Comparison of four measuring techniques to assess growth inhibition in standardized tests with seven freshwater algae and cyanobacteria

As representatives of primary producers, algae and cyanobacteria play an important role in assessing the risk of chemicals. However, the list of standard algal species commonly used for toxicity testing comprises very few species so that there is an urgent demand to identify further non-standard species which can be used for higher-tier risk assessment in general and the analysis of species sensitivity distributions in particular. In this study, four measuring techniques to assess growth inhibition were compared using five non-standard and two standard algal species and 3,5-dichlorophenol as reference substance. Regarding sensitivity and suitability, the measuring techniques were ranked in the following descending order: delayed fluorescence, prompt fluorescence, photometric absorbance, and microscopic cell count. All five non-standard species fulfilled the validity criteria if tested with delayed fluorescence.