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Toxicity to aquatic algae and cyanobacteria

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Description of key information

In all loading rates tested, inhibition on algal growth was observed.
NOEL based on the average growth rates: <37.8 mg/L (wwt) < 18 mg/L (dwt.)
EL50 based on the average growth rates: 12 883 mg/L (wwt) 6055 mg/L (dwt.)

Key value for chemical safety assessment

EC50 for freshwater algae:
6 055 mg/L

Additional information

Exponential growth in the negative control cultures was observed. During the 72 h incubation period the cell density in the controls increased by a factor of about 118, corresponding to about 6.9 generations.

Different loading rates of Green liquor sludge were prepared in the test medium and the preparations were filtrated before for the test.

Based on the average growth rates in comparison to the negative controls: In all loading rates tested, the influence on algal growth ranged from 15.5 % to 85.3 % inhibition.

Based on the average growth yields in comparison to the negative controls: In all loading rates tested, the influence on algal growth ranged from 48.1 % to 99.1 % inhibition. The test culture containing the lowest loading rate showed an inhibition of 69.8 %, and therefore no EC50 value based on the yield can be calculated.

Results:

NOEL based on the average growth rates: <37.8 mg/L (wwt.) < 18 mg/L (dwt.)

EL50 based on the average growth rates: 12 883 mg/L (wwt) 6055 mg/L (dwt.)

The test showed a diffuse dose-response. The reasons for observed algae growth inhibition in all tested concentrations should be clarified by repeating the test applying more tailored testing protocol. Repeating the test by using a modified and more advanced testing protocol could reduce uncertainties in the final PNEC derivation. The CSA guidance R10 advises (pg. 8) "If the endpoint is critical for the outcome of the regulatory decision, a repetition of the study may sometimes be the easiest and most efficient solution, especially for non-vertebrate tests".

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