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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

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).
Following a preliminary range-finding test, Scenedesmus subspicatus was exposed to an aqueous solution of the test material at concentrations of 0.070, 0.14, 0.28, 0.55 and 1.1 mg/l (three replicate flasks per concentration) for 72 hours, under constant illumination and shaking at a temperature of 24 + 1°C.
Samples of the algal populations were removed daily and cell concentrations determined for each control and treatment group, using a Coulter Multisizer Particle Counter.
Exposure of Scenedesmus subspicatus to the test material gave an EbC50 (72 h) value of 0.15 mg/l; 95% confidence limits 0.13 - 0.18 mg/l and an ErC50 (0 - 72 h) value of 0.36 mg/l; 95% confidence limits 0.26 - 0.50 mg/l. The No Observed Effect Concentration was 0.070 mg/l.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.36 mg/L
EC10 or NOEC for freshwater algae:
0.07 mg/L

Additional information

In the key study (Vryenhoef & McKenzie, 2005; SPL project number: 1666/076) for the algal inhibition to Scenedesmus subspicatus, the study was conducted according to the OECD Guideline 201 (Alga, Growth Inhibition Test).

This study is presented as the key information as the reliability rating for this study is 1, according to the criteria of Klimisch, 1997, and this study was conducted most recently and therefore is considered the most reliable study.

The following supporting studies are also avaiable for this endpoint:

The Ward, Boeri & Magazu, 1994 study is considered to have a reliability rating of 2, according to the criteria of Klimisch, 1997.

Restriction due to the lack of analytical confirmation of test concentrations.

Based on the number of cells/ml, the 72 hour EC50 is 100 mg/L and the 96 hour EC50 is 97 mg/L. Based on the average specific growth rate, the 72 hour EC50 is 270 mg/L and the 96 hour EC50 is 240 mg/L.

Based on the number of cells/ml or the average specific growth rate, the 72 and 96 hour NOEC values are 62 mg/L

Regrowth of inhibited cultures from the 350 mg/L test level revealed that the effect at this concentration of the test material was algistatic.

Effect levels in this study were reported in terms of concentration, however as WAFs (water accommodation fraction) were used, the results should be reported in terms of loading levels (e.g. NOELR and EL50).

The Scholz, 1992 study is considered to have a reliability rating of 4, according to the criteria of Klimisch, 1997 as the information was obtained from the 2006 SIDS dossier due to the original report being unavailable. Further restrictions due to the lack of analytical confirmation of exposure concentrations.

On the basis of growth rate the 72 hr ErC50 was > 0.765 mg/L 10% inhibition of growth rate was attained at > 0.765 mg/L The NOEC was 0.442 mg/L. Effect levels in this study were reported in terms of concentration, however as WAFs (water accommodation fraction) were used, the results should be reported in terms of loading levels (e.g. NOELR and EL50).