Flood-borne pesticides are transferred from riparian soil via plants to phytophagous aphids

Surface waters are known to be polluted by a number of contaminants including synthetic pesticides. As flooding events intensify due to climate change, the flood-mediated transfer of pesticides to terrestrial ecosystems may also increase, potentially resulting in unforeseen exposure for terrestrial food-webs. To assess the uptake and trophic transfer of flood-mediated pesticide entries, we simulated riparian soil contamination caused by floodwater in a climate chamber pot experiment. The floodwater contained 31 fungicides and insecticides at environmentally relevant concentrations. We exposed potted stinging nettle plants (Urtica dioica) which were colonized by aphids to four sequential simulated flooding events and measured the pesticide concentrations in the soil, plant roots, plant stems and leaves, and aphids using HPLC-MS/MS. After four flooding events, the sum of insecticide and fungicide concentrations increased six-fold in soil and over thirty-fold in nettle plants compared to the concentrations after one flooding event. Bixafen and etofenprox showed the highest concentration in nettle leaves and stems, indicating bioaccumulation. After the four flooding events, thirteen pesticides were detected at concentrations up to 13.7 μg kg^-1 in the phytophagous aphids with picoxystrobin, fipronil, trifloxystrobin, spiroxamine, and fluopyram showing biomagnification. This study shows that commonly applied pesticides can be transferred to riparian soils by flooding events, taken up by plants and biomagnify in herbivorous insects.