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Environmental fate & pathways

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Although TBBS is not readily biodegradable with a biodegradability of 0 % observed in 28 days, it is abiotically unstable in aquatic environment with a hydrolysis half-life of 7.76 to 9.53 hours at pH 7.0 and 25 °C. Mercaptobenzothiazole (CAS: 149-30-4) and tert-butylamine (CAS: 75-64-9) were identified hydrolysis products. The described metabolites are also not readily biodegradable. But mercaptobenzothiazole shows also fast hydrolysis in aquatic environment.

Due to the fast hydrolysis, the BCF and adsorption coefficient of the degradation products are relevant for risk assessment of TBBS in the environment. The experimentally determined BCF of MBT is lower than 8 and the one of tert-butylamine lower than 9; and hence TBBS is considered to have very low potential for bioaccumulation. Simultaneously, MBT has moderate adsorption potential in soil/sediment with the adsorption coefficient (log Koc) of 2.51 – 3.55. Tert-butylamine however has only a low affinity to adsorption with a logKoc of 1.43. With QSAR estimation a logKoc of 2.76 was caluclated for TBBS using Kow Method.

TBBS is essentially non-volatile with the calculated Henry's law constant 0.000085 Pa m³/mol at 25 °C. The estimated half-life in air of TBBS is much shorter than 48 hours and hence no potential for long-range transport of TBBS in air is expected.

The distribution of TBBS in a "unit world" was calculated according to the Mackay fugacity model level I based on the physico-chemical properties. The main target compartment for TBBS is water of 72.65 % and sediment of 13.31 %, followed by soil of 13.16 %.