Alcohols, C9-11-branched and linear

Adsorption / desorption

Description of key information

Adsorption/desorption: Koc = 211 for nonan-1-ol (OECD 121)

Adsorption/desorption: Koc = 1490 for decan-1-ol (OECD 106)

Adsorption/desorption: Koc = 2006 for undecan-1-ol (OECD 121)

Additional information

A recent and reliable study of adsorption and desorption using the batch equilibrium method (in compliance with OECD 106 and GLP) has been conducted with decan-1-ol (a constituent of Alcohols C9-11-branched and linear). Based on tests with four soil samples and one sludge sample, the K_ocvalue on average was 1460. Regression of the K_dvalues from this test against percentage organic carbon shows a very well correlated linear relationship, passing through the origin, which confirms that decanol is interacting only with the organic carbon constituents of the substrates, and corroborates the conclusion of K_ocof approximately 1500.

Estimated K_oc values for nonan-1-ol, decan-1-ol and undecan-1-ol (constituents of Alcohols C9-11 branched and linear) have been derived in the HPLC adsorption test (OECD 121), supported by various QSAR. A Koc study using HPLC (OECD 121) methodology was conducted for a range of linear aliphatic alcohols in accordance with ISO 17025 (Shell Global Solutions, 2013). The K_oc result for nonanol from this study was 211, the Koc result for decanol was 802 and the K_oc result for undecanol was 2006. The good performance of the OECD 211 method for alcohols in this category is demonstrated by the close results obtained for decan-1-ol by the batch equilibrium method (OECD 106), which were within a factor of 2 of the result from OECD 121 for the same substance. The chemical safety assessment assesses the 'essentially-linear' and linear constituents of same carbon number together as a single assessment entity, and the Koc values for 'essentially linear' constituents are read across from the values for the linear alcohols of same carbon number.

For comparison purposes, K_oc values of 1425, 956 and 93 were obtained for nonanol and K_oc values of 220-8400 were obtained for undecanol using the well-established QSAR calculation method for 'predominantly hydrophobic' substances; the method for 'non-hydrophobic' substances and the method for 'Alcohol' substances respectively, developed by Sabljic and Güsten (1995) for the European Commission, and recommended in EU Guidance. The range of predictions covers the measured and HPLC values. Further details are presented in the endpoint study record.

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols:

Substantial evidence exists within the alcohols Category, in the form of sewage sludge adsorption measurements, literature values, High Performance Liquid Chromatography (HPLC) estimates conducted in accordance with OECD Guideline 121, and a recent OECD Guideline 106 test in soils and a wastewater treatment plant sludge. Predictive methods based on log K_ow and MCI have also been explored for members of this Category. The available measured data supports the following conclusions:

- The HPLC predictions correlate very well with the available measured Koc data, requiring no additional correction.

- Adsorption results in the OECD Guideline 106 study indicate that the alcohol interacts only with the organic carbon in the soils. This confirms the expectation that setting a value of Koc is sufficient to understand adsorption to the relevant substrates (soil, sediment, sludges).

- There are no confounding factors anticipated for the alcohols in this Category (e.g. unusual interaction with the stationary phase). Based on the structure and simple physical chemistry of decan-1-ol, there is every reason to believe that the Koc value obtained from the OECD 121 guideline study is valid and fit-for-purpose.

- Different log Kow-based QSAR predictions of K_oc vary widely depending on which equation is selected.

- HPLC measured Koc values across the series show a predictable increase in Koc value as the carbon number increases. Regression analysis shows that the linear relationship between carbon number and log Koc value measured using this method is extremely well correlated with very low error.

Reference:

Sabljic A and Güsten H (1995) QSARs for soil sorption. in: overview of structure-activity relationships for environmental endpoints. Hermens JLM (ed), report prepared wtihin the framework of the project "QSAR for prediction of fate and effects of chemicals in the environment", an international project of the Environmental Technologies RTD programme (DG XII/D-1) of the European Commission under contract number EV5V-CT92-0211.