This is the 2004 Science article: http://www.albany.edu/ihe/salmonstudy/salmon_study.pdf.
This is a following, 2006, study on chemicals in farmed and wild fish: http://www.puresalmon.org/pdfs/Huang_et_al_Environmental_Research.pdf. The title is: 'Consumption advisories for salmon based on risk of cancer and non-cancer health effects'. The chemicals found in farmed fish include: PCBs, dioxins/furans and chlorinated pesticides. PCBs and other chemical families can have more than 100 different metabolites and affect multiple locations in the body.
"We found that contaminant levels were about an order of magnitude higher in farmed and market samples than in wild Pacific salmon." The study has a good discussion of the different advisory guidelines and that farmed and wild salmon contain other organic chemicals for which there are non-cancer advisories. See Table 2: Non-cancer effects of chlorinated pesticides, PCBs, and dioxins.
The study found that farmed fish from northern Europe should be eaten only once in five months based on USEPA guidelines. North and South America farmed fish should ONLY be eaten 0.4 to 1 per month.
In comparison, and adding all the chemicals together, wild salmon should be eaten between 1 and 5 times per month. But with only one chemical, the rate could be as high as eating wild salmon 47 times per month. That stat says it all. Eat wild salmon.
Another quote: 'While dioxin-like activity is found in almost all animal food products that contain fat, the levels in the farmed and market salmon that we have analyzed are higher than those in almost all other foods.'
See this 2005 article: http://www.ncbi.nlm.nih.gov/pubmed/15866762. 'Risk-based consumption advice for farmed Atlantic and wild Pacific salmon contaminated with dioxins and dioxin-like compounds.'
See this 2008 study: http://www.ncbi.nlm.nih.gov/pubmed/18313722. 'Polybrominated diphenyl ethers (PBDEs) in farmed and wild salmon marketed in the Northeastern United States.'
See this 2009 study: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2697370/. 'A Simplified Method to Distinguish Farmed (Salmo salar) from Wild Salmon: Fatty Acid Ratios Versus Astaxanthin Chiral Isomers.' Farmed salmon is often mis-labelled as to source and salmon species, for ex. marketed as wild chinook.
See this 2005 link:http://pubs.acs.org/doi/abs/10.1021/es050898y 'Lipid Composition and Contaminants in Farmed and Wild Salmon.' The current diet of western world people is already excessive in consumption of Omega 6s and a full complement of Omega 3s can be obtained from vegetable oils and meats.
FYI, the lipid level in fatty fish accounts for the greater concentrations of organic chemicals, as well as Omega 3ths and 6s. Farmed salmon are higher in body fats because of their feed and so they are higher in organic pollution.
Kris-Etherton et al. (37), speaking for the American Heart Association, states, “The fish recommendation must be balanced with concerns about environmental pollutants, in particularPCBandmethylmercury, described in state and federal advisories.”
See this, 2011, link for a Swedish study that finds European, including Norwegian, farmed fish have organic chemicals 61 times above the legal limit: http://wap.nrk.no/m/artikkel.jsp?art_id=17882460. See Google to translate, but here is a reference: Conservation Association writes on its website , it found the content of pollutants in salmon that is 61 times higher than the EU's proposed limit.
See this link for ten pages of short abstracts on polluting chemical agents in farmed salmon: http://scholar.google.ca/scholar?q=Lipid+Composition+and+Contaminants+in+Farmed+and+Wild+Salmon&hl=en&as_sdt=0&as_vis=1&oi=scholart
See this link for a 2011 article: The Role of Persistent Organic Pollutants in he Worldwide Epidemic of Type 2 Diabetes Mellitus and the Possible Connection to Farmed Atlantic Salmon (Salmo salar)
Walter J. Crinniom, 2011: http://www.altmedrev.com/publications/16/4/301.pdf.
Here is one conclusion: the PCBs you get from one meal of farmed salmon will not be fully cleared out of the body for between 50 and 75 years.
See this link for a 2012 article on drugs in [chicken-based] feather meal, commonly used in fish farm feed, that results in bacteria, including e-coli, that are resistant to the antibiotics we use to treat humans for disease: http://pubs.acs.org/doi/abs/10.1021/es203970e?journalCode=esthag.In 12 feather meal samples, which were collected from six states and China, they found 59 pharmaceuticals and personal care products. Each sample was found to contain antibiotic residues (testing positive for between 2 and 10 different drugs).
Keeve Nachman, at Johns Hopkins Center for a Livable Future, said they were shocked at the variety of pharmaceuticals they were able to detect.