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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The adsorption coefficient of substance TM 10-202 was determined to be be in the range 1.18 E+04 to 1.63 E+04, with a log10 Koc in the range 4.07 to 4.21 according to the OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge test using the HPLC method.

Key value for chemical safety assessment

Koc at 20 °C:
16 300

Additional information

Quantification of the adsorption and desorption behaviour of the test item to soils of differing pH, organic carbon content and textural classification,using a batch equilibrium method was concluded not to be feasible. Methods under consideration were OECD Method 106, 21st January 2000 and Method C18 Adsorption – Desorption using a Batch Equilibrium Method, Commission Regulation (EC) No 440/2008 of 30 May 2008.

 

This conclusion was derived from low solubility of the test item in water, such that the permitted working nominal concentration for the investigation of behaviour in soils exceeded the lower recommended limit for the methodology. As a result of the low solubility, it was also not possible to satisfy the analytical method requirements of the method guidelines. Further to this, partition coefficient data available for the test item also exceeded the recommended domain for the methodology, as the expected high percentage adsorption would result in insufficient test item remaining in the aqueous phase for analysis. 

 

In such an extreme case, the method guidelines recommend the use of an alternative estimation method, such as those based on available partition coefficient data and established relationships between partition coefficient and adsorption coefficient, and/or HPLC estimation methods. Since issue of the above referenced batch equilibrium method guidelines, the HPLC estimation method has been formalized within the guideline Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001.

 

Estimations of the adsorption coefficient were obtained by calculation using Quantitative Structure Activity Relationships (QSAR’s), the details of which are provided in the technical guidance documents in support of Commission Directive 93/67/EEC on risk assessment for new substances, and from the specialized predictive software KOCWIN, version 2.00, September 2010, © 2000 to 2008, United States Environmental Protection Agency. The results were an adsorption coefficient (log10 Koc) range of 3.57 to 3.83.

 

Applying the HPLC estimation method to the test item, using a procedure designed to be compatible with Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001, resulted in an adsorption coefficient (log10 Koc) range of 4.07 to 4.21.

[LogKoc: 4.21]