The adsorption value is a primary input in leaching models for both parent compounds and metabolites. In the case of low sorbing compounds, any experimental error can lead to high uncertainty in the adsorption value and a questionable modeling endpoint. According to OECD 106, “Accurate determination is possible if the value which results by multiplying the Kd with the soil/solution ratio is &gt; 0.3, when measurements are based on concentration decrease in the aqueous phase (indirect method), or &gt; 0.1, when both phases are analysed (direct method)”. The current regulatory approach in Europe is to test the reliability of the adsorption value according to this “p-criterion” calculation, and to consider an adsorption value of zero if the “p-criterion” is failed. Such conservative adsorption values create hurdles in the hazard-based European leaching assessment, and underpin the importance of experimental methodologies which can increase the accuracy of the adsorption value for low adsorbing compounds. To this end, a high speed centrifugation plus filtration technique is proposed to enable the accurate determination of adsorption values for low adsorbing compounds. This technique, consistent with current OECD 106 guidance, can increase the soil/solution ratio from 1 kg/L for traditional sorption experiments to ca. 10 kg/L, increasing accuracy of the sorption measurement down to ca. 0.03 L/kg. The high speed centrifugation plus filtration technique will be described in detail. Results will also be presented and discussed, and compared with the results of traditional (indirectly measured) sorption experiments.

Accurate determination of adsorption values for low adsorbing compounds

252nd National Meeting (2016)

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