2,7-NAPHTHALENEDISULFONIC ACID 5-[[4-CHLORO-6-(ETHYLPHENYLAMINO)-1,3,5-TRIAZIN-2-YL]AMINO]-3-[[5-[(2,3-DIBROMO-1-OXOPROPYL)AMINO]-2-SULFOPHENYL]AZO]-4-HYDROXY-,SODIUM SALT

Toxicity to aquatic algae and cyanobacteria

Description of key information

In freshwater algae the 72-h ErC50 is >100 mg/L and the 72-h ErC10 is 2.3 mg/L. These effect values are used as critical values in the assessment.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

2.3 mg/L

Additional information

The toxicity of the test substance towards aquatic algae was investigated in a GLP-compliant test according to OECD 201 (RCC, 1994).

In this study, freshwater alga (Scenedesmus subspicatus) were exposed for 72 hours to nominal concentrations of 0, 0.1, 0.32, 1.0, 3.2, 10, 32 and 100 mg test substance/L under static conditions. In addition, to differentiate between a direct toxic effect on algal growth, as induced by the test substance, and an indirect effect on growth caused by light absorption of the coloured test substance in solution, alga were exposed to medium without test substance under varying reduced light conditions. The analytically determined test item concentrations in the test media varied in the range from 85.9 to 105.0% of the nominal values indicating that the test item was stable during the test period of 72 hours under the conditions of the test. Therefore, the reported biological results are based on the nominal concentrations of the test item.

All test media down to the test concentration of nominal 0.32 mg/L were little to strongly coloured by the test substance. A moderately higher inhibition effect on the algal growth was observed in experimental part A, where the algae grew in the test solutions with dissolved test substance compared to the inhibition effect only by light absorption in experimental part B. Hence, the EC-values based on the results in experimental part B were higher than the corresponding EC-values in experimental part A. In experimental part A, the 72-hour NOEC for the biomass parameter was 0.10 mg/L. The growth rates µ after 72 hours test period were slightly less affected, the 72-hour NOEC being 0.32 mg/L. In experimental part B (light effect only), the 72-hour NOEC for both growth parameters algal biomass b and growth rate µ was 3.2 mg/L. For the quantification of the algicidal effect versus the growth inhibition due to the pure light filter effect, the differences between the percentages of the inhibition rates in experimental parts A and B after the 72 hours test period were calculated. For the biomass of algae these differences varied in the range of 4.0 % to 46.6 %, for the growth rate µ between 0.6 % and 15.8 %. These moderate differences between the inhibition rates in parts A and B were obviously caused by a real toxic effect of the test substance on the algal growth. The real toxic effect of the test substance amounted to in maximum about 47 % growth inhibition up to the highest test concentration of 100 mg/L. Based on these data, the ErC50 and EbC50 are both determined at >100 mg/L. The ErC10 and EbC10 values are calculated to be 2.3 and 0.11 mg/L, respectively and the NOErC and NOEbC finally, are set at 0.32 and 0.10 mg/L, respectively.