Disentangling moxidectin routes of exposure to non target taxa: a multi approach study

Abstract

Macrocyclic lactone moxidectin is a widely used anthelmintic in livestock farming, designed to combat gastrointestinal parasites. Due to its lipophilic properties and limited metabolism in animals, substantial amounts of the parent compound are excreted in dung, increasing environmental exposure to non-target organisms. While some negative effects on arthropods inhabiting dung have been reported, there is limited understanding of other potential exposure routes and impacts, especially those involving indirect effects on aboveground ecological interactions. This project investigates both direct and indirect pathways of moxidectin exposure affecting non-target taxa, including various arthropod groups and crop plant species. Through a series of outdoor and indoor experiments, we assessed how moxidectin presence in soil, via treated soil, influences plant performance and arthropod responses. Outdoor trials examined moxidectin uptake and accumulation in crop plant species and its impacts on vegetative and reproductive development. Indoor experiments evaluated how pollinators interacting with treated plants were affected in terms of performance and reproductive behavior. Additionally, germination assays explored the potential for carryover effects of moxidectin on seeds harvested from previously exposed plants. Our findings show that moxidectin exposure can adversely impact the early vegetative growth and reproductive traits of crop plant species. Treated plants exhibited reductions in height, leaf production, flower number, and branching. Germination and root development were also negatively influenced, suggesting phytotoxic potential at environmentally relevant concentrations. Indirect effects on herbivores were observed, including delayed development and reduced growth in individuals feeding on treated plants. In contrast, some arthropods showed unchanged survival or altered reproductive output when interacting with exposed hosts, indicating species-specific sensitivities. These results emphasize the importance of understanding the broader ecological consequences of veterinary pharmaceuticals like moxidectin. Given the increasing global use of such compounds, often without sufficient oversight, identifying and mitigating unintended effects on beneficial non-target organisms is essential. This research contributes to improved management practices for pasturelands and supports the development of environmental monitoring strategies aimed at protecting ecosystem services.