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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Link to relevant study record(s)

Description of key information

Not toxic to algae:
EC50 > 100 mg/L
EC10 > 100 mg/L
NOEC > = 100 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
100 mg/L

Additional information

An aqueous dispersion of Indigo and Cremophor RH 40, which ends up as a deep-blue emulsion in the stock solution (1000 mg/L and 200 mg/L, respectively) has been tested. The tested concentrations are 3.91, 7.81, 15.63, 31.25, 62.5, 125, 250, and 500 mg/L. No information is given on the colour of the tested concentrations, however based on the fact that the stock solution gave a deep blue emulsion, it can be anticipated that the test solutions showed also considerable shades of blue discolouration. The effects on algae growth in this study is hence most likely an algae‑static effect due to light absorption of the dye and not an algae-toxic effect of the test substance. Both, effects of light absorption and the use of an emulsifier which leads to an artificial und untypical emulsion have not been discussed in this study. This study is hence not considered relevant and reliable for the assessment of the registered substance.

Only limited information is given in the OECD SIDS document on this algae study and the original study report is not publically available. Therefore, not sufficient information on the test substance identity and on the study conduct could be gained from the summary report to include this study in the Indigo assessment of the registered substance. The only substance information is the Indigo content of 96% derived from the information on the acute fish test without information on impurities contained. Concentrations of 1.8 to 18 mg/L were tested in presence of the co-solvent DMSO without any information on the amount of DMSO used, the solubility of Indigo in this solvent or effects seen in the vehicle control group. No analytical monitoring took place during the study. The test concentrations used lie above the water solubility reported to be 0.99 mg/L in the OECD SIDS report.

Due to the missing information on substance identity and study conduct, the study was considered not to be reliable and cannot be used for assessment of the registered substance.