Assessing impacts of ivermectin, a key agricultural parasiticide, on freshwater organisms in a multi-stressor context

Ivermectin (and similar) (hereafter "avermectins") are veterinary antiparasitic medications that were historically considered safe. However, more recent research indicates that avermectins may have adverse effects on a range of invertebrates, including coleopterans, annelids, crustaceans, and dipterans[1,5,7]. While avermectins generally decompose on short time scales within compost[8], they are found to persist in both animal tissue[4] and manure[7] long enough to affect invertebrates.
Currently, avermectins are used to treat livestock; historically, they were used to treat aquacultured salmon though this is now much less common (T. Telfer, pers. commun.). Avermectin contamination sources would be manure and tissue composition by livestock and transport may occur differentially based on factors such as precipitation and biotic transport of dead matter. Avermectins decompose quickly in compost[8], so high variation across contamination sites stemming from recency of treatment, severity and type of contamination, and ecological factors such as temperature and wetness may arise.
Investigating the effects of avermectins may allow for a re-evaluation of its safety and the conditions of its use. Furthermore, the capacity for avermectin pollution to have different effects on certain organisms or different waterbody types may influence management and conservation decisions and allow for monitoring in high-risk areas, which may prevent unexpected contamination-related die-off from interfering with species conservation. This research may also lay the groundwork for mitigation of avermectin-derived effects, should its use be continued.