Bekämpningsmedelsläckage från grundvatten till ytvatten - Undersökning av ett avrinningsområde i södra Skåne

From a small stream draining an agricultural catchment area in south Sweden, a temporal analysis of the occurrence of legacy pesticides was carried out and correlated with contemporary groundwater levelling, precipitation and flow rate of the stream, in order to evaluate groundwater outflow as an entry route for pesticides in the stream. Based on continuous measurement data from two periods of 12 respectively 16 months, in total eight legacy pesticides and three metabolites of legacy pesticides, were detected from early spring to late autumn, when runoff water to the stream was low and groundwater constituted the main water source of the stream. The detections ceased during the winter months following increased stream flow, suggesting a shift in the hydraulic head between the stream and the aquifer leading to a break in groundwater outflow. Alternatively suggesting a dilution of the legacy pesticides due to the increased volume of runoff water compared to groundwater in the stream. In this way at least seven out of the eleven pesticides detected, showed clear indications of being derived from groundwater outflow, while two correlates with peaks in precipitation and stream flow. This indicates that they may originate from atmospheric deposition, leakage from soil or point sources, or from unauthorised use. The result demonstrates that groundwater outflow constitutes a significant entry route for pesticides in surface water, and that groundwater accordingly is of high importance for surface water quality and aquatic ecosystems in its outflow area. The result further illustrates the general problem with contaminated groundwater that provides for long-lived and long-distance transport of xenobiotics in the environment decades after its been banned, supporting recent studies indicating that legacy pesticides should not be neglected in monitoring programs and risk assessments. Similarly, the substances we use and spread today could potentially pose a threat to future generations.From a small stream draining an agricultural catchment area in south Sweden, a temporal analysis of the occurrence of legacy pesticides was carried out and correlated with contemporary groundwater levelling, precipitation and flow rate of the stream, in order to evaluate groundwater outflow as an entry route for pesticides in the stream. Based on continuous measurement data from two periods of 12 respectively 16 months, in total eight legacy pesticides and three metabolites of legacy pesticides, were detected from early spring to late autumn, when runoff water to the stream was low and groundwater constituted the main water source of the stream. The detections ceased during the winter months following increased stream flow, suggesting a shift in the hydraulic head between the stream and the aquifer leading to a break in groundwater outflow. Alternatively suggesting a dilution of the legacy pesticides due to the increased volume of runoff water compared to groundwater in the stream. In this way at least seven out of the eleven pesticides detected, showed clear indications of being derived from groundwater outflow, while two correlates with peaks in precipitation and stream flow. This indicates that they may originate from atmospheric deposition, leakage from soil or point sources, or from unauthorised use. The result demonstrates that groundwater outflow constitutes a significant entry route for pesticides in surface water, and that groundwater accordingly is of high importance for surface water quality and aquatic ecosystems in its outflow area. The result further illustrates the general problem with contaminated groundwater that provides for long-lived and long-distance transport of xenobiotics in the environment decades after its been banned, supporting recent studies indicating that legacy pesticides should not be neglected in monitoring programs and risk assessments. Similarly, the substances we use and spread today could potentially pose a threat to future generations