Scientific Opinion on the development of a soil ecoregions concept using distribution data on invertebrates

A modelling approach for defining soil ecoregions within Europe was developed to improve the realism of exposure scenarios for plant protection products. Biological information on four soil animal groups (earthworms, enchytraeids, collembolans and isopods) was used to assign each species to different life forms, representing depth horizons in which they occur. Based on information from three countries covering a North-South gradient (Finland, Germany, Portugal), species presence-absence data were modelled using pedological and climatological information. With a triangular diagram it was possible to visualise life-form distributions for the organisms groups. Ecoregion maps were produced for earthworms and enchytraeids and revealed marked differences between the three countries. The information on the spatial distribution of the dominance classes could be transformed into depth profiles for any ecotoxicologically relevant concentration to be modelled. This procedure allows defining realistic “worst” case exposure depth profiles for risk assessment. The approach could be extended to the entire EU territory, provided more biogeographical data are available. A better resolution might also be achieved by adjusting the – presently geometrically derived – sizes of the 7 classes in the triangular diagrams. For an improved risk assessment of plant protection products it is recommended to extend exposure modelling to the litter layer. This approach would imply a refinement of the environmental risk assessment of plant protection products which needs to be discussed with risk managers. For most of the situations in Europe, the worst case soil depth profile for short term risk assessment would be litter (if present) or 0 to 1 cm depth instead of the currently used 0 to 5 cm depth.