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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The 72-h ErC50 of 46.9 mg/L and the 72-h NOErC of 3.2 mg/L in freshwater algae are used in the assessment.

Key value for chemical safety assessment

EC50/LC50 for freshwater algae:
46.9 mg/L
EC10, LC10 or NOEC for freshwater algae:
3.2 mg/L

Additional information

The toxicity of the test substance towards aquatic algae was investigated in a GLP-compliant test according to OECD 201 (RCC, 2005).

In this study, freshwater alga (Scenedesmus subspicatus) were exposed for 72 hours to nominal concentrations of 0, 1.0, 3.2, 10, 32 and 100 mg test substance/L under static conditions. In addition, to differentiate between a direct toxic effect on algal growth, as induced by the test substance, and an indirect effect on growth caused by light absorption of the coloured test substance in solution, alga were exposed to medium without test substance under varying reduced light conditions. The analytically determined test item concentrations in the test media varied in the range from 95 to 108% of the nominal values indicating that the test item was stable during the test period of 72 hours under the conditions of the test. Therefore, the reported biological results are based on the nominal concentrations of the test item.

Alga exposed to concentrations from 10 mg/L test substance showed increased inhibition on growth rate and biomass compared to alga exposed to test media without test substance under varying reduced light conditions. Therefore, only a part of the algal growth inhibition was obviously caused by the pure light effect and at the higher test concentrations a real toxic effect of the test item on algal growth cannot be excluded. For this reason, the results of the experimental part in which algae are exposed to the test substance are taken into consideration for the determination of toxicity (as in a usual algae test). From the available data the ErC50 and EbC50 values were calculated to be 46.9 and 20.4 mg/L, respectively. The NOEC was determined at 3.2 mg/L for both endpoints.