N-tert-butylbenzothiazole-2-sulphenamide

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

fish early-life stage toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Justification for type of information:

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. “


TBBS hydrolyses with a DT50 of 1.8h (MITI 1996) or 9.53h (Monsanto 1984) thus falling in the category where either parent or degradation product could be tested. In the following considerations are discussed which kind of study is recommended:


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 MBT and TBBS available. The results are presented in the table below (effect values are based on measured concentrations):


TBBS (mg/L) MBT (mg/L)
Daphnia 48h-EC 50 1.3 0.71
Daphnia 21d-NOEC >0.16 0.08
Fish 96h LC 50 1.38 0.73
Fish 89d NOEC use MBT data 0.048
Algae 72h-EC 50 0.071 0.5
72-hNOEC 0.023 0.066


Whereas for algae, TBBS appears to be more toxic, the effect values for TBBS and MBT in acute daphnia and fish exhibit comparable. This can also be seen in the chronic tests in daphnia. These results suggest that TBBS and its degradation product MBT have a similar toxicological profile and no relevant differences in a chronic fish test for TBBS would be expected.


As a conclusion the existing chronic fish test for MBT is sufficient to explain the toxicity of TBBS.

Principles of method if other than guideline:

Method: Federal Register 50:TSCA Test Standard No. 797.1600. This test is comparable with the OECD-Guideline 210.

GLP compliance:

yes

Specific details on test material used for the study:

- Common name: 2-mercaptobenzothiazole

Analytical monitoring:

yes

Vehicle:

yes

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

Unfertilised rainbow trout eggs and sperm were individually packaged and shipped under refrigeration from Mount Lassen Farm, a certified disease-free trout hatchery located in Red Bluffs, California.

Test type:

flow-through

Water media type:

freshwater

Total exposure duration:

89 d

Hardness:

26 - 30 mg/L CaCO3 = 1.46 - 1.68 °dH

Test temperature:

12 +/- 2°C

pH:

6.9 - 7.4

Dissolved oxygen:

7.1 - 11.2 mg/L

Key result

Duration:

89 d

Dose descriptor:

NOEC

Effect conc.:

0.041 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

larval development

Key result

Duration:

89 d

Dose descriptor:

LOEC

Effect conc.:

0.078 mg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

larval development

Details on results:

MATC = Maximum Acceptable Toxicant Concentration
geometric mean = 0.057 mg/l

At the termination of the test, data obtained on embryo viability, survival at hatch, larval survival and larval growth (wet weight and total length) were statistically analysed to establish treatment level effects.

Validity criteria fulfilled:

not applicable

Conclusions:

For benzothiazole-2-thiol as hydrolysis product of TBBS, the Maximum Acceptable Toxicant Concentration (MATC) in an early-life stage test on rainbow trout was determined to be 0.041 - 0.078 mg/L within 89 days. The concentration of 0.078 mg/L was reported as LOEC and 0.041 mg/L as NOEC.

Executive summary:

For benzothiazole-2-thiol as hydrolysis product of TBBS, the Maximum Acceptable Toxicant Concentration (MATC) in an early-life stage test on rainbow trout was determined to be 0.041 - 0.078 mg/L within 89 days. The concentration of 0.078 mg/L was reported as LOEC and 0.041 mg/L as NOEC.

Description of key information

For benzothiazole-2-thiol (MBT) as hydrolysis product of TBBS, the Maximum Acceptable Toxicant Concentration (MATC) in an early-life stage test on rainbow trout was determined to be 0.041 - 0.078 mg/L within 89 days. The concentration of 0.078 mg/L was reported as LOEC and 0.041 mg/L as NOEC.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

NOEC

Effect concentration:

0.041 mg/L

Additional information

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. “

 

TBBS hydrolyses with a DT50 of 1.8h (MITI 1996) or 9.53h (Monsanto 1984) thus falling in the category where either parent or degradation product could be tested. In the following considerations are discussed which kind of study is recommended:

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 MBT and TBBS available. The results are presented in the table below (effect values are based on measured concentrations):

 

                                  TBBS (mg/L)       MBT (mg/L)

Daphnia 48h-EC50       1.3                     0.71

Daphnia 21d-NOEC       >0.16              0.08

Fish 96h-LC50              1.38                   0.73

Fish 14d-LC50              1.02               0.67 (8d-LC50)

Fish 89d NOEC       use MBT data        0.048

Algae 72h-EC50            0.071              0.5

          72h-NOEC        0.023        0.066

Whereas for algae, TBBS appears to be more toxic, the effect values for TBBS and MBT in acute daphnia and fish exhibit comparable. This can also be seen in the chronic tests in daphnia. These results suggest that TBBS and its degradation product MBT have a similar toxicological profile and no relevant differences in a chronic fish test for TBBS would be expected.

As a conclusion the existing chronic fish test for MBT is sufficient to explain the toxicity of TBBS.