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Toxicity to aquatic algae and cyanobacteria

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Description of key information

NOEC (72 and 96 hours, Scenedesmus subspicatus) = 20 mg/l (nominal)

Key value for chemical safety assessment

Additional information

The toxicity of the test item to aquatic algae was evaluated in a 96-hour experimental study on Scenedesmus subspicatus according to the OECD Guideline 201 (1984). 10 000 cells/ml cultivation of S. subspicatus were exposed to test item concentrations of 0.3125, 1.25, 5.0, 20 and 80 mg/l and cells were counted after 24, 48, 72 and 96 hours. Change in cell count over time was represented graphically to form dose-response curves for each concentration, and toxicity was analysed by comparison of the area under respective growth curves of treated and untreated samples. A positive control (potassium dichromate) was also tested in parallel. pH was adjusted to 7.7 ± 0.3 at the start of the test using HCl, then monitored at the end of the study period. Stability of the test item in test media was evaluated by comparison of nominal and measured test item concentration at the start and end of the study period (0 and 96 hours). EbC50 was measured using the LOGIT-Model, and the NOEC and LOEC were evaluated using the dose-response curve.

Only EbC50 (72 h and 96 h) were reported in the study report. Based on the available data on number of cell at the different time points, a range of the percentage of inhibition considering the growth rate is calculated. The ErC50 (96 h) is expected to be between 20 -80 mg/L (% inhibition at 20 mg/L and 80 mg/L is ca. 5 % and 70 % respectively). It is worth noting that the evaluation of the toxicity potential of the substance to algae presents some limits due to the nature of the substance (dye). Specifically, it cannot be distinguished whether the effects are due to the colour of the test item (and hence the coloured test medium) or they are due to an intrinsic algicidic potential.

Based on the read across consideations same results apply to the target substance.