results:

Category 1B (indication of skin sensitising potential) based on GHS criteria

Conclusions:

Considering the reported data of this sensitization test, it can be stated that the test article Isooctyl mercaptopropionate causes reactions identified as sensitization, as the stimulation index was above 3.0 for each concentration tested. Based on the category approach, ODMP is considered as skin sensitizer and has to be classified as Skin Sens. 1B

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the category hypothesis and the presence of one thiol group, BuMP should be classified as Skin Sens 1B.