Hexadecyl palmitate

Endpoint summary

Additional information

There is only limited data available for the environmental fate of the target substance hexadecyl palmitate (CAS 540-10-3). Thus, a read-across approach was pursued to compile relevant data from structurally and chemically 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 the 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 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 physico-chemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity.

The target substance hexadecyl palmitate (CAS 540-10-3) is an ester formed by the reaction of palmitic acid (C16, vegetal origin) with cetyl alcohol (C16, vegetal origin). The endpoint for biodegradation was covered by the source substance docosyl docosanoate (CAS 17671-27-1), which consists of a fatty acid and fatty alcohol with chain lengths of 22 carbon atoms each. Thus, the source substance is considered a suitable representative for the assessment of the ready biodegradability of the target substance. The C-chain length is the determining factor for biodegradation. Thus, the larger molecule of the source substance is considered to be a worst-case for prediction of biodegradability of the target substance. Based on the high degree of similarity between the physico-chemical properties of the target and source substance, the target substance is expected to have a similar environmental fate profile. A detailed read-across justification is provided in IUCLID section 13 of the technical dossier.

The target substance hexadecyl palmitate (CAS 540-10-3) is characterized by low water solubility (< 0.846 µg/L, at 20 °C, OECD 105), a high estimated log Kow (> 10.0, QSAR, Vega version 1.1.3 - three models: Meylan/Kowwin version 1.1.4, MLogP version 1.0.0, ALogP version 1.0.0) and a high estimated log Koc (> 5.0, 25 °C, QSAR, EPISuite v4.11, KOCWIN v2.00), indicating that the substance is highly lipophilic and has a high potential for adsorption to soil and sediment particles. The substance has as an estimated vapour pressure of < 0.0001 Pa (20 °C, QSAR, ARChem SPARC. version 4.6). Experimental results from a standard biodegradation study with the closely related source substance docosyl docosanoate (CAS 17671-27-1) suggest that the target substance can be expected to be readily biodegradable (75.3% BOD after 28 d, OECD 301 C). Thus, abiotic degradation via hydrolysis and evaporation into the atmospheric compartment are presumably not relevant removal pathways.                              

Due to the ready biodegradability and high potential for adsorption, the substance can be effectively removed in conventional sewage treatment plants (STPs) by biodegradation and by sorption to biomass. 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.