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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The 72-h ErC50 for algae of 0.143 mg AO/L is calculated as the geometric mean of the results from four reliable studies performed using C12-14 AO on Pseudokirchnerella subcapitata which appears to be the most sensitive algal species based on the available data.
The 28-d NOEC of 0.067 mg AO/L is derived from a periphyton microcosm study in which more than 110 taxa of algae were exposed to the substance.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.143 mg/L
EC10 or NOEC for freshwater algae:
0.067 mg/L

Additional information

One study is available for C12-18 AO. In this study [Scheerbaum D (2000)] performed according to OECD TG 201 under GLP Desmodesmus subcapitata were exposed to C12-18 AO under static conditions for 72 hours at nominal concentrations of 0.019, 0.038, 0.075, 0.15 or 0.3 mg AO/L. The ErC50 (72 h) was 0.24 mg AO/L. Six reliable studies are available for C12-14 AO. In a study performed according to OECD TG 201 under GLP [Ginkel & Kroon (1990)] Pseudokirchnerella subcapitata were exposed to C12-14 AO under static conditions for 72 hours at nominal concentrations of 0, 0.020, 0.039, 0.078, 0.155 or 0.31 mg AO/L. The ErC50 (72 h) was 0.266 mg AO/L. In three supporting studies performed according to OECD TG 201 Pseudokirchnerella subcapitata were exposed to C12-14 AO for 72 hours under static conditions. ErC50 values of 0.159 mg AO/L [Brill J (2010)], 0.12 mg AO/L [Hanstveit & Oldersma (1997)] and 0.082 mg AO/L [Hanstveit & Oldersma (1997)] were reported. Exposure of Chlorella vulgaris to C12-14 AO for 72 hours under static conditions in accordance with OECD TG 201 resulted in an ErC50 of 1.14 mg AO/L [Vreys (2003)], whilst exposure of Desmodesmus subspicatus to C12-14 AO for 72 hours under static conditions in accordance with OECD TG 201 resulted in an ErC50 of 0.25 mg AO/L [Scheerbaum (2000)].

According to the Guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures, page 408, when larger data sets (four or more values) are available for the same species, the geometric mean of toxicity values may be used as the representative toxicity value for that species. Taking this guidance into account, the geometric mean 72 -h ErC50 for Pseudokirchnerella subcapitata is 0.143 mg AO/L.

C12-18 AO and C12-14 AO exhibit similar toxicity to algae based on the studies with both substances using Desmodesmus subspicatus. On this basis, the key value for the CSA is read across from the C12-14 studies performed using Pseudokirchnerella subcapitata, i.e. 0.143 mg AO/L.

The toxicity of C12-14 AO to algae was evaluated in a 28 -day freshwater periphyton microcosm assay. The microcosm was composed of a complex consortia of bacterial, cyanobacterial, algal, and fungal species, and included 110 taxa of algae (notably 87 diatom, 12 green, 7 blue-green, 2 euglenoid, 1 chrysophyte and 1 red). Two substrates (tiles, cobbles) were naturally colonised for 5 weeks in high quality flowing streams/rivers in. The periphyton-colonised tiles & cobbles were then brought into the laboratory and placed in a 28 day flow through test of the C12-14 AO. Periphyton communities were exposed to 0, 6.25, 12.5, 25, 50 or 100 ug AO/L (nominal) for 28 days. Mean measured concentrations were 4.3 (control), 8.6, 9.2, 16.1, 33.1 or 67.1 ug AO/L. There were clear location (i.e. colonisation stream) and substrate effects in this study. Tile and cobble were substantially different, as were the Little Miami River and Big Derby Creek communities. Adverse responses were absent by day 28 in all three communities. There were significant increases in some endpoints at the 2 highest test concentrations (50, 100 ug/L, nominal), but there were no significant decreases (adverse effects) for any endpoint. The No-Observed Effect Concentration (NOEC) of the substance to the periphyton community was determined to be >67 ug AO/L, the highest test concentration evaluated (mean measured concentration).

The studies performed using C12-18 AO and C12-14 AO show that algae appear to be relatively insensitive to changes in the alkyl chain length. It is considered valid in this case to read across the result of the periphyton study to C12-18 AO.