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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption ot the substance to the solid soil phase under environmentally relevant conditions is expected.

Key value for chemical safety assessment

Koc at 20 °C:
38 306

Additional information

QSAR - Disclaimer:

In Article 13 of Regulation (EC) No 1907/2006, it is laid down that information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI (of the same Regulation) are met. Furthermore, according to Article 25 of the same Regulation testing on vertebrate animals shall be undertaken only as a last resort.

According to Annex XI of Regulation (EC) No 1907/2006 (Q)SAR results can be used if (1) the scientific validity of the (Q)SAR model has been established, (2) the substance falls within the applicability domain of the (Q)SAR model, (3) the results are adequate for the purpose of classification and labeling and/or risk assessment and (4) adequate and reliable documentation of the applied method is provided.

For the assessment of modified 2-ethyl-N,N-bis(2-ethylhexyl)hexylamine (CAS 1860-26-0) (Q)SAR results were used for the estimation of the adsorption potential. The criteria listed in Annex XI of Regulation (EC) No 1907/2006 are considered to be adequately fulfilled and therefore the endpoint(s) sufficiently covered and suitable for risk assessment.

Therefore, further experimental studies on the adsorption potential are not provided.

Assessment:

The Koc was estimated using both models of KOCWIN v2.00 of EPI Suite v4.11. Using the Molecular Connectivity Index (MCI) which is regarded as more reliable compared to the log Kow method, the log Koc for the uncharged molecule was estimated to be 6.3 (Koc = 1954000 L/kg). Based on the estimated log Kow of 10.13 (@ pH 25°C, BASF SE 2019), the log Koc was estimated to be 6.46 (Koc = 2904000 L/kg) using the log Kow method. Both estimates refer to the uncharged molecule; the substance was within the applicability domain of both models (BASF SE, 2019).

However, the measured pKa of 10.4 (BASF SE 2019, see IUCLID Ch. 4.21) indicates that the substance will primarily exist as a cation in the environment. Cations generally adsorb stronger to soils containing organic carbon and clay than their neutral counterparts. Franco & Trapp (2008, 2009, 2010) have developed a method to take this effect into consideration when assessing the adsorption potential. The model is not yet validated; in addition, the applicability domain is not clearly defined. Nevertheless, the Koc values of the Franco & Trapp method give a good indication on the adsorption potential of a substance depending on the pH conditions of soil. The method is based on the dissociation constant pKa and the log Kow for the uncharged molecule.

Regarding the charged molecule, at pH 7 the log Koc was estimated to be 4.6 (Koc = 38306 L/kg) following the method of Franco & Trapp (2008, 2009, 2010) and using the estimated pKa of 10.4 (BASF SE 2017, see IUCLID Ch. 4.21) and the calculated log Kow for the uncharged molecule of 10.1, EPI Suite v4.11, BASF SE, 2019). The correction was performed for pH 5, 7, and 8, which represents 98% of the European soils. The value at pH 7 will be used as key value, i.e. for PEC and PNEC calculations.

In conclusion, the log Koc of the charged molecule is expected to be > 3 (pH 7, 25 °C). Therefore, adsorption of the substance to the solid soil phase is expected.