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Efficacy tests of algicides

Biocidal products against algae (algicides) are i.a. used in aquariums, garden ponds, swimming ponds, swimming pools (product type 2) or in cooling water systems (product type 11). For biocidal product authorisation efficacy data must be submitted to weigh up benefits and risks of the product. Authorisation of a biocidal product will only be granted if the product is shown to be sufficiently effective.

Suitable efficacy data is thus to be provided to clearly demonstrate that the product fulfills its label claims. The product claims are the precondition and base for efficacy testing.

So far, there are no binding standards for the efficacy testing of algicides. However, discussions with the competent authorities show that the standard algae growth inhibition test (e.g. according to OECD 201) is not considered to be a suitable approach as proof of efficacy, since the algae inoculum density at the start of the test is very low compared to the conditions of use of algicides. Instead of the inhibition of the algae growth rate, the decrease of the algal biomass is considered as a suitable endpoint. Furthermore, other types of algae, e.g. filamentous algae, might be requested as test organism depending on the product claims.

We offer laboratory studies to test whether your product meets its label claims under conditions specified for use. Tests are carried out in accordance with standard protocols (CEN, ISO, OECD) and are modified to meet the actual application according to the use instructions. Tests can be performed in accordance with Good Laboratory Practice (GLP). This is, however, not mandatory for efficacy tests.


We perform the efficacy tests with various species such as suspended green algae (e.g. Raphidocelis subcapitata, Desmodesmus subspicatus), filamentous green algae (e.g. Spirogyra sp.) or cyanobacteria (e.g. Synechococcus leopoliensis, Anabaena flos-aquae). To evaluate the efficacy the reduction of biomass caused by different active substance concentrations are determined. Biomass is monitored by measuring chlorophyll fluorescence at various time points over a certain period of time (hours to weeks). The tests always include a negative control without active substance to compare the reduction of biomass in the batches with active substance with the increase of biomass in the control. The tests can be modified according to criteria defined (concentration range, algae species, algae start density, temperature, application method, time of exposure, etc.)