PCBs and dioxins in salmon
Organochlorine Contamination of Salmon
20 January 2004 -- A survey reported in the journal Science (09.01.04) compared the level of organochlorine contaminants, including PCBs and dioxins, in farmed versus wild salmon collected from around the world. Most organochlorine substances analysed in the study show a significantly higher level of contamination in farmed than in wild salmon.
This study is the largest conducted so far, in particular relating to the direct comparison between farmed and wild salmon. The results reported specifically for dioxins and PCBs are well within the range of previous studies. Dioxins and dioxin-like compounds are important substances that can affect human health. They are persistent environmental pollutants that enrich via the food chain. Dioxins and PCBs are associated with industrial discharges, including discharges into the sea, and ocean fish have varying levels of these substances often directly related to the proximity of their habitat to discharge areas. The level in farmed fish normally reflects the contamination level of the feed used, which has been also shown in above mentioned study by the detection of dioxins and PCBs in commercial fish feed.
WHO, in collaboration with FAO, has considered dioxins and dioxin-like compounds on several occasions. Most recently in June 2001, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) examined new evidence on the toxicity of these chemicals and established a Provisional Tolerable Monthly Intake (PTMI) of 70 picograms of dioxins and dioxin-like PCBs. When evaluating standard diets in different parts of the world the results indicated that the estimated intakes of these chemicals approach or exceed this PTMI. Based on the mean contamination levels reported in above study, eating one or two portions per week of farmed salmon would result in a monthly intake below this level. However, an overall dietary risk assessment would require inclusion of other dietary sources of dioxins and dioxin-like PCBs.
In order to address these risks, several steps have been taken to reduce or eliminate emissions of dioxins, dioxin-like PCBs and other related persistent organic pollutants (often referred to as POPs). Many countries have now implemented the Stockholm Convention on POPs (2001), which suggests to end commercial use of 12 POPs and reduce or eliminate their emission into the environment. To monitor reduction in human exposure WHO and UNEP run a monitoring program for POPs in breastmilk. A steady decline in levels has been observed since 1980 for most countries.
In regard to food contamination, the FAO/WHO Codex Alimentarius Commission, which is a risk management body comprised of 169 member countries, is developing a draft code of practice for dioxins and dioxin-like PCBs in food, which identifies source-directed measures to reduce their presence in food, including fish, as well as a position paper, which provides an evaluation of the need for possible regulatory measures, such as limits in food and feed.
The results of this new study in salmon and other studies should be used to maintain the focus on reducing the exposure of humans to dioxins and dioxin-like PCBs. Specifically, efforts to reduce the level of such substances in animals used for human consumption should be actively supported, in particular source-directed measures such as reduction of contamination levels in animal feed.
FAO and WHO consider fish to be an important component of a nutritious diet, and that the risk of consuming contaminated fish must be weighted in view of the beneficial nutritive effects of fish. FAO and WHO plan to develop general guidance for such risk-benefit considerations, with the contamination of fish as case studies.