Risk and Benefits from consuming salmon and trout: A Canadian Perspective

In view of recent reports on the presence of persistent chemicals/contaminants in wild and farmed salmon, health professionals and consumers alike are often confused regarding the safety of regular fish consumption as source of DHA/EPA omega-3 fatty acids for cardiovascular health and DHA omega-3 fatty acids during pregnancy and lactation in women. A recent advisory from the USDA and USEPA has advised women of reproductive age to avoid the consumption of four species that are highly contaminated by methyl mercury, namely king mackerel, shark, swordfish, and tilefish. Thus, this Canadian study was conducted to determine the levels of the omega-3 fatty acids as DHA/EPA in wild and farmed salmon and rainbow trout while also measuring the concentrations of mercury, polychlorinated biphenyls, dioxins and furans so as to assess the expected exposure to such contaminants by the consumption of 2 fish servings (180 g each) per week (i.e., two six-ounce servings per week).

Analyses of farmed and wild Atlantic salmon and rainbow trout as available in the province of Quebec in Canada was determined with the wild fish being obtained from fishermen in the various regions and farmed fish being purchased from supermarkets in the province of Quebec. A combination of capillary column gas chromatography, high-resolution mass spectrometry, with appropriate analytical conditions, standards, etc. was utilized in the analyses performed. The results indicated that the concentrations of key contaminants in the various fish analyzed were low such that regular consumption of these fatty fish species at two servings per week (a total of 360 g or 12 ounces) would not cause significant health risks based on the TDI (Tolerable Daily Intakes) for methyl mercury provided by regulatory agencies in the U.S. and Canada. Furthermore, expected exposures to bio-accumulated chemicals such as polychlorinated biphenyls (PCBs) and polychlorinated dioxins/furans (PCD/Fs) at two servings a week were also below the acceptable limits provided by North American regulatory agencies and the World Health Organization (WHO). Interestingly, the levels of total mercury in the fish showed both farmed salmon (18 ug/kg) and trout (21 ug/kg) to have significantly lower levels (more than 50% lower) as compared to the corresponding wild fish samples. The total levels of PCBD/Fs (pg TEQ/kg) tended to be lower in the farmed as compared to the wild fish with the mean levels in the farmed salmon showing concentrations approximately one-half those for the wild fish samples.

With respect to the levels of the omega-3 fatty acids as DHA/EPA (combined), the farmed rainbow trout showed levels which were approximately triple those for the wild trout (731 mg/ 100g vs. 232 mg/ 100g) whereas the farmed and wild Atlantic salmon showed very similar concentration (855 for farmed vs. 749 for wild). The authors conclude that consuming wild or farmed rainbow trout or Atlantic salmon from this Canadian study at levels of two servings (6 ounces each) per week, as recommended by various health agencies, can be expected to markedly increase DHA/EPA intakes towards optimal values without concerns about the putative health risks. The authors also comment on their results which contrast with those reported from the U.S. by Foran et al (J. Nutr., 135: 2631-2643 (2005)) likely due to the method used for assessing health risks between these two studies. The present authors note that 60-85% of the Atlantic salmon fillets (farmed fish) sold in the Quebec markets originate from Chilean farms with the remainder being supplied by Canadian farmed sources. They also note that 87% of the farmed salmon fillets imported into the U.S. in 2005 also originated in Chile.