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Long-term toxicity to aquatic invertebrates

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Description of key information

No effects up to the limit of water solubility (OECD 211; OECD 202, part 2)

Key value for chemical safety assessment

Additional information

Since no studies investigating the long-term toxicity to aquatic invertebrates of Fatty acids, C16-18, C16-18-alkyl esters (CAS 97404-33-6) are available for this endpoint, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 a read across to the three structurally related category members dodecyl oleate (CAS 36078-10-1),2-ethylhexyl oleate (CAS 26399-02-0) and (Z)-octadec-9-enyl oleate (CAS 3687-45-4) was conducted.

Compared to Fatty acids, C16-18, C16-18-alkyl esters, the read-across substance 2-ethylhexyl oleate is characterized by a similar fatty acid component (C18:1 compared to C16-18 (target)) and a similar fatty alcohol moiety (2-ethylhexanol compared to C16-C18 (target)). The second read-across substance dodecyl oleate is characterized by C18 unsatd. fatty acid compared to C16-18 (target) and a smaller alcohol chain lengths (C12 compared to C16-18 (target)). The smaller alcohol chain length increases the water solubility and therefore the bioavailability in the water. Water solubility is negatively correlated with the C-chain length of the fatty alcohol and fatty acid (Lide, 2005). Therefore, it is possible to extrapolate from a category member with higher water solubility since it has an increased bioavailability in the water phase (ECHA, 2008). The third read-across substance(Z)-octadec-9-enyl oleate is the structurally most similar compared to the target substance (C18:1 fatty acid and C18:1 fatty alcohol).This read-across is justified in detail in the overall summary (IUCLID Section 6.1) and within the category justification in IUCLID Section 13. In this case of read-across, the best suited (highest degree of structural similarity, nearest physico-chemical properties) read-across substance was used for the assessment. Nevertheless, as it can be seen in the data matrix of the category justification in section 13 and the overall summary, all reliable data in the category support the hazard assessment of each category member by showing a consistent pattern of results.

The first study with the read-across substance dodecyl oleate (CAS 36078-10-1) was performed according to OECD 211 under GLP conditions with the water flea Daphnia magna (Brunswik-Titze, 2013). Five nominal concentrations up to 100 mg/L were tested in a semi-static exposure system as Water Accommodated Fractions (WAF). No effects on the reproduction of D. magna were observed after 21 d. One dead animal was recorded at 50 mg/L but it was reported that it was no substance specific effect (accident during medium change). Therefore, a NOELR (21 d) of ≥ 100 mg/L (nominal) was derived. The chemical analysis resulted in concentrations below the analytical detection limit of 0.005 mg/L reflecting the very low water solubility of the test item.

The second study with the read-across substance (Z)-octadec-9-enyl oleate (CAS 3687-45-4) was performed according to OECD 211 (GLP) with the water flea Daphnia magna under semi-static conditions (Höger, 2013). Due to the very low water solubility (< 0.05 mg/L) a limit test with a Water Accommodated Fraction (WAF) of nominal 100 mg/L was performed. No effects on reproduction and mortality were recorded after 21 d resulting in a NOELR (21 d) of ≥ 100 mg/L. 0% mortality was recorded in the control whereas 5% mortality was observed in the treatment. This mortality is regarded as natural and tolerated by the test guideline. The chemical analysis resulted in concentrations below the analytical detection limit of 0.0423 mg/L reflecting the very low water solubility of the test item.

The study with the third read-across substance 2-ethylhexyl oleate was performed according to OECD 202, part 2 (1993) under GLP conditions (Küch, 1995). Daphnia magna was exposed to two nominal concentrations (1 and 100 mg/L) which were both measured to be < 0.01 mg/L indicating similar concentrations in both test vessels. Effects to Daphnia magna were observed after 21 d with 90% mortality (on day 19) at 100 mg/L and no effects at 1 mg/L. The authors stated, that the mortality in the higher concentration could be attributed to sample contamination. 23% reduction of reproduction in the 100 mg/L sample occurred after 21 d, whereas no effects were observed at 1 mg/L resulting in a NOEC (21 d) ≥ 1 mg/L. The nominal concentration of 100 mg/L was not taken into account for the assessment due to the possible contamination of test solutions.

Based on the available result from three structurally related read-across substances (in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5) which are characterized by a similar ecotoxicological profile and comparable structure, it can be concluded that fatty acids, C16-18, C16-18-alkyl esters will not exhibit long-term effects on aquatic invertebrates up to the limit of water solubility.