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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 cannot be excluded.

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. 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 Isophoronediamine (CAS 93940 -97 -7, MIPDA) (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. Moreover, the chemical is readily biodegradable

 

Assessment:

In accordance with column 2 of REACH Annexes VIII and IX, a study on the adsorption potential 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. At environmentally relevant conditions modified Isophoronediamine (CAS 93940-97-7) has a log Kow of 2.0 (measured @ pH 6, 23°C; BASF SE, 2017, report no. 17L00094).

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 2.67 (Koc = 465.9 L/kg). Based on the measured log Pow of 2.0 (@ pH 6, 23°C, BASF SE 2017, report no. 17L00094), the log Koc was estimated to be 2.39 (Koc = 247 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, 2017).

 

However, the measured pKa of 7.2 (BASF SE 2017, report no. 17L00094) indicates that the substance MIPDA (CAS 93940 -97 -7) 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 3.39 (Koc = 2479 L/kg) following the method of Franco & Trapp (2008, 2009, 2010) and using the measured pKa of 7.2 (BASF SE 2017, report no. 17L00094) and the measured log Kow for the uncharged molecule of 1.85 (@ pH 9.2, 23°C, mean of two obtained values; BASF SE 2017, report no. 17L00094). 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 cannot be excluded.