Dioxins

Dioxins (Polychlorinated Dibenzo-para-Dioxins (PCDD) and Polychlorinated Dibenzo Furans (PCDF)) are chlorinated organic environmental toxins, which are formed as a byproduct in various industrial processes and by combustion. Dioxins that accumulate in fatty tissues are hard to break down and become concentrated in food chains – in that respect the marine food chain is particularly vulnerable. People are exposed to dioxins via their diet, and the main sources are animal products such as fish, dairy products and meat.

Content of dioxin in food is given in picograms WHOTE/g (or nanograms/kg). TE stands for toxic equivalents and is calculated from toxic equivalency factors (TEF) or weighting factors that have been established for a number of dioxins and dioxin-like PCB compounds.

The table shows test results for 35 samples of Norwegian farmed salmon from 2002 and 2003 (NIFES, unpublished data). The EU has set an upper limit for dioxin (PCDD and PCDF) in fish of 4 pg WHO-TE/g. Test results for Norwegian salmon show 0.58 pg WHO-TE/g on average, with a range from 0.25 to 1.19 pg WHO-TE/g. The trend is a reduction in content of dioxins in Norwegian farmed salmon. The last six years represents a reduction of 39%, from 0,95 pg WHO-TE/g (SNT. 1997) to 0.58 pg WHOTE/g.

The EU has also set a limit value for the sum of dioxins and dioxin-like PCBs. This was established in February 2006 and is 8 pg WHO-TE / g.

Dioxin and dioxin-like PCBs in samples of farmed salmon ( ng/WHO-TEQ/kg)
p = number of samples (wet weight).
Source: NIFES

The EU has set a limit for tolerable weekly intake of dioxin (PCDD and PCDF) and dioxin-like PCB compounds of 14 pg WHO-TE/kg body weight. Test results for Norwegian salmon show 1.56 WHO-TE/g on average, with a range from 1.05 to 2.16 pg WHO-TE/kg. For example, a person weighing 70 kg could ingest 980 pg WHO-TE per week without exceeding the EU’s threshold value. A 200 g salmon fillet yields, with values from the study of Norwegian fish, 312 pg WHO-TE per meal. Concerned with risk assessment of carcinogenic agents, the guidelines for the EU and the WHO show that differentiation between substances that harm the genetic material directly and substances that do not, is scientifically accepted. For substances that do not harm the genetic material directly, like PCB and dioxins, threshold limits for effect are commonly given. Values below this threshold limit should imply no risk.

PCBs

PCB stands for polychlorinated biphenyls and is a collective term for a group of 209 different substances. The use of PCBs is prohibited today in the Western world, but continues to enter the environment via leaks from landfills and other sources. Because there are so many different PCBs, a measurement standard has been arrived at in which 7 different PCB congenes (PCB7) are measured and used in estimating pollution. For Norwegian farmed salmon the sum is 0.016 mg/kg. The EU does not have any threshold value here, but a threshold of 0.6 mg/kg has been set in the Netherlands.

Even though salmon is within this threshold value, particularly vulnerable individuals such as small children and foetuses are conceivably at risk. Jacobs et al. (2001) found that high consumption of farmed salmon by children under 5 could lead to a higher intake of PCBs than the tolerable daily and weekly intake. Jacobs (2002) reiterated that there is reason for concern for heavy consumers of farmed salmon, unless producers are careful about their selection of raw materials. Her concern was particularly true of heavy consumers of salmon who are pregnant or nursing.

p = number of samples, microgram/kg (wet weight).
Source: NIFES