Fatty acids, C8-18 and C18-unsatd.

Toxicity to aquatic algae and cyanobacteria

Description of key information

Worst-case EC50 for growth rate > 7.6 mg/L - no effects up to the limit of water solubility are expected.

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 here no study on algae is available. Thus a read-across is prepared to studies conducted with the pure homologues C12 (CAS 143 -07 -7), C14 (CAS 544 -63 -8) and C16 (CAS 57 -10 -3) some of the main components of the mixture.

For the evaluation of the mixture only studies available for pure homologues which were determined as key were chosen for read-across. All linked studies conducted with the pure homologues were used in a weight of evidence approach to cover the endpoint "toxicity of aquatic algae" for the considered fatty acid mixture.

Fatty acid homologue	EC50for growth rate (as reported in the study)	Water solubility*	Test design and species	Reference
C12 - CAS 143-07-7 lauric acid	> 7.6 mg/L (initial mean measured)	4.81 mg/L at 20 °C	72 h, static, Pseudokirchneriella subcapitata	NITE, 2001d
C14 - CAS 544-63-8 myristic acid	> 2.1 mg/L (measured)	< 0.13 at 20 °C	72 h, static, Pseudokirchneriella subcapitata	NITE, 2003d
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

* see category justification

In the study available for lauric acid (12: CAS 143 -07 -7), which was conducted according to the OECD guideline 201, algae (Pseudokirchneriella subcapitata) were exposed with the test substance in a dose-response experiment under GLP-conditions (NITE, 2001d). In the static test an EC50 for growth rate > 7.6 mg/L (initial measured) was determined, which is above the reported limit of water solubility for this homologue.

The homologue myristic acid (C14: CAS 544 -63 -8) was tested on Pseudokirchneriella subcapitata in a static limit test according

to OECD 201 in compliance with GLP-requirements (NITE, 2003d). The tested concentration of 2.1 mg/L (measured) was above the limit of water solubility reported in the category justification for the C14 fatty acid homologue (< 0.13 mg/L). As no effects could be observed at this concentration the EC50 for growth rate is reported to be above 2.1 mg/L.

The palmitic acid (C16: CAS 57 -10 -3) was tested on Pseudokirchneriella subcapitata as well under OECD 201 in a GLP-study (NITE, 2003b). As described for the C14 fatty acid homologue, only 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).

From the reported results of the test available for the fatty acid homologues C12, C14 and C16 no adverse effects of the considered fatty acid mixture are expected on algae. In all cited tests no effects up to the water solubility limits of the pure homologues were reported. Thus the EC50 based on growth rate is expected to be > 7.6 mg/L for the fatty acid mixture.