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Environmental fate & pathways

Adsorption / desorption

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Description of key information

A high log Koc for Fatty acids, C16-18 and C18-unsaturated, branched and linear is expected: 4 < log Koc < 5 and is accepted for the chemical safety assessment.

Key value for chemical safety assessment

Additional information

Because the substance is a composition of different homologues, the Koc values of well-defined representative structures were calculated with EPISUITE (KOCWIN v2.00). The result is estimated by the means of the weight of evidence approach.

Adsorption potency is predicted by QSAR method. The main factor determining the log Koc value of fatty acids is the chain length. Each carbon atom added contributes to Koc ca. 1/4 of the logarithmic unit. Taking into account that both predicted and experimental values for acetic acid CC(=O)O are close to 0, we see that adding 16 carbon atoms increases the log Koc to ca. 16x1/4 = 4. This is the minimum value to be expected for the category members. Introducing double bonds and branching may decrease this value, but not very significantly For monomers, C16 to C18, the calculated log Koc values are between 3.2 (heptamethylnonanoic acid, MCI method) and 4.7 (octadecanoic acid, Kow method) and therefore the overall contribution of monomers fulfils the condition: 4 < log Koc < 5. The calculated results for potential dimeric constituents are higher. As the content of oligomers should be maintained as small as possible, it can be assumed that this contribution is negligible. By higher content of residual dimeric components (> ca. 5%), the worst case log Koc > 5 has to be considered.

Thus, it can be concluded that for Fatty acids, C16 -18 and C18 -unsatd., branched and linear (CAS 68955 -98 -6) adsorption to organic carbon in soils and sediments is to be expected (log Koc is high: 4 < log Koc < 5). No additional tests on adsorption/desorption are to be conducted.