pH-dependent sorption behaviour of pesticides and metabolites can be handled in various ways in environmental exposure modelling within the regulatory procedure of pesticide registration in the European Union. In the groundwater model FOCUS-PEARL 4.4.4, pH-dependent sorption can either be addressed by parameterising a sigmoidal function based on Kfom,ac, Kfom,bas (Freundlich adsorption coefficient of the protonated (Kfom,ac) and deprotonated (Kfom,bas) form of a substance normalised for organic matter content) and pKa-value or by entering directly horizon-specific Kf-values that again can be calculated externally in different ways. The presentation will introduce both approaches, discuss sorption representation in detail based on: sigmoidal relationship between Kfom and soil pH (pKa-value necessary); sigmoidal relationship between Kf and soil pH (pKa-value necessary); linear relationship between Kf and soil pH (pKa-value not necessary); and horizon specific sorption versus Kf-values employed in modelling based on top-soil pH-value (pKa-value not necessary), and then compare the effects in view of the Predicted Environmental Concentration (PECgw) at different locations of the European FOCUS scenarios. These options addressing pH-dependent sorption will be compared with other (national) approaches such as separately deriving appropriate Kfoc-values from studies conducted with alkaline and acidic soils and neglecting scenario specific pH-conditions.

Comparing different modeling approaches of pH-dependent sorption with FOCUS-PEARL

244th National Meeting (2012)

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