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

Abstract

Veterinary pharmaceuticals, such as ivermectin, are widely used in livestock pro-duction and reach nearby wetlands primarily bound to cattle dung, yet theirenvironmental behavior within aquatic vegetation remains poorly understood. Thisstudy assessed the accumulation and distribution of environmentally relevant con-centrations of ivermectin in two macrophytes with contrasting life forms from theMiddle Paraná River floodplain (Argentina): the rooted emergent Ludwigia peploides(Kunth) P.H. Raven and the free-floating Salvinia biloba Raddi and in their epi-phytic biofilms. A 10-day outdoor mesocosm experiment was conducted usingivermectin-spiked cattle dung to simulate input from grazing livestock. Ivermectinconcentrations were quantified in roots, leaves, biofilm, and sediment under single-and mixed-species treatments. Ivermectin was detected in all analyzed matrices, withhigher concentrations generally observed in L. peploides. Root concentrations werehigher in L. peploides (≈18 ng g−1) than in S. biloba (≈8 ng g−1). Ivermectin con-centrations in the biofilm of L. peploides were also notable (≈9 ng g−1), whereas inS. biloba they were lower or below detection limits. Leaf concentrations remainedcomparatively low in both species (generally below 3 ng g−1). Comparison betweensingle- and mixed-species treatments showed species-dependent responses that var-ied across matrices. These results indicate that plant life forms influence ivermectinaccumulation patterns, with roots and epiphytic biofilms as the primary retention compartments. Macrophyte-biofilm assemblages may therefore act as temporarysinks, while also representing potential reservoirs for ivermectin transfer throughaquatic food webs, highlighting their relevance for understanding the environmentalfate of veterinary pharmaceuticals in livestock-impacted wetlands.