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

Short-term toxicity to aquatic invertebrates

Description of key information

No effects on invertebrates up to the limit of water solubility. 
LC50 for marine invertebrates: 357.5 mg/L in brackish test water

Additional information

Studies are available for the pure homologue members of the fatty acid category. In addition some studies are summarized 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 fatty acid mixture under consideration, which contains as main homologues C16 and C18, one study is available for a marine copepod. In addition read-across is performed to studies available for the pure homologues C16 (palmitic acid, CAS 57 -10 -3) and C18 (stearic acid, CAS 57 -11 -4). For the evaluation of the mixture only studies available for the pure homologues which were determined as key studies or used to cover the endpoint via weight of evidence 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 "short-term toxicity to invertebrates" for the considered fatty acid mixture.

Fatty acid homologue	LC/EC50 (as reported in the study)	Water solubility*	Test design and species	Reference
C16 - CAS 57-10-3 palmitic acid	> 4.8 mg/L (measured, geom. mean)	< 0.05 at 20 °C	48 h, static,Daphnia magna	NITE, 2000a
C18 - CAS 57-11-4 stearic acid	> 32 mg/L (nominal)	insoluble	47 h, static,Daphnia magna	Hooftman, 1991
	> 20 mg/L (nominal)		Artemia salina, saltwater	Curtis et al.,1970
C14 - 18, C16 - 18 unsatd.- CAS 67701-06-8	357.5 mg/L	No data available for brackish water	48 h, semi-static,Acartia tonsa, brackish water	Thomson, 2006

* see category justification

Palmitic acid (C16: CAS 57 -10 -3) was tested on daphnids in a 48 h static test (NITE, 2000a) under GLP. In the limit test a nominal test concentration of 10 mg/L (corresponding to a measured concentration (geom. mean) of 4.8 mg/L) was used. No effects on mobility of daphnids could be observed during the test period of 48 h. Thus the EC50 is reported to be above 4.8 mg/L (measured concentration) which is far above the limit of water solubililty (see table above and category justification).

For the evaluation of toxic effects of stearic acid (C18: CAS 57 -11 -4) on aquatic invertebrates two studies were taken into account. A static test was conducted on daphnids over 47 hours according to the EU method C.2 in compliance with GLP requirements (Hooftman, 1991). Different concentrations were tested in the study using test water of different hardness. In this study the EC50 -value was reported to be above 32 mg/L (nominal). This result is in line with the EC50 given in the other available study for stearic acid (C18: CAS 57 -11 -4). In the publication of Curtis et al. (1970) Artemia salina were tested. The authors reported an EC50 > 20 mg/L.

The C14 - C18 and C16 - C18 unsaturated fatty acid mixture (CAS 67701 -06 -8) was tested on the marine copepod Acartia tonsa using brackish water (Thomson, 2006). The semi-static test was conducted according to ISO 14699 in accordance with GLP-requirements. Different test concentrations were used and the LC50 after 48 h was reported to be 357.5 mg/L.

Concluding from the results reported for the pure homologues C16 and C18 no toxic effects on invertebrates within the range of water solubility are expected for the considered fatty acid mixture. The LC50 determined for marine species was reported to be 357.5 mg/L tested in brackish water.