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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption to the solid soil phase is not to be expected under environmentally relevant conditions.

Key value for chemical safety assessment

Additional information

The Koc for the uncharged molecule of 4,4'-Diamino-3,3',5,5'-tetramethyl-dicyclohexylmethan (CAS 65962 -45 -0) was estimated using both models of KOCWIN v2.00 of EPI Suite v4.11 (BASF SE, 2013). These estimates are representative for the uncharged molecule. 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 3.51 (Koc = 3204 L/kg). Based on the measured log Kow of 3.0 (pH 11.0; BASF SE, 2013; report no. 11L00284), the log Koc was estimated to be 1.87 (Koc = 74 L/kg) using the log Kow method. Both methods are based on fragment corrections. Since the identified fragment (Nitrogen-to-Cycloalkane, aliphatic) occurs at a higher number than the training data set of the models, the estimates are less accurate.

The pKa of 10.68 (calculated: SPARC v4.5) indicates that the molecule will exist primarily as a cation in the environment. Cations generally adsorb stronger to soils containing organic carbon and clay than their neutral counterparts. Hence, the results from the KOCWIN models may underestimate adsorption to organic carbon since it does not consider the ionic structure of the molecule.

 

Regarding the charged molecule, the log Koc was estimated to be 4.0 (Koc = 10343 to 10363 L/kg, pH 5 to 8) following the method of Franco & Trapp (2008, 2009, 2010) and using the pKa of 10.68 and the measured log Kow for the uncharged molecule of 3.0 (pH 11; BASF SE, 2013; report no. 11L00248). The correction was performed for pH 5, 7, and 8, which represents 98% of the European soils.

 

In addition to the estimation methods, the log Koc was also determined according to OECD guideline 121. The log Koc was determined to be 2.6 at 23 °C and pH 7.0 (BASF SE, 2013). At pH 9 no reliable Koc could be determined as the retention time on the HPLC system was larger than for the reference substances (log Koc > 5.63). As 98% of the European soils have a pH within a range of 5 to 8, the value determined at pH 9 is not relevant for the assessment of the substances environmental fate.

 

Due to the uncertainty of the estimated data (applicability domain) as well as the higher environmental relevance of the experimentally determined Koc (log Koc = 2.6 at pH 7), the latter value was used for the environmental risk assessment.