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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption to solid soil phase is not expected.

Key value for chemical safety assessment

Additional information

The Koc of the Reaction product of 2,4-Dinitrotoluene and 2,6-Dinitrotoluene and hydrogen (EC 939-489-9) was determined according to OECD 121 (BASF SE, 2011, report no. 11L00071). The Koc was determined for the ionised molecule at pH 7 and for the non-ionised molecule at pH 10. At pH 7 the log Koc was determined to be 1.2. At pH 10 the log Koc was determined to be larger than 5.63. In addition, the adsorption of the reaction product on activated sludge was determined according to ISO 18749 test (BASF, 2013). The adsorption (measured by DOC-removal) was lower than 10% after 72h.

 

In order to assess the adsorption potential of the substance, the Koc value was also estimated using QSAR models for 2-methylcyclohexane-1,3-diamine (CAS 13897-56-8) and 4-methylcyclohexane-1,3-diamine (CAS 13897-55-7) which are representative constituents of the reaction product of of 2,4-Dinitrotoluene and 2,6-Dinitrotoluene and hydrogen (MCDA EC 939-489-9). According to the MCI method of the KOCWIN v2.00 module of EPI Suite v4.11, the 2-methylcyclohexane-1,3-diamine (CAS 13897-56-8) has a Koc of 11.86 and the 4-methylcyclohexane-1,3-diamine (CAS 13897-55-7) has a Koc of 11.62. 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 (measured log Kow: 0.12, BASF SE, Rep. 11L00071, 2011). The latter method resulted in a Koc of 1.89. These estimates are representative for uncharged molecules; however, the substances are not within the applicability domain of the estimation model, thus the Koc values for both constituents may be overestimated.

 

At environmentally relevant conditions the Reaction product of 2,4-Dinitrotoluene and 2,6-Dinitrotoluene and hydrogen (EC 939-489-9) is present in ionized form (pKa=10.4 BASF SE, Rep. 11L00071, 2011 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 at pH 5-8 is 53 L/kg (log Koc:1.73). Based on the available information on the log Koc (log Koc = 1.2, pH 7, OECD 121, BASF SE, 2011, rep. 11L00071) and supported by a weight-of-evidence approach from calculated data, it can be concluded that adsorption to the solid soil phase of MCDA (EC 939 -489 -9) is not expected under environmentally relevant conditions.