N,N-dicyclohexylbenzothiazole-2-sulphenamide

Toxicity to terrestrial plants

Administrative data

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study planned

Justification for type of information:

TESTING PROPOSAL ON TERRESTRIAL PLANTS: SEEDLING EMERGENCE AND GROWTH TEST OECD 208

NON-CONFIDENTIAL NAME OF SUBSTANCE:
- Name of the substance on which testing is proposed to be carried out: N,N- dicyclohexylbenzo-thiazole-2-sulphenamide. The following public name is used: DCBS

- Name of the substance for which the testing proposal will be used [if different from tested substance]: This substance itself only.

CONSIDERATIONS THAT THE GENERAL ADAPTATION POSSIBILITIES OF ANNEX XI OF THE REACH REGULATION ARE NOT ADEQUATE TO GENERATE THE NECESSARY INFORMATION:
- Available GLP studies: There are no GLP studies available for this substance covering the endpoint of terrestrial toxicity on plants.

- Available non-GLP studies: No further studies on terrestrial toxicity on plants are available for this substance.

- (Q)SAR: There are no QSAR models available for this higher tier ecotoxicological endpoint that are sufficiently validated and acceptable (according to OECD Q/SAR validation criteria).
- Weight of evidence & Grouping and read-across: The endpoint terrestrial toxicity to soil organisms is currently covered by studies from substances within the sulfenamide group (N-tert-butylbenzothiazole-2-sulphenamide, public name: TBBS and N-cyclohexylbenzothiazole-2-sulfenamide, public name: CBS): For the toxicity of TBBS to terrestrial plants, the lowest NOEC of 3.16 mg/kg soil dry weight (dw) was obtained after 16 d by a conservative evaluation of the diverging results of two test runs with P. sativum. For CBS the lowest NOEC of 31.6 mg/kg soil dw was determined for A. cepa, B. rapa, P. sativum and S. lycopersium. Additionally, information on the other trophic levels were obtained by studies according to TG OECD 222 and OECD 216. For E. fetida NOECs of 133.4 mg/kg soil dw for TBBS and ≥500 mg/kg soil dw for CBS were determined after a test period of 56 d. The test on microbial nitrate formation resulted in a NOEC of 205 mg/kg soil dw for TBBS and of 128 mg/kg soil dw for CBS after 28 days. Hence, terrestrial plants are identified as the most sensitive species for soil organisms for the sulfenamide group.
However, TBBS, CBS and DCBS differ significantly in their adsorptive properties as indicated by logKow (TBBS) = 3.36 (exp.); logKoc (TBBS) = 2.7 (calc.); logKow (CBS) = 5.02 (exp.); logKoc (CBS) = 3.56 (calc.) and logKow(DCBS) = 5.95 (calc), logKoc(DCBS) = 4.7 (calc.). Consequently, the water solubility for DCBS with a measured value of 1.9 µg/L is lower than the water solubility of both TBBS (1.74 mg/L) and CBS (0.32 mg/L). The substance is considered not readily biodegradable, it has a high potential to adsorb to soil as indicated from its physico-chemical properties and terrestrial plants have been indicated to be the most sensitive species in soil from tests with TBBS and CBS. Hence, DCBS is proposed to be even more adsorptive with a potentially higher toxicity towards the soil compartment. Thus, the registrant intends to elucidate the long-term effect of DCBS on terrestrial plants.
This assessment is supported by section 9.4, column two in annex IX: ‘In particular for substances that have a high potential to adsorb to soil or that are very persistent, the registrant shall consider long-term toxicity testing instead of short-term.’

Overall, the registrant has carefully considered all general adaptation procedures as listed in Annex XI of the REACH regulation, however the registrant has concluded that available studies have proven the plant to be the most sensitive soil organism regarding the sulfenamide group. The registrant therefore proposes to conduct an OECD TG 208 study as the best course of action to elucidate the toxicity towards the terrestrial compartment and deems to comply with the standard requirements for the present tonnage band (>1.000 tpa) according REACH regulation annex X 9.4.6 taking the category approach into account.

CONSIDERATIONS THAT THE SPECIFIC ADAPTATION POSSIBILITIES OF ANNEXES VI TO X (AND COLUMN 2 THEREOF) OF THE REACH REGULATION ARE NOT ADEQUATE TO GENERATE THE NECESSARY INFORMATION:
- The registrant has carefully considered the available adaptation possibilities applicable for the discussed endpoint. Adaptation according to REACh Annex IX 9.4 column 2 is not proposed as the exposure assessment indicates that emissions to the environment cannot be excluded.
FURTHER INFORMATION ON TESTING PROPOSAL IN ADDITION TO INFORMATION PROVIDED IN THE MATERIALS AND METHODS SECTION:

- The registrant intends to perform the long-term toxicity to terrestrial plants according to OECD TG 208 Terrestrial Plant Test: Seedling Emergence and Seedling Growth Test. According to the guideline, the study design of this study will fit to the physico-chemical properties of the test substance, as this study can deal with substances with low water solubility. (cf. OECD TG 208).

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 208 (Terrestrial Plants, Growth Test)

Test material

Test material information

Constituent 1

Reference substance name:

N,N-dicyclohexylbenzothiazole-2-sulphenamide

EC Number:

225-625-8

EC Name:

N,N-dicyclohexylbenzothiazole-2-sulphenamide

Cas Number:

4979-32-2

Molecular formula:

C19H26N2S2

IUPAC Name:

N-(1,3-benzothiazol-2-ylsulfanyl)-N-cyclohexylcyclohexanamine