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If a substance has a low potential for bioaccumulation and/or a low potential to cross biological membranes, or if direct and indirect exposure of the aquatic compartment is unlikely, then in accordance with Regulation (EC) No 1907/2006, Annex IX, 9.3.2, column 2, studies on bioaccumulation are not required. This is the case for the dimerised fatty acids and their derivatives, and in this particular case for Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68783-41-5).

Due to the potential of these substances to adsorb, one may assume that the uptake may occur through the ingestion of soil or sediment. However, uptake of dimers and trimers is expected to be low based on the fact that the dimerised fatty acids are relatively large molecules (C16-18 as monomers, C36 as dimers and C54 as trimers) with high molecular weights (dimeric acids 561 g/mol, trimeric acids 838 g/mol). Thus, according to Lipinski’s rule of five (Lipinski et al., 2001), they have a low potential to cross biological membranes.

Additionally, from the toxicokinetic behaviour of mono- and oligomeric fatty acids in mammals it can be assumed that unsaturated monomeric C16-C18 fatty acids are more readily absorbed than saturated fatty acids like octadecanoic and isooctadecanoic acid, but less readily than fatty acids with shorter chain length. 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 like the citric acid cycle, sugar synthesis, and lipid synthesis.

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

Finally, dimerised fatty acids have a very low water solubility (subcategory dimers and trimers: all < 0.52 mg/L), therefore only low concentrations in the aquatic environment and thus low concentrations in aquatic organisms can be expected, if at all.

Hence, Fatty acids, C18-unsaturated, dimers, hydrogenated (CAS No. 68783-41-5) does not pose a risk to organisms with regard to bioaccumulation/biomagnification.

References:

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

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.

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.