Bioaccumulation of organic contaminants from contaminated food sources, might pose an underestimated risk towards shredding invertebrates. This assumption is substantiated by monitoring studies observing discrepancies of predicted tissue concentrations determined from lab-based experiments compared to measured concentrations of systemic pesticides in gammarids. To elucidate the role of dietary uptake in bioaccumulation, gammarids were exposed to leaf material from trees treated with a systemic fungicide mixture (azoxystrobin, cyprodinil, fluopyram and tebuconazole), simulating leaves entering surface waters in autumn. Leaf concentrations, spatial distribution, and leaching behaviour of fungicides were characterised using LC-HRMS/MS and MALDI-MS imaging. The contribution of leached fungicides and fungicides taken up from feeding was assessed by assembling caged (no access) and uncaged (access to leaves) gammarids. The fungicide dynamics in the test system were analysed using LC-HRMS/MS and toxicokinetic modelling. Additionally, a summer scenario was simulated where water was the initial source of contamination and leaves contaminated by sorption. The uptake, translocation and biotransformation of systemic fungicides by trees was compound dependent. Internal fungicide concentrations of gammarids with access to leaves were much higher than in caged gammarids of the autumn scenario, but the difference was minimal in the summer scenario. In food choice and dissectioning experiments gammarids did not avoid contaminated leaves and efficiently assimilated contaminants from leaves indicating the relevance of this exposure pathway in the field. The present study demonstrates the potential impact of dietary uptake on in situ bioaccumulation for shredders in autumn, outside the main application period. Obtained toxicokinetic parameters facilitate modelling of environmental exposure scenarios. The uncovered significance of the dietary uptake for detritivores warrants further consideration from scientific but also regulatory perspectives.
