3,5-diiodothyronine

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

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Vehicle:

no

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Test temperature:

18.2 – 20.9 °C

pH:

7.7 - 7.9

Nominal and measured concentrations:

Nominal concentrations [mg/L]: 0, 1, 3.2, 10, 32, 100
At the beginning and at the end of the test, the content of the test item in the test solutions was determined using HPLC-UV. The concentrations determined at the start of the test were between 17 % and 21 % of the nominal concentration. At the end of the test the de-termined concentrations were between 14 % and 21 % of the nominal concentration. Therefore, the determination of the biological results was based on the geometric mean of the measured concentrations.

Details on test conditions:

For each treatment, 200 mL of the respective test item solution was mixed with the neces-sary amount of algal pre-culture (0.334 mL) to achieve a cell concentration of 2.0 *103 cells/mL. For the blank control, 350 mL nutrient medium was used instead of test item so-lution and mixed with the necessary amount of algal pre-culture (0.584 mL). In this mix-ture, the pH-value was measured.
The real cell concentration at the beginning of the test was measured with an electronic particle counter in the blank control solution. This measured value was used as start cell concentration for all replicates.
Samples for the analytical determination were taken before addition of algal pre-culture.
The test vessels were filled with 45 ± 1 mL of the respective test solution and incubated open (covered with perforated plastic foil acting as a stopper) for 72 hours, shaken on an orbital shaker to keep the algae in suspension. Before the start of incubation and every 24 hours, the cell number was determined with an electronic particle counter. After the test, samples for the analytical determination were taken, afterwards the pH value in treatments and blank control was measured again.
At the end of the test, the treatments were examined microscopically in order to assess the appearance of the algae and detect abnormalities (e.g. caused by the exposure to the test item).
The concentration of the test item in the test vessels was measured at the start and at the end of the test.
For elimination of the algal cells before analytical determination at the end of the test, samples were centrifuged.

Reference substance (positive control):

yes

Remarks:

potassium dichromate

Key result

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

> 20.89 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.:

> 20.89 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

cell number

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 20.89 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 20.89 mg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

test mat.

Basis for effect:

cell number

Validity criteria fulfilled:

yes

Conclusions:

Based on the test results the NOEC, 72 h can be stated to be > 20.89 mg/L and the EC50, 72 h can be stated to be > 20.89 mg/L, respectively.
Due to the results of the study, the test material does not meet the criteria for a classification as acute or chronic aquatic toxic.

Executive summary:

One valid experiment was performed.

The study was performed using 5 concentrations ranging from 1 to 100 mg/L (nominal concentration). The treatments showed no toxicity. Because slight stimulation of algal growth was observed in the highest concentration, no statistical evaluation was performed.

At the beginning and at the end of the test, the content of the test item in the test solutions was determined using HPLC-UV. The concentrations determined at the start of the test were between 17 % and 21 % of the nominal concentration. At the end of the test the determined concentrations were between 14 % and 21 % of the nominal concentration. Therefore, the determination of the biological results was based on the geometric mean of the measured concentrations.

The 72h-EC₅₀values of potassium dichromate were determined in a separate reference test. For the estimation of the 72h-EC₅₀values of the positive control, the fits showed sufficient statistical correspondence of the data with the dose-response-equation. The values were within the range of the laboratory.

The pH of the blank control should not fluctuate by more than 1.5 units. The change was 0.1 units in the blank control.

All validity criteria were met.

No observations were made which might cause doubts concerning the validity of the study outcome. The result of the test can be considered valid.

Description of key information

One study was performed according to OECD 201.

Based on the test results the NOEC, 72 h can be stated to be > 20.89 mg/L and the EC50, 72 h can be stated to be > 20.89 mg/L, respectively.

Due to the results of the study, the test material does not meet the criteria for a classification as acute or chronic aquatic toxic.

Key value for chemical safety assessment

EC50 for freshwater algae:

20.89 mg/L

EC50 for marine water algae:

20.89 mg/L

EC10 or NOEC for freshwater algae:

20.89 mg/L

EC10 or NOEC for marine water algae:

20.89 mg/L