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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption of the hydrolysis product valeric acid to solid soil phase is not 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 labeling and/or risk assessment and (4) adequate and reliable documentation of the applied method is provided.

For the assessment of the hydrolysis product valeric acid (CAS 109 -52 -4) (Q)SAR results were used for adsorption / desorption. 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

Valeryl chloride rapidly hydrolyses in contact with water to form valeric acid (CAS 109 -52 -4) and hydrogen chloride (CAS 7647-01-0). Due to this rapid hydrolysis, the assessment of the adsorption potential of the parent compound is considered to be of low relevance. Therefore, the assessment of adsorption potential is based solely on the data available for valeric acid.

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. Valeric acid is readily biodegradable according to OECD criteria (see IUCLID Ch. 5.2.1). In addition, the substance has an experimental log Kow of 1.39 (PhysProp database of EPI Suite v4.11). Therefore, a study does not need to be conducted.

In order to assess the adsorption potential of valeric acid (CAS 109 -52 -4), 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 0.68. 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 0.92. These estimates are representative for uncharged molecules; the substance is within the applicability domain of the estimation models.

At environmentally relevant conditions, the substance will be present in ionized form (pKa = 4.84; PhysProp database of EPI Suite v4.11). 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 are 66 L/kg to 49 L/kg (log Koc 1.82 to 1.69) at pH 5 to 8.

It can be concluded that adsorption to the solid soil phase is not expected under environmentally relevant conditions.