N,N-dicyclohexylbenzothiazole-2-sulphenamide

Endpoint summary

Additional information

For the environmental hazard assessment of DCBS, MITI studies are mostly used as key studies with the most sensitive results. The original reports have been used for the RSS. However, detailed information regarding material, methods and results are also presented in OECD-SIDS (2004) for N,N-Dicyclohexyl-2-Benzothiazolessulfenamide (DCBS). Acute toxicity of DCBS was tested for three freshwater species and no toxic effect was observed close to its water solubility (i.e.1.9 μg/L CERI 2001). Two long-term studies are available on Daphnia and Algae. No toxic effects were found to aquatic organisms, therefore no PNECs can be derived.

 

No toxic effect was found to microorganisms up to the highest nominal concentration tested (10000 mg/l) according to the ISO 8192 -1986/B.

 

For hydrolysable substances used in aquatic ecotox tests, REACH Guidance Document R7b (2017), p. 86 states: :
“Where degradation is rapid (e.g. half-life < 1 hour), the available test data will frequently define the hazard of the degradation products since it will be these that have been tested. These data may be used to classify the parent substance in the normal way.
Where degradation is slower (e.g. half-life > 3 days), it may be possible to test the parent substance and thus generate hazard data in the normal manner using a suitable renewal regime. The subsequent degradation may then be considered in determining whether an acute or chronic hazard class should apply.
Where degradation rates fall between these two, testing of either parent and/or degradates should be considered on a case-by-case basis. “

 

DCBS hydrolyses with a DT50 of 53 h thus falling in the category where either parent or degradation product could be tested.

 

1. In the case of the sulphenamide category, a study with the degradation product benzothiazole-2-thiol (MBT) is already available. This study (FELS test) has been performed in accordance similar to an accepted international guideline (OECD 210, FELS test) and has been evaluated as Klimisch 2.
2. There are acute and chronic ecotox studies with DCBS and the relevant transformation products MBT and N,N-dicyclohexylamine available. The results are presented in the table below (effect values are based on measured concentrations):

 

	DCBS (mg/L)	MBT (mg/L)	N,N-dicyclohexylamine (mg/L)
Daphnia 48h-EC 50	>0.031	0.71	8 (EA Japan, 1999)
Daphnia 21d-NOEC	>0.033	0.08	0.049 (EA Japan, 1999)
Fish 96h LC 50	>0.033	0.73	62 mg/L (Bayer, 1992)
Fish 89d NOEC	n/a	0.048	n/a
Algae 72h-EC 50 72h-NOEC	>0.012 >0.012	0.5 0.066	>1 (Bayer 1992)* 0.016 (Bayer 1992)

*nominal concentration

 

For DCBS no toxicity to aquatic organisms was found in all available acute and chronic toxicity studies. For the transformation products data for almost all endpoints are available. The relevant effectvalues all lie considerably above the water solubility of DCBS (1.9 µg/L, CERI 2001). Therefore, even after complete hydrolysis the concentration of the transformation products might not exceed the respective thresholds.

The conclusion therefore holds true and no aquatic toxicity can be derived for DCBS also considering its transformation products, which is also discussed in the Read Across Justification.