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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The 72-h ErC50 is >100 mg/L and the 72-h ErC10 is 4.2 mg/L in freshwater alga (S. subspicatus).

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
4.2 mg/L

Additional information

In a GLP compliant study, performed according to the OECD guideline 201, the influence of the test substance on the growth of the green alga Scenedesmus subspicatus was investigated in a 72-hour static test. The nominal test concentrations were 0, 0.32, 1.0, 3.2, 10, 32 and 100 mg/L of the test substance. The analytically determined test substance concentrations varied from 83% to 116% of nominal values.The mean measured concentrations (calculated as the average over all measurements per test concentration) ranged from 94 to 115% of nominal. Consequently, the test item concentrations were sufficiently constant during the test period of 72 hours under the conditions of the test, and the reported biological results are based on the nominal concentration of the test item.

As all test media were slightly to strongly coloured by the test substance, the test method was slightly modified to determine the growth inhibition effect due to reduced light intensities in the coloured test media. In experiment A, the normal test was performed, but in experiment B, growth inhibition of Scenedesmus subspicatus was observed when the algae grew in test water without test item, but under reduced light intensities by the filter effect of the colored test media. The growth inhibition effect of the test substance on Scenedesmus subspicatus was caused in part by the indirect effect, the light absorption in the colored test solutions. However, at the highest test concentration a real toxic effect of the test item on the growth of Scenedesmus subspicatus can not be excluded. Therefore, the results of this experimental part, where the algae grew in the test media with dissolved test item as in a usual algal growth inhibition test should be taken into consideration for the determination of the toxic effect of the test item on the growth of Scenedesmus subspicatus.Therefore, the results of experimental part A, where the algae grew in the test media with dissolved test item were used for the determination of the toxic effect. Based on these findings, the 72-hour ErC50 for growth inhibition and the EbC50 for biomass were determined at >100 mg/L and 17 mg/L respectively. The ErC10 and EbC10 values were 4.2 mg/L and 0.76 mg/L respectively and the NOEC was 1 mg/L for both endpoints.