Heptasodium bis[4-hydroxy-5-[(2-hydroxy-1-naphthyl)azo]-3-[(2-hydroxy-3-nitro-5-sulphophenyl)azo]naphthalene-2,7-disulphonato(5-)]cobaltate(7-)

Short-term toxicity to aquatic invertebrates

Description of key information

EC₅₀(48 h,Daphnia magna) > 66.9 mg/l (measured concentration; equivalent to 100 mg/l nominal)

EC₅₀(48 h,Daphnia magna) > 52.9 mg/l (measured concentration; equivalent to 100 mg/l nominal)

Additional information

No data on the test item was available, thus a read-across approach was adopted using two similar substances. In particular, available data on Similar Substance 01, i.e. a cobalt complex with 2 phenyl-azo-naphtyl ligands functionalised by similar groups was used. A detailed description of the read-across approach is attached in section 13.

The short-term toxicity of Similar Substance 01 towards aquatic invertebrates was assessed in 2 acute toxicity studies with Daphnia magna according to OECD guideline 202.

As the first study (2015) was not GLP compliant, a second study (2017) was conducted with the same batch of test substance. 

In both studies, nominal test solutions of 0, 6.25, 12.5, 25, 50, and 100 mg/l were used. The colour of the test solutions increased from very light pale pink to a deep purple color. In the first study, test solution colour remained unchanged throughout the test, however at test completion, reddish grains were observed at the bottom of the test vessels in the 12.5 mg/l test solution, and dark red/purple precipitate was observed in the 50 mg/l and 100 mg/l test vessels. In the second study, suspended particles of test item were visible in the 50 mg/l and 100 mg/l test concentrations from the start of the test. Throughout the test the color of test solutions remained consistent. The test endopoints were based on the mean measured concentration of test item in both studies since the measured concentrations were not within 80 -120 % of the nominal concentrations. The mean measured concentrations were 5, 10.1, 18.8, 35.3, and 66.9 in the first study and 5.0, 9.6, 18.3, 34.1, and 52.9 mg/l in the second study.

As undissolved material was present in both studies, it can be concluded that the daphnids in the test solutions were exposed to the highest achievable concentration (nominal 100 mg/l; measured 66.9 mg/l and 52.9 mg/l, respectively). Neither study revealed effects in any of the concentration groups, not even in the highest one (nominal 100 mg/l) which displayed precipitated test material.

In conclusion, up to the solubility limit no effects were noted.

Additional supporting data for Similar substance 02 is available, as follows.

Similar Substance 02 was tested according to OECD guideline 202 under static exposure conditions with Daphnia magna. Nominal concentrations of 0, 45, 100 and 220 mg/l were used, corresponding to actual mean concentrations of 0, 17, 58 and 131 mg/l. In the nominal concentrations of 100 and 220 mg/l, a sediment at the bottom of the test vessel was noted after 24 h. As measured concentrations did not fall within 80 -120 % of nominal concentrations, mean measured concentrations were used to derive results. No effects in terms of immobilisation or abnormal behaviour were noted in controls and test concentrations. Therefore, the EC0 value after 48 h was determined to be 131 mg/l, the EC50 and EC100 values were higher than 131 mg/l.