N-cyclohexylbenzothiazole-2-sulfenamide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

GLP compliance:

no

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge

Details on inoculum:

- activated sludge: 6.0 g/l dry mass per liter
- inoculum: 50 ml sludge/ l test volume

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20.2 - 22.8°C

pH:

7.2 - 8.1

Nominal and measured concentrations:

Test solutions were prepared through direct weighting.
- Nominal concentrations of test substance: 100, 1000, 10000 mg/l
- Nominal concentrations of reference substance: 1 and 20 mg/l

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorphenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 10 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

The EC50 for the reference substance was determined as ca. 6 mg/L, which is within the normal range of 5 to 30 mg/L for this test. A respiration inhibition of 4 % was observed in the test concentration of 1000 mg/L and an inhibition of 11 % in the concentration of 10 000 mg/L. Thus it can be concluded that EC50 > 10 000 mg/L.

Conclusions:

Toxicity of CBS to activated sludge was evaluated by Bayer AG (1989) according to the ISO 8192 -1986/B yielding an EC50 value of > 10000 mg/L after 3 hours exposure at a pH 7.2 - 8.1 and temperature of 20.6 - 22.8 °C.

Executive summary:

Toxicity of CBS to activated sludge was evaluated by Bayer AG (1989) according to the ISO 8192 -1986/B yielding an EC50 value of > 10000 mg/L after 3 hours exposure at a pH 7.2 - 8.1 and temperature of 20.6 - 22.8 °C.

Description of key information

Toxicity of CBS to activated sludge was evaluated by Bayer AG (1989) according to the ISO 8192 -1986/B yielding an EC50 value of > 10000 mg/l after 3 hours exposure at a pH 7.2 - 8.1 and temperature of 20.6 - 22.8 °C.

Key value for chemical safety assessment

EC50 for microorganisms:

10 000 mg/L

Additional information

In sewage treatment plant, large amount of test substance might be present in both dissolved and undissolved form. To represent a more realistic situation, the tested concentrations are much higher than the water solubility of the test substance (i.e. 10.3 mg/l). Therefore the reported concentrations in Bayer AG study (1989) represent the combined effect of dissolved and undissolved test substance on the activity of microorganism in the sewage treatment plant.

CBS can be rapidly degraded by hydrolysis and benzothiazole (BT) is the main degradation product appearing during the time frame of acute tests. In a respiration inhibition test using activated sludge according to OECD 209, a 3h-EC50 of 650 mg/l was obtained (Yoshioka et al., 1986) for BT. A similar test according to a national guideline resulted in a 3h-EC50 of 635 mg/l and an EC10 of 274 mg/l (Bayer AG, 1990). A nitrification inhibition test was performed with Nitrosomas isolated from wastewater. NH4 removal was analysed in a model of sediment columns charged with quartz sand. Effects were found with BT concentration of 0.2 mg/l (Reemtsma, 1994). Results from 2 growth inhibition tests for Tetrahymena pyriformis are available. EC50 values of 135 mg/l (Yoshioka et al., 1986) and 160 mg/l (Schultz, 1997) were obtained. Some further data are available for the two other main metabolites from CBS, like MBT and MBTS. Toxicity of MBT to activated sludge was evaluated by Bayer AG (1990) according to the ISO 8192 -1986/B yielding an EC50 of 3301 mg/l and an EC10 of 279 mg/l after 3 hours exposure at a pH 7.5 - 8.2 and temperature of 19.6 - 20 °C. Tomlinson (1966) studied the inhibition of the first nitrification step (oxidation of NH4 to NO2) and obtained after 2-4 h exposure EC75 values of 3mg/l for non-adapted sludge. With the protoza Tetrahymena pyriformis a 24-hour EC50 of 10 mg/l related to growth rate was determined for MBT (Yoshioka, 1985). A large number of experimental results were reviewed already in the appendix I of EU-risk assessment of CBS (95-33-0), which reveal the effect concentrations ranging from 0.25 mg/l for Nitrosomas (Reemtsma, 1994) to 500 mg/l for Mycobacterium tuberculosis (Foltinova Blöckinger, 1970). In a respiration inhibition test of MBTS using activated sludge similar to OECD 209, no effects were observed in concentrations up to 10 g/l after 3 h of incubation (Bayer AG, 1988). Tomlinson (1966) studied the inhibition of the first nitrification step (oxidation of NH4 to NO2) and obtained a 4 h-EC75 value of 38 mg/l.