Selection of Scenarios for Exposure of Soil Organisms to Plant Protection Products
European scenarios for exposure of soil organisms to plant protection products are currently not available. As part of the revision of the Guidance Document on Persistence in Soil (9188/VI/97 rev 8 published in 2000), the PPR-panel was therefore asked to start the development of tiered exposure-assessment approaches for soil organisms in which European exposure scenarios play an important role. This report contributes to this revision by developing a systematic approach to the selection of realistic worst-case scenarios for exposure of soil organisms. Realistic worst-case conditions are defined as the 90th spatial percentile of the exposure concentration (the maximum over time) in the intended area of use in each of three regulatory zones defined in Council regulation (EC) 1107/2009. Separate scenarios were developed for the concentration in total soil (mg kg -1) and for the concentration in the liquid phase (mg l-1), giving six scenarios to be developed. The scenario selection began with the compilation of a coherent database. Then, a simplified model was selected to generate maps of the concentration in total soil and the concentration in the liquid phase over the entire area of annual crops in the three zones. In the subsequent two steps, procedures were applied to account for parameter uncertainty and scenario uncertainty (i.e. the likelihood that a scenario that is derived for one substance is not conservative enough for another). In the final step, the six scenarios were selected by defining their air temperature, soil organic matter content and their soil textural class. The concentration in total soil was shown to decrease in the order North>Central>South, whereas the concentration in the liquid phase showed an opposing trend with the highest concentration in the Southern European scenario. The scenario development was based on the total area of annual crops in the EU-27, but the endpoint of the exposure assessment is the 90th percentile of the intended use area. The scenarios may therefore not be conservative enough. To ensure that the selected scenarios are sufficiently conservative, safety factors were derived.