Presence and distribution of PAHs, PCBs and DDE in feed and sediments under salmon aquaculture cages in the Bay of Fundy, New Brunswick, Canada

1. Wastes from feed and faeces can result in the deposition of contaminants in sediments around aquaculture sites. Five types of feed pellet, a commercial fish oil and 76 sediment samples collected under and up to 100m away from salmon aquaculture cages in the south-western Bay of Fundy between 1998 and 2000 were analysed for polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and chlorinated pesticides. 2. Five alkylated naphthalenes (aNAs) were consistently detected in fish oil (116-180 ng g-1, per aNA), in pellets (25-51 ng g-1, dry weight, per aNA), and sediments (< 1-45 ng g-1, dry weight, per aNA). Other PAHs were detected at variable levels in feed or in sediments. 3. IUPAC congener 153 (a PCB) and p,p'-dichlorodiphenyldichloroethylene (p.p'-DDE) were detected more frequently than other chlorinated targets in oil (108 ng g-1 and 176 ng g-1 respectively), feed (<1-14 ng g-1 and 1.7-28.2 ng g-1 respectively) and sediments (<0.08-3 ng g-1 and <0.5-7 ng g-1 respectively). 4. Trends were observed during the first year of sediment sampling (1998), with higher organic carbon, PCBs and p,p'-DDE levels below the cages than 50m away. The PAHs other than aNA showed an opposite trend with distance. In 1999, levels of p,p'-DDE and PCBs were somewhat reduced under the cages, but were detected up to 100m away from the cages. 5. Levels of aNA tended to be higher at some sites in 1999 relative to 1998, reflecting variability in feed and/or differential transport or degradation of contaminants relative to the environmental background. When detected, mean levels of PCBs and DDE were 2-10 times lower in 2000 than in 1999, and PAHs were 30-40% lower in 2000 than in 1999. 6. Interpretation of the results is done cautiously, since the exact locations of the sites sampled is only known to an intermediate facilitating the work between farmers and scientists. Levels of contaminants are compared with international results, interpreted relative to potential toxicity, uptake from feed, from deposited sediments, and in the framework of an aquaculture decision-support system published recently.