July 31, 2003

PCBs in Farmed Salmon: Wild versus farmed

Wild versus farmed

Standard fish farming practices, which include the use of contaminated fishmeal and the intentional fattening of farmed stock, create a cascade of problems that ultimately drive down the nutrient content of farmed salmon, and drive up the contamination levels relative to wild-caught salmon.

Farmed salmon are fed contaminated fishmeal. Farmed salmon are fed from a global supply of fishmeal and fish oil manufactured from small open sea fish, which studies show are the source of polychlorinated biphenyls, or PCBs, in most farmed salmon. In three independent studies scientists tested 37 fishmeal samples from six countries, and found PCB contamination in nearly every sample (Jacobs 2002, Easton 2002, and CFIA 1999).

After testing fishmeal and fish oil, a team of U.K. scientists noted that “While diets based on marine fish oils are currently favored by the aquaculture industry, it is likely that these oils are contributing greatly to the contamination of farmed salmon by [persistent organic pollutants]” (Jacobs 2002b).

PCBs build up in salmon at 20 to 30 times the levels in their environment and their feed (Jackson et. al 2001), so even low concentrations of PCBs in fishmeal can become a concern for human health.

An expert food safety panel recently convened by the National Academy of Sciences noted that because of the “intensive management approach” of the aquaculture industry, PCBs in fishmeal can accumulate in fish tissues. The panel recommended that the government restrict the use of feed obtained from areas known to have high pollution levels (NAS 2003). Wild Alaskan salmon eat Pacific Ocean fish that the Academy scientists note are naturally lower in persistent pollutants.

Farmed salmon are intentionally fattened and can therefore accumulate more PCBs. The salmon farming industry intentionally fattens its fish to maximize market weight (Jacobs 2002), a process similar to fattening cows or hogs in a feed lot. As a result, an ounce of farmed salmon contains 52 percent more fat than an ounce of wild salmon, according to the U.S. Department of Agriculture (USDA 2002). PCBs collect in fat, as opposed to muscle or other organs. Farmed salmon, because they are intentionally fattened, are efficient collectors of PCBs. Leaner, wild Alaskan salmon are less likely to accumulate high levels of PCBs.

Farmed salmon contains five to 10 times the PCBs of wild salmon. EWG’s tests confirm findings from three prior, independent studies in which scientists observed differences in contaminant levels between farmed and wild salmon. The average level of total PCBs in EWG's ten farmed salmon samples was 27.3 ppb, or 5.2 times higher than the average PCB level of 5.3 ppb in four wild salmon tested by Canadian scientists (Easton et al. 2002). Differences in the 12 dioxin-like PCBs appear to be even greater. In Ireland, Scotland, British Columbia, and Alaska studies show higher concentrations of dioxin-like PCBs in farmed salmon than in wild salmon (Easton et al. 2002, FSIA 2002a and 2002b, Axys 2003, and Jacob et al. 2002). In most of these cases, wild salmon were harvested from environments relatively free of industrial pollution. Farmed fish raised in these same environments ate fishmeal with higher levels of PCBs than the native fish consumed by wild salmon (Figure).

farmed salmon contains more PCBs than regular salmon informational graphic

Farmed salmon contains higher levels of many other persistent pollutants. An influential study published last year showed that PCBs are just one family in a complex mixture of persistent pollutants that appear to concentrate in farmed salmon. The Canadian scientists found that farmed salmon tissue contained significantly higher levels of 151 out of the 158 chemical contaminants that were detected in both farmed and wild salmon samples (Easton et al. 2002). In addition to 110 different PCBs, these chemicals included brominated flame retardants, organochlorine pesticides like DDT and dieldrin, and carcinogenic combustion byproducts called polynuclear aromatic hydrocarbons (PAHs). While PCBs may dominate human health risks from farmed salmon, many other contaminants contribute to the overall health concerns associated with these fish.

Farmed salmon may contain two to 40 times more PCBs than any other major protein source. An analysis of data from studies on dioxin-like PCBs in commercial seafood, beef, pork, milk, and poultry shows that farmed salmon may be more contaminated than any other protein source in the U.S. (NAS 2003, EPA 2002, Fiedler et al 2000). On average, farmed salmon from EWG’s supermarket study contained 40 times more PCBs than milk, 4 times the PCB levels of beef, and at least 3.4 times the PCB levels of other commercial seafood.

In their recent review of human exposures to dioxins and certain PCBs, an expert panel of the National Academy of Sciences noted that “it is in the public’s best interest for the government to develop a strategic action plan that includes interim steps to reduce exposures as long as the steps do not lead to undesirable consequences to human health,” and further recommended that the government focus on reducing exposures for girls and young women in the years well before pregnancy, since some PCBs are linked to brain damage and immune deficiencies for exposures in utero and in early childhood (NAS 2003). Although the Academy specifically recommends drinking skim instead of whole milk, even greater reductions of PCB exposures would be realized if women who eat farmed salmon ate wild salmon instead.

The fat in farmed salmon contains less healthy omega-3 fatty acids than the fat in wild salmon. Salmon fat is rich in omega-3 fatty acids, essential nutrients important to fetal brain development and linked to reductions in the occurrence or symptoms of autoimmune disease, headaches, cramps, arthritis, other inflammatory diseases, hardening of the arteries, Alzheimer's disease, and heart attacks. But USDA testing data show that the fat of farmed salmon contains an average of 35 percent less omega-3 fatty acids (USDA 2002).

Wild salmon fat healthier than farmed salmon fat informational graphic

Because farmed salmon contain 52% more total fat than wild salmon, the total omega-3 fatty acid content of farmed and wild fish is similar. However, in the case of farmed salmon, the fat is contaminated with PCBs and over 100 other pollutants and pesticides. Frequent farmed salmon eaters may exceed government health limits for these pollutants, which are linked to immune system damage, fetal brain damage, and cancer (Easton et al. 2002).


  • Canadian Food Inspection Agency (CFIA). 1999. Summary report of contaminant results in fish feed, fishmeal and fish oil. Accessed online July 21, 2003 at http://www.inspection.gc.ca/english/anima/feebet/dioxe.shtml.
  • Easton MD, Luszniak D, Von der GE. Preliminary examination of contaminant loadings in farmed salmon, wild salmon and commercial salmon feed. Chemosphere. 2002 Feb;46(7):1053-74.
  • Fiedler H, Cooper K, Bergek S, Hjelt M, Rappe C, Bonner M, Howell F, Willett K, Safe S. PCDD, PCDF, and PCB in farm-raised catfish from southeast United States--concentrations, sources, and CYP1A induction. Chemosphere. 1998 Oct-Nov;37(9-12):1645-56.
  • Food Safety Authority of Ireland (FSAI). 2002a. Summary of investigation of dioxins, furans, and PCBs in farmed salmon, wild salmon, farmed trout and fish oil capsules. March 2002. Accessed online July 21, 2003 at http://www.fsai.ie/industry/Dioxins3.htm.
  • Food Safety Authority of Ireland (FSAI). 2002b. Investigation on PCDDs/PCDFs and several PCBs in fish samples (salmon and trout). Analysis and report provided by ERGO Forschungsgesellschaft mbH, Germany. Accessed online July 21, 2003 at http://www.fsai.ie/industry/Fishoilreport.pdf.
  • Jackson LJ, Carpenter SR, Manchester-Neesvig J, Stow CA..PCB congeners in Lake Michigan coho (Oncorhynchus kisutch) and chinook (Oncorhynchus tshawytscha) salmon. Environ Sci Technol. 2001 Mar 1;35(5):856-62.
  • Jacobs M, Ferrario J, Byrne C. 2002a. Investigation of polychlorinated dibenzo-p-dioxins, dibenzo-p-furans and selected coplanar biphenyls in Scottish farmed Atlantic salmon (Salmo salar). Chemosphere. 2002 Apr;47(2):183-91.
  • Jacobs MN, Covaci A, Schepens P. 2002b. Investigation of selected persistent organic pollutants in farmed Atlantic salmon (Salmo salar), salmon aquaculture feed, and fish oil components of the feed. Environ Sci Technol. 2002 Jul 1;36(13):2797-805.
  • National Academy of Sciences (NAS). 2003. Dioxins and dioxin-like compounds in the food supply: Strategies to decrease exposure. NAS Institute of Medicine, Food and Nutrition Board, Committee on the Implications of Dioxin in the Food Supply. The National Academies Press. Washington, D.C.
  • U.S. Department of Agriculture, Agricultural Research Service. 2002. USDA National Nutrient Database for Standard Reference, Release 15. Nutrient Data Laboratory Home Page, http://www.nal.usda.gov/fnic/foodcomp.