Registration Dossier

Administrative data

Description of key information

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion
Endpoint conclusion:
adverse effect observed (sensitising)
Additional information:

In a mouse local lymph node assay conducted according to OECD Test Guideline 429 (CiToxLAB, 2011) the stimulation index (SI) was greater than 3 at concentrations of 25% and above (3.62, 4.26 and 30.43 at 25%, 50% and 100% concentrations respectively). Therefore tertiobutylmercaptan was considered to be sensitising. The EC3 value (estimated test substance concentration that will give an SI of 3) was calculated to be 20%.

2-methylpropane-2-thiol was also found to be a dermal sensitizer in a dermal sensitizing study in guinea pigs by modified Buehler (Douds, 1995).

Following a pilot study to determine the appropriate concentrations of test material to use in the induction and challenge phases, Hartley-derived albino guinea pigs (10/sex) were dermally treated with undiluted 2-methylpropane-2-thiol (0.4 ml, 4 cm2area) once /week for 6 hours/exposure for three consecutive weeks.   Following a 2 week rest period, the test animals and a naïve control group (5/sex) were dermally challenged with 75 % test substance W/V in mineral oil. The animals were scored (0-3 scale) for skin sensitising reactions at 24 and 48 hours following the challenge phase. Hexylcinnaldehyde historical positive control data were cited as demonstrating susceptibility of the test system to a sensitising agent. 

The primary challenge resulted in 13/20 animals (65%) exhibiting scores2 at 24 hours and 11/20 animals (55%) exhibiting similar scores at 48 hours post-challenge. The mean dermal score for the entire test group was 1.9 at 24 hours and 1.7 at 48 hours.  All control group animals exhibited a grade 1 response at 24 hours with all but one reporting the same response at 48 hours. Based on the severity and incidence of the sensitisation response observed in the test group, 2-methylpropane-2-thiol is considered to be a dermal sensitizer in guinea pigs with moderate potency according to ECHA guidance (REACH Chapter R.8 (Characterisation of dose [concentration] –response for human health); Appendix R.8-10.

Derivation of a DNEL is not warranted for this endpoint.

Migrated from Short description of key information:
The key mouse LLNA study (CiToxLAB, 2011) found the test substance to be sensitising. The Buelher supporting study also found the test substance to be sensitizing.

Justification for selection of skin sensitisation endpoint:
Studies were conducted according to an appropriate guideline and in compliance with GLP.

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

Based on the available data tertiobutylmercaptan requires classification for skin sensitisation as Skin Sensitiser Category 1B: (H317: May cause allergic skin reaction), according to Regulation (EC) No 1272/2008, as amended.