Fatty acids, C14-18 and C16-18-unsatd.

Toxicity to aquatic algae and cyanobacteria

Description of key information

No effects up to the limit of water solubility are expected.
EC50 for growth rate (72 h) for marine species: 205.42 mg/L

Additional information

Studies are available for some pure homologue members of the fatty acid category. In addition some studies are available for certain fatty acid mixtures. Generally it could be stated that toxicity of fatty acids to aquatic organisms increases with increasing chain length up to the water solubility limit at a chain length of C12. For longer chains no effects at saturation are observed.

For the mixture under discussion a study conducted with the marine algae Skeletonema costatum is available. In addition a read-across is performed to a study (key study) conducted with a fresh water algae exposed to the pure homologue C16 (CAS 57 -10 -3), one of the main components of the mixture. For the other main constituent, stearic acid, no test on algae is available.

The results of both studies are summarzied in the following table:

Fatty acid homologue	EC50for growth rate (as reported in the study)	Water solubility*	Test design and species	Reference
C16 - CAS 57-10-3 palmitic acid	> 0.9 mg/L (initial mean measured)	< 0.05 at 20 °C	72 h, static, Pseudokirchneriella subcapitata	NITE, 2003b
C14 - C18 and C16 - C18 unsatd. CAS 67701-06-8	205.42 mg/L	No data available for marine water	72 h, static, Skeletonema costatum	Hudson, 2006

* see category justification

Palmitic acid (C16: CAS 57 -10 -3) was tested on Pseudokirchneriella subcapitata under OECD 201 in a GLP-study (NITE, 2003b). One test substance concentration was used (10 mg/L nominal, corresponding to 0.9 mg/L initial mean measured), which was above the reported water solubility limit for this substance (< 0.05 mg/L according to the category justification). As no effects could be observed at this test concentration, the EC50 for growth rate is reported to be above 0.9 mg/L (initial mean measured).

The C14 - C18 and C16 - C18 unsaturated fatty acid mixture (CAS 67701 -06 -8) was tested on the marine algae Skeletonema costatum (Hudson, 2006). The static dose-response test was conducted according to ISO 10253 in accordance with GLP-requirements. The test resulted in an EC50 for growth rate of 205.42 mg/L after 72 h exposure.

From the reported results of the test available for the fatty acid homologue C16 no adverse effects of the considered fatty acid mixture are expected on algae. In the cited test no effects up to the water solubility limits of the pure homologues were reported. Thus for the considered fatty acid mixture no effects within the range of water solubility is expected. The EC50 for growth rate determined for marine species was reported to be 205.42 mg/L after 72 h exposure.