Comparison of pesticide leaching potential to groundwater under EU FOCUS and site specific conditions

The EU FOCUS scenarios are a set of nine standard scenarios based on a combination of crop, soil and weather data used throughout Europe to evaluate the leaching potential of pesticides to groundwater. In Ireland, two predefined EU FOCUS scenarios (Okehampton and Hamburg) appear to be the most appropriate to Irish conditions. However, there is concern that these scenarios may not accurately represent Irish specific conditions, especially in terms of soil and climatic weather. Therefore, the objective of this study was to parameterise a number of site specific locations in Ireland (represented by Oakpark, Clonroche, Rathangan and Elton series soils) and to compare simulated leachate levels at these locations to EU FOCUS scenarios using the PELMO (Pesticide Leaching Model) simulation model. The hydrological processes were validated using observed data for soil tension and leachate. The appropriate EU FOCUS scenarios were then simulated for the given locations and compared to the parameterised scenario. All scenarios were run using the same version of PELMO, therefore eliminating any software impacts. The models were run for 26 years using appropriate meteorological data. The results showed significant difference between the parameterised model pesticide leaching and that resulting from the EU FOCUS scenarios, the latter overestimating site pesticide leaching from 42 to 99%. The results indicated a significant conservatism in using EU FOCUS scenarios to determine potential pesticide concentration in the leachate under Irish specific conditions and ensure the desired level of protection against pesticide contamination of national water resources.