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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

EC50 =12.23 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
12.23 mg/L

Additional information

Determination of the toxicity of the test item towards Desmodesmus subspicatus was performed according to OECD 201 resp. EU C.3.

Four experiments were performed. In the 1st and 2nd experiment one of the validity criteria was not met. Therefore, the experiments were repeated. The 3rd experiment was performed using 5 concentrations ranging from 0.01 to 1 mg/L (nominal). Because the inhibition of algal growth for the endpoint growth rate in the 3rd experiment was only 13.5 %, a 4th experiment was performed for determination of an exact EC50 value. The 4th experiment was performed using 7 concentrations ranging from 0.1 to 100 mg/L (nominal). The determination of the biological results was based only on the results of the 4th experiment.

Incubation time (test system Desmodesmus subspicatus) was 72 hours. The cell concentration of each replicate was determined by measuring the cell numbers every 24 hours with an electronic particle counter. Growth rate μ and the yield2 were determined from the cell number at the respective observation times. Significant inhibition of algal growth was observed at all concentrations for growth rate and yield in the 4th experiment.

At the beginning and at the end of the test, the content of Titanium (Ti) as component of the test item in the test solutions was determined using ICP-OES-determination. The test item showed a very good solubility and the measured concentrations lay between 69 % and 84 % of the nominal concentrations at the beginning of the 3rd experiment (based on the Ti content of 27.64 % given by the sponsor and between 11 % and 65 % of the nominal concentrations at the end of this test. At the start of the 4th experiment, the measured concentrations lay between 66 % and 82 % of the nominal concentrations. At the end of this experiment, the test solutions were filtrated because of turbidity in the higher concentrated test solutions. Therefore, only very low values of Ti could be measured at the end of the test, because Ti was removed by filtration. Nevertheless, it was shown that the test item was present throughout the test. Therefore, the determination of the biological results was based on the measured start concentrations of the 4th experiment.

The 72h-EC50 values of potassium dichromate (K2Cr2O7, CAS No. 7778-50-9) were determined in a separate reference test. The values lay within the range of the laboratory (growth rate 0.65 - 1.10 mg/L, yield 0.21 – 0.66 mg/L). The pH of the blank control should not fluctuate by more than 1.5 units. The change was 0.2 and 0.1 units in the blank control of the 3rd and 4th experiment. All validity criteria were met.

The following results for the test item were determined:

Growth rate: NOEC < 0.07 mg/L; LOEC ≤ 0.07 mg/L; EC10 = 0.08 mg/L; EC50 =12.23 mg/L

Yield: NOEC < 0.07 mg/L; LOEC ≤ 0.07 mg/L; EC10 = 0.02 mg/L*; EC50 =0.23 mg/L