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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption/desorption: Koc 5098 for dodecan-1-ol, 13149 for tridecan-1-ol, 33983 for tetradecan-1-ol and 89883 for pentadecan-1-ol (OECD 121). Koc values for essentially-linear constituents are read across from the available measured values for linear isomers.

Key value for chemical safety assessment

Additional information

Estimated Koc values for constituents of Alcohols, C12 -15 -branched and linear have been derived in the HPLC adsorption test (OECD 121), supported by various QSAR methods. 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 Koc results for dodecan-1-ol, tridecan-1 -ol, tetradecan-1 -ol and pentadecan-1 -ol from this study were in the range 5098 - 89883, showing a predictable relationship with carbon number. The good performance of the OECD 121 method for alcohols in this category is demonstrated by the close results obtained for decan-1-ol by OECD 121 as part of the same study and by the batch equilibrium method (OECD 106), which were within a factor of 2 for the same substance.

It is notable that significant technical difficulties were encountered during method development for the study of decan-1 -ol (CAS 112-30-1) in natural standard soils, in that it was not possible to detect sufficient substance and establish equilibrium in non-sterilised soil samples, due to the rapid rate of biodegradation of the test substance by the soil microbiota. The HPLC technique avoids the complications of biodegradation in the soil test substrate.

Koc values in the range 390-28000 (C12), 440-37000 (C13), 710-97000 (C14) and 1000 -210000 (C15) were obtained using the well-established QSAR calculation method for 'predominantly hydrophobic' substances; the method for 'Alcohol' substances and the method for 'non-hydrophobic' subtances, developed by Sabljić and Güsten (1995) for the European Commission, and recommended in EU Guidance. The 'non-hydrophobics' method prediction is closest to the HPLC value in each case. 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 Kowand 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 conducted with the structural analogue decan-1 -ol 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 hexan-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 Koc 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:

Sabljić 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.