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Toxicity to aquatic algae and cyanobacteria

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Description of key information

One toxicity test with algae was performed. The test is well described and performed according OECD guideline 201 applying GLP conditions. The test is performed in natural river water i.e. applying the bulk approach and resulted in a 72 hr ErC10 of 34.5 µg/L  and 72 hr ErC50 of 119 µg/L.

Key value for chemical safety assessment

EC50 for freshwater algae:
119 µg/L
EC10 or NOEC for freshwater algae:
34.5 µg/L

Additional information

Cationic surfactants sorb strongly to anionic matrixes like glassware, river water constituents and algae. Extraction of cationic surfactants from these surfaces is possible but at the lower end of the concentration range the extraction efficiency is in relation to the detection limit in many cases not high enough. Especially in algae studies where at the low end of the concentration range the number of algae is still increasing with sometimes close to two orders of magnitude it has been shown to be difficult to recover the test substance. The use of the mean measured initial concentration to base the dose response upon is under these conditions adviced by OECD guideline 201 (point 40).

Tests with this type of substances using realistic worst-case (with a low DOC and suspended matter content) river water i.e. using the bulk approach as described in ECETOC technical report 88, are environmentally more relevant because the river water constituents stabilize the test substance in the test solution in a similar way as it would occur in the environment. Results from bulk approach tests are therefore ideal for risk assessment purposes. For classification and labeling however mitigation by riverwater constituents is not considered to be acceptable. To compensate for this mitigation, the endpoints are corrected by dividing the values by a factor of 10.

This factor of 10 is considered to be a realistic worst-case value because only a factor of ±2 difference in effect was observed in the algae tests with oleyl diethanolamine.

ErC50 (bulk) = 34.1 µg/L; ErC50 (normal) = 15.6 µg/L

ErC10 (bulk) = 86.7 µg/L; ErC50 (normal) = 53.8 µg/L

Thus for risk assessment purposes of this substance, the study following the bulk approach with an ErC10 of 34.5 ug/L is used and for classification and labeling a realistic worst-case ErC10 of 3.5 µg/L and ErC50 of 11.9 µg/L.