Comp Biochem Physiol C Toxicol Pharmacol 2025 Nov 13;:110392. doi: 10.1016/j.cbpc.2025.110392.

Anti-sea lice products azamethiphos and hydrogen peroxide effects on five coastal marine organisms.

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Azamethiphos and hydrogen peroxide are active ingredients (AI) of formulations used as water-bath pesticides in Atlantic salmon aquaculture to remove ectoparasitic copepods. Despite their long-term use, unknowns and concerns are still present, particularly regarding the toxicity towards non-target commercially and ecologically important species in Atlantic Canada, and potential differences in toxicity between the AI and the formulated product. Here, we tested the acute effects of azamethiphos and hydrogen peroxide on five marine species. Hazard data (half maximal effective and lethal concentrations, respectively EC50 and LC50) were determined for 10 endpoints, assessed at various timepoints, during the exposure of Stage I larval American lobster Homarus americanus, green sea urchin Strongylocentrotus droebachiensis gametes, haemocytes and adults of blue mussel Mytilus edulis, common periwinkle snail Littorina littorea, and copepod Acartia tonsa. To investigate whether formulations had the same effect as the AI, for azamethiphos, both the AI and the formulation (Salmosan® Vet) were tested. For hydrogen peroxide, potential differences in the toxicity of three formulations (purchased solutions 50 %, 35 %, and 3 %) were compared. Results suggest no differences between the azamethiphos and Salmosan® Vet, with similar L/EC50 values. Little differences were found among the three hydrogen peroxide formulations. For azamethiphos, the most sensitive species was the American lobster, followed by sea urchin, whereas for hydrogen peroxide, sea urchin was the most sensitive, followed by A. tonsa. L. littorea was the least sensitive species tested. Overall, results showed that all the endpoints were greater than the Environmental Quality Standard previously determined for the two compounds.

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