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Toxicity of Cu, Co, Hg and Fe on the freshwater green algae Chlorella kessleri and Raphidocelis subcapitata using microplate algal bioassay compared to standard Erlenmayer flask assay

Algae have been shown to be sensitive to a wide range of toxic compounds and thus they have been used in a regulatory testing. The standard algal toxicity test on Erlenmayer flasks has several modifications that attempt to improve some of the dissadvantages of this procedure, and one of the modifications is the miniaturization of the test procedure. In this paper toxicities of CuCl2 • 2H2O, CoCl2• 6H2O, HgCl2 and FeCl3• 6H2O were tested using algal growth inhibition bioassays on two freshwater green algae Raphidocelis subcapitata (=Selenastrum capricornutum) and Chlorella kessleri. The aim was to compare the algal growth inhibition EC50s obtained from the toxicity testing of four metal compounds on microplates with the standard flask assay, as well as to compare the sensitivity of tested algae to selected metal compounds. Mercury showed to be the most toxic element for both algae. The toxicity hierarchy for both algae, according to the mean values from both methods was: Hg>Cu>Co>Fe. In both methods C. kessleri was more sensitive (0.11 – 8 mg l-1, with average value of 1.777 mg l-1) than R. subcapitata (0.33 – 15.34 mg l-1 ; average 3.68 mg l-1) to tested metal compounds. Algal bioassay in microplates gave comparable results to standard flask bioassay for both tested algae. The increasing number of environmental samples and chemicals that need to be tested for toxicity is requiring time and cost effective alternatives such as the miniaturization of testing procedures which we can according to our results recomend.

metals; EC50; growth bioassay; growth rate; Chlorella kessleri; Raphidocelis subcapitata

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