Sodium 2,4-diamino-5-(4-(2-sulfoxyethanesulfonyl)phenylazo)benzenesulfonate

Toxicity to aquatic algae and cyanobacteria

Description of key information

The reduction in growth of Scenedesmus subspicatus were considered to be algaestatic effects due to light absorption by the coloured test substance.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

Additional information

Introduction.A study was performed to assess the effect of the test material on the growth of the green alga Scenedesmus subspicatus.The method followed that described in the OECD Guidelines for Testing of Chemicals (1984) No 201, "Alga, Growth Inhibition Test" referenced as Method C.3 of Commission Directive 92/69/EEC (which constitutes Annex V of Council Directive 67/548/EEC) and further refined for coloured test substances, to differentiate between a reduced growth of algae due to a true toxic effect of the chemical or due to an indirect effect, a reduction in growth by light absorption of the coloured test substance, (Memmertet al1994).

Methods.Following a preliminary range-finding test, Scenedesmus subspicatus was exposed to an aqueous solution of the test material for 72 hours, under constant illumination and stirred continuously via magnetic stirrer at a temperature of 24 ± 1°C. The test was conducted using two experimental methods performed in parallel.

Experiment A

In Experiment A the algae were exposed to test material concentrations of 3.2, 10, 32, 100 and 320 mg/L (three replicate vessels per concentration). Glass petri dishes above the test vessels contained culture medium alone. Therefore, inhibition of algal growth in these test vessels was due to a combination of both the toxic effects of the test material and reduction in light intensity.

Experiment B

In Experiment B the glass petri dishes above the test vessels contained test material solutions atconcentrations of 3.2, 10, 32, 100 and 320 mg/L. The test vessels (single replicate per concentration) contained algal cells in culture medium alone. Therefore inhibition of algal growth was due to a reduction in light intensity alone.

The difference between the inhibition values obtained in Experiment A and B can be interpreted as the true toxic effect of the test material on the algal cells.

Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter^®Multisizer II Particle Counter.

Results.

Experiment A

Exposure of Scenedesmus subspicatus to the test material in Experiment A gave an E_bC₅₀(72 h) value of 70 mg/L and an E_rC₅₀(0-72 h) value of 400 mg/L. The No Observed Effect Concentration was 3.2 mg/L.

These results indicate the combined toxic nature of the test material and the reduction in light intensity.

Analysis of the test preparations from Experiment A showed measured test concentrations to be in the range of 91% to 100% of nominal and so the results are based on nominal test concentrations only.

Experiment B

In Experiment B, reduction in light intensity resulted in reduction of algal growth. The following EC₅₀values were calculated based on the concentration of the test material in the glass petri dishes above the test cultures.

The reduction in growth of Scenedesmus subspicatus exposed to light passed through the test material solutions gave an E_bC₅₀(72 h) value of 94 mg/L and an E_rC₅₀(0-72 h) value of greater than 320 mg/L. The No Observed Effect Concentration was 32 mg/L.

These results indicate the effect of the test material due to a reduction in light intensity alone.

Given that significant inhibition of growth was observed in Experiments A and B it was considered that the test material exhibited an effect and that this effect was due to a reduction in light intensity, not the toxic nature of the test material.

 

The substance is not considered to be harmful to algae on the basis of toxicity.