Summary and conclusions, Miljøstyrelsen

Study of dioxin pollution and sources of dioxin in the Baltic Sea

Summary and conclusions

The background for this project is that the Danish authorities need to be prepared for actions according to the EU Commission Regulation No. 466/2001 of 8 March 2001 about establishment of limit values for dioxin in foodstuff. If EU limits are exceeded, the Danish EPA shall seek to explore the possible origin of the dioxin source and the extent of the area likely to be affected by pollution. Dioxin in fatty fish from the Baltic Sea is supposed to be the most likely candidate for exceeding limits in Denmark as it is in Sweden and Finland, where fatty fish from the Baltic Sea already have too high contamination level and have got a temporary exception from the regulation.

The main focus in the report is on occurrence of dioxins and furans in the Baltic Sea but because there are PCB (polychlorinated biphenyl) family members (coplanar PCBs) with a similar toxicity as dioxin, and which are included in risk assessment of the daily intake of dioxin, data on PCB is also collected and evaluated. Coplanar PCBs are until further excluded from the EU regulation. But inclusion is to be expected at a later stage.

Dioxins and PCBs are organochlorine substances, which are extremely hazardous to the environment. It is very stable, lipophilic and persistent chemicals, which in spite of low volatility are widespread in the global environment, and the highest levels occur associated in fats. Their toxicity includes both acute toxicity and chronic effects such as cancer and reproductive effects.

"Dioxin" is a short name for polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF). There are in total 210 different members of the dioxin family called congeners. Specifically, the 17 dioxins with 2,3,7,8-chlorine substitution are the most toxic and bioaccumulating and most abundant in animal and humans. The most toxic congener is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or the Seveso-dioxin. In order to aggregate the results for the various congeners in a sample and get a total dioxin content, some international systems for calculating dioxin toxicity equivalence (TEQ) have been developed. All these systems are based on a relative ranking system giving the congeners toxicity equivalence factors (TEF) with TCDD assigned the factor 1. The newest system (WHO-TEF) was recommended by a WHO Working Group.

Dioxin and PCB are included in many international conventions and agreements on persistent organic pollutants (POPs), which require ban on uses and prevention or limitation of emissions.

The Baltic Sea is the largest brackish sea area in the World and has a great variations in salinity, climate, flora and fauna from The Bothnian Bay and Bothnian Sea in North, The Gulf of Finland, Baltic Proper and to the southern part of the Baltic Sea. Some large rivers flow into the shallow Baltic Sea which has an average depth of 60 m and maximal depth of 459 m. The narrow Danish sounds and belts limit the water exchange, and a total exchange is estimated to take 20-25 years.

Through the last 50 years the Baltic Sea has received dioxin input from municipal wastewater, waste water from industries located at the coast and from rivers supply. Thus, there has been a relatively large accumulation of persistent organic pollutants, and wide-spread euthrofication has happened occasionally.

There is both a supply and removal of these substances with the water exchange through Øresund, Storebælt and Lillebælt. In addition there will be evaporation of substances from the water and deposition of substances emitted from land based sources. The supply is larger than the removal thus a continuing accumulation of dioxin in the Baltic Sea. The later years many initiatives to pollution prevention mean that a less pollutants are emitted than 20-30 years ago.

Dioxins have a very low solubility in water, and there is only one investigation of the concentration of dioxins in the Baltic Sea water. The average level was 2,8 fg/L (ng/m³) surprisingly with 2,3,4,7,8-PeCDD as the most WHO-TEQ contributing congener.

Sediments at the sea bottom are in general an important end station for lipophilic and persistent substances such as dioxins. In sediments the substances can accumulate locally and with no disturbances be there almost indefinitely. The half-lives of dioxin congeners in the Baltic have been estimated to between 20 and 275 years. Sediment cores are in some instances been used to study time trend of pollution with dioxin and other POPs.

Nevertheless, by time some small amounts of dioxin will be released from these enormous reservoirs and be biological available in the food webs. The release will however be less than the deposition. Especially, the release happens from fresh surfaces and sediments, which are disturbed.

Investigations of dioxin in surface sediments are available from Danish, Swedish, Finnish and German areas. The concentrations of dioxins are typically 500-1500 ng (PCDD+PCDF)/kg dry weight. The highly chlorinated congeners and less water soluble, including OCDD and OCDF, dominate, and many dioxins in sediment samples are not 2,3,7,8-substituted, thus as basis of toxic equivalents this is only corresponding to 10-30 ng WHO-TEQ/kg dry weight. In the neighbourhood of point sources such as pulp industries and vinyl chloride plants dioxin concentrations in sediments may be ten to hundred times higher. In addition, coplanar PCBs contribute with 1-2 ng WHO-TEQ dry weight, or 3-20% of the total WHO-TEQ.

The biodiversity of the Baltic Sea is relatively low. There is only a limited number of fish species. Most abundant and economically important is Baltic herring and salmon. Cod is only living in the southern part. Herring and salmon are fatty fish, which also contains most dioxin. The degree of contamination may have variations geographically, yearly and with the season (highest in the spring), fat content, size and age. The main WHO-TEQ contributing congener of dioxin in Baltic herring is 2,3,4,7,8-PeCDF.

If the purpose of a study is environmental monitoring, results are mostly given on fat basis, and if the purpose is food control, results are given as fresh weight data. When applying risk assessment of dioxin it is necessary to include the contribution from coplanar PCBs. Regards herrings from Baltic Proper dioxin contributes to a little more 50% of the TEQ.

Most dioxin fish data are concerning herring, however, there are still only data from Denmark, Sweden and Finland. In the south western part of the Baltic and in Danish waters the average dioxin content in herrings is now 2-2,5 ng WHO-TEQ/kg fresh weight. In comparison, levels are about the double in Baltic Proper and the Gulf of Finland and four times higher in the Bothnian Sea and in the southern part of the Bothnian Bay - far exceeding the EU limit value. It is particularly in these areas the paper and pulp industries for many years’ emitted great amounts of dioxins. In the northern part of the Bothnian Bay dioxin concentrations are again similar to the levels in the south western part of the Baltic.

In some areas a clear decrease in levels by time has been demonstrated. This has been especially clear for PCB, which occur in many times higher concentrations. No dioxin data is available for herring catched in Poland and in the Baltic States but because the PCB concentrations in herrings are comparable with herrings in Sweden and Finland, it is likely that dioxin concentrations also are comparable.

Typical dioxin levels in Baltic wild salmons are presently 2-8 ng WHO-TEQ/kg fresh weight or comparable with herrings. Twenty years ago ten times higher dioxin levels were measured in wild salmon from the Umeå area. Farmed or lake salmons had ten times lower dioxin levels.

Most other Baltic fish do have less fat content and lower dioxin levels on fresh weight basis but rather similar levels calculated on lipid weight. Only in the case of fish catched close to a point source, there will be a risk to exceed the EU limit value concerning dioxins - but only if the contribution from coplanar PCB is included. That is especially relevant for eels for which the TEQ-contribution from PCB is much more important (85% of WHO-TEQ) than the dioxin contribution.

Mussels have an important role in the circulation of dioxins. Mussels increase the net deposition of these substances on the sea bottom and make them more available for organisms living at the bottom. In addition mussels increase the residence time of the substances in the water masses and accumulate the substances and excreted them again.

Marine mammals living in the Baltic are ringed seal, grey seal, common seal and harbour porpoises. These mammals are placed at the top of marine food webs and do have a high intake of persistent organic pollutants. Normally, adult females will have lower dioxin residues caused by mobilization from fat deposits during lactation.

There are only very few dioxin data on marine birds from the Baltic. Sea gulls and cormorants are not at all studied, and for guillemots there are older data for eggs and muscles indicating a high level of contamination with a congener pattern similar to that for fish and ospreys. The WHO-TEQ-contribution from PCB is, however, about 5.000 times greater than the contribution from dioxin.

Sea eagles and ospreys are top predators and have traditionally been the most contaminated with POPs. When Søren Jensen in 1965 discovered PCB as a widespread environmental contaminant, it started with analysis of muscle tissue from white-tailed eagles found dead in the Stockholm’s archipelago. The levels were extremely high and about 14 gram PCB/kg fat. Later studies in the Baltic Sea have shown large variation in levels down to ten thousands less. Similar variations are to be expected concerning dioxin levels. In a relatively new investigation of white-tailed eagles from German territories the total TEQ-levels were between 6 and 2880 ng WHO-TEQ/kg fresh weight, of which dioxin alone contributed with 20%.

The large amounts of dioxin previously released from the large Swedish and Finnish pulp industries seem to be the explanation, why the dioxin levels in fish still are especially high in the northern part of the Baltic Sea, and regards herring and salmon exceed the EU limit value of 4 ng WHO-TEQ/kg fresh weight. In contrary, the largest pollution by PCB occurs in the Baltic Proper and the southern part of the Baltic and near densely populated industry areas and river mouths.

The Baltic sea is surrounded by nine countries, each of which has contributed and will continue to contribute with dioxin to the Baltic Sea. Concerning Germany and Russia most of their national emissions will mainly end in other recipients than the Baltic, whereas most of the emissions from Finland and the Baltic States will end in the Baltic Sea. Most parts of Poland and a part of Belarus are also a part of the Baltic catchment area.

The dioxin emissions to the Baltic directly with waste water are nowadays considered insignificant compared to the deposition from air of dioxin formed by larger land based point sources, such as waste incineration plants and metal industries or more diffuse sources as products of preserved wood.

The latest Danish inventory showed that the annual dioxin emission into air was 11-148 gram I-TEQ. The most important sources were in fact waste incineration plants and metal industries. In Sweden the annual dioxin emission was estimated to 26-98 gram I-TEQ with wood preservation and residential heating with wood as most important. In Finland the annual dioxin emission was estimated to 64-82 gram I-TEQ with metal sintering and residential heating with wood as the most important. In Estonia the annual dioxin emission was about 14 gram I-TEQ with power stations and uncontrolled combustion processes as most important. In Latvia the annual dioxin emission was about 23 gram I-TEQ with uncontrolled combustion processes and metal industries as most important. In Lithuania the annual dioxin emission was about 17 gram I-TEQ with uncontrolled combustion processes and residential heating with wood. Poland has a large annual dioxin emission of 490 gram I-TEQ with incineration of hazardous waste, metal industry and uncontrolled combustion processes as most important. According to an older inventory the annual dioxin emission in Germany was 333 gram I-TEQ and it was mainly from various metal industries. Municipal waste incineration in Germany has been improved considerable in recent years and is not as important a source as before.

In general, the inventory figures from the various countries are very uncertain estimates, and in particular regards Russia, which now potentially may be the largest releaser of dioxin to the Baltic Sea, reliable data and estimates are totally absent. According to a TNO report more than 3 kg dioxin (I-TEQ) were released from the Helcom countries and half of it from Russia. Since then great progress and improvements in pollution preventions have been enforced in the western countries, and the termination of chlorine bleaching of pulp in these countries has eased the pressure on the Baltic Sea. The possibilities for further improvements and limitation of dioxin emissions in the eastern countries will depend on economically conditions. Modernisation of paper and pulp industries, chemical industry, metal industries, power stations and waste incineration will improve the situation. In addition, phase-out of chlorine containing wood preservatives and a more controlled collection and disposal of solid waste and waste oils will be helpful.

Present and future regulations will not be able to remedy and clean the Baltic Sea for dioxin already emitted. These chemicals will stay in the bottom sediments and pollute the Baltic for centuries. Never the less, further regulation limiting the future dioxin input to the Baltic is useful and necessary because it will decrease further build-up of the most biological available dioxin, and thus slowly decrease the burden on the organisms living in the Baltic Sea and on the populations in surrounding countries.