THE ENVIRONMENTAL FATE AND NON-TARGET EFFECTS OF SEA LICE PESTICIDES USED IN SALMON AQUACULTURE  

In recent years, attention has been directed at the aquaculture industry's use of chemicals, including those used in disinfectants, anti-fouling paints, and feed additives, that have resulted in the local contamination.  Of immediate concern the use of pesticides and feed formulas used to treat pathogens in aquaculture.  Chemical therapeutants available or proposed for use in controlling sea lice in Canada include 5 chemotherapeutants: azamethiphos, hydrogen peroxide, deltamethrin, cypermethrin and emamectin benzoate. Predictions of the persistence and toxicity of these chemicals to non-target organisms has proven difficult, and data gaps make estimations of risk highly inaccurate. The two main objectives of this study were to assess 1) the environmental persistence and partitioning of these compounds, and 2) their acute and sublethal toxicity to non-target marine organisms.

Representative sediment samples and seawater were collected in the same local area as an operating aquaculture facility and spiked with known concentrations of each of the 5 test chemicals in 1L tall-form glass cylinders.  Both water and sediments were sampled over time and analyzed for each chemical by HPLC or GC-MS. Emamectin benzoate, cypermethrin and deltamethrin partitioned mainly into sediments while azimethiphos and hydrogen peroxide remained in the aqueous phase. Concentration-time course data were modeled to determine half-lives and other kinetic parameters.

The acute toxicity of these compounds to non-target marine species was determined using standardized toxicity tests.  Generally, susceptibility to each chemical was species specific and no general trends were evident. Kelp Macrocystis pyrifera germination and growth were only affected by hydrogen peroxide and not the other 4 compounds. Echinoderm Strongylocentrotus purpuratus fertilization was not affected by exposure to azimethiphos, but was affected by the other chemicals with the highest toxicity attributed to cypermethrin > deltamethrin > emamectin benzoate > hydrogen peroxide. Bivalve Mytilus edulis development was affected by hydrogen peroxide > emamectin benzoate > azamethiphos at concentrations well above concentrations used in aquaculture. For the mysid Americamysis bahia, all chemicals tested were highly toxic at concentrations far below those used in aquaculture. Deltamethrin was most toxic, followed by cypermethrin > emamectin bezoate > azimethiphos > hydrogen peroxide.

This research yields important information required to ensure the proper and safe use of aquaculture pesticides, and to appropriately regulate these important aquaculture chemicals to protect the environment.