Biodegradation potential of aquaculture chemotherapeutants in marine sediments Jonathan P Benskin 1 , Michael G Ikonomou 1 , Blair D Surridge 2 , Cory Dubetz 1 & Erik Klaassen 1 1 Institute of Ocean Sciences, Fisheries and Oceans Canada (DFO), Sidney, BC, Canada 2 Applied Chemistry and Biotechnology, Camosun College, Victoria, BC, Canada Correspondence: M G Ikonomou, Institute of Ocean Sciences, Fisheries and Oceans Canada, 9860 West Saanich Road, P.O. Box 6000, Sidney, BC, Canada V8L 4B2. E-mail: michael.ikonomou@dfo-mpo.gc.ca Abstract The commercial chemotherapeutant formulations SLICE â and AlphaMax â [active ingredients ema- mectin benzoate (EB) and deltamethrin respectively] are used in fin fish aquaculture to control parasitic sea lice. In some regions, the use of these substances has drawn concern from the commercial fishing industry regarding potential adverse effects on non- target organisms. In the present work, biodegrada- tion of EB and deltamethrin, and their commercial formulations, was investigated over 135 days at 4 and 10°C in fresh marine sediments collected from underneath an active open net-pen salmon farm. EB incubated as either pure substance or commercial formulation was recalcitrant at both temperatures under abiotic and biotic conditions. Deltamethrin incubated alone or as its commercial formulation degraded slowly at 10°C(t 1/2 = 330 Æ 107 and 201 Æ 27.1 days respectively). At 4°C, deltameth- rin degradation was only significant following incu- bation as commercial formulation (t 1/2 = 285 Æ 112 days). Degradation rates of EB and deltameth- rin as pure substances versus their commercial for- mulations were not statistically different. Depletion of deltamethrin was observed in 10°C inactive sedi- ments indicating that transformation occurred (at least in part) via an abiotic pathway. Overall, these data provide further insight into the fate and persis- tence of EB from the ongoing use of SLICE â in British Columbia’s salmon aquaculture industry. Alpha- Max â is not registered in Canada but is used in other salmon farming countries to control sea lice. Keywords: biodegradation, chemotherapeutants, sediment, emamectin benzoate, deltamethrin, sea lice Introduction In 2010, ~80 open net-pen salmon farms were in operation in British Columbia (B.C.), Canada, mak- ing this province the fourth largest producer of farmed salmon in the world, after Norway, Chile and the United Kingdom (Province of B.C. 2010). Among the challenges facing B.C.’s aquaculture industry is the susceptibility of cultured fish to infection from bacterial, viral and parasitic patho- gens. Sea lice (primarily the Lepeophtheirus salmonis species) are the most common naturally occurring parasitic threat to farmed salmon raised in open net-pens (Burridge, Weis, Cabello & Pizarro 2010). Sea lice feed on surface tissue, leading to a range of deleterious health effects, including disruption of osmoregulation, secondary infections, behavioural changes, and eventually, mortality (Torrissen, Jones, Asche, Guttormsen, Skilbrei, Nilsen, Hors- berg & Jackson 2013). In B.C., the most common treatment for sea lice infestation is SLICE â , a feed-based commercial chemotherapeutant consisting of 0.2% (by weight) of emamectin benzoate (4″-deoxy-4″-epi-methyla- minoavermectin; EB) (Bright & Dionne 2004). EB belongs to a class of substances known as aver- mectins, which are particularly toxic to nerve cells (Burridge et al. 2010). Once absorbed, EB is dis- tributed throughout the salmon’s peripheral tis- sues and is subsequently ingested by the louse, resulting in paralysis and, eventually, death. Con- cerns around the use of this chemotherapeutant have centred primarily on its effects on non-target organisms, in particular crustaceans (Bright & Dionne 2004). Premature moulting has been reported in lobsters exposed to a single gavage dose of 1 lgg À1 bodyweight of EB (Waddy, © 2014 John Wiley & Sons Ltd 1 Aquaculture Research, 2014, 1–16 doi: 10.1111/are.12509