Alga, Growth Inhibition test (OECD Guidelines for the Testing of Chemicals No. 201)

The test estimates the growth inhibition of freshwater green algae or cyanobacteria by water soluble chemical substances. The green algae are exposed to various concentrations of the test substance over several generations under defined conditions. The inhibition of growth in relation to a control culture is determined over 72 hours.

The following species are considered suitable:

– Pseudokirchneriella subcapitata (previously called: Selenastrum capricornutum

– Desmodesmus subspicatus (previously called: Scenedesmus subspicatus)

The test design should include preferably three replicates and minimum 5 member dilution series at each test concentration.

Culturing apparatus: a cabinet or chamber is recommended in which a temperature in the range 21 to 25°C can be maintained at ± 2°C and continuous uniform illumination provided with a quantum flux ranging between 60-120 μE/m²s.

The cell concentration of the alga culture shall be measured daily. Counting may be performed microscopically or by electronic particle counter or by measurement of optical density or chlorophyll content.

The endpoint of the test is the highest concentration to inhibit growth by at least 50 per cent relative to the control or stop growth completely (EC50), and additionally, statistically, one can determine the highest concentration without observable effect (NOEC) or the lowest concentration with observable effect (LOEC).