Soil contamination by pesticide residues – what and how much should we expect to find in EU agricultural soils based on pesticide recommended uses?

Pesticides are heavily used in agriculture to reduce crop losses due to pests, weeds and pathogens. The intensive and long-term use of pesticides raises major health and environmental concerns since a substantial part of applied pesticides does not reach the target and is distributed into the environment instead. Exposure data (i.e. data on occurrence and levels of different pesticide residues), a pre-requisite to perform comprehensive and cumulative pesticide risk assessments, are scarce and fragmented, especially for soil. As analysing all EU soils for pesticide residues is not realistic, the contamination status of EU soils has to be inferred. Given pesticide use data limitations, the representative uses of the active substances (a.s.) allowed in the EU market, which cover different application schemes and recommended application rates, can be used as a proxy to estimate the type and amount of pesticide residues in EU soils. These representative uses are also considered in the calculation of predicted environmental concentrations in soil (PECs), the closest to a soil quality indicator when it comes to residues in soils of currently used pesticides. Although both pesticide representative uses and PECs are publicly available, this information is presented for individual a.s., in respective EU dossiers, which up to now were never compiled into a database and explored as such. Therefore, our study provides the first predictions on the total pesticide content in EU soils, calculated for 8 different crops (i.e. cereals, maize, root crops, non-permanent industrial crops, permanent crops, grapes, dry pulses-vegetables-flowers, and temporary grassland), 3 EU regions (i.e. Northern, Central and Southern Europe), and 2 pesticide use scenarios (i.e. all pesticides applied and no herbicides used). Such predictions are integrated into the Soil Quality Mobile App SQAPP, a recently launched and freely available tool that integrates existing soil quality information (covering both soil properties and soil threats) and provides tailored recommendations to improve soil quality. Furthermore, we present soil quality thresholds for all these crop-region-use combinations in terms of the number of active substances and the total pesticide content expected in soil. Our results indicate a much higher variety of products allowed in cereals than in other crops, yet the highest pesticide load is expected in dry pulses-vegetables-flowers and in grapes. At the most heavy use scenario (i.e. all allowed substances are applied, at the same time, and at the worst recommended use patterns), pesticide input can exceed 1,200 kg a.s. ha^-1 year^-1 (dry pulses-vegetables-flowers). Pesticide input is expected to be the highest in Southern Europe, and the lowest in Northern Europe or Central Europe, depending on crop type. Predicted pesticide levels in soil were in line with application data, with the highest contents in dry pulses-vegetables-flowers, and in Southern Europe. Predictions-based thresholds resulted in very low soil protection, especially when compared to measured data in literature, and measurement-based thresholds. Finally, our results reinforce the need of monitoring and surveillance programs for pesticide residues in soil, proper risk evaluation procedures for mixtures, as well as the need to establish threshold methodologies for pesticides.