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Partition coefficient

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Description of key information

log Pow  > 4

Key value for chemical safety assessment

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The value for partition coefficient log Pow of UVCB substance CAS 61788-89-4 (Fatty acids, C18-unsaturated, dimers) is based on a weight of evidence using experimental and QSAR results for the components of the substance. Due to the complex nature of the UVCB substance not all components of the substance are known. For the evaluation of the influence of the dimerisation and branching, the hypothetical structures were examined with use of a QSAR model (KOWWIN v1.68).

The experimental literature partition coefficient log Pow for C18 fatty unsaturated and saturated acids are log Pow=7.05 for linoleic acid, 8.23 for octadecanoic acid, 7.64 for 9-octadecenoic acid and 6.46 for linolenic acid. The partition coefficient of the substance increases with the increase of number the C chain incrementally. Log Pow of the dimer of C18 fatty acids is then expected to be much higher than log Pow of monomers. It is also proven by QSAR prediction for example dimer structure (log Pow = 14.81). The branching does not affect the log Pow substantially and it was calculated by KOWWIN v1.68 for an example structure of C18 acid to be 7.36.

 The log Pow was also determined by HPLC method (OECD 117) with fatty acids, C-18 unsaturated, dimers (CAS 61788-89-4). The test substance had however estimated values outside the recommended for the method range 0-6. Additionally, chromatograms contain peaks at retention times corresponding to partition coefficients outside this range. In mobile phase adjusted to pH 2, only hydrophilic components (tR< 2 min; ca. 20% of total area) have been eluted and detected under the chromatographic conditions employed. Based on the preliminary solubility of the test item in octanol and water and taking into consideration all the limitations of the test design, the log Pow of Fatty Acids, C-18 unsaturated, dimers should be judged to be > 4.

All available results show that the log Pow of CAS 61788-89-4 (Fatty acids, C18-unsaturated, dimers, “Dimer”) is high and well above 4. Therefore log Pow >4 as a limit value is accepted for the chemical safety assessment.