Science Advisory Report  2012/070

Guidelines on Defining Potential Exposure and Associated Biological Effects from Aquaculture Pest and Pathogen Treatments: Anti-Sea Lice Bath Treatments in the Bay of Fundy, New Brunswick

Summary

An internal peer review meeting was held to assess preliminary results from research related to three anti-sea lice pesticides (“bath treatments”) currently, or recently, used by the salmon aquaculture industry in the Bay of Fundy, New Brunswick in order to provide scientific advice to regulators and policy makers.  This is the first meeting in a two-part process looking at the potential for key non-target organisms to be exposed to bath treatment effluents and for that exposure to result in biological effects.  Part two of this process, anticipated for 2013, will be broader in scope and include a full CSAS Science Advisory Process.  Specifically, this review examined: 1) field data and initial models of potential pesticide exposure following bath treatments; 2) the toxicity of three pesticides on three non-target species indigenous to the Bay of Fundy, New Brunswick, and their various life stages and; 3) preliminary estimates of the potential biological effects based upon the predicted exposure profile.

The following is a summary of the advice and conclusions reached during the peer review meeting:

• Numerous physical, chemical, operational and husbandry factors were identified that can influence the exposure profile following pesticide bath treatments.
• Based on dye dispersion studies, the therapeutant plume shape following release of treated water from tarp and well boat bath treatments is generally elliptical.  The area enclosed within the ellipses associated with tarp releases increases with time in a manner that is consistent with the diffusion diagrams of Okubo (1971, 1974).
• Concentrations of therapeutants that are greater than levels of laboratory derived biological effects (i.e., LC50 and NOEC) can extend tens to thousands of meters (i.e., a few kilometres) away from the effluent source over a 1–3 hour period.  These distances depend upon the circulation, toxicity of the individual therapeutant and the quantity of therapeutant used.
• Well boat discharge configurations vary with vessel.  Following release from vessels with horizontally directed discharges, the plume initially follows a typical jet dynamic which evolves into the standard turbulent transport and dispersal regime.
• Laboratory studies show that acute lethal toxicity (LC50 after 1 hour exposure) levels vary with the therapeutant, exposed species and life stage.
• American lobster, a commercially important species, was consistently more sensitive to therapeutants than Crangon and Mysid shrimps tested.
• There is evidence of sub-lethal and delayed effects in adult American lobsters from Salmosan® 50WP from repeated pulse exposures below prescribed treatment concentrations.
• Preliminary estimates of effects thresholds based upon the predicted exposure profile, the prescribed treatment concentrations and the LC50s after 1 hour exposure indicate that the potential magnitude of effects increases from Interox-Paramove® 50 (active ingredient: hydrogen peroxide) to Salmosan® 50WP (active ingredient: azamethiphos) to AlphaMax® (active ingredient: deltamethrin).
• Laboratory and field estimates of toxicity potential suggest that there is a high risk of lethal effects in exposed non-target organisms that are located immediately adjacent to treated net pens following tarp treatments with AlphaMax® (active ingredient: deltamethrin).
• Given the high number of environmental variables and husbandry factors which can influence the risk of impact, development of field monitoring protocols for exposure and biological effects of therapeutants around aquaculture cages in parallel to laboratory toxicity studies are recommended.

This Science Advisory Report is from the November 2–3, 2011 meeting on Defining Potential Exposure and Associated Biological Effects from Aquaculture Pest and Pathogen Treatments.  Additional publications from this process, including the Proceedings and Research Documents, will be posted as they become available on the DFO Science Advisory Schedule.

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