Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

There is only limited data available on the environmental fate of Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8). Therefore, QSAR calculations were conducted where necessary to fulfill the standard information requirements laid down in Annex VIII, 1.5, of the REACh Regulation (EC) No. 1907/2006.

Isohexadecyl 12-[(1-oxooctadecyl)oxy]octadecanoate (CAS 97338-28-8) is characterized by high molecular weight (> 500 g/mole), low water solubility (1.39 µg/L, 20 °C, pH 6.3, OECD 105), a low estimated vapour pressure (< 0.0001 Pa, 20 °C, KOCWIN v2.00), a high estimated log Kow (> 10, KOWWIN v1.68) and a high estimated log Koc (> 5.0, KOCWIN v2.00, MCI). Experimental results from a standard biodegradation study showed that the substance is readily biodegradable (86.0% in 28 d, OECD 301 F). Thus, neither abiotic degradation via hydrolysis nor evaporation and indirect photodegradation in air are relevant environmental fate pathways.

According to the Guidance on information requirements and chemical safety assessment, Chapter R.7b, readily biodegradable substances can be expected to undergo rapid and ultimate degradation in most environments, including biological Sewage Treatment Plants (STPs) (ECHA, 2017). Due to ready biodegradability and high potential for adsorption, the substance can be effectively removed in conventional STPs by biodegradation and sorption to biomass. Furthermore, the Guidance also states that once insoluble chemicals enter a standard STP, they will be extensively removed in the primary settling tank and fat trap and thus, only limited amounts will come into contact with activated sludge microorganisms. Therefore, only negligible amounts of the substance are expected to be released into the environment through conventional STPs, if at all. Whatever fraction is released into the aquatic environment will undergo extensive biodegradation and will preferentially distribute into the sediment compartment through sorption to organic matter, leading to a rapid reduction of the bioavailability of the substance in water. Thus, the relevant route of uptake in aquatic organisms is expected to predominantly occur by ingestion of particle bound substance, but the bioavailability of the substance is presumably very low based on its physico-chemical properties.

Experimental data for bioaccumulation is not available and the estimated log Kow is high (> 10), which may be indicative of a potential for bioaccumulation. However, based on current knowledge, a calculated log Kow of 10 or above is taken as an indicator of reduced bioconcentration, as stated in the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R. 7c: Endpoint specific guidance (ECHA, 2017) and Chapter R. 11: PBT/vPvB assessment (ECHA, 2017). In addition, no chronic mammalian toxicity was recorded in the available studies indicating that the substance is not chronically toxic and or not taken up to a significant extent. Together with other information, this information can be used in a weight-of-evidence approach to conclude that the substance is not B/vB, according to the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT/vPvB assessment v3.0 (ECHA, 2017). This reasoning is in line with the estimated BCF of 0.893 L/kg (BCF/BAF, Arnot-Gobas, including biotransformation, upper trophic) for this substance indicating negligible potential for bioaccumulation.

In case of absorption by aquatic organisms, long chain aliphatic esters are expected to be enzymatically hydrolyzed by carboxylesterases, yielding the corresponding alcohol and fatty acid. Both hydrolysis products are metabolized in aquatic organisms. The metabolization of the hydrolysis products is well established and not of concern in terms of bioaccumulation (for further information see section 5.3 of the technical dossier).

In summary, the substance is not expected to persist in the aquatic environment and chronic exposure, uptake and bioaccumulation is thus unlikely to occur. In the unlikely case of absorption by aquatic organisms, the substance is expected to be rapidly hydrolyzed to the respective fatty acid and fatty alcohol and the potential for bioaccumulation of both the substance as well as its metabolites is considered low.

Overall, the available information on the environmental behavior and metabolism, in combination with QSAR estimates, provide sufficient information to cover all the data requirements set out in Regulation (EC) No. 1907/2006, Annex VIII.