The Leaching Calculator: a tool for predicting leachability within the framework of the new mobility-related hazard...

In this study, we propose a new metric for substance mobility in extension to the already implemented use of the log Koc as a sorption constant to the organic carbon content of soils. The new metric is based on the leachability of a compound in soil, i.e., the fraction thereof that is predicted to be transported to shallow groundwater. Apart from including climate and soil properties of European regions, the degradation half-life in soil is used in addition to the log Koc as an important parameter. This improves the applicability of the mobility concept for substances used under European environmental conditions due to the important role of degradation on a substance's potential to pass drinking water barriers such as soil or sediment. To factor in these additional parameters, the meta-model Leaching Calculator was developed. It is based on FOCUS (FOrum for Coordination of pesticide models and their USe) PELMO (PEsticide Leaching MOdel) as the underlying model to calculate the leachability of substances. FOCUS PELMO is a mechanistic leaching model that may provide a more comprehensive understanding of a chemical's movements in the environment. While calculations with FOCUS PELMO require many substance parameters and well-defined pedo-climatic scenarios, the Leaching calculator only uses the log Koc and the half-life in soil as input parameters, and subsequently calculates the leachability based on a set of PELMO computations. Mobility assessments are then derived from proposed leachability thresholds.