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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 item on the growth of the green alga Pseudokirchneriella subcapitata.  The method followed was designed to be compatible with the 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 growth rate EC50 was 69 mg/L with 95 % confidence limits of 62 - 78 mg/L. The NOEC was 16 mg/L and the LOEC was 40 mg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
69 mg/L
EC10 or NOEC for freshwater algae:
40 mg/L

Additional information

The test substance was assessed for acute toxicity to freshwater algae according to OECD Guidelines for Testing of Chemicals (2006) No 201.

 

The test item was suspected to be volatile and hence testing was conducted in completely filled, stoppered test vessels in order to minimize possible losses due to volatilization. Following the recommendations of published data (Hermanet al 1990) in order to prevent inhibition of growth due to the restriction of gaseous exchange, additional sodium bicarbonate was added to the culture medium to provide a source of carbon dioxide for algal growth. The 40 mg/L test cultures were observed to be pale green dispersions whilst the 100 mg/L test cultures were observed to be clear colorless solutions.

 

Analysis of the test preparations at 0 and 72 hours showed measured test concentrations to range from 89% to 98% of nominal and so the results are based on nominal test concentrations only.

 

The growth rate EC50 was 69 mg/L with 95 % confidence limits of 62 - 78 mg/L. The corresponding growth rate EC10 was 40mg/L. The NOEC was 16 mg/L and the LOEC was 40 mg/L.

The preferred observational end point in this study is algal growth rate inhibition 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.