The impact of anti-sea lice pesticides, azamethiphos and deltamethrin, on European lobster (Homarus gammarus) larvae in the Norwegian marine environment

Anti-sea lice pesticides, used in the salmonid aquaculture industry, are a growing environmental concern due to their potential to adversely affect non-target crustaceans. Azamethiphos and deltamethrin are two bath treatment pesticides used on salmon farms in Norway, however, limited information is available on their impact on European lobster (Homarus gammarus) larvae in the Norwegian marine environment. Here, we firstly report the lethal (LC50) and effective (EC50) concentrations of azamethiphos and deltamethrin for stage I and stage II larvae, following 1-h exposures. Using a hydrodynamic model, we also modelled the dispersal of both compounds into the marine environment around selected Norwegian farms and mapped the potential impact zones (areas that experience LC50 and EC50 concentrations) around each farm. Our data shows that azamethiphos and deltamethrin are acutely toxic to both larval stages, with LC50 and EC50 values below the recommended treatment concentrations. We also show that the azamethiphos impact zones around farms were relatively small (mean area of 0.04–0.2 km2), however deltamethrin impact zones covered much larger areas (mean area of 21.1–39.0 km2). These findings suggest that deltamethrin poses a significant risk to European lobster in the Norwegian marine environment while the impact of azamethiphos may be less severe. [Display omitted] •Azamethiphos and deltamethrin are acutely toxic to European lobster larvae.•Calculated LC50 and EC50 values below recommended treatment doses for salmon farms.•Azamethiphos impact zones around fish farms relatively small.•Deltamethrin impact zones around fish farms covered large areas.•Deltamethrin a significant risk to lobster larvae living near fish farms. Azamethiphos and deltamethrin were acutely toxic to European lobster larvae. Simulated azamethiphos impact zones around Norwegian fish farms were relatively small, while deltamethrin impact zones covered large areas suggesting this compound is a significant risk to sensitive non-target crustaceans living near aquaculture sites.