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Adsorption / desorption

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Description of key information

Experimental procedure is technically not feasible. Prediction with KOCWINv2.00: logKoc: 15.43-16.46 (Chain lengths C15 and C36, respectively)

Key value for chemical safety assessment

Koc at 20 °C:
28 840 315 031 266 120

Additional information

The determination was not carried out using the HPLC screening method, designed to be compatible with Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001 and Method C.19 Adsorption Coefficient of Commission Regulation (EC) No 440/2008 of 30 May 2008 as the method was shown not to be applicable.

The HPLC method is not applicable to strong acids. Although calcium sulfonate target substance (C15 -C36) is not an acid, the sulphonate group is the conjugate base to sulphonic acid. When dissolved in a polar solution, the substance will dissociate since it requires an anion exchange column to obtain consistent retention times. However, under environmental conditions, dissociation of the substance is not possible (only in presence of a strong acid). Trial injections were attempted on a cyanopropyl (CN) column with a mobile phase of methanol:water (55:45 v/v) but the peak detected varied in the retention time for each injection separately. It can be assumed, that secondary interactions occurred.

Anionic sulphonate components would need to be analyzed at a pH far below the limits of the test (pH 4.5 to 8.5). However, the adsorption coefficient would then be determined for the dissociated organic component and not for the full, nondissociated structure.

Based on this consideration, the adsorption coefficient of the non-dissociated test substance can be expected to be significantly higher than the value which would result by a HPLC determination.

Therefore, the soil adsorption coefficient of the calcium sulfonate read across substance (C15 -C36) was determined by the computer program KOCWIN v2.00 (EPIWIN software) by US-EPA (Chemservice S.A., 2013). This tool estimates the organic carbon-normalized sorption coefficient for soil (and also for sediment), which is designated as Koc. Two different models are used for this estimation: the Sabljic molecular connectivity (MCI) method as well as with the traditional method which is based on logPow. For the first representative structure of the UVCB substance calcium sulfonate target substance, the traditional method gives a logKoc of 16.70 L/kg and the MCI method reveals a comparable value of 16.46 L/kg as result. The second structure reveals logKoc values of 15.70 L/kg and 15.43 L/kg concerning the traditional and MCI method, respectively. The MCI method is taken more seriously into account due to the fact, that it includes improved correction factors.

[LogKoc: 16.46]