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Diss Factsheets

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Discussion of biotic and abiotic stability in water:

DCBS is not readily biodegradable with a degradation rate of 2% after 28 days. However it is abiotically unstable in aquatic environment with a hydrolysis half-life of 53 hours at pH 7.0 and 25°C. The main hydrolysis products of DCBS were identified as dicyclohexylamine and 2-mercaptobenzothiazole (MBT). Dicyclohexylamine is readily biodegradable with a 96% biodegradation observed in 20 days, but MBT is not readily biodegradation with only 2.4% biodegradation observed in 14 days.

The concentrations used in the biodegradation studies were 100 mg/L which is much higher than the water solublity (in the range of 1 to 5 µg/L). In these ready-tests DCBS is not dissolved, presumably adsorbed to surfaces and therefore not available to bacterial attack. For these reasons, an inherent test under optimised conditions according to MITI II were initiated by the registrant using

- lower concentrations of DCBS and

- higher concentrations of bacteria. The lowest concentration which could be quantitatevly analysed in an oxygen consumption test was 10 mg/L which is magnitudes above the water solubility.

- prolongation to 60 days. After 28 days, 46% biodegradation were recorded. The test was finished after 60 days where 66% biodegradation was observed.

Further test for inherent biodegradation (Currenta 2013 a, Currenta 2013 b, Currenta 2014 a, Currenta 2014 b) were finally assessed as not useful for the assessment of the P criterion.

Discussion of stability in sediment:

A planned study was waived as the outcome of a soil simulation test yielded a classification vP.

Discussion of stability in soil:

A study according to OECD 307 in four soils at 12°C yielded only limited degradation of DCBS within the test duration of 120 days. The half-lives were calculated to be >180 days (315 to 615 days). Another test under anaerobic conditions also showed DCBS to be stable (half life 783 days at 12°C).

Discussion of bioaccumulation

DCBS is bioaccumulative with a BCF of 7310 on Cyprinus carpio as test organism observed within 6 weeks at test concentration of 0.01µg/l. In contrast the hydrolysis products of DCBS, dicyclohexylamine and MBT, are both non-bioaccumulative and also the described metabolites of MBT in the Appendix A of EU-Risk Assessment for CBS. On the other hand, DCBS has not been found in aquatic organisms (fish, mussels) in a monitoring study performed in Japan. No residues could be found with a detection limit of 4.4 µg/kg. These data suggest that the accumulation behaviour of the substance in the real environmnent is lower than estimated with the standard OECD 305 guideline.

Discussion of transport

Simultaneously, DCBS has a very high adsorption potential in soil/sludge with the estimated adsorption coefficient (log Koc) of 4.70 – 4.92. However, dicyclohexylamine has a low sorption potential in soil and sediment compartment and MBT has a moderate sorption potential. DCBS is essentially non-volatile with the estimated Henry's law constant 0.069 Pa m3/mol at ambient temperature (20-25°C). In air DCBS has a half-life of 3.38 hours estimated by AOPWIN v1.92 with a rate constant of 1.13 *10-10cm3/(molecule*sec), considering an OH-concentration of 500,000 radicals/cm³. The estimated half-life in air of DCBS is much shorter than 48 hours; and hence no potential for long-range transport of DCBS in air is expected. The distribution of DCBS 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 DCBS is sediment with 49.72 % and soil with 49.17%, followed by water with 0.7 % and suspended sediment with 0.4%.

Discussion of monitoring data

DCBS was analysed in a two monitoring programs in Japan.

MITI 1998: DCBS in 13 sites of surface water <0.3 µg/L

MITI 1998: DCBS in 13 sites of bottom sediment <E-05 mg/kg d.w.

MITI 2009: DCBS in 23 sites of surface water <1.1 µg/L

MITI 2010: DCBS in 29 sites of sediment <7E-04 mg/kg. d.w.

MITI 2010: DCBS in 11 marine and estuarine wildlife <0.044 mg/kg d.w.

Currenta 2017: Analysis of tyres part prepared using DCBS. In 8 of 9 samples from tyres manufactured using DCBS, DCBS was found to be below the limit of quantitation (0.005%). One sample contained DCBS just above the limit of quantitation in a concentration of 0.015%. The results prove that DCBS is consumed during vulcanisation. Only small traces might survive under certain conditions.

Currenta 2018: N, N-dicyclohexylbenzothiazole-2-sulphenamide – Determination in dust from DCBS Downstream Users during the use of DCBS in the production of tyres and general rubber goods. Six of seven results showed emissions of DCBS to air in the milligram to gram range per year. One site showed an emission of about 700 g/year.