Based on a Member State consultation EFSA initiated a revision of the guidance for the soil exposure assessment including development of EU scenarios for numerical models. The aim of the exposure assessment was to obtain a 90th percentile of the PEC in space and time considering all fields in the regulatory zones North, Centre and South grown with the target crop where this active substance is applied. The types of ecotoxicologically relevant concentrations considered were both the concentration in total soil and the concentration in pore water averaged over the top 1, 2.5, 5 or 20 cm of soil (both peak and TWA concentrations for time windows up to 56 d). The scenario selection was based on a simple analytical model that calculates the concentration in soil assuming that degradation (first-order kinetics at a constant rate) is the only loss process from the 20-cm plough layer. The concentration in the pore water was calculated assuming a linear sorption isotherm assuming that sorption is proportional to organic matter. Concentration maps were calculated at a resolution of 1x1 km2 for the whole area of annual crops in each of the regulatory zones North, Centre and South. Simulations including uncertainty in the dry bulk density and in substance properties such as the Kom and the DegT50 showed that a spatial 95th percentile has to be selected for obtaining an overall 90th percentile when median or geomean values of these substance properties are used as input for the scenario calculations in the regulatory process. So the target was to select a spatial 95th percentile. Scenario were selected based on maps of the peak concentrations in total soil and in pore water that were generated for 19 substances and averaging depths of 1 and 20 cm. The selected scenarios for concentration in total soil have all relatively high organic matter contents and low temperatures. However, the selected scenarios for the pore water concentration have all relatively low organic matter contents because the pore water concentration is almost directly proportional to the inverse of the organic matter content for substances that show significant sorption. Calculations with the simple analytical model for a number of example substances showed that the concentration in total soil increased in the order South-Centre-North and that the concentration in the pore water increased in the order North- Centre-South (so opposite orders for these two types of concentration).
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