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Environmental fate & pathways

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There is only limited data available for the environmental fate of the target substance Fatty acids, C16-18, isononyl esters (CAS 91031-57-1). Therefore, a read-across approach was pursued to compile relevant data from structurally and physico-chemically related substances in order to fulfill 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.” With 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 target substance Fatty acids, C16-18, isononyl esters (CAS 91031-57-1) is a multi-constituent substance, consisting of a C16 and C18 fatty acids esterified with the branched fatty alcohol isononanol (C9iso). The endpoint for biodegradation was covered by two source substances whose fatty acids and alcohols are of similar chain lengths. The source substance 2-ethylhexyl oleate (CAS 26399-02-0) is an ester of oleic acid (C18) and the branched and chiral fatty alcohol 2-ethylhexanol (C8). It is a mono-constituent substance. The source substance Fatty acids, C16-18 and C18-unsatd., 2-ethylhexyl esters (CAS 85049-37-2) is a UVCB consisting of esters of the fatty alcohol 2-ethylhexanol and various fatty acids ranging from C14 to C18. Based on the high degree of similarity between the physico-chemical properties of the target and source substances, the target substance is expected to have a similar environmental fate profile. A detailed analogue justification is provided in IUCLID section 13 of the technical dossier.

The target substance Fatty acids, C16-18, isononyl esters (CAS 91031-57-1) is characterized by low water solubility (< 13.3 µg/L, 20 °C, pH 6.3, OECD 105), a high log Kow (> 10.0, Vega v.1.1.3) and a high estimated log Koc (> 5.0, 25 °C, EPI Suite v4.11), indicating a high potential for adsorption to soil and sediment particles. The substance has a very low, estimated vapor pressure (< 0.0001 Pa, 20 °C, SPARC v4.6) and is readily biodegradable (76 – 81% within 28 d, 301 B). Thus, abiotic degradation via hydrolysis and evaporation into air and transport through the atmosphere to other environmental compartments is not expected. Therefore, sediment and soil are expected to be the main compartment for environmental distribution. However, the substance is not expected to persist due to its ready biodegradability, which is also supported by QSAR calculations for the target substance itself (VEGA, IRFMN 1.0.9). According to ECHA Guidance R.7b (Guidance on Information Requirements and Chemical Safety Assessment, Endpoint specific Guidance, Version 3.0, ECHA, 2016) a positive result in a test for ready biodegradability can be considered as indicative of rapid and ultimate degradation in most environments, including biological sewage treatment plants (STPs). Therefore, only negligible concentrations of the substance are likely to be released into the environment through conventional STPs (if at all) and whatever fraction is released will undergo extensive biodegradation or sorption onto organic matter. Consequently, the bioavailability of the substance in the water column will be rapidly reduced and the relevant route of uptake by aquatic organisms is expected to predominantly occur by ingestion of particle bound substance. However, based on the physico-chemical properties, its bioavailability to sediment organisms is presumably also low (due to strong binding).

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