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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

ErC50 (72 hours, Scenedesmus subspicatus) = 14.6 mg/l (mean measured)

Key value for chemical safety assessment

EC50 for freshwater algae:
14.6 mg/L

Additional information

The toxicity of the test item to algae was evaluated in an experimental study on Scenedesmus subspicatus according to the OECD Guideline 201 (1984) and the EU Method C.3 (1992). The test method was modified to quantify the algicidal effect of the test item, but also the growth inhibition effect due to the reduced light intensities in the coloured test media. 10,000 Scenedesmus subspicatus per ml of test media were cultured and inoculated, then allowed to grow in 50 ml Erlenmeyer flasks containing 15 ml algal suspension, in triplicate, at test item concentrations of 1.9, 6.1, 19.5, 62.5 and 200 mg/l for 72 hours in a temperature-controlled, continuously lit water bath. A control containing no test item (six replicates) was also tested in parallel. Cell densities were recorded at 24, 48 and 72 hours.

The analytically determined test substance concentrations in the analysed test media at the start of the test varied in the range from 88 % to 96 % of the nominal values. During the test period of 72 hours a decrease of test substance concentration in the test media was determined. The mean measured test concentrations (calculated as the average over all measurements per test concentration) varied in the range of 77 % to 91 % of the nominal values. Therefore, the reported biological results are related to the mean measured test substance concentrations.

Test media of concentrations of 6.1 mg/l test item and over were slightly to strongly discoloured by the test item. Toxicity was due in part to the indirect effect of inhibited light absorption due to discolouration caused by the test item, however at higher test item concentrations a real toxic effect of the test item on the growth of Scenedesmus subspicatus cannot be excluded. The 72-hour EC50 was determined to be 14.6 mg/l based on the growth rate, and 4.8 mg/l based on biomass.