Environmental toxins in the ocean are concentrated in the marine food chain and accumulate in fat. This means that predatory fish can have a high content of environmental toxins. Particularly large pike (Exos lucius) fished in polluted lakes have a high content of, e.g., mercury (SNT, 2002), and are humorously referred to as "hazardous waste". But farmed salmon can also acquire a considerable content of environmental toxins if the feed contains much marine fat from polluted ocean areas. To reduce the content of environmental toxins in fish feed the content of raw materials close to the sources of pollution (particularly European waters) has largely been reduced in favour of raw materials from South America, which at the outset is the biggest producer of fish oil and fishmeal.
In Norway the concentrations of environmental toxins in farmed salmon are carefully monitored by National Institute for Nutrition and Seafood Research (NIFES), through an annual testing programme (Julshamn et al., 2002). Threshold values for many environmental toxins are set by the EU, CODEX (UN) and individual nations to protect the health of their citizens. NIFES monitors alien substances in fish according to EU directive 96/23-2003. The programme includes 64 different chemical compounds divided into 13 groups of substances. Farmed salmon is monitored with respect to heavy metals, PCB, dioxins, dioxin-like PCB compounds, residues of pharmacological substances, residues of hormonal substances, pesticides and brominated flame retardants among other substances.