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There is only limited data available for the aquatic toxicity of Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8). Therefore, the acute aquatic toxicity of the target substance was assessed by a read-across approach to a structurally and chemically closely related source substance according to Regulation (EC) No 1907/2006, Annex XI, 1.5.

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.” For aquatic toxicity in particular, 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 source substance 2-octyldodecyl isooctadecanoate (CAS 93803-87-3) is characterized by similar but smaller fatty acid esters and is therefore considered a suitable representative for the assessment of the toxicity of the target substance to aquatic organisms. A detailed justification of the analogue approach is provided in IUCLID section 13.

By means of the read-across approach in conjunction with the available experimental data, GLP guideline studies are available for the assessment of the aquatic toxicity of the target substance Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8), covering the short-term toxicity to all three trophic levels and the long-term toxicity to two trophic levels (aquatic invertebrates and algae). The compiled data for acute toxicity (fish, aquatic invertebrates and algae) do not indicate any short-term toxicity toward aquatic organisms up to the limit of water solubility of the source substance (< 0.05 mg/L). The compiled data for chronic toxicity (aquatic invertebrates and algae) indicate long-term effects on aquatic invertebrates. One experimental long-term study on aquatic invertebrates is available for the target substance itself, in which a limit test was performed according to OECD guideline 211. After 21 d, no mortality was observed in the limit concentration treatments but the reproductive performance (mean offspring per parent animal) was significantly reduced by 58.5%, resulting in a NOEC (21 d) for reproduction of < 7.0 µg/L (nominal). No long-term toxicity to aquatic algae was observed up to the limit of water solubility of the source substance (< 0.05 mg/L). Furthermore, no toxic effects towards microorganisms of activated sludge were observed.

Due to the ready biodegradability and high adsorption potential, the target substance is expected to be eliminated from sewage treatment plants to a high extent. Release to surface waters and subsequent exposure of sediment is therefore highly unlikely. In the unexpected event where absorption by aquatic organisms should occur, the substance is expected to be rapidly metabolized via enzymatic hydrolysis into its corresponding fatty acids and fatty alcohols, which are known from literature to metabolize well in aquatic organisms. Against this background, the potential for chronic exposure is judged to be very low.

Therefore, it is concluded that Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) does not exhibit short-term effects to aquatic organisms up to the limit of water solubility (< 0.05 mg/L), does not negatively affect the degradation process in sewage treatment plants but may cause long-term effects in aquatic organisms.