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Toxicity to aquatic algae and cyanobacteria

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Schmidt, 1989, reported the concentration of 3 -chloro-p-toluidine causing fluorescence inhibition after 30 min exposure with EC10 = 1.8 mg/L and EC50 = 17.4 mg/L. Furter, results of a growth inhibition test after 168 hours exposure were determined to give EC10 = 2.1 mg/L and EC50 = 22.3 mg/L.
However, this study showed some shortcomings: According to the Guidance on information re-quirements and chemical safety assessment, Chapter R.7b (ECHA, 2008), results based on growth rate are preferred over growth inhibition since that endpoint is independent of the test design. Fluorecence measurement is not a preferred endpoint.
Further, algae test should be evaluated after 72 h exposure. EC values of both tests detaild by Schmidt, 1989, were determined at completely different times. Thus, it is unclear whether effects were determined in the monotone exponential growth phase. Follwing this, the study was rated as not assignable with significant methodological deficiencies.
Despite the detailed drawbacks the study also provides useable and relevant informations: The tests used Desmodesmus subspicatus (former Scenedesmus subspicatus) as test organism which is a preferred algae test species. Therefore, results should in principal be accepted. De-rived EC values allow to restrict the possible concentration range of the investigated compound. The study may, therefore, be used for weight-of-evidence although the exact EC value might not be reflected.
With respect to ¿classification and labelling¿ the algal test would not be decisive since a test with Daphnia magna was far more toxic with EC50 being 10 - 100times lower and < 1 mg/L (EC50 = 0.62 mg/L). Thus, 3-chloro-p-toluidine is R50 classified which is the worst classification for environment. A new algae test would not be relevant for C&L.

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