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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Based on the log Koc value adsorption to the solid soil phase is not expected.

In addition, the substance is readily biodegradable.

Key value for chemical safety assessment

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.

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 2 -aminoethanol (MEA, CAS 141 -43 -5), (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

According to Regulation (EC) No 1907/2006, Annex VIII, Section 9.3.1, Column 2, the study on adsorption/desorption screening does not need to be conducted if based on the physicochemical properties the substance can be expected to have a low potential for adsorption (e.g. the substance has a low octanol water partition coefficient), or the substance and its relevant degradation products decompose rapidly. 2-Aminoethanol (MEA, CAS 141-43-5) has a low log Kow of -2.3 (at 25 °C at pH 6.8 to 7.3; Sasol GmbH, 2009; see IUCLID Ch. 4.7) and is readily biodegradable according to OECD criteria (BASF AG, 1995; see IUCLID Ch. 5.2.1).

Although a study could be waived, 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 0.07 (Koc = 1.2 L/kg). Based on the measured log Pow of -2.3 (see Ch. 4.7), the log Koc was estimated at -0.78 (Koc = 0.166 L/kg) using the log Kow method. Both estimates refer to the uncharged molecule (BASF SE, 2013). While the substance was completely inside the applicability domain of the MCI model, the log Kow of MEA was slightly outside of the range of the training set of the Kow method. Therefore, the estimate of the log Kow method may be less accurate.

However, the measured pKa of 9.5 (Perrin, 1964) 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 moelcule. The pKa of MEA is 9.5 (measured; Perrin, 1964). For the log Kow of the uncharged molecule, the estimated value of -1.61 (KOWWIN v1.68) was used.

Regarding the charged molecule, at pH 7 the log Koc was estimated to be 1.16 (Koc = 15 L/kg) following the method of Franco & Trapp (2008, 2009, 2010) based on these data. 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.

There is one experimental result available for an adsorption coefficient Kd which was determined for a Canadian soil (silty sand with less than 1% clay, ca. 1% Corg) at three different pH values (6.5, 7.5, and 8.5; Sorensen et.al. (1997); disregarded as only summary available). The Kd was published as a range between 2.21 and 4.91. Based on the given Corg content of 1%, this value was converted to a Koc range between 221 and 449 (log Koc = 2.3 to 2.7). As only one soil was used to determine the Kd (Koc), this value should only be used as an indicative value to support the calculated Koc.

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