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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption of MCHAmix to the solid soil phase is expected.

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 labelling and/or risk assessment and (4) adequate and reliable documentation of the applied method is provided.

 For the assessment of the reaction product of 2,4-Dinitrotoluene and 2,6-Dinitrotoluene and hydrogen, deaminated (EC 943-517-5, MCHAmix) (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

No experimental data on the adsorption potential for the target compound are available. In order to assess the adsorption potential of the substance MCHAmix (EC 943-517-5), the Koc values were estimated using QSAR models for its two representative constituents: 2-Methylcyclohexylamine (CAS 7003-32-9) and 4-methylcyclohexylamine, mixed isomers (CAS 6321-23-9).

According to the MCI method of the KOCWIN v2.00 module of EPI Suite v4.11, both constituents have a log Koc of 1.71. The difference in the adsorption potential is negligible (CAS 7003-32-9: Koc = 52.7; CAS 6321-23-9: Koc = 51.6). The MCI module is more reliable than the log Kow method of KOCWIN v2.00, which estimates the KOC based on the n-octanol/water partition coefficient (identical values for both substances: log Kow: 2.05, calculated @25°C, KOWWIN v1.68 of EPI Suite v4.11). The KOW method resulted in a log Koc of 1.70 (Koc = 50.3), which is in good agreement with the MCI method. The substances are within the applicability domain of the estimation model. These estimates are representative for uncharged molecules.

At environmentally relevant conditions both representative constituents are present in ionized form (CAS 7003-32-9: pKa = 10.38; CAS 6321-23-9 = 10.39; calculated with SPARC On-line calculator, see IUCLID Ch 4.21). Therefore, the adsorption coefficient was calculated according to Franco & Trapp (2008, 2009, 2010) to correct for the charged molecule at pH 5, 7, and 8. This pH range is representative for 98% of the European soils. 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. The resulting Koc values for both constituents are listed in the table below:

 

Substance

pH 5

pH 7

pH 8

Koc

Log Koc

Koc

Log Koc

Koc

Log Koc

2-Methylcyclohexylamine (CAS 7003-32-9)

1550

3.19

1549

3.19

1544

3.19

4-methylcyclohexylamine, mixed isomers (6321-23-9)

1538

1537

1533

 

Based on the calculated data for the representative constituents and the structurally similar substance, it is concluded that adsorption of MCHAmix is expected for the charged molecule under environmentally relevant conditions.