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Research Document - 2013/050

A review of potential environmental risks associated with the use of pesticides to treat Atlantic salmon against infestations of sea lice in southwest New Brunswick, Canada

By Dr. L. Burridge


Recently, pesticide bath treatments have been used in southwest New Brunswick in order to control sea lice on farmed Atlantic salmon in open netpens. As part of the emergency registrations for anti-sea lice bath treatments, Health Canada’s Pest Management Regulatory Agency was seeking additional information on the biological effects of pesticides on non-target organisms. This review analyzed three pesticides evaluated for their biological effects on non-target organisms were: Salmosan® (active ingredient: azamethiphos), AlphaMax® (active ingredient: deltamethrin), and Paramove® 50 (active ingredient: hydrogen peroxide); however, only Salmosan® and Paramove® 50 are currently being used. This review found that in lab studies, acute lethal toxicity varied with the pesticide, the non-target species, and the life stage. Azamethiphos (active ingredient in Salmosan®) is a neurotoxin, and the formulation is soluble in water and therefore unlikely to accumulate in sediment or bioaccumulate in tissue. In acute lethal toxicity tests, adult lobster and shrimp were the most susceptible species to azamethiphos (48-h LC50 for adult lobster: 1.39 µg azamethiphos L-1; 96-h LC50 for Mysids: 0.52 mg azamethiphos L‑1), while adult lobsters repeatedly exposed to below prescribed treatment concentrations showed sublethal behavioural effects, such as affecting reproduction in females. Deltamethrin is a synthetic pyrethroid which interferes with nerve membrane function and is known to be highly toxic to crustaceans (96-h LC50: for adult lobsters - 1.4 ng L-1; stage III and IV lobster larvae - 3.7 – 4.9 ng L-1 and 28.2 ng L-1, respectively; amphipods – between 1.7 and 8.0 ng L-1). It has low solubility in water and due to its high lipophilicity and adsorption coefficients can persist in sediments. It is rapidly metabolized by fish and therefore unlikely to accumulate in tissues. The hydrogen peroxide in Paramove® 50 forms bubbles in the gut and haemolymph to paralyze muscles, which causes sea lice to float to the water surface. It is fully miscible in water, does not persist or bioaccumulate, and degrades to oxygen and water in about 7 days. There is little information on the toxicity of hydrogen peroxide to marine organisms. Bath treatments against sea lice have been inconsistent and effectiveness is dependent on water temperature. In summary, in laboratory lethal toxicity tests with active ingredients, lobsters were consistently more sensitive to therapeutants than Crangon and Mysid shrimps tested. The degree of toxicity was therapeutant specific with Paramove® 50 being the least toxic of the three formulations tested, while AlphaMax® was the most toxic.

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