~ Dr. Claudette Bethune, Feb. 9, 2014
While wild caught seafood is generally known to be a healthy food choice, and as the human population increases so does the demand for seafood. Due to the high level of toxins that transfer from feed to filet in farmed salmon, this product can no longer be considered a nutritious food source for consumers.
Consumers at highest risk from farmed salmon consumption are the most vulnerable in our population, our women and children. As reported last year in the highly cited Journal of Nutrition, “Staggering” levels of polychlorinated biphenyls (PCBs) have been found in farmed salmon1. Prenatal exposure to PCBs has been linked to lower birth weights, smaller head circumferences, and abnormal reflex abilities in newborns and to mental impairment in older children1.
Direct research by the primary institute that examines the seafood safety of farmed Atlantic salmon, the Norwegian Institute for Nutrition and Seafood Research (NIFES) in Bergen, Norway, has documented in 2011 that persistent organic pollutants (POPs) found in fish feeds carry over into farmed salmon2. The carry-over of potentially hazardous POPs from feed to fillet was assessed in consumption sized Atlantic salmon (Salmo salar). Relative carry-over (defined as the fraction of a certain dietary POP retained in the fillet) was assessed in a controlled feeding trial, which provided fillet retention of dietary organochlorine pesticides (OCPs), dioxins (PCDD/Fs), polychlorinated biphenyls (PCBs), and brominated flame retardants (BFRs). Highest retention was found for OCPs, BFRs and PCBs (31-58%), and the lowest retentions were observed for PCDD/Fs congeners (10-34%).
National monitoring data on commercial fish feed and farmed Atlantic salmon on the Norwegian market found levels of toxaphene above permissible levels. Commercially relevant feed-to-farm salmon fillet transfer factors (calculated as fillet POP level divided by feed POP level), ranged from 0.4 to 0.5, which is 5-10 times higher than reported for terrestrial meat products. Application of the model to the current EU upper limit for toxaphene in feed (50 μg kg(-1)) gave maximum fillet levels of 22 μg kg(-1), which exceeds the estimated permissible level (21 μg kg(-1)) for toxaphene in fish food samples in Norway2.
In 2004, NIFES, documented that the most toxic forms of dioxins accumulate in farmed salmon3. Adult Atlantic salmon (Salmo salar) were fed on four diets containing polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) for 30 weeks. Lipid-normalized concentrations showed that all congeners were equally partitioned between whole-fish and fillet samples. Skinned fillet accumulated approximately 30% of the total PCDD/F and PCB content in fish. Accumulation efficiencies in whole fish were 43% for 2,3,7,8-chlorinated dibenzo-p-dioxins and dibenzofurans, 83% for dioxin-like PCBs, and 78% for other PCB congeners. Among PCDD/Fs, tetra- and pentachlorinated congeners were preferentially accumulated in salmon, whereas hepta- and octachlorinated dibenzo-p-dioxins were excreted in the feces. Substitution patterns that were associated with a preferential accumulation of PCBs in salmon included non-ortho substitution and tetrachlorination. Accumulation efficiencies and lipid-normalized biomagnification factors (BMFs) were not influenced by the PCDD/F and PCB concentrations of the diets. Biomagnification (BMF > 1) of tetra- and pentachlorinated dibenzo-p-dioxins and dibenzofurans and of all the PCBs was observed. Differences in the behavior of PCDD/F and PCB congeners resulted in a selective enrichment of the most toxic congeners in salmon.
Current national guidelines typically indicate consumption of 2 meals a week of fatty fish such as farmed salmon. Norway recommends that 200 grams comprise a serving size. Farmed salmon are typically 10% higher in fat than wild salmon, with mean values approximately 13-23% total fat in the filet (NIFES Database, 2010), that is 23-43 grams of fat (with 160 mg cholesterol, typically) consumed in a single 200-gram serving. This high fat content in farmed salmon is this reason that fat-soluble contaminants such as the POPs are found in such high concentrations in farmed salmon. The ratio of the beneficial omega-3 fatty acids to that of the detrimental omega-6 fatty acids is much lower in farmed compared to wild salmon, again discounting the potential benefits of consuming fatty farmed salmon3.
With regards dioxins and PCBs, on 30 May 2001, the EU Scientific Council for Food (SCF) adopted an opinion on dioxins and dioxin-like PCBs in food, updating its 22 November 2000 opinion, fixing a tolerable weekly intake (TWI) of 14 picograms of the World Health Organization toxic equivalent (WHO-TEQ)/kg bw for dioxins and dioxin-like PCBs. The tolerable weekly intake is divided by seven to arrive at a tolerable daily intake of 2 picogram WHO-TEQ/kg bw for comparison to other national agencies dioxin exposure guidelines. The Joint United Nations Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA, 2001) established a provisional tolerable monthly intake of 70 pg/kg/month (equivalent to a tolerable daily intake of 2.3 picogram/kg bw/day).
More than 90% of human dioxin and dioxin-like PCB exposure derives from food; food of animal origin normally contributes to about 80% of the overall exposure. In most countries, young children have a higher dietary exposure to dioxins and dioxin-like PCBs per kg body weight than adults. On a body weight basis, the intake of breast-fed infants has been estimated to be one to two orders of magnitude higher than the average adult intake. The EU SCF found, in 2000, that the range covered by the fish distribution is between one and two orders of magnitude greater than those of the other foods.
Tolerable Daily intake:
· the WHO defines the upper range of the tolerable daily intake as 4 picograms TEQ/kg body weight, which should be considered a maximal tolerable intake on a provisional basis and that the ultimate goal is to reduce human intake levels below 1 pg WHO-TEQ/kg body weight per day.
o (Source: Assessment of the health risk of dioxins: re-evaluation of the Tolerable Daily Intake (TDI) WHO Consultation, May 25-29 1998, Geneva, Switzerland. WHO European Centre for Environment and Health International Programme.)
Dioxin and Dioxin-like PCB concentrations in Norwegian farmed Atlantic salmon for the years 2005 to 2010 indicate an average concentration of 1.2 ng WHO-TEQ/kg of wet weight fish filet. Concentrations ranged from a minimum of 0.4 ng WHO-TEQ/kg to 2.2 ng WHO-TEQ/kg of filet.
o A single 200 gram serving provides 2-times greater dioxin and DL-PCBs than the EU tolerable daily intake for adults and 4-times the tolerable daily intake for children.
In December 2012, the European Food Safety Authority (EFSA) updated its scientific advice on mercury in food. The Authority established Tolerable Weekly Intakes (TWIs) for the main forms of mercury found in food: methylmercury and inorganic mercury. Methylmercury is the predominant form of mercury in fish and other seafood, and is particularly toxic to the developing nervous system including the brain.
The CONTAM Panel considered new scientific information regarding the toxicity of these forms of mercury and established a TWI for methylmercury of 1.3 µg/kg bw. Average exposure to methylmercury in food is unlikely to exceed the TWI, but the likelihood of reaching such a level increases for high and frequent fish consumers. This group may include pregnant women, resulting in exposure of the fetus at a critical period in brain development.
For heavy metals, a NIFES 2012 report indicates that the levels of methylmercury was detected at 0.37 mg/kg in farmed salmon. This level would result in nearly double the EU tolerable weekly intake of 1.3 ug/kg bw of a 60 kg individual with just the farmed salmon consumption if the recommended 2 meals (400 grams/week) are actually eaten.
Based on these documented findings and emerging data relating to the human toxicity to the contaminants listed above that are found in high levels in farmed salmon, health practitioners are now advising against consuming farmed salmon due to the established health risks from the pollutants it contains.
1. Sarah E Santiago, Grace H Park, Kelly J Huffman. Consumption habits of pregnant women and implications for developmental biology: a survey of predominantly Hispanic women in California. Nutrition Journal, 2013; 12 (1): 91 DOI: 10.1186/1475-2891-12-91
2. Berntssen MH, Maage A, Julshamn K, Oeye BE, Lundebye AK. Carry-over of dietary organochlorine pesticides, PCDD/Fs, PCBs, and brominated flame retardants to Atlantic salmon (Salmo salar L.) fillets. Chemosphere. 2011 Mar;83(2):95-103. doi: 10.1016/j.chemosphere.2011.01.017. Epub 2011 Feb 1.
3. Strobel C, Jahreis G, Kuhnt K. Survey of n-3 and n-6 polyunsaturated fatty acids in fish and fish products. Department of Nutritional Physiology, Institute of Nutrition, Friedrich Schiller University Jena, Dornburger Str, 24, Jena, Germany.Lipids Health Dis. 2012 Oct 30;11:144. doi: 10.1186/1476-511X-11-144.
4. NIFES, 2012 official report on farmed Atlantic Salmon (http://www.nifes.no/file.php?id=2097)