Présentations Colloques

Oral Presentation
Session 5.04: Emerging contaminants in the water cycle and risk to Groundwater
Baran Nicole
Pesticides released into the environment may contribute to complex mixtures of parent molecules and metabolites in surface and ground-waters. Diffuse pollution linked to agricultural activities is a significant issue for water management policies and notably the European Water Framework Directive. Several decades may be needed to detect the effects of past and present land-use practices in groundwater. Consequently it’s still a challenging task to link current pesticides uses and subsequent impacts on groundwater quality. ****In the “Ariège River” alluvial plain (c.a. 538 km2), a monthly monitoring of water quality was performed during four years at 16 locations. Groundwater catchment was delineated for each of these points. Land-uses and agricultural practises were determined referring to farmer declarations. ****A strong spatial and temporal variability of the contamination exists and the predominance of metabolites over parent molecules can often be highlighted. Short time transfers from soil to groundwater were punctually observed for different parent molecules. For these points, the annual variability of pesticides concentrations appeared to be driven by both land-uses and climatic conditions. ****High transmissivity of the aquifer enabled rapid renewal of the water in the saturated zone leading in some cases to a short residence time of contamination as shown by frequent measurements. At the opposite, a constant release of molecules from soil and vadose zone can lead to persistent groundwater contamination.****For metabolites, some time lag between spraying at surface and impact on groundwater may exist. For example, polar metabolites of chloroacetanilides can be detected after application and also during forthcoming recharge events (next year or some years after). As for parent molecules, hydrodynamic (climatic) conditions had evident impact on observed concentrations.****This long-term monitoring allowed a better characterization of trends and timeframes of metabolites that were not routinely investigated in France in groundwater. The identification of these pesticides and their metabolites is of primary importance as they can have adverse effects on current and future quality of groundwater.**