Fatty acids, C16-18, isononyl esters

Endpoint summary

Additional information

There are no data available investigating the aquatic toxicity of the substance fatty acids, C16-18, isononyl esters (CAS 91031-57-1). Therefore, the aquatic hazard of the target substance was assessed by a read-across approach to three structurally and chemically closely related substances in order to fulfil the standard information requirements laid down in Annex XI, 1.5, of the REACH Regulation (EC) No 1907/2006. According to Article 13 (1) of this regulation, "information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI are met.” In particular for aquatic toxicity, information shall be generated whenever possible by means other than vertebrate animal tests, which includes the use of information from structurally related substances (grouping or read-across). In regard to the general rules for grouping of substances and the read-across approach, the regulation specifies (Annex XI, Item 1.5) that substances may be predicted as similar provided that their physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity.

The evaluation of the aquatic toxicity of the target substance fatty acids, C16-18, isononyl esters (CAS 91031-57-1) is based on read-across to the source substances fatty acids, C16-18 and C18-unsatd., 2-ethylhexyl esters (CAS 85049-37-2), 2-ethylhexyl oleate (CAS 26399-02-0) and Decyl Oleate (CAS 3687-46-5). The selected source substances are considered suitable representatives for the hazard assessment of the aquatic toxicity of the target substance due to the high degree of similarity between the structural and physico-chemical properties. On this basis, it is assumed that the target substance will exhibit a similar ecotoxicological profile as the source substances. A detailed read-across justification is provided in IUCLID section 13 of the technical dossier.

By means of the read-across approach, reliable effect concentrations are available for the acute aquatic toxicity to three trophic levels (aquatic algae, invertebrates and fish) and chronic aquatic toxicity to two trophic levels (aquatic invertebrates and algae), as well as for the toxicity to aquatic microorganisms and sediment organisms. Based on the structural and chemical similarity of the target and source substances, the target substance is expected to exhibit a similar ecotoxicological profile. 

Experimental results from the studies performed with the source substances showed no acute or chronic effects to aquatic and sediment organisms including activated sludge microorganisms up to the limit of water solubility. These experimental findings are in line with what is known from literature, indicating that very long chain alcohols (> C16) and long chain fatty acids (> C14) are not harmful to aquatic organisms. The toxicity of long chain fatty acids and fatty alcohols is known to correlate with the hydrophobicity (log Kow) of a substance (Onitsuka et al., 1989) and a threshold value of 4.2 has been established above which aquatic toxicity is negligible.

The target substance is poorly soluble in water (< 13.3 µg/L) and has a high potential for adsorption (log Koc > 5.0), which is indicative of a high degree of elimination in sewage treatment plants. Consequently, release to surface water is very unlikely. In the case the substance should reach surface waters, it is not expected to persist in the aquatic environment due to its ready biodegradability. Thus, chronic exposure, uptake and bioaccumulation in aquatic organisms are expected to be low.

Moreover, the target and source substances are expected to be readily metabolized and excreted or catabolized by common enzymatic pathways in aquatic organisms. Long chain aliphatic esters are expected to be initially hydrolysed by carboxylesterases/esterases into the corresponding free fatty acids and alcohols. Carboxylesterase activity has been noted in a wide variety of tissues in invertebrates as well as in fish (Leinweber, 1987; Soldano et al, 1992; Barron et al., 1999, Wheelock et al., 2008). The catalytic activity of this enzyme family leads to a rapid biotransformation/ metabolism of xenobiotics which reduces the bioaccumulation or bioconcentration potential (Lech & Bend, 1980). It is known for esters that they are readily susceptible to metabolism in fish (Barron et al., 1999) and literature clearly indicates that esters do not readily bioaccumulate in fish (Rodger & Stalling, 1972; Murphy & Lutenske, 1990; Barron et al., 1990). In fish species this might be caused by the wide distribution of carboxylesterase, high tissue content, rapid substrate turnover and limited substrate specificity (Lech & Melancon, 1980; Heymann, 1980). The enzymatic hydrolysis products (fatty acid and fatty alcohol) can serve as energy source and are major constituents of living organisms (e.g. phospholipid bilayer, muscle tissue and liver).

Everything being taken into account, it is assumed that aquatic toxicity is unlikely.