Ecotoxicological effects of the emerging contaminant ivermectin on Rhinella arenarum: A comparative study of active ingredient and commercial formulation.

ABSTRACT

Ivermectin (IVM) is a broad-spectrum veterinary antiparasitic used worldwide in cattle breeding. The aim of this study was to evaluate the lethal effects of the active ingredient and a commercial formulation of IVM (1 % active ingredient) in the embryonic stage (S. 4-6) and larval stage (S. 25) of the South American amphibian Rhinella arenarum through chronic standardized bioassays. Also, behavior analysis and oxidative stress and cholinergic effects biomarkers were analyzed at 1, 10 and 100 µg IVM/L concentrations. For the embryonic stage, the active ingredient (96 h- LC50 15900 µg/L) was more toxic than the commercial formulation (96 h-LC50 51230 µg/L) during the acute period, while at chronic exposure the commercial formulation was more toxic (504 h-LC50 10.25 µg/L), compared to the active ingredient (504 h-LC50 312.80 µg/L). For the larval stage, in acute exposure, the active ingredient (96 h-LC50 800 µg/L) was more toxic than the commercial formulation (96 h-LC50 1550 µg/L). In the chronic exposure, the commercial formulation (504 h-LC50 77.33 µg/L) was more toxic than the active ingredient (504 h-LC50 195.25 µg/L). Overall, larvae exhibited greater sensitivity to both the active ingredient and the commercial formulation. However, during chronic exposure, embryos were more sensitive to the commercial formulation than larvae. The commercial formulation primarily induced oxidative stress, and both forms of the compound affected behavior and cholinergic effect biomarkers, even at low environmentally relevant concentrations (1 µg/L). These results highlight the potential impact of IVM on aquatic ecosystems.