Benzothiazole-2-thiol

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

The skin sensitizing potential of MBT is known from several animal studies (for review see BG Chemie 2000). In addition, 2-mercaptobenzothiazole is one of the preferred and recommended positive control substances recommended in OECD Guideline 406 and 429.

The below mentioned studies are examples for the skin sensitising potential of MBT.

The skin sensitizing potential of MBT was evaluated in a GLP and OECD guideline study (TG 406, Guinea-pig maximisation test) with female guinea pigs (Bayer AG 1999). The test substance was formulated in physiological saline solution to yield a suspension up to 40 %. Ten animals were administered with the test substance suspensions. A control group of five animals were treated with physiological saline solution. In the treatment group the intradermal induction was done with 5 % and the topical induction with 25 % test substance solution. The challenge was done with 12 % test substance solution and led to skin effects in 7 of 10 animals in the treatment group and to one animal in the control group after 48 hours. Six of 10 animals showed skin effects in the treatment group after 72 hours. In the control group none of the animals showed skin effects after 72 hours. The total number of animals with skin reactions was 70 % in the test substance group and 20 % in the control group.

This finding was confirmed by another GLP and guideline study (TG 406, Guinea-pig maximisation test), which revealed skin reactions in animals of the treatment group (6/10 animals after 48 h and 72 h), whereas no effects were noted in the negative control group (Bayer AG 1998).

In a Buehler assay with male guinea pigs (TG 406) skin reactions was noted in treated animals after challenge with ca. 56 % test substance suspension. After 24 hours 5/12 animals and after 48 hours 3/12 animals showed skin reactions. 72 hours after the challenge 2/12 animals showed skin reactions. Skin reactions was also detected after challenge with 30 % test substance suspension after 24 hours (1/12 animals). No effects were noted in the negative control group (Bayer AG 1992).

Human information

The skin sensitizing potential of MBT was evaluated in a maximization test with human volunteers (Kligman 1966). Twenty-four human volunteers were patch-tested with MBT and 9/24 showed skin reactions after challenge with 10 % test substance. Thus, indicated a skin sensitizing potential of MBT in humans.

The skin sensitizing potential of MBT in humans is discussed in literature (for review SCCP 2005, BG Chemie 2000) and revealed that MBT is a relevant allergen for worker and general public (for review SCCP 2005, BG Chemie 2000).

Migrated from Short description of key information:
The test substance MBT is a recommended positive control for skin sensitizing according to OECD Guideline 406 and OECD Guideline 429. The skin sensitizing potential of MBT was revealed by findings from several guinea pig tests, e.g. guinea pig maximisation test, and Buhler test (Bayer AG 1999, 1998, 1992). The skin sensitizing potential of MBT was also revealed in humans. In a maximization test with human volunteers 9/24 persons showed an allergic skin reaction (Kligman 1966). In several publications the relevance of MBT as skin sensitizer in humans is discussed and revealed that MBT is a relevant allergen for worker and general public (BG Chemie 2000).
Thus data from animal studies and data from human volunteers as well as data from epidemiological studies etc. demonstrated a contact sensitization potential of MBT. In consequence, existing classification with R 43 is confirmed. According to criteria published in REACH guidance document chapter R. 8, MBT was categorised as moderate skin sensitizer.

Justification for classification or non-classification

The test substance MBT is classified as skin sensitizer (22 ATP) according to the classification criteria 67/548/EWG and regulation no. 1272/2008 (GHS).