Fatty acids, C8-24

Toxicity to aquatic algae and cyanobacteria

Description of key information

EC50 (growth rate) > 100 mg/L - 241.22 mg/L for freshwater and marine species

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 one study on algae is available. In addition to the available study, a read-cross is performed to studies conducted with the pure homologues C12 (CAS 143 -07 -7), C14 (CAS 544 -63 -8) and C16 (CAS 57 -10 -3) and the mixture C14 -22 (CAS 68424 -37 -3). On the basis of the additional read-across a better comparison of the aquatic endpoints are given, as for fish and daphnids no mixture studies are available.

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
C14 - C22 - CAS 68424-37-3	> 100 mg/L (nominal)	Approx. 113 mg/L at 20 °C	96 h, static,Desmodesmus subspicatus	Mühlberg, 1993
C8 - C24 - CAS 71076-48-7	241.22 mg/L (nominal)	Approx. 113 mg/L at 20 °C	72 h, static,Skeletonema costatum	Hudson, 2005

* 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.

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).

The C14 -22 fatty acid mixture (CAS 38424 -37 -3) was tested on Desmodesmus subspicatus over a period of 96 h (Mühlberg, 1993). The static test was conducted according to DIN 38412 under GLP-conditions. In that test no effects on algae up to the highest test concentration is reported, thus the EC50 is above 100 mg/L.

In a study available for the mixture C8 -24 fatty acids, marine algae (Skeletonema costatum) were exposed for 72 h in a static system to the test substance (, 2005). In that test an EC50 for growth rate is reported to be 241.22 mg/L.

From the reported results of the test available for the fatty acid homologues C12, C14 and C16 as well as the mixtures C14 -22 (CAS 68424 -37 -3) and C8 -24 (CAS 71076 -48 -7) 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.

Concluding from the results of all available tests it is expected that the EC50 (growth rate) for algae will be in a range of > 100 mg/L (freshwater species) and 241.22 mg/L (marine species).