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In accordance with Regulation (EC) No 1907/2006 (REACH) Annex IX 9.3.2 Column 2, a bioaccumulation study does not need to be conducted, since Fatty acids, C18 unsaturated, trimers, hydrogenated has a low potential for bioaccumulation and a low potential to cross biological membranes.

As Fatty acids, C18 unsaturated, trimers, hydrogenated is poorly soluble in water (< 0.001 mg/L), only low concentrations in the aquatic environment and thus low concentrations in aquatic organisms can be expected at all. The U.S. EPA HPV report (2009) judged also an expected low bioaccumulation potential based on the negligible solubility and their anionic nature (low absorption potential).

Due to the potential of Fatty acids, C18 unsaturated, trimers, hydrogenated to adsorb, one may assume that the uptake may occur through the ingestion of soil or sediment. However, uptake is expected to be low based on the fact that the constituents of Fatty acids, C18 unsaturated, trimers, hydrogenated are relatively large molecules with high molecular weights (trimeric acids ca. 850 g/mol). Thus, according to Lipinski’s rule of five, they have a low potential to cross biological membranes (Lipinski, 2001).

Additionally, from the toxicokinetic behaviour of mono- and oligomeric fatty acids in mammals it can be assumed that the absorption of Fatty acids, C18 unsaturated, trimers, hydrogenated is low. Very low absorption is reported for dimeric and trimeric fatty acids via the gastro intestinal tract and thus, most of the ingested fatty acids will be excreted in the faeces (≥ 80% for dimeric acid methyl esters (Hsieh and Perkins, 1976; Paschke et al. 1964)). In case of absorption fatty acids will undergo rapid metabolisation and excretion (either in the expired CO2 or as hydroxylated or conjugated metabolite in the urine in the case of cyclic fatty acids) as they feed into physiological pathways such as the citric acid cycle, sugar synthesis, and lipid synthesis.

Fatty acids are naturally stored in the form of triacylglycerols primarily within fat tissue until they are used for energy production. It is therefore concluded that there will be no risk to organisms from bioconcentration/biomagnification of fatty acids within the food chain.

QSAR calculations using BCFBAF v3.01 were performed for three representative constituents: polycyclic, cyclic and acyclic trimers. Using the regression based method BCF values of 3.16 were obtained for all constituents. The Arnot-Gobas method, including biotransformation, resulted to even lower BCF and BAF values, both 0.893 for all constituents. The QSAR estimations may not be fully reliable as the log Kow range of the constituents is not covered by the training set of these models. However, they do support the assumption of low bioaccumulation potential.

In conclusion, as Fatty acids, C18 unsaturated, trimers, hydrogenated is poorly soluble (0.001 mg/L), the aqueous concentration will be very low and consequently, exposure to the aquatic environment would be extremely low, if at all. This automatically reduces, if not eliminates, the uptake of the chemical through the aquatic environment. Additionally, Fatty acids, C18 unsaturated, trimers, hydrogenated has a low potential to cross biological membranes due to the large molecular size of its constituents. In case of uptake and absorption, rapid metabolism of fatty acids occurs. Hence, Fatty acids, C18 unsaturated, trimers, hydrogenated does not pose a risk to organisms in regard to bioaccumulation/biomagnification.

References:

Hsieh, A. and Perkins, E.G. (1976). Nutrition and Metabolic Studies of Methyl Ester of Dimer Fatty Acids in the Rat. Lipids, 11(10):763-768.

Lipinski et al. (2001) Experimental and computational approaches to estimate solubility and permeability in drug discovery and development settings, Adv. Drug Del. Rev., 2001, 46, 3-26.

Paschke, R.F. et al. (1964). Dimer acid structures. The dehydro-dimer from methyl oleate and Di-t-butyl peroxide. Journal of the American Oil Chemists' Society 41(1):56-60.

U.S. Environmental Protection Agency (2009). Risk-Based Prioritization Document. Initial Risk-Based Prioritization of High Production Volume (HPV) Chemicals – Fatty Acid Dimers and Trimer Category. pp 1-19. Report date: April 2009.