Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Although MBTS is not readily biodegradable with a biodegradability of 0% observed in 28 days (Bayer, 1988) and hydrolytically stable under environmentally relevant pH and temperature (Hasson & Agrup, 1993), it is photolytically unstable in water with a half-life of direct phototransformation in water of 3 hours (Monsanto, 1980).

The main abiotic degradation products of MBTS and its reductive product MBT are BT (CAS: 95-16-9) and BTon (CAS: 934-34-9). In the EU-Risk Assessment, BT and BTon are reported as persistent under environmental conditions. Another described metabolite from MBT is MeSBT, which is also reported as resistant both to biodegradation and photolysis.

MBTS is not bioaccumulative with the highest observed BCF of 51 at concentration of 0.2 mg/l (MITI, 1992). All the potential metabolites of MBTS are also not bioaccumulative. However, MBTS has a high adsorption potential in soil/sludge with the estimated adsorption coefficient (log Koc) of 3.72 - 5.75 (Currenta, 2010). The adsorption coefficients of the potential metabolites of MBTS distribute also in the same range as the one of MBTS. Only BTon (estimated log Koc of 1.93) has very low adsorption potential.

MBTS is essentially non-volatile with the estimated Henry's law constant of 2.37*10-8 hPa m3/mol at 25°C (Currenta, 2010). All the potential metabolites of MBTS have a HLC lower than 1 Pa m3/mol and hence are considered as non-volatile. MBTS has a half-life in air of 1.22 h estimated by AOPWIN v1.92 with a rate constant of 3.15 *10-10 cm3/(molecule*sec), considering an OH-concentration of 500,000 radicals/cm³. The estimated half-life in air of MBTS is much shorter than 48 hours and hence no potential for long-range transport of MBTS in air is expected.

The distribution of MBTS in a "unit world" was calculated according to the Mackay fugacity model level I (Currenta, 2010) based on the physico-chemical properties. The main target compartment for MBTS is soil with 41.34 % and sediment with 41.80 %, followed by water with 16.53% and suspended sediment with 0.27%.