Occurrence, fate, and environmental loss of antiparasitic veterinary drugs in animal waste.

Antiparasitic veterinary drugs, specifically anthelmintics, anticoccidials and ectoparasiticides, are increasingly recognised as global environmental contaminants, entering agroecosystems primarily via animal excreta and accumulating in manure and slurry before transfer to soils, water bodies and crops. This review provides a comprehensive synthesis of these drug classes, covering usage patterns, excretion and persistence dynamics, occurrence in manure and slurry, within-manure transformation pathways, environmental fate and transport pathways, ecotoxicological effects on non-target organism, and mitigation strategies. Excretion and transformation behaviour are governed by compound lipophilicity and chemical structure: highly lipophilic macrocyclic lactones and benzimidazoles persist predominantly in faecal matter and undergo class-specific transformation reactions, whereas the transformation pathways of pyrethroids within manure remain almost entirely uncharacterised despite well-documented soil-phase chemistry. Occurrence data are sparse and dominated by isolated farm- or species-specific studies rather than systematic surveys and validated analytical methods for pyrethroids and its transformation products in manure are scarce. Environmental fate is strongly governed by lipophilicity: macrocyclic lactones and pyrethroids move primarily via particle-associated surface run-off, whereas benzimidazoles and ionophores show moderate mobility and can leach into surface waters. Ecotoxicological risks are most critical for dung-colonising invertebrates exposed to macrocyclic lactone residues and for aquatic organism exposed to pyrethroid-contaminated sediments. Mitigation strategies, including composting, storage, bioaugmentation, and source-based interventions, show compound-specific efficacy and are rarely validated at farm scale. The review identifies three primary barriers to robust environmental risk assessment: the scarcity of validated multi-residue analytical methods, particularly for pyrethroids and its transformation products, the lack of systematic occurrence and usage monitoring; and the limited farm-scale evaluation of mitigation technologies.