N-tert-butylbenzothiazole-2-sulphenamide

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

also cited in OECD SIDS.

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source (i.e. manufacturer or supplier) and lot/batch number of test material: batch no. 612040, name of the supplier not included in the report
- Purity, including information on contaminants, isomers, etc.: 96.8%

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
The test materials were stored in a refrigerator in our laboratory.
The infrared absorption spectra of the available test substance were measured and confirmed to be consistent with the structure of the test substance. At the end of the test, the infrared absorption spectrum was also measured and compared with the spectrum measured before the start of the test. As a result, there was no change in the spectrum, and the test substance was judged to have been stable during storage.

Analytical monitoring:

yes

Details on sampling:

At the beginning (0 hr) and at the end (72 hrs) of the exposure, 2.0 mL of the test solution was taken from each of the three test containers in each concentration group and mixed. At the beginning (0 hr) and the end (72 hr), 2.0 mL of the test solution was taken from each of the three test containers and mixed. 0.75 mL of the test solution was used as the analysis sample at the beginning, and 0.75 mL of the supernatant liquid was used as the analysis sample at the end after centrifugation of the algae (3000 rpm, 10 min).
An equal volume of acetonitrile was added to each analysis sample, and after mixing, the samples were analyzed by HPLC. The concentration of test substance in each test solution was determined from the ratio of the peak area of the standard solution.

STABILITY OF THE TEST CHEMICAL SOLUTIONS:
The concentration of TBBS at the end of the exposure period was between 19 and 90 % of the nominal value at the start of study.
Geometric mean measured values were used for calculation of the growth inhibition concentration.

Vehicle:

yes

Details on test solutions:

STOCK AND TEST SOLUTION AND THEIR PREPARATION:
Vehicle, solvent: HCO-50 and DMF
Concentration of vehicle/solvent: 100 mg/L

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

Initial cell concentration: 10000 cells/mL

The strain ATCC22662 was obtained from the American Type Culture Collection on June 20, 1996 and has been cultured aseptically in our laboratory. The growth inhibition concentration (EbC50) of the reference material (potassium dichromate, reagent grade) for 72 hours was 0.41 mg/L (linear regression analysis).

Preculture
The algae to be tested were pre-cultured for 3 days prior to the start of exposure under the same conditions as the test conditions.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

23.5 +/- 0.7 °C

pH:

Initial = 7.8, Final 7.8 - 9.7 (increased pH seen at dose levels of =< 0.032 mg/L)

Nominal and measured concentrations:

Concentrations: Control, vehicle control, 0.004, 0.008, 0.016, 0.032, 0.063, 0.13, and 0.25 mg/L (nominal)

measured concentrations 0 hours: control, vehicle control both <0.0005, 0.0047, 0.0089, 0.0148, 0.0317, 0.0634, 0.128, 0.250 mg/L

measured concentrations 72 hours: control, vehicle control both <0.0005, 0.0036, 0.0056, 0.0078, 0.0162, 0.024, 0.0379, 0.0468 mg/L

in the OECD SIDS the geometric mean of the test concentrations over 72 h was calculated to be: control, vehicle control, 0.0041, 0.007, 0.011, 0.023, 0.039, 0.069, 0.11 mg/L

Details on test conditions:

TEST SYSTEM:
Test type: Static, Shaking culture (100 rpm)
Concentrations: Control, vehicle control, 0.004, 0.008, 0.016, 0.032, 0.063, 0.13, and 0.25 mg/L (nominal)
Renewal of test solution: No
Exposure vessel type: 300 mL glass Erlenmeyer flask fitted with a breathable silicone plug.
Number of replicates: 3 replicates per test concentration.
Test temperature: 23.5 +/- 0.7 °C
pH: Initial = 7.8, Final 7.8 - 9.7 (increased pH seen at dose levels of =< 0.032 mg/L)
Adjustment of pH: None
Intensity of irradiation: 4000 - 5000 lux
Photoperiod: continuous light

Reference substance (positive control):

no

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

0.071 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

0.023 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

In the original study (MITI 1997) the effect concentrations were determined based on the nominal concentrations. In the OECD SIDS the geometric mean of the test concentrations over 72 h was calculated to be: control, vehicle control, 0.0041, 0.007, 0.011, 0.023, 0.039, 0.069, 0.11 mg/L. Based on these measured concentrations, the effect concentrations were determined to be ErC50 = 0.071 mg/L and NOECr = 0.023 mg/L. The NOECr in the OECD SIDS was determined based on the exposure phase 24 - 72h. The raw data was reevaluated to validate that the NOECr will also be 0.023 mg/L over the total exposure of 0 - 72h, which was confirmed.

Validity criteria fulfilled:

yes

Conclusions:

The toxicity to aquatic plants e.g. algae (Selenastrum capricornutum) of TBBS was determined as growth rate with an ErC50 of 0.071 mg/L after a period of 72 hours. A NOECr of 0.023 mg/L was calculated.

Executive summary:

The toxicity to aquatic plants e.g. algae (Selenastrum capricornutum) of TBBS was determined According to the OECD guideline 201 "Algae, Growth Inhibition Test". In the original study the effect values have been determined based on the nominal concentrations. In the OECD SIDS on the substance, the effect values were reevaluated based on the geometric mean concentration over the total study duration 0 - 72h. The growth rate was calculated to be ErC50 = 0.071 mg/L after a period of 72 hours. A NOECr of 0.023 mg/L was determined.

Description of key information

The toxicity to aquatic plants e.g. algae (Selenastrum capricornutum) of TBBS was determined as growth rate based on geom. mean measured concentrations with an ErC50 of 0.071 mg/L after a period of 72 hours. A NOECr of 0.023 mg/L was calculated.

Key value for chemical safety assessment

EC50 for freshwater algae:

0.071 mg/L

EC10 or NOEC for freshwater algae:

0.023 mg/L

Additional information

Due to fast hydrolysis of TBBS the observed effect is most probably a combined effect from both, TBBS and MBT. Thus, the value determined on TBBS was chosen as key study. The most sensitive value in an aquatic system was the NOEC for TBBS on algae, and hence it was used for PNEC derivation.