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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.

Key value for chemical safety assessment

Koc at 20 °C:
29

Additional information

In accordance with column 2 of REACH Annexes VIII (section 9.3.1) and IX (section 9.3.3), 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 N-N’ dimethylacetamide (CAS 127-19-5) has a log Kow of -0.77 (IUCLID chapter 4.7). In addition, the substance is assessed to be readily biodegradable (see IUCLID chapter 5.2).

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, N-N’ dimethylacetamide has a Koc of 3.34 L/kg. 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 (log Kow: -0.77; HSDB, 2006). The latter method resulted in a Koc of 2.83. These estimates are representative for uncharged molecules; the substance is within the applicability domain of the estimation models.

However, the pKa of -0.19 (Riddick, 1985; in HSDB) indicates that the substance will primarily ionize at environmentally relevant conditions. 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. The pKa of N-N’ dimethylacetamide is -0.19 (see IUCLID chapter 4.21). For the log Kow of the uncharged molecule, the calculated value of -0.77 (HSDB, 2006; see IUCLID chapter 4.7) was used.

Regarding the charged molecule, at pH 7 the log Koc was estimated to be 1.46 (Koc = 29 L/kg) following the method of Franco & Trapp (2008, 2009, 2010) based on these data. 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 is not to be expected at environmentally relevant conditions.

 

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 N-N’ dimethylacetamide (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.

[LogKoc: 1.46]

[LogKoc: 1.46]