Contrasting accumulation of ivermectin in rooted emergent and free-floating macrophyte-biofilm assemblages from...

Veterinary pharmaceuticals, such as ivermectin, are widely used in livestock production and reach nearby wetlands primarily bound to cattle dung, yet their environmental behavior within aquatic vegetation remains poorly understood. This study assessed the accumulation and distribution of environmentally relevant concentrations of ivermectin in two macrophytes with contrasting life forms from the Middle Paraná River floodplain (Argentina): the rooted emergent Ludwigia peploides (Kunth) P.H. Raven and the free-floating Salvinia biloba Raddi and in their epiphytic biofilms. A 10-day outdoor mesocosm experiment was conducted using ivermectin-spiked cattle dung to simulate input from grazing livestock. Ivermectin concentrations were quantified in roots, leaves, biofilm, and sediment under single- and mixed-species treatments. Ivermectin was detected in all analyzed matrices, with higher concentrations generally observed in L. peploides. Root concentrations were higher in L. peploides (≈18 ng g^-1) than in S. biloba (≈8 ng g^-1). Ivermectin concentrations in the biofilm of L. peploides were also notable (≈9 ng g^-1), whereas in S. biloba they were lower or below detection limits. Leaf concentrations remained comparatively low in both species (generally below 3 ng g^-1). Comparison between single- and mixed-species treatments showed species-dependent responses that varied across matrices. These results indicate that plant life forms influence ivermectin accumulation patterns, with roots and epiphytic biofilms as the primary retention compartments. Macrophyte-biofilm assemblages may therefore act as temporary sinks, while also representing potential reservoirs for ivermectin transfer through aquatic food webs, highlighting their relevance for understanding the environmental fate of veterinary pharmaceuticals in livestock-impacted wetlands.