Fatty acids, C12-18

Short-term toxicity to aquatic invertebrates

Description of key information

Worst-case EC50 (48 h) expected to be 3.6 mg/L.

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 acute 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 acute effects at saturation are observed.

For the fatty acid mixture under consideration, which contains as main constituents C12, C14, C16 and C18, read-across is performed to studies available for the pure homologues C12 (lauric acid, CAS 143 -07 -7), C14 (myristic acid, CAS 544 -63 -3), 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	EC50(as reported in the study)	Water solubility*	Test design and species	Reference
C12 - CAS 143-07-7 lauric acid	3.6 mg/L (measured, geom. mean)	4.81 mg/L at 20 °C	48 h, semi-static, Daphnia magna	NITE, 2001
C14 - CAS 544-63-8 myristic acid	> 3.2 mg/L (nominal) > 1.7 mg/L (measured, geom. mean)	< 0.13 at 20 °C	48 h, semi-static, Daphnia magna	NITE, 2003b
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

* see category justification

In the study conducted with lauric acid (C12: CAS 143 -07 -7) according to the OECD guideline 202, daphnids were exposed in a dose-response experiment under GLP-conditions (Anonymous, NITE, 2001). In the semi-static test an EC50 of 3.6 mg/L (mean measured - geometric mean) was determined.

The study available for myristic acid (C14: CAS 544 -63 -8) was conducted according to OECD 202 following GLP-requirements (NITE, 2003b). In the semi-static limit-test daphnids were exposed to 3.2 mg/L of the test substance (purity of the test substance: 98.9%). The resulting EC50 was reported to be higher than 3.2 mg/L (nominal) corresponding to a mean measured value (geometric mean) of > 1.7 mg/L. Nevertheless in the study higher water solubility is given than that mentioned in the table above (0.34 mg/L vs. < 0.13 mg/L) the reported EC50 -values are far above the limit of water solubility.

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. The 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 acids (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. However, the authors did not mention the test duration and hence the study was only rated with a reliability of 4. Nevertheless, the result of the study indicates that no toxic effects were observed which is in line to the results obtained from the freshwater study. Therefore it might be concluded that the test duration might have been similar to the duration of the freshwater test. Both tests demonstrate the lack of adverse effects in aquatic invertebrates caused by stearic acid.

Concluding from the results reported for the pure homologues C12, C14, C16 and C18, effects on invertebrates within the range of water solubility are only expected for the C12 homologue (lauric acid). For the other homologues contained in the mixture no effects up to the limit of water solubility are reported. Thus a worst-case EC50 of 3.6 mg/L is assumed.