Zinc di(benzothiazol-2-yl) disulphide

Endpoint summary

Additional information

ZMBT is an organic complex, in which MBT structure is present. The dissolution of MBT determines the hazard profile of ZMBT aqueous solution; and hence the environmental fate and behavior of MBT is used as read-across approach for the phototransformation in water to support the risk assessment of ZMBT.

In a hydrolysis study (Currenta 2019) ZMBT was dissolved to the maximum achievable concentration and the identity of the substance was determined by 1H-NMR before acidification (pH = 7 - 8) and after (pH = 3). Because of the low solubility and consequential sample preparation the initial concentration of the test solution was not determinable.

It can be summarized that the test item ZMBT is hydrolytically stable at a pH value of 7 -8. However, ZMBT is hydrolytically unstable at a pH value of approx. 3. At this pH value ZMBT is completely hydrolytically degraded to MBT after a period of less than nine minutes.

In a supporting non-GLP study (Currenta 2019) rapid degradation to MBT following a short term extraction with 3% acetic acid could be demonstrated qualitatively by HPTLC, wheras no degradation after a short term extraction with water was indicated.

In a supporting study (Currenta 2020) the hydrolytical stability of ZMBT for the purpose of the completion of genotoxicity studies (OECD 476 In vitro Mammalian Cell Gene Mutation Tests using the Hprt and xprt genes, OECD 487 In vitro Micronucleus Assay) was investigated, where the laboratory employed an extended sample preparation, i.e. dissolution of the sample ZMBT in DMSO and consequent heating (50 °C) and sonication for complete dissolution.

It can be summarized that ZMBT is hydrolytically stable in DMSO under neutral conditions over the course of 24 h as well as during sample preparation under heating (50 °C) and sonication conditions for 90 minutes.

In absence of light and oxygen 2-mercaptobenzothiazole is hydrolytically stable with no hydrolysis products observed and 85% recovery within 7 days. According to expert judgment MBT can be oxidized by atmospheric oxygen to 2,2`-dithiobisbenzothiazole (MBTS) in aqueous solution. Hansson & Agrup reported 60% conversion of MBT into MBTS in phosphate buffer at pH 6.5 within 2 hours with the presence of atmospheric oxygen.

The phothlytic breakdown of 2-mercaptobenzothiazole occures rapidly with a half-life under one hour. The calculated half-life was 27.4 minutes for synthetic humic water and 31.1 minutes for pure water. 2 -Mercaptobenzothiazole was classified as "photolabile".

In the atmosphere a half-life of 4.3 hours for ZMBT due to reaction with photochemically produced hydroxyl radicals is estimated by AOPWIN v1.92 with a rate constant of 9.03 *10-11cm3/(molecule*sec), considering an OH-concentration of 500,000 radicals/cm³ as a 24-h average (Currenta, 2010). The estimated half-life in air of ZMBT is much shorter than 48 hours and hence no potential for long-range transport of ZMBT in air is expected.