OECD 201: Freshwater alga and cyanobacteria, growth inhibition test
Determination of the effects of a test substance on the growth of freshwater microalgae and cyanobacteria according to OECD Test Guideline 201 (equivalent to EU Method C.3 under Commission Regulation (EC) No. 440/2008 on REACH test methods).
In the test, exponentially growing algal or cyanobacterial cultures are exposed in batch vessels to a minimum of five test concentrations, typically with three replicates per concentration, to generate a concentration–response relationship. Tests are run in nutrient-sufficient medium under continuous fluorescent illumination, with pH recorded at the start and end of the exposure. Microscopic checks are performed to verify a normal, healthy inoculum at the outset and note any morphological abnormalities at termination. Growth is quantified over time using a biomass surrogate such as cell number and/or fluorescence, from which average specific growth rate and yield are derived as the primary response variables.
Chemical analysis of the test medium is recommended at the start and end of exposure, with additional intermediate sampling where concentration losses are expected; for dissolved concentration measurements, algae can be separated from the medium prior to analysis (e.g. by low-g-force centrifugation). Results are reported as concentration–response curves with ErC50 and NOEC/LOEC values calculated from average specific growth rate and yield, based on initial/nominal concentrations or exposure-based metrics such as geometric means or modelled decline where applicable. pH values and microscopic observations are included in the final report.
The OECD 201 method is recognised in regulatory submissions under the EU REACH regulation as part of aquatic hazard characterization, and under the U.S. Toxic Substances Control Act (TSCA), where EPA may require algal toxicity testing to OPPTS 850.5400/OECD 201 for new chemical substances.
- Suitable sample matrices
- Chemicals, chemical formulations, mixtures
- Available quality systems
- Accredited testing laboratory
- Standard
- Method expert
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