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Toxicity to aquatic algae and cyanobacteria

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Several studies on algae conducted on dark dyes, including those with a modified test system for coloured substances, showed that the growth inhibition is not due to a toxic effect of the dye, but to the light absorption of the stained water. Modified test system is usually conducted putting the dye above the algae testing solution, in a different vessel and not into contact with the alga. The same toxicity expressed as grow rate and yield inhibition has been observed at the same level as in the experiments with the algae is into contact with the dye. It has been deduced that the observed toxicity was related to the shading effect of the dye. This method has some limitation because it focuses on the shadow effect but gives no information on the real potential toxicity for algae of the tested substance. According to a broad agreement by EU Competent Authorities, the Lemna test is a suitable alternative to an algal test for strongly coloured substances, as mentioned in the introduction to the method C.26 “Lemna sp. Growth inhibition test” of the European Commission Regulation No 761/2009 of 23 July 2009. " This method is equivalent to OECD TG 221 (2006). The EU authorities’ agreement refers to the Manual of Decision (EU Manual of Decisions dated July 2006, at 13.5.3 Alternatives to the algae growth inhibition test with coloured substances). The method is also in conformity with the content of the Guidance on information requirements and chemical safety assessment — Chapter R.7b: Endpoint specific guidance; Table 7.8.3 Summary of difficult substance testing issues, available at: as indicated in the Guidance on the Application of the CLP Criteria v 4.0, section Commission Directive 2001/59/EC of 6 August 2001 adapting to technical progress for the 28th time Council Directive 67/548/EEC on the approximation of the laws, Regulations and administrative provisions relating to the classification, packaging and labelling of dangerous substances, paragraph, that states that “where it can be demonstrated in the case of highly coloured substances that algal growth is inhibited solely as a result of a reduction in light intensity, then the 72h EC50 for algae should not be used as a basis for classification. ”