Improved assessment of pesticide peak exposure in cultivated mountain watersheds

Agricultural activities can involve the use of plant protection products (PPPs) and the use of such chemicals can occur near surface waters bodies, thus creating a potential for adverse effects on aquatic ecosystems. Due to the spatio-temporal variability of chemical applications and of the processes regulating their fate and transport to surface waters, ecosystems are often exposed to pulses of contaminants. In certain environmental scenarios, such as small mountain watersheds, where runoff fluxes are particularly rapid due to side slopes, exposure peaks can be shorter but much higher. Monitoring campaigns are often inadequate or too expensive to be carried out and modelling tools are therefore vital for exposure assessment and their use is encouraged by current legislation. However, currently adopted models and scenarios (e.g., FOCUS for PPPs) are often too conservative and/or “static” to accurately capture exposure variability, and the need for more realistic and dynamic tools is now one of the major challenges for risk assessment. In a previous work, the new fate model DynAPlus was developed to improve pesticide fate predictions in cultivated mountain basins. The model was successfully evaluated against chlorpyrifos water concentrations measured in the Novella River (Non Valley, Northern Italy), where more than 1000 ha of apple orchards surround the river and its tributaries. However, the need for some model improvements and application to other chemicals and scenarios was highlighted. In this work, the DynAPlus model was improved to increase realism, by including vegetation to both terrestrial and aquatic environments, dissolved organic carbon (DOC) in water, and a soil-erosion module to compute particle-mediated chemical transport to surface waters. The improved DynANet was first applied to the Novella River case study and the new predicted chlorpyrifos concentrations were compared to measurements, suggesting an improvement of model performance, particularly due to the inclusion of the soil-erosion module and DOC. The model was then parameterized to simulate another cultivated mountain basin located in Northern Italy and applied to simulate the fate of three pesticides with different physical-chemical properties and persistence. The resulting peak exposure profiles were discussed to highlight the added value of such a dynamic modelling approach in providing information on exposure which could not emerge from the application of current approaches.