Søren Rysgaard, Rune Dietz, Gert Asmund, Henrik Skov, Torkel Gissel Nielsen, Jesper Christensen, Frank Riget
Mercury compounds are bio-accumulated. As a consequence the highest levels of mercury are measured in top predators like seals, toothed whales, polar bears, and also humans. The main mercury source for humans is the diet but the processes that links emission with effects through the transport chain: emission atmospheric transport atmospheric deposition transport to seawater ( reemission transport to seawater) uptake in plankton transfer to higher trophic levels are at present insufficiently known. The complexity of the problem stresses the need of contributions from many disciplines. Therefore 3 departments of NERI (ATMI, MAR and AM) are contributing to the work and traditional biological, chemical and physical disciplines are presented. The first measurements ever of atmospheric mercury fluxes have been carried out within the present project. The flux measurements in the campaigns have demonstrated that AMDEs (Atmospheric Mercury depletion Episodes) more than doubles the input of mercury to the Arctic environment through the transformation of GEM (Gaseous elemental Mercury) to RGM (Reactive Gaseous Mercury) and the deposition of RGM to the snow. These findings have been used to establish a new parameterisation of the removal of atmospheric mercury for Danish Eulerian Hemispheric Model (DEHM) and to validate the model. As a first estimate about 200 tons/year is deposited to the surface north of polar circle. In undisturbed sediment cores the mercury concentration and the mercury sedimentation are generally higher in present day sediments than in sediments formed 50 and 100 years ago. This can be interpreted as anthropogenic input. Thus this study of marine sediments from Greenland supports the conclusion from other studies that approximately half of the mercury flux in the Arctic is anthropogenic, Preliminary results in seawater indicate that 80% of total mercury is found in dissolved form or associated with particles < 0.45 µm. Mercury content is clearly dependent on trophic position in the food web. Significant increase in mercury content is found in predators such as crabs, fish, birds and seals. The coupling between transport pathways of carbon and mercury is weak at lower trophic levels. A substantial decrease of Hg concentrations in teeth and hair of polar bears since 1960 was found. Hg concentrations in hair of polar bears sampled in East Greenland during 1999-2001 was 8.3 times higher than baseline levels in West Greenland obtained from 1300 AD. Of 12 trend analyses performed on three birds of prey, 11 analyses showed increasing trend, however, only 4 groups from West Greenland were found to be significant (immature gyrfalcon all peregrines, and immature and adult White-tailed eagle). The increase of these time series ranged between 0.008 mg/kg dw per year to 0.05 mg/kg dw per year. The present joint effort aiming at understanding the link between transport, deposition and bioaccumulation in the Arctic environment shows that such a model is not easily established. However, continued effort on developing such a model may fulfil the goal of predicting future trends and effects on humans and exposed target species. However, at present this connection is not established. We need to carry out joint field campaigns to study the connection between the atmospheric input during AMDEs, the pelagic food chain and the transfer to higher trophic levels. Large uncertainties on the inter-compartment fluxes still exist and future activities should be organised as joint campaigns having a more holistic approach with focus on periods and target areas with AMDEs. Based on the obtained knowledge a model has to be developed that can explain the observed levels and inter compartment transport patterns. Finally scenario calculations have to be performed to demonstrate the sensitivity of the model and the system towards changes in climate, emissions and the food web.
Fate of Mercury in the Arctic (foma), 2004, p. 33-41