Algae Tests

Abstract

Unicellular Algae are an important food source in the aquatic ecosystem, thus representing a relevant trophic level in the aquatic ecotoxicity test battery. The algal growth inhibition test is described in ISO 8692 (2004) and OECD 201 (2006). After the classical setup, the ISO protocol also describes a miniaturized setup to be used for screening purposes. Both protocols were performed within this ring test, using very different test volumes. Also two algal species were used: Desmodesmus subspicatus (44%) and Pseudokirchneriella subcapitata (56%). In total 143 test results were presented, of which 106 were accepted. The invalid tests were rejected mainly because reference data were lacking or out of range, and in a few cases because of low growth rate in controls. As almost no practical problems were reported, and the mean EC₅₀ value of the reference substance showed low variation despite the differences in setup, it can be concluded that the algal test is robust and reliable. The interlaboratory variation to the EC₅₀ values was more considerable for the complex waste samples. The samples clearly differed in toxicity WOO > INC > SOI. Mean LC₅₀ values were respectively 1.3%, 8.8% and >highest test concentration for Desmodesmus, and 0.22%, 2.4% and >highest test concentration for Pseudokirchneriella. The differences between the species were not statistically significant. The sensitivity of the algal growth inhibition test for these waste samples was comparable to the results of the Daphnia acute immobility test. The algal test is recommended as part of the waste test set because of its ecological relevance and robustness. No preference for species or setup was detected.