Over a 30-year period, scientists have analysed blood samples taken repeatedly from the same 54 men in Tromsø. For several POPs the concentrations had declined to just 20% of the peak concentrations. Photo: Helge M. Markusson, The Fram Centre. Front photo: The Norwegian Scientific Committee for Food Safety recommends eating fish at least twice a week, like cod (click on frame for full wiew). Photo: WWF.
By Torkjel M. Sandanger, UiT – Arctic University of Norway, Department of Community Medicine and NILU – Norwegian Institute for Air Research and Pernilla Carlsson, AMAP, Arctic Monitoring and Assessment Programme and Akvaplan-niva
Persistent organic pollutants (POPs) are a group of environmental contaminants that break down very slowly, accumulate in living organisms – and are poisonous. Many of them have now been banned or strictly regulated in the world and are therefore called “traditional” POPs. Some were used as flame retardants (polybrominated diphenyl ethers), some as insecticides (hexachlorocyclohexanes and DDT) and some mainly in hydraulic oils and electronic insulators (PCBs). When the old POPs were phased out, new chemicals were developed to replace them. One class of replacement chemicals, perfluorinated alkylated substances (PFAS), has raised concerns during the last decade after being detected in animals in remote areas, such as marine mammals and birds in the Arctic. The PFAS are used in fire extinguishers, Goretex® and ski wax. Although their effects differ from those of the traditional POPs, they also interfere with cellular processes in humans and animals.
Not only manmade compounds are of concern. Mercury, lead and cadmium are all present naturally in the environment. However, our use of these heavy metals has led to increased levels in nature and in the food we eat.
All these pollutants cause concern because of their potential to harm living organisms. Several of the POPs are structurally similar to hormones, which means they can interfere with endocrine systems. Mercury can have detrimental effects on brain development and the immune system. To make matters worse, the pollutants affect health even at low concentrations.
POPs are semi-volatile and persistent. Because of their ability to evaporate and their resistance to breakdown, they can be transported great distances by air and ocean currents. Those that reach the Arctic accumulate primarily in the marine food chain. The highest concentrations of POPs are found in fatty tissues of fish and animals high up in the food chain.
Seafood: a source of POPs – and nutrients
People who harvest their food from the marine food chain have historically been exposed to higher levels of POPs than the general population. Blubber of marine mammals and fish liver have both been a major source of POPs. At the same time, these foods are extremely nutritious with high concentrations of fat-soluble vitamins (A, D, E) and essential fatty acids. For some communities in the remote Arctic, marine mammals and fish are still a significant source of nutrients. Seagull eggs – also highly contaminated – are not equally problematic; they are cherished as a traditional spring delicacy, but have never been a major component of the diet.
Once POPs were banned and regulated, their concentrations decreased considerably both in the environment and in humans. Over a 30-year period, we analysed blood samples taken repeatedly from the same 54 men in Tromsø. For several POPs the concentrations had declined to just 20% of the peak concentrations. The men in our study belong to an older generation, known to consume more seafood than the average population, and are thus expected to have higher concentrations of POPs. But a similar decrease has been observed in other people, as well as in seafood.
Dietary advice and POPs
In view of the fact that the concentrations of POPs are much higher in marine food chains than in land-based food chains, much dietary advice has been focused on seafood in Norway. However, now that the POP concentrations are decreasing, a number of these guidelines have been revised. The general precautionary guidelines about fish liver have been removed and replaced with more detailed advice about consumption of fish caught in specific fjords or near sites known to be contaminated. In our opinion, dietary advice to the public often lacks precision. Despite revision, the guidelines may still cause unnecessary concern and make people choose other food than fish, which might be a problem from a public health perspective.
The main route for human exposure to mercury is via seafood. Nevertheless, the amount of mercury in fish is no cause for concern for the general population in Norway.
Public health perspective
The main public health challenges in Norway today include obesity, diabetes and cardiovascular diseases, which are all partly linked to unhealthy diets. Norwegians eat less fish than before, and the intake of saturated fats and sugar has increased considerably. Increased intake of fish is known to counteract the negative effects of a number of conditions such as cardiovascular disease. Questioning the safety of seafood can thus have major consequences for public health if it prevents people from eating fish with high nutritional value and low concentrations of POPs.
The concentrations of POPs in fish from the coast of Northern Norway are now low. The health benefits of consuming seafood clearly outweigh the potential negative effects of POPs. Granted, some highly polluted “hotspots” remain, where special dietary advice is warranted, and there are precautionary guidelines for consumption of seagull eggs. Nonetheless, the Norwegian Scientific Committee for Food Safety recommends eating fish at least twice a week.
Nøst TH, Breivik K, Fuskevåg OM, Nieboer E, Odland JØ, Sandanger TM. (2013) Persistent organic pollutants in Norwegian men from 1979 to 2007: intraindividual changes, age-period-cohort effects, and model predictions. Environ Health Perspect 121(11-12): 1292-1298
Read the full story in Fram Forum 2014.