Anthropogenic sources and transfer of trace metals from the environment to brown trout (Salmo trutta) in mountainous rivers.

Mountainous ecosystems are particularly sensitive to global change and are affected by both historical and current anthropogenic activities. For instance, past and contemporary mining and agriculture are responsible for increasing metal contamination in riverine systems. This study investigated the sources and transfer routes of copper (Cu), zinc (Zn), arsenic (As) and lead (Pb) across soil, biofilm, sediment and fish (Salmo trutta) along a gradient of human activity (mining, agriculture, urbanization) in the French Pyrenees. Drawing on a comprehensive data set obtained from X-Ray Fluorescence probe and TQ-ICP-MS analysis, in combination with a statistical Structural Equation Modelling approach, we found that historical mining activities, although no longer active, were the primary source of Zn and Pb contamination in the soil, as well as Pb contamination in the biofilm, whereas contemporary agricultural activities were the main source of Cu, As and Pb contamination in the biofilm. This underscores the long-lasting impacts of human activities on riverine pollution. Furthermore, we showed that several environmental parameters could modulate metal content in fish. For instance, finer substrate particle size and lower oxygen levels increased Cu and Zn uptake in fish tissue. This study provides new insights into the complex dynamics of trace metals in riverine ecosystems and emphasize the importance of using large-scale, multi-compartment and multi-metal approaches to assess metal contamination of aquatic ecosystems.