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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The acute toxicity of the test substance to algae was assessed according to OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) No 761/2009.  The EC50 based on growth rate was 10.2 mg/L with 95 % confidence limits of 9.7 - 11 mg/L.  The growth rate EC10 was 8.2 mg/L, the NOEC was 3.3 mg/L and the LOEC was 9.0 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
10.2 mg/L
EC10 or NOEC for freshwater algae:
8.2 mg/L

Additional information

The test substance was assessed for acute algal toxicity according to OECD Test Guideline 201.

Preliminary solubility work conducted indicated that the test item was practically insoluble in water using traditional methods of preparation e.g. ultrasonication and high shear mixing. Based on this information the test item was categorized as being a ‘difficult substance’ as defined by the OECD Guidance Document on Aquatic Toxicity Testing of Difficult Substances and Mixtures (OECD 2000). Therefore a media preparation trial was conducted in order to determine the solubility of the test item under test conditions. This trial indicated that a dissolved test item concentration of approximately 42 mg/L could be obtained using a saturated solution method of preparation.

Analysis of the test preparations at 0 hours showed measured test concentrations to range from 1.4 to 33 mg/L. There was no significant change in the measured concentrations at 72 hours and so the results are based on 0-Hour measured test concentrations only.

The growth rate (r) and yield (y) of Pseudokirchneriella subcapitata (CCAP 278/4) were affected by the presence of the test item over the 72-Hour exposure period.

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results based on the 0-Hour measured test concentrations: The growth rate EC50 was 10.2 mg/L with 95 % confidence limits of 9.7 - 11.0 mg/L. The growth rate EC10 was 8.2 mg/L, NOEC was 3.3 mg/L and the LOEC was 9.0 mg/L.

The preferred observational end point in the algal growth inhibition test is growth rate because it is not dependent on the test design (ECHA guidance Chapter R.7b v1.1). The EU CLP regulation (No 1272/2008 and its adaption 286/2011) also states that classification should be based on the ErC50. The preferred observational endpoint in long-term studies is the EC10 value because it is derived from the dose response curve. In contrast the NOEC depends on the experiment design (e.g. the concentrations used in the test). Thus the 72-h EC50 and EC10 based on growth rate are used for classification purposes.