Science Advisory Report 2021/013

Advice to Inform the Development of a Drug and Pesticide Post-Deposit Marine Finfish Aquaculture Monitoring Program in Support of the Aquaculture Activities Regulations

Summary

• As is the case in most forms of farming, farmed fish are affected by diseases and parasites. Effective integrative health management relies on a suite of tools that include both authorized drugs and registered pesticides and non-chemical (physical, biological, or site management and husbandry) approaches. Annually, approximately three quarters of the active marine finfish aquaculture sites in Canada used at least one drug or pesticide (2016-2018). The drugs and pesticides used vary across the country by regulation (e.g., in British Columbia, sea lice control thresholds not related to farmed fish health are mandated through conditions of license) and management practices, as does the quantity of chemicals used and number and timing of treatments.
• Under the Aquaculture Activities Regulations, prior to the administration of drugs or pesticides, the owner/operator must first consider the use of alternatives to drug and pesticide treatments. This is an area of active research, resulting in a number of new and emerging technologies. Some are in the research and development stage and others have widespread, commercial use, with ongoing optimization and refinements. There remain knowledge gaps including those related to efficacy, environmental interactions, and fish welfare.
• In considering the use and application of authorized drugs and registered pesticides for health management, attending licensed veterinarians follow extensive and complex processes. This includes site-specific information on infection, fish, environment, husbandry, and input from site managers, as well as logistical and other factors. For the prescription of in-feed drugs, the veterinarian uses this information to prescribe an optimized treatment, which can include off-label use, and can result in additional active ingredients being used than noted on the label information. Similar analyses are undertaken when using pesticides; however, the pesticide application must follow label instructions, as well as additional provincial regulatory requirements.
• Under the Aquaculture Activities Regulations, from 2016-2018, the Canadian marine finfish aquaculture industry reported use of ten drugs authorized for use by Health Canada’s Veterinary Drugs Directorate and two pesticides registered for use by the Pest Management Regulatory Agency within Health Canada, for the purpose of fish health control or management with the following active ingredients:
• In-feed antibiotic drugs: oxytetracycline, florfenicol, erythromycin, ormetoprim with sulfadimethoxine, trimethoprim with sulfadiazine powder
• In-feed pest control drugs: emamectin benzoate, ivermectin, praziquantel, lufenuron, selamectin
• Bath pesticides: azamethiphos, hydrogen peroxide

Monitoring Program Considerations

• Clear environmental protection and pollution prevention objectives are critical prior to the design and implementation of a robust, risk-based monitoring program to quantify drug and pesticide residues in the marine environment following their use by the aquaculture industry. Clarity on the explicit objectives for an aquaculture post-deposit monitoring program are required, therefore the following advice is of a general nature.
• Designing a monitoring program is a multistep process that first considers the hazards (e.g., toxicity) and the environmental exposure (e.g., fate and pattern of use) of the drugs and pesticides used. This information helps to then define and evaluate what is appropriate to be measured in alignment with the program objectives (receptor group), the definition of thresholds of change, and the required level of confidence in assessing whether pre-defined levels of change have been exceeded. In evaluating the overall design, consideration of worker safety and technical feasibility are also required. Refinements of a monitoring program can occur when additional information is available.

Hazard and Environmental Exposure

• Currently, in-feed drugs used in marine finfish aquaculture enter the environment as feces, excretions, and any uneaten medicated feed. They are expected to be present primarily in sediments and secondarily in water or the water/sediment interface, and biota. Following the end of the treatment period, these drugs and their metabolites have been detected in sediments although their persistence varies (months to years) and is dependent on a variety of factors (e.g., the chemical properties of the specific drug, water temperature, sediment type, etc.).
• Pesticides, azamethiphos and hydrogen peroxide, enter the marine environment following release from tarps or well-boats. Treatment of a whole site may require sequential treatment of cages over a period of days. Based only on the chemical properties of the active ingredients, these pesticides are expected to remain in the water column following release, and will disperse, making sampling design challenging. These pesticides have been assessed to be non-persistent.

Methods to Define Thresholds for Drug and Pesticide Residues in the Environment

• Applicable regulatory thresholds can be designed in a variety of ways, including alignment with regulatory agencies, consistent with the development of benchmarks and/or environmental quality standards.
• Consistent with the Canadian Council of Ministers of the Environment (CCME) Canadian Environmental Quality Guidelines (1999; 2007), European guidelines for data-poor situations (TGD, 2018), and an overall weight of evidence approach, the development of Environmental Quality Standards (EQS) include explicit consideration of the quantity and quality of relevant studies, and the biological, environmental, and data uncertainties.
• Depending on the environmental protection goal and the receptor (water, sediment, biota), an EQS can be set for short- or long-term exposures. Water EQS can be divided into two main types: one related to maximum acute chemical exposure and one to chronic exposure. For sediment EQS, there is no short-term EQS (i.e., organisms would be constantly exposed while living in the sediment). To account for scientific uncertainties, data quality and quantity, a correction or assessment factor is applied.

Modelling Exposure

• To predict the concentrations in water and sediment of in-feed drugs and bath pesticides, models may include various components such as discharge, transport, dispersal, and chemical fate and behaviour. Model predictions can assist in the identification of sampling locations and times, and the shape and location of zones of exposure and influence.
• There is a range of transport, dispersion and deposition models available; the choice of modelling approach taken needs to consider the purpose for the model output. Models that incorporate a few simplified components can be used to estimate concentrations in a generalized area for generalized time scales, whereas models that incorporate more detailed and/or additional components can be used for higher resolution estimates
• Regardless of the model type, refinements with additional empirical data, and site-specific aspects may contribute to enhanced accuracy. The underlying uncertainties associated with the model inputs and parameterizations will influence the accuracy of the predictions.
• Modelling outputs should be validated with empirical data.

Sampling and Analysis

• Structured, probabilistic sampling designs (i.e., based on randomized selection of possible sample locations and times) allow for quantitative estimates of desired parameters and the associated uncertainties. Judgement-based design (i.e., based on existing knowledge of the area to be sampled) do not allow for statistical inference. Judgement-based design can be useful in determining what to sample (receptor or analytical endpoint) and in the design of a stratified random sampling program. A grid-based design is appropriate for capturing footprints, whereas randomized designs are more appropriate to infer population-level changes. Depending on the management objectives and other considerations, including uncertainties, either a probabilistic- or a judgement-based approach to sampling design may be appropriate.
• The sampling design needs to consider the required confidence level for evaluation of samples against the threshold, the limitations related to sample collection and handling, sample analysis, etc. All estimates of post-discharge concentrations are dependent on the initial concentration, which can vary. Therefore, in the design of post-deposit monitoring, sampling of the pre-discharge bath-water or medicated feed should be considered to confirm treatment concentrations and interpretation of results. To inform sampling design, consideration of the biological, physical and chemical characteristics of the benthic environment of the site is recommended.
• Regarding laboratory analysis for drug and pesticide quantification, a number of factors need to be considered and performance requirements established. These include stringent sample collection, storage and shipment, as well as pre-determined analytical parameters (e.g., analytes, matrices, and client-specified obtainable concentration levels).
• The mandatory laboratory requirement is to have the methods validated. Accreditation would be beneficial and may be necessary to demonstrate the competency of the laboratory for the method. Once monitoring thresholds are set, there will be a need to ensure analytical methods are fit for purpose. There is currently limited capability and capacity within Canada to conduct these analyses with validated methods.
• Antimicrobial resistance (AMR) is a natural phenomenon in bacteria. Antibiotic use in farming can change the relative abundance of antibiotic resistant genes (ARGs) in the environment. Early empirical data on marine finfish aquaculture shows that benthic bacterial communities change in relation to distance from the farm, as do the relative frequency of ARGs.
• One method for conducting a large-scale environmental assessment of AMR is by measuring ARGs in benthic bacteria detected around marine finfish aquaculture sites. Sampling needs to consider other factors, including information about antibiotic use, background environmental levels, and persistence. There remain knowledge gaps over potential pathways, non-target organisms, spatial and temporal ecological interactions of bacterial communities, and the frequency of ARGs around marine finfish aquaculture sites. Should ARGs be found, secondary assays could be implemented, such as culture-based techniques to assess AMR.
• A post-deposit monitoring program will generate additional data that, along with new scientific data, including biological results, can be used to further refine the program over time. Standardized data reporting, transparent requirements and quality standards, and data management are important considerations for robustness of the program.

This Science Advisory Report is from the March 2-6, 2020 National Peer Review on Advice to inform the development of a drug and pesticide post-deposit marine finfish aquaculture monitoring program in support of the Aquaculture Activities Regulations. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2021/013 (PDF, 989 KB)

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