Registration Dossier
Registration Dossier
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EC number: 224-207-2 | CAS number: 4246-51-9
Adsorption / desorption
Administrative data
Link to relevant study record(s)
Description of key information
Adsorption to the solid soil phase is not expected under environmentally relevant conditions.
Key value for chemical safety assessment
Additional information
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. The substance has a measured log Kow of -1.25 (at pH 11.1, 25 °C, BASF AG 1989, report no.: BRU89.027; see IUCLID Ch. 4.7). Therefore, a study does not need to be conducted.
Nevertheless, the adsorption coefficient was measured according to the HPLC method (OECD 121). At pH 9.0, the HPLC retention times of the substance were greater than those of the reference substances. Therefore, the log Koc was determined as > 5.63. At pH 7.0, two peaks were detected. The first peak with a log Koc of 1.5 represents 25 area%, while the second peak with a log Koc of 2.1 represents 75 area% (BASF SE, 2013, study no. 11L00204).
In addition, in order to assess the adsorption potential of the substance, the Koc value was estimated using QSAR models. According to the MCI method of the KOCWIN v2.00 module of EPI Suite v4.11 the substance has a log Koc of 1.42. 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. The latter method resulted in a log Koc of -0.08. These estimates are representative for uncharged molecules; the substance is not within the applicability domain of the estimation models.
At environmentally relevant conditions, the substance will be present in its ionized form (pKa =10.1, 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 value is 14 L/kg (log Koc = 1.16) at pH 5 to 8.
Based on the weight of evidence approach, it can be concluded that adsorption to the solid soil phase is not expected under environmentally relevant conditions.
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