OECD 201: Freshwater Alga and Cyanobacteria, Growth Inhibition Test

Algae are primary producers in freshwater and marine ecosystems. They provide the basis of the aquatic food chain. Herbivorous organisms depend directly on algae as nutrition. But also the consumers are indirectly concerned via the trophic cascade. Therefore, possible toxic effects on the growth of algae have to be assessed for plant protection products, biocides, industrial chemicals and medicinal products for human and veterinary use that may get into aquatic environment. Algae are very sensitive to xenobiotics and standardised tests systems are established since many years.

Study Design

Test organisms

We offer tests with different algae species, which are supplied by official breeders and cultivated in the IBACON laboratory under standardised conditions.

Green Algae
  • Pseudokirchneriella subcapitata (recently renamed as Raphidocelis subcapitata, formerly known as Selenastrum capricornutum)

  • Desmodesmus subspicatus

  • Navicula pelliculosa

  • Anabaena flos-aquae

Algae in test vessels with test item of different concentrations

Course of the test

The test is performed with three replicates per test item group and six replicates in the control. The test item is mixed into the test water homogenously. Afterwards, algae are added to achieve a species dependent initial algal cell number per water volume. Cell densities are determined during the test and at the end of the test by examining samples from the flasks by spectrophotometry or microscopy. Test substance concentrations are analysed at test start and test end to verify dosage of the test item. A toxic reference, tested twice per year, proofs the sensitivity of the test system.

Closed Vessel Studies

Test items with high vapour pressure are tested in closed vessels to avoid evaporation of the test item. Furthermore adaptions of the test media are necessary to compensate the missing air exchange.

Recovery Studies

The recovery potential of algae can be monitored with recovery studies. After an acute algal test, an aliquot of some samples is introduced in pure test medium and the samples are exposed for some further days. Growth of the algae is compared to the growth of a control.

Species Sensitivity Destribution

In order to determine a species sensitivity distribution (SSD), additional algae species can be tested on request e.g. chlorella vulgaris or tetraedron caudatum.


Cell densities of the algae or Cyanobacteria are determined after 24, 48, 72 and, if required, after 96 hours. Growth is measured as the increase of cell density over the test period. EC50 (EC20, EC10), NOEC and LOEC are calculated for growth rate, yield and/or biomass. Additionally, algal shape is observed microscopically at the end of the test.

Guidelines and Literature

  • OECD Guideline for Testing of Chemicals, No. 201: "Freshwater Alga and Cyanobacteria, Growth Inhibition"
  • Commission Regulation (EC) No 761/2009 amending Regulation (EC) No 440/2008, Annex, Part C, C.3.: "Algal Inhibition Test", p. 36-56, Official Journal of the European Union (EN)
  • EPA Ecological Effects Test Guidelines OPPTS 850.5400 Algal Toxicity, Tiers I and II