Science Advisory Report  2011/082

Assessment of the Fate of Emamectin Benzoate, the Active Ingredient in SLICE®, near Aquaculture Facilities in British Columbia and its Effect on Spot Prawns (Pandalus platyceros)

Summary

• Sea lice infections at salmon farms in British Columbia are monitored and controlled to minimize impacts on farmed fish and reduce the risk of infecting fish that live outside the farm. The chemotherapeutant used to control sea lice on B.C. salmon farms is SLICE®, an in-feed treatment in which the active ingredient is emamectin benzoate (EB).
• A Regional Science Advisory Process was undertaken to review the results of DFO research to determine the environmental concentrations of EB near two B.C. salmon farms following the application of SLICE®, and to assess the uptake and potential toxicological impacts of EB in the Pacific spot prawn (Pandalus platyceros) under laboratory and field conditions.
• Using a new and very sensitive analytical method, concentrations of EB and its main conversion product 4’-deoxy-4’-epi-amino avermectin B1a (AB) were measured in water, sediment and spot prawns collected at two salmon farm sites with differing hydrodynamic and biophysical characteristics before, during, and after the application of SLICE®.
• Low levels of EB were detected in the sub-surface water beneath each farm during SLICE® treatment. EB released into the water column dissipated quickly and was undetectable 4 to 5 weeks after treatment.
• The amount of EB measured in surface sediments varied between the two sites. At one site EB in sediment remained close to the limit of quantification (LOQ) of the analytical method. Most of the EB reaching the sediment at the other site remained localized, with levels falling to below the LOQ within 150 m of the farm. EB was detected in sediment from this site over 1.5 years after SLICE® treatment. AB concentrations were less than 30% of the concentration of EB in all sediments.
• The amount of EB estimated in sediment accounts for a small fraction of the EB applied during a full-cycle SLICE® treatment. It was not possible to generate a complete mass balance for EB with the available data.
• EB measured in the tissues of spot prawns collected within 150 m of each salmon farm increased over a period of 100 days following the application of SLICE®. The level and duration of exposure in the field differed from those used in the laboratory exposure experiments that formed part of the same study, so it was not possible to correlate directly the results of the lab experiments with field measurements of EB.
• Laboratory experiments suggest that short-term (8-day) exposure of spot prawns to sediment containing EB at concentrations significantly greater than those measured in the field can alter the expression of certain genes in muscle tissue. No clear dose-response relationship could be established for the mortality or differential gene expression observed during these experiments. Additional studies involving standard toxicological measurements, different life-cycle stages, and environmentally relevant EB concentrations are recommended, along with further gene expression studies under both laboratory and field conditions.
• Studies that include a broader range of salmon farm sites in B.C. are also recommended. Information regarding SLICE® usage, site conditions, and local prawn fisheries is available from a number of government and industry sources and can be used when planning and interpreting the results of future studies.
• Current research shows that the spatial and temporal distribution of EB near salmon farms varies from site to site and that, under certain conditions, EB can remain and so potentially build up in sediments close to salmon farms, depending on the extent and frequency of SLICE® usage. EB is also bioavailable and can be measured in the muscle tissues of spot prawns near salmon farms treated with SLICE®. More research is needed to assess the potential biological impacts of low concentrations of EB and its metabolites on spot prawns and other non-target organisms.

This Science Advisory Report has resulted from a Fisheries and Oceans Canada, Canadian Science Advisory Secretariat (CSAS) regional advisory process (RAP) meeting held on October 18-19, 2011 to assess the Environmental Impact of the Treatment of Sea Lice with SLICE® at Aquaculture Facilities in British Columbia. Additional publications from this process will be posted as they become available on the DFO Science Advisory Schedule.

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