Sodium benzothiazol-2-yl sulphide

Endpoint summary

Additional information

SMBT is an organic salt of strong base NaOH and weak acid of MBT and it is solely marketed as aqueous solution. The presence of MBT determines the hazard profile of SMBT aqueous solution; and hence the environmental fate and behavior of MBT is used as read-across approach to support the risk assessment of SMBT.

MBT is not readily biodegradable with a biodegradability of 2.5% observed in 14 days and also not inherently biodegradable with only 2% biodegradability observed during 35 days exposure to adapted bacterial inoculum. On the other hand MBT is also hydrolytically stable at pH 7 and ambient temperature, but it is abiotically unstable in aquatic environment in presence of atmospheric oxygen with 60% conversion to MBTS within 2 hours at pH 6.5 and in presence of light with a direct photolysis half-life in water of ca. 30 mins at 32-40°C. The main abiotic degradation products of MBT and its described metabolites (e.g. MBTS) are BT (95-16-9) and its further product as BTon (934-34-9). In the appendix A of EU-risk assessment for CBS (95-33-0), BT and BTon are reported as persistent under environmental conditions. Another described metabolite from MBT is MeSBT (615-22-5), which is also reported in EU-risk assessment as resistant both to biodegradation and photolysis. MBT is not bioaccumulative with a measured BCF of 8 at 0.01 mg/l determined on Cyprinus carpio in a flow-through system. The described metabolites of MBT are also not bioaccumulative. Simultaneously, MBT has moderate adsorption potential in soil/sediment with the adsorption coefficient (log Koc) of 2.51 – 3.55. The adsorption coefficients of the described metabolites of MBT distribute also in the same range as the one of MBT. MBT is essentially non-volatile with the estimated Henry's law constant lower than 3.6*10-6 hPa m3/mol at 25°C. All the described metabolites of MBT have a HLC lower than 1 Pa m3/mol and hence are considered as non-volatile. SMBT has a half-life in air of 8.5 h estimated by AOPWIN v1.92 with a rate constant of 4.5 *10-11cm3/(molecule*sec), considering an OH-concentration of 500,000 radicals/cm³. The estimated half-life in air of SMBT is much shorter than 24 hours and hence no potential for long-range transport of SMBT in air is expected. The distribution of MBT 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 MBT is water with 95.96 %, followed by soil with 2.00 % and sediment 2.02 %.