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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Log Koc has been experimentally estimated by HPLC to be >5.6.

Key value for chemical safety assessment

Koc at 20 °C:
398 107

Additional information

Log Koc values for three ionisable components of the test material (C14-, C16- and C18-components) were estimated by HPLC and also using chemical modelling software. The HPLC method was equivalent to OECD Guideline 121 (with acceptable deviations), and to GLP. Isocratic elutions of test and reference compounds from a cyanopropyl column with 55 % methanol/45 % citric acid buffer (pH 6) mobile phase were performed. Under the circumneutral pH conditions of the column the test material components were in their dissociated forms and had high affinity for the solid phase resulting in their non-elution after injection. A log Koc value of >5.6 was assigned to all three test material components in their dissociated form on the grounds that the reference substance (DDT) with the greatest k’ value has a log Koc value of 5.63.

 

Estimation of log Koc of the undissociated test material was performed using PCKOCWIN chemical modelling software giving values of 5.1 to 6.1. Estimation of log Kow of both the undissociated and dissociated test material components were performed using KOWWIN chemical modelling software giving values of 9.2 to 11.1 and 5.1 to 7.0 respectively. The KOWWIN log Kow values were fitted to an equation defining the relationship between log Kow and log Koc for organic acids, giving log Koc values of 4.8 to 5.7 for the undissociated components and 2.9 to 3.8 for their dissociated conjugates.

 

At typical soil pH (i.e. pH 5 to 9) the ionisable components (pKa = 3.4) would be largely dissociated and as such, the most environmentally relevant log Koc values from this study are those determined for the dissociated forms (i.e. HPLC estimation and KOWWIN-based calculation of dissociated forms of test material). Therefore, an experimentally (HPLC) estimated log Koc of >5.6 for dissociated forms of all three test material components or calculation-based log Koc values (using KOWWIN derived log Kow values) of 2.9, 3.4 and 3.8 for dissociated forms of C14-, C16- and C18-components are considered most representative.

 

Further information

In accordance with Section 2 of Annex XI of the REACH regulation, the registrant proposes to waive the testing to determine further information on adsorption/desorption as required in Section 9.3.3. of Annex IX as testing is not considered to be technically feasible due to the intrinsic nature of the substance. The material is a complex multi-constituent substance with a low water solubility, which in itself can be considered to justify omission of the study. Whilst it is theoretically possible that such studies could be carried out using radio-labelled test material, for complex materials such as this, it is not considered technically feasible to generate such radio-labelled samples due to the substance’s composition.

Furthermore, the exposure scenarios developed in the chemical safety report as a result of the chemical safety assessment indicate that there is no need to investigate further effects on the aquatic environment as there is no release to the environment; thus the grounds to waive the study are strengthened in accordance with the general adaptations set out in Section 3 of Annex XI of the REACH regulation.

[LogKoc: 5.6]