Reaction mass of copper complex of [(2,6-difluoroheterocycl-4-yl)amino]hydroxy{[2-hydroxy-3-sulfonato-5-(vinylsulfonyl)phenyl]diazenyl}naphthalene sulfonic acid, dialkali salt and copper complex of [(2,6-difluoroheterocycl-4-yl)amino]-hydroxy{[2-hydroxy-3-sulfonato-5-{[2-(sulfonatooxy)ethyl]sulfonyl}phenyl]diazenyl}naphthalene sulfonic acid, trialkali salt

Toxicity to aquatic algae and cyanobacteria

Description of key information

The reduction in biomass gain and growth rate in this test was the result of light absorption effects of the test substance instead of a toxic effect. Consequently, the results from this test are not appropriate to evaluate the toxicity of the test substance for algae. The EC50 value (in terms of chemical toxicity) could not be determined, but the hypothetical EC50 and NOEC values are likely to be substantially higher than the limit test concentration of 100 mg/L.

Additional information

A study was performed to assess adverse effects of the test substance on the growth (= increase in cell density) and the growth rate (= rate of increase in cell density with time) of the planktonic freshwater algal species Desmodesmus subspicatus over several generations. The study was conducted in accordance with EU method C.3 'Algal inhibition test' which is in most parts equivalent to the OECD guideline 201 'Alga, Growth Inhibition Test'. The test included a modification to enable determination of light attenuation by coloured test substances as a possible cause of growth inhibition as published by Memmert & Knoell (RCC Umweltchemie, August 1992).

Exponentially growing algal cells were exposed to a range of test substance concentrations for a period of 72 hours, nominally 0.62, 1.4, 3.0, 6.6, 14.5, 32 and 70.4 mg/l of test substance dissolved in water (PART I). A second series (PART II) of test vessels was treated in the same way as the controls, but placed below glass vessels containing the same range of test item concentrations as described above, but without algae. This test design allowed to distinguish between algistatic (indirect effect caused by light absorption) and algicidal (toxic) effects.

The cell densities were measured at 24 hour intervals. Inhibition of the algal population was measured as reduction in growth (index b) and growth rate (index r), relative to control cultures grown under identical conditions. Growth and growth rates were used to calculate a 'No Observed Effect Concentration' and a 'Lowest Observed Effect Concentration' according to DUNNETT (1955, 1964).

All results are expressed in terms of nominal concentrations. Measured concentrations ranged from 101 to 113 % of nominal values at 0 hours, and from 99 to 110 % of nominal values at 72 hours.

There was only little difference in growth inhibition between trials exposing algae directly to the test substance and trials using the test substance as a light filter only (test vessels with algae covered with glass dishes containing test item solution). For the nominal concentrations 14.5 and 32 mg/l differences of 10.1 and 18.4 % were determined, respectively. The concentrations above (70.4 mg/l) and below (6.6 mg/l) resulted in 0.6 % and 4.9 % difference, respectively. Accordingly, no concentration-response relationship demonstrating a true algicidal effect could be established. Therefore, the inhibition of growth observed in this study appeared to be caused by light absorption only. Consequently, the effect concentrations from this test are not appropriate for evaluating the toxicity of the test substance to algae.