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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Considering that the test substance could influence the photosynthesis capacity of algae cells in the test solution, it was considered a test using Lemna spp as test organism.

Key value for chemical safety assessment

Additional information

Coloured substances are often assumed to be not adequately assessed by the algal growth inhibition test due to shading effects on algae. Coloured substances can absorb photosynthetically active light and hence limit growth of algal cultures. Absorption will be proportional to test substance concentration and, as a consequence, it can result in growth inhibition which is difficult to distinguish from inherent toxicity.

Several studies on algae conducted on dark dyes, including those with a modified test system for dye-stuffs, showed that the growth inhibition is mainly correlated to the reduced light absorption, caused by the stained water and not due to an effective toxicity of the dye.


A modified test design has been proposed by the cooperation of the Ecological and Toxicological Association of Dyes and Organic Pigments Manufacturers (ETAD) (Memmert et al) in order to eliminate the effect of shading. Nonetheless this method has some limitations, as it focuses on the shadow effect, giving no information on the real potential toxicity for algae of the tested substance.

Considering that the test substance is a dye, a test using Lemna as a test organism was run, according to OECD guideline 221, as suggested also in the Guidance on Information Requirements and Chemical Safety Assessment Chapter R.7b: Endpoint specific guidance, published by ECHA.



Memmert U, Motschi H, Inauen J, W. Uthrich V. Inhibition of algal growth caused by coloured test substances. ETAD Project E 3023. Ecological and Toxicological Association of Dyes and Organic Pigments Manufacturers, Basel, Switzerland, 1994.