Vikelsøe, J., Hovmand, M.F., Andersen, H.V., Bossi, R., Johansen, E. & Chrillesen, M. 2006, NERI Technical Report 565, 83 p.
Summary
Aims
The aim of the present investigation has been to measure the level of dioxins in the atmosphere and bulk deposition in Denmark. The dioxins consist of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, with the abbreviation “PCDD/F”. The geographical and seasonal variations and influence from different sources have been investigated through measurements at selected rural, urban and marine sites. The annual Danish deposition is estimated from the measurements and compared to the dioxin content found in soil, lake and sea sediment and in milk and fish.
Measuring campaign
The investigation began in the fall 2001 with preliminary experiments, and was then gradually expanded until springtime 2005. PCDD/F were measured in bulk deposition at three forest sites in the Danish background area: the western part of Jutland (Ulborg), northern part of Zealand (Frederiksborg) and Bornholm (in the Baltic Sea) and at one urban site (Copenhagen). In addition through fall was measured in Frederiksborg. Through fall is the wet deposition passing the crown of the trees. The PCDD/F concentrations in the ambient air were measured in Frederiksborg and Copenhagen and periodically in a village (Gundsømagle) close to residences with wood stoves.
Methods
The sampling method for bulk deposition was developed for the project and is based on absorption of dioxins on a filter in the field. Air was sampled according to US-EPA specifications. Samples were taken monthly or in some cases over two months or pooled as two months values. The analytical method comprised extraction in toluene, followed by classic clean up by liqiud chromatography on silica and alumina. Detection and quantification was done by high resolution GC/MS.
Air results
The results for air show a pronounced seasonal variation with maxima in the winter and a small year to year variation. The air concentrations in North-Zealand and Copenhagen are very alike, pointing to long range transport as a potential contributor to atmospheric PCDD/F at these sites. The village winter maximum is very pronounced, being the highest measured in the programme. The high concentrations are must likely caused by local emissions from wood stoves during the heating season.
Bulk deposition results
The bulk deposition results show a winter maxima, though not as pronounced as for the air concentrations. Some variation between the years are also observed. The geographical distribution showed the highest annual fluxes in Copenhagen and lowest in West-Jutland. Apart from Copenhagen, the geographical variation was within a factor two. This modest variation indicates that the dioxins in the bulk deposition most likely are dominated by contributions from long-range transport of dioxin from distant sources.
Through fall results
The through fall results show some variation throughout the seasons and the level is somewhat higher than the bulk deposition. The higher level is probably caused by a contribution from airborne PCDD/F, captured by the spruce canopy and later on transferred to the ground by precipitation or adsorbed to organic material.
Annual national deposition
The measurements of bulk deposition at the background stations are used to estimate an annual load to the Danish land area. The load is estimated to 4.5 pg/m2•day I-TEQ, corresponding to a total annual bulk deposition over the Danish land area of 72 g/year I-TEQ. The Danish atmospheric emissions are estimated to be in the range 11-148 g/year I-TEQ.
Congener TEQ profiles
The main TEQ-contributor is 2,3,4,7,8-PeCDF followed by 1,2,3,7,8-PeCDD, 2,3,7,8-TCDD and the HxCDDs, despite the site, season and type of samples, i.e. air samples, bulk deposition or through fall.
Correlation analysis
Highly significant correlations are found between the air concentrations in Frederiksborg and Copenhagen. A correlation is observed between bulk deposition and through fall in Frederiksborg. No significant correlation is seen between air concentrations and bulk deposition or air concentrations and through fall in Frederiksborg.
Role for soil
The bulk deposition can roughly account for the dioxin content found in rural soil. Even though the bulk deposition measured in Copenhagen is higher than the rural results, it is not large enough to explain the high soil concentrations found here.
Role for sediment
An investigation of the content of dioxin in sediments of lakes shows results that generally are too high to be explained by bulk deposition as the only source. This is also the case for sea sediment.
Human intake, fish
The total atmospheric deposition to the surface of the western Baltic Sea is estimated to 1.3 mg I-TEQ/km2•year. From measurements of the content of dioxin in fatty pelagic fish (herring and salmon) and an estimation of the yearly production of biomass, it is demonstrated that the uptake in fish corresponds to 0.4% of the flux of dioxins deposited from the atmosphere. This means, that the atmospheric deposition carries a large surplus of dioxins into the Baltic Sea available for uptake in the food chains. Fish is an important source for human intake of dioxins.
Human intake, dairy
From the measurements the average deposition to the Danish land area during the summer is estimated to 2.8 pg/m2•day I-TEQ. This flux is about six times more than the amount of dioxins in the milk produced pr area unit by grazing cows in summer time. This substantial surplus makes it likely that atmospheric deposition is responsible for a major part of the PCDD/F in cow milk and related dairy products, which, next to fish, are the most important source to human intake of dioxin.
Other studies
The air concentrations of dioxin measured in Denmark are at the same level as reported from Sweden, all though results from the Swedish west coast show lower levels. Atmospheric concentration levels from other European sites have in general shown higher results. The results found for the bulk deposition is in good agreement with results from Northgermany.
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