OECD 221: Lemna sp. Growth Inhibition Test

Lemna gibba is a representative species for higher aquatic plants. The plants are small, easy to cultivate and sensitive towards chemicals. Testing of Lemna is required for plant protection products acting as an herbicide or a plant growth regulator. The Lemna test is also considered as a suitable alternative to an algal test (OECD 201) for strongly coloured substances. If your product shows considerable toxicity, a Lemna recovery study or a test with other higher aquatic plants e.g. Myriophyllum or Glyceria may be indicated.

Study Design

Test organisms

We sustain our own laboratory culture of Lemna gibba. The plants are kept in exponential growth by transferring them regularly into new test vessels.

Course of the test

Depending on the properties of your substance, Lemna studies can be performed in a static test design without test item renewal. For precipitating or degrading substances a semi-static test design with renewal of the test item is suitable. Usually, a dose response study is performed. The exposure duration is 7 days with assessments usually on day 3 and 5. The number of fronds will be counted and the dry weight will be determined at the end of the test.

Test substance concentrations are analysed at test start and test end to verify the dosage of the test item. A toxic reference, tested twice per year, proves the sensitivity and suitable condition of the test system. The focus of our studies is the determination of the EC50 and the no observed effect concentration (NOEC). Depending on the usage of your product and its environmental fate properties, duration and number of exposure and recovery periods can be adapted.

Recovery studies

Where on the basis of the standard Lemna test a high risk to aquatic plants is identified, a recovery study can be useful to provide further information on the extent of effects of the test item to aquatic higher plants.

After a defined time of exposure, e.g. after seven days as the standard exposure period, the fronds are rinsed and 12 fronds are transferred into pure test water without test item. The growth of the control plants is compared to the growth of the plants previously exposed to the test item. The recovery periods may be extended until a recovery in growth is observed.


NOEC, LOEC and EC50 (EC20, EC10) for yield and growth rate based on frond number and dry weight.

Guidelines and literature

  • OECD Guideline 221: Lemna sp. Growth Inhibition Test
  • Commission Regulation (EC) No 761/2009, Annex, Part C, C.26.: "Lemna sp. Growth Inhibition Test", Official Journal of the European Union (EN)
  • OECD Guideline 23: Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures