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Environmental fate & pathways

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There is only limited data available on the environmental fate of the target substanceFatty acids, C16, C18 and C18-unsaturated, C12-15 alcohol (linear and branched), esters. Therefore, (Q)SAR calculations according to the REACH Guidance R.6 on QSARs (ECHA, 2008) were performed in order to complete the standard information requirements laid down in Annex X of REACH Regulation (EC) No 1907/2006.

The target substanceFatty acids, C16, C18 and C18-unsaturated, C12-15 alcohol (linear and branched), estersis a UVCB substance consisting of long-chain aliphatic esters with fatty acid chain lengths ranging from 16 to 18 (unsaturated and branched) and C12 – C15 alcohol components. It is characterized by amolecular weight of 424.74 – 492.86 g/mole, extremely low water solubility (< 6.57 µg/L at 20 °C, pH 6.3, OECD 105), low vapour pressure (< 0.00001 Pa, 20 °C SPARC v4.6), a high estimated log Kow (> 10.0, QSARs) and a high estimated log Koc (> 5.0, KOCWIN v2.00, MCI method, 25 °C). Based on experimental results from a standard biodegradation study, the substance is readily biodegradable according to guideline criteria (89.9% in 28 d, OECD 301 B). Thus, abiotic degradation via hydrolysis is not relevant. Furthermore, due to the low vapour pressure, the substance is not likely to evaporate into the atmospheric compartment. Therefore, neither transport through the atmosphere to other environmental compartments is expected nor is phototransformation in air expected to be a relevant environmental fate pathway.

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 concentrations of the substance are likely to be released into the aquatic environment through conventional STPs, if at all. Whatever fraction is released 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 the water column. Thus, the relevant route of uptake in aquatic organisms is expected to predominantly occur via ingestion of particle bound substance, but the bioavailability of the substance is presumably very low based on the physico-chemical properties of the substance (i.e. strong binding).

Experimental data for bioaccumulation is not available for the target substanceFatty acids, C16, C18 and C18-unsaturated, C12-15 alcohol (linear and branched), esters.The estimated logKow is high (> 10.0, QSAR models), which may be indicative of a potential for bioaccumulation.However, the log Kow presumably overestimates the true bioaccumulationpotential of a substance since it does not take into account the metabolization of substances in living organisms. Based on current knowledge, a log Kow of 10 or above is taken as an indicator of reduced bioconcentration, according to the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7c: Endpoint specific Guidance (ECHA, 2017). Moreover, the target substance is a long-chain aliphatic ester. In the case of absorption by aquatic organisms, long-chain aliphatic esters are expected to beenzymatically hydrolyzed by the ubiquitous family of carboxylesterases, yielding the corresponding alcohol and fatty acid. It is well established that the hydrolysis products of this metabolization are also readily metabolized and therefore not of concern in terms of bioaccumulation (for further information see chapter 5.3 of the technical dossier). Hence, 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 low.

This conclusion is supported by (Q)SAR calculations for BCF values in fish. The BCF values obtained by the regression-based estimate ranged from 3.16 L/kg wet-wt to 22.7 L/kg wet-wt. The BCF values obtained by the Arnot-Gobas method (including biotransformation, upper trophic) were around 0.90 L/kg wet-wt for all constituents. Thus, the estimated BCF values are well below the threshold value of 2000 L/kg for bioaccumulative substances, as laid down by the REACH regulation (EC) No 1907/2006, section 1 of Annex XIII.

In summary,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 preferentially distribute into the sediment compartment where the bioavailability of the substance is presumably very low based on the physico-chemical properties of the substance (i.e. strong binding properties). Moreover, the available information on environmental behavior, metabolism and bioaccumulation provide evidence that the overall potential for bioaccumulation of the target substance is low. In conclusion, the available information is sufficient to cover the data requirements set out in Regulation (EC) No 1907/2006, Annex X.

 

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