Objective of the study

The purpose of this test is to determine the effects of a pesticide on the growth of freshwater microalgae and/or cyanobacteria.

Circumstances under which the study is recommended to be required

Data with the technical-grade active ingredient (TGAI) are recommended to support all outdoor uses of the pesticide, including on turf.

Principle of the test

Exponentially growing test organisms are exposed to the test substance in batch cultures over a period of normally 72 hours. In spite of the relatively brief test duration, effects over several generations can be assessed.

The system response is the reduction of growth in a series of algal cultures (test units) exposed to various concentrations of a test substance. The response is evaluated as a function of the exposure concentration in comparison with the average growth of replicate, unexposed control cultures. For full expression of the system response to toxic effects (optimal sensitivity), the cultures are allowed unrestricted exponential growth under nutrient sufficient conditions and continuous light for a sufficient period of time to measure reduction of the specific growth rate.

Test organism

Testing is recommended to be carried out at least on one green alga. For active ingredients that are known phytotoxicants such as herbicides, desiccants and defoliants, a test on a second species from a different taxonomic group is recommended to be performed (e.g. a diatom)

Several species of non-attached microalgae and cyanobacteria may be used. The strains listed in the table below have been shown to be suitable.

If other species or strains are used, the strain and/or origin should be reported. It should be confirmed that exponential growth of the selected test alga can be maintained throughout the test period under the prevailing conditions.

Test substance

The test should be conducted with the technical grade active ingredient. In certain cases the test can additionally be done with the typical end-use product.

Typical endpoints of the study

The purpose of the test is to determine the effects of the test substance on the growth of algae. Two response variables should in principle be reported:

(a)    Average specific growth rate: this response variable is calculated on the basis of the logarithmic increase of biomass during the test period, expressed per day; and

(b)    Yield: this response variable is the biomass at the end of the test minus the starting biomass.

Testing guidelines

The following test guidelines may be used for determination of algal toxicity:

• OECD Guidelines for the Testing of Chemicals. Test No. 201: Freshwater alga and cyanobacteria, growth inhibition test
• US-EPA OCSPP Harmonized Test Guidelines. Ecological Effects Test Guidelines: OCSPP 850.4500  Algal Toxicity
• US-EPA OCSPP Harmonized Test Guidelines. Ecological Effects Test Guidelines: OCSPP 850.4550 Cyanobacteria (Anabaena flos-aquae) toxicity