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Short-term toxicity to aquatic invertebrates

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Description of key information

The acute toxicity of the test substance to the aquatic freshwater invertebrate Daphnia magna was studied under GLP in accordance with OECT TG 202.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
6.7 mg/L

Additional information

In order to assess the toxicity of the test item containing different sparingly soluble components, water accommodated fractions (WAFs) with loading rates of 4.6, 10, 22, 46 and 100 mg/L were tested. Additionally, a control (test water without test item) was tested in parallel. The preparation of the test media was based on the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures, 2000. For preparation of the WAFs, individual dispersions of the test item with the loading rates as mentioned above were prepared. The dispersions were stirred for 96 hours to dissolve a maximum amount of the different components of the test item in the dispersion. Then, the dispersions were filtered through membrane filters (0.45 µm) and the undiluted filtrates were tested as WAFs. At the start of the renewal periods (Day 0/Day 1), the measured concentrations (based on main peak evaluation) of the test item in the analyzed test media (loading rates of 4.6, 10, 22, 46 and 100 mg/L) amounted to 1.21/1.24, 1.29/1.90, 2.23/1.46, 1.98/2.56 and 3.28/2.92 mg/L, respectively. At the end of the renewal periods (Day 1/Day 2), the measured concentrations were 0.950/1.16, 1.16/1.66, 2.14/1.23, 1.90/2.21 and 3.08/2.53 mg/L, respectively.

At the start of the renewal periods (Day 0/Day 1), the measured concentrations (based on main peak evaluation) of the test item in the analyzed test media (loading rates of 4.6, 10, 22, 46 and 100 mg/L) amounted to 1.21/1.24, 1.29/1.90, 2.23/1.46, 1.98/2.56 and 3.28/2.92 mg/L, respectively (see analytical results and Table 2 in the corresponding appendix). At the end of the renewal periods (Day 1/Day 2), the measured concentrations were 0.950/1.16, 1.16/1.66, 2.14/1.23, 1.90/2.21 and 3.08/2.53 mg/L, respectively.

During the first 24 hours of the test, no immobilized test organisms were determined in the control. At the lowest loading rate of 4.6 mg/L, one test organism was found to be immobile. This low immobilization rate of 5%, although tolerated by the guidelines in the control, was estimated as a toxic effect, because at the next higher loading rate of 10 mg/L the immobilization rate was already 65%. At the three highest loading rates of 22, 46 and 100 mg/L, the immobilization rate was between 65 and 75%.

The 24-hour EC50 was estimated to be 11 mg/L.

The 24-hour EC0 was below the lowest loading rate tested (4.6 mg/L). The 24-hour EC100 was clearly above the highest loading rate tested (100 mg/L).

After 48 hours of exposure, no immobilized test organisms were determined in the control. At the lowest loading rate of 4.6 mg/L, the immobilization rate increased to 35%. From the loading rate of 10 mg/L onwards all daphnids were found to be immobile with the exception of one surviving test organism at the loading rate of 46 mg/L.

The 48-hour EC50 was calculated to be 6.7 mg/L with 95% confidence limits of 3.3 and 11.2 mg/L, based on loading rates.

The 48-hour EC0 and NOEC were both below the lowest loading rate of 4.6 mg/L. The 48-hour EC100 was at the loading rate of 10 mg/L.

The observed dose-response relation at the loading rates of 4.6 and 10 mg/L and the almost constant toxic effects at the loading rates of 10 to 100 mg/L indicate, that the solubility limit of the toxic component(s) lies between the loading rates of 4.6 and 10 mg/L.

No remarkable observations were made concerning the appearance of the test media. All test media were clear solutions throughout the entire test duration.

At the beginning and end of the test medium renewal periods, the pH values of the test media were between 7.8 and 8.0 . The dissolved oxygen concentrations in the test media and control were at least 8.1 mg/L , and water temperature was maintained at 20 °C during the test