Mercury Transport and Transformations in the Wider Idrija Region and the Gulf of Trieste

The Idrija mercury mine in Slovenia is the site of the second largest Hg mine in the world, which was in operation continually for 500 years until about 20 years ago. Over five million metric tonnes of Hg ore was mined, and much of the residues were spread around the town and its vicinity. It has been estimated that 73 percent of the Hg mined was recovered, and the remaining 17 percent dissipated into the environment. Mercury in the terrestrial environment of the region is effectively transferred from soil (and air) to vegetation, herbivores and carnivores further up the food web. Interestingly, a higher accumulation of MeHg was observed in those environments polluted with high concentrations of inorganic mercury compared to less contaminated and control areas. The tailings and contaminated soils in the Idrija region are continuously eroded and serve as a continuous source for the river, the flood plains, and the Gulf of Trieste. This is confirmed by the fact that even after 10 years of closure of the Hg mine, Hg concentrations in river sediments and water are still very high and there are no signs of the expected decrease of Hg in the Gulf of Trieste. Recent studies in the Idrijca - Soca - the Gulf of Trieste region are mainly directed towards the quantification of Hg fluxes and better understanding of the fate of mercury, its accumulation in the flood plain, and its final input to the marine environment. An assessment of the extent of contamination in the Gulf of Trieste after the closure of the Hg mine was also made and mass balance calculated. One of the most interesting finding was that the main source of inorganic Hg in the Gulf of Trieste is due to river input, while the main source of MeHg is the bottom sediment of the coastal region leading to increased levels of mercury in marine fish. In order to develop realistic strategies for minimizing the effects of the Idrija mining on human health and the environment a more integrated approach is needed. The paper will provide a short review of Hg reserch activities carried out in the region and the its major outcomes with recommenations.