Fatty acids, C8-24

Short-term toxicity to fish

Description of key information

Worst-case LC50 (96 h) expected to be 5.0 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 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 fish" for the considered fatty acid mixture.

Fatty acid homologue	LC50(as reported in the study)	Water solubility*	Test design and species	Reference
C12 - CAS 143-07-7 lauric acid	5 mg/L (measured, geom. mean)	4.81 mg/L at 20 °C	96 h, semi-static, Oryzias latipes	NITE, 2001a
C14 - CAS 544-63-8 myristic acid	> 3.2 mg/L (nominal) > 1.9 mg/L (measured, geom. mean)	< 0.13 mg/L at 20 °C	96 h, semi-static, Oryzias latipes	NITE, 2003a
C16 - CAS 57-10-3 palmitic acid	> 1000 mg/L (nominal)	< 0.05 mg/L at20 °C	96 h, semi-static, Danio rerio	Richterich and Mühlberg, 2001b
C18 - CAS 57-11-4 stearic acid	> 10000 mg/L (nominal)	insoluble	48 h, static, Leuciscus idus	Richterich and Mühlberg, 2001c

* see category justification

The homologue C12 (CAS 143-07-7) was tested on rice fish, medaka (Oryzias latipes) (NITE, 2001). The test followed the OECD-guideline 203 and was conducted under GLP in a semi-static system. Nominal test concentrations used in the study were 1.0, 1.7, 3.1, 5.6 and 10.0 mg/L. As test concentrations were analysed, in addition, mean measured concentrations based on geometric mean were given to be < 0.8, 1.2, 1.6, 4.1 and 8.5 mg/L. After 96 h of exposure the LC50-value was determined to be 5.0 mg/L on the basis of mean measured concentrations.

The study available for the pure homologue C14 (myristic acid: CAS 544 -63 -8) was conducted according to OECD 203 following GLP-requirements (NITE, 2003). In the semi-static limit-test rice fish were exposed to 3.2 mg/L of the test substance (purity of the test substance: 98.9%). The resulting LC50 was reported to be higher than 3.2 mg/L (nominal) corresponding to a mean measured value (geometric mean) of > 1.9 mg/L. Nevertheless in the study a higher water solubility is given than that mentioned in the table above (0.34 mg/L vs. < 0.13 mg/L) the reported LC50 -values are hence far above the limit of water solubility.

The homologue C16 (palmitic acid: CAS 5 7 -10 -3) was tested on zebrafish (Danio rerio) according to ISO 7346 -1 in a semi-static test (Richterich and Mühlberg, 2001b). In the study nominal concentrations of 0.1, 0.5, 2.8, 16, 90, 250 and 1000 mg/L were tested. No mortality was observed at any test concentration and thus up to the limit of water solubility which is below 0.05 mg/L. In the study the LC50 was reported to be above 1000 mg/L.

The homologue C18 (stearic acid: CAS 57 -11 -4) was tested on golden orfe (Leuciscus idus) (Richterich and Mühlberg, 2001c). In the static test, which was conducted according to DIN 38412/15, the fish were exposed to different concentrations of the test substance (1000, 3000, 10000 mg/L nominal). In the study no effects on fish were reported, resulting in a LC50 > 10000 mg/L.

Concluding from the results reported for the pure homologues C12, C14, C16 and C18 a worst-case LC50 of 5.0 mg/L could be expected for the considered mixture based on the toxicity of lauric acid (C12: CAS 143 -07 -7).