Elsevier

Chemosphere

Volume 67, Issue 9, April 2007, Pages 1762-1775
Chemosphere

Dioxin concentrations in sediments of the Baltic Sea – A survey of existing data

https://doi.org/10.1016/j.chemosphere.2006.05.125Get rights and content

Abstract

Recent survey results for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs, dioxins) in Baltic Sea sediments from Finland, Sweden and Denmark were merged with previously published Baltic Sea data. Regional distribution of concentration levels, differences in congener patterns, and temporal changes in sediment profiles were examined. One of the main objectives was to study if any major point sources for different PCDD/F congeners could be identified on a regional scale, based on sediment records. The survey confirmed the impact of chlorophenol production derived highly chlorinated PCDF-congeners on the total toxicity in sediments in the Gulf of Finland near the Kymijoki river estuary. Signatures of other point sources or combined point sources pertinent to specific industry branches or particular production processes (such as pulp bleaching, vinyl chloride production, thermal processes) may be discerned. However, the findings did not support any of the known point sources significantly influencing those congeners that are most abundant in Baltic herring and salmon. Instead, regional distributions in the Baltic Sea indicate that atmospheric deposition may act as a major source for those congeners and especially for 2,3,4,7,8-PeCDF. There were clear indications of declines in levels in sediment in some areas, but generally the levels of highly chlorinated PCDD/Fs on the northern coast of the Gulf of Finland were still high when compared with other areas of the Baltic Sea. Major areas with data gaps cover the south-eastern and eastern coastal regions of the Baltic Proper and the southern Gulf of Finland.

Introduction

The Baltic Sea region is one of the areas most contaminated by persistent organic pollutants (POPs) including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). The high load of dioxins in fish has lead to recommendations to restrict the use of contaminated fish from the Baltic for human consumption. Uncertainties about sources, the geographical distribution of these contaminants, their cycling and fate in the sea, the pathways of bioaccumulation and possible ecotoxicological and human health effects are of concern.

Basic knowledge of the sources of PCDD/Fs found in the Baltic Sea is scarce. The inventories and estimates of emissions of PCDD/Fs are severely limited and the comparison of different approaches and their results is difficult. The emission factors used are in many cases based on few samples and probably not representative of fluxes. In addition, information on activity rates and emission profiles is scarce (Wenborn et al., 1999) although for some processes increasingly representative and reliable data have been published (see discussion below). Furthermore, more importance should be attached to cumulative emissions over time and, as part of them, secondary emissions from earlier fluxes and pools, e.g. soils, solids and products and wastes (see e.g. Bergqvist et al., 2005, Assmuth and Jalonen, 2005).

In general, PCDD/Fs enter the Baltic Sea via atmospheric deposition, river input and point sources along the coast. The ultimate sink for the majority of the compounds is the open sea and coastal sediments, although some fraction enters the food chain. Importantly, vertical profiles of sediments reveal past changes in PCDD/F accumulation and inputs, although modifying factors confound such reconstructions. Therefore, analysis of sediment has been widely used to study regional and temporal trends of dioxin pollution in freshwater, estuaries and oceans (e.g., Koistinen et al., 1995, Vartiainen et al., 1995, Vartiainen et al., 1997, Bruckmeier et al., 1997, Witt et al., 1997, Sakurai et al., 2000, Frignani et al., 2001, Green et al., 2001, Wu et al., 2001, Isosaari et al., 2002a, Isosaari et al., 2002b, Marvin et al., 2002, Gotz and Lauer, 2003, Barabas et al., 2004). The Baltic Sea has been one of the most studied sea areas for dioxin-like compounds as well. Only a fraction of the analytical results have been published in scientific papers, however (Rappe and Kjeller, 1987, Rappe et al., 1989, Jonsson et al., 1993, Kjeller and Rappe, 1995, Dannenberger et al., 1997, Koistinen et al., 1997, Witt et al., 1997, Isosaari et al., 2000, Isosaari et al., 2002b, see also Ishaq et al., 2003). Here we summarize and evaluate information on regional distributions of certain congeners of dioxins in surface sediments and in six sediment cores from the Baltic Sea. New survey data from Finland, Sweden and Denmark is merged and compared with data of earlier sediment surveys and case studies.

The purpose of this paper is to

  • 1.

    Provide a “draft” picture of the regional distribution of key PCDD/Fs (possible hot spots, major regional differences) in surface sediments along the Finnish–Swedish–Danish–German coastal and open sea sites in the Baltic.

  • 2.

    Analyze differences in congener distributions (source identification).

  • 3.

    Examine temporal changes reflected in sediment profiles.

  • 4.

    Identify major areas with data gaps.

Section snippets

Finland

Surface sediment samples along the Finnish coast, one sediment profile from the Gulf of Finland (AKL) and one sediment profile from the previously poorly studied Gulf of Bothnia (SR5) were taken by the Finnish Environment Institute (SYKE) and the Finnish Marine Research Institute in 1997–2003 (Table 1). The samples were collected from known sedimentation areas both near the coast and offshore using pistonless corers with an inner diameter from 9.0 to 13 cm. All the sediment cores were divided

Results and discussion

The main interest was to study the spatial distribution of dioxins and the contribution of identified point sources in Finland and Sweden to sediment dioxin levels. For this purpose, we focused on certain point source-identified congeners. The selected congeners reflecting specific point sources were 2,3,7,8-TCDD (TCDD), 2,3,7,8-TCDF (TCDF), and OCDF as indicators of pulp bleaching and vinyl chloride production (Rappe et al., 1989; Koistinen et al., 1992; Isosaari et al., 2000), and

Conclusions

The survey confirms the impact of Kymijoki-derived, highly chlorinated, PCDF-congeners to the total toxicity in sediments in the Gulf of Finland. However, the findings do not support that any of the known point sources would significantly influence those congeners that are most abundant in Baltic herring and salmon. Instead, regional distributions in the Baltic Sea indicate that atmospheric deposition may act as a major source for those congeners. On the other hand, some signatures of point

Acknowledgements

We thank all technical personnel involved in the sampling and laboratory analysis. The work was partially funded by the Ministry of Environment, Finland, the Swedish EPA, the Geological Survey of Sweden and the Danish Environment Protection Agency.

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    Present address: VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT.

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