286
A. Gnamus and M. Horvat
airborne mercury inside the closed narrow valley area and the slopes of the
surrounding hills. Otherwise moderate winds in the upper air layers of the Idrija
area flow predominantly from the south-southeast, and also periodically from the
north (Petkovsek 1980), causing the highest Hg deposition rates in the prevailing
wind directions.
However, the Idrija Hg deposits with the mine-smelter complex represent one
of the biggest point source contributions of Hg to the atmosphere. The area of
the town and surrounding hills is densely covered with numerous tailing sites
from the past. According to some estimates, an area of approx. 90 km 2 out of
425 km
2
of the Idrija community has been used for deposition of waste ignition
residues from smelting. It is also subjected to severe contamination by airborne
Hg from the mercury mine ventilation shafts, and periodically by flue gases from
the smelting works. Since the mine with its ventilation shafts, smelting complex
and neighbouring tailings sites, as well as the area especially rich in geological Hg
deposits (i.e. Hg-bearing rocks) named Pront, are all positioned in a relatively
closed valley separated by less than 1 km, the area may be regarded as a uniform
point source of pollution. These characteristics and a high rate of the ground Hg
contamination distinguish the whole area as a unique natural laboratory for the
investigation of biogeo transformations and food-chain transfer of mercury in the
terrestrial environment.
3
Experimental
3.1
Sample Collection and Sampling Procedures
Collection of samples in the Idrija district started in 1990 as part of a long-term
complex study using environmental and biota samples to reveal the extent of
contamination and transformations of Hg deposited in the area heavily affected
by naturally and anthropogenically increased Hg concentrations. In this
biogeochemical and ecological survey the wider mine and smelter area was taken
into consideration. To evaluate contamination with mercury in the heavily
polluted natural terrestrial environment, forest soil profiles, composite plant
samples and tissues of animals that graze on selected plant species were selected.
Since it is planned that the mine and smelter will be permanently closed within the
next few years, the opportunity has been chosen to determine the consequences of
a semi-millenium of continual mercury ore processing. One of the aims of our
survey was to record the ultimate state as regards contamination of the
surrounding environment with the objective of observing the following restoration processes in the affected area. In addition, our objective was to estimate the
fate and significance of Hg accumulated in the soils based on the bed- rock parent
characteristics and individual soil types, and to determine the factors that
influence the transfer of Hg to plants. For comparison with the heavily polluted
A. Gnamus and M. Horvat
airborne mercury inside the closed narrow valley area and the slopes of the
surrounding hills. Otherwise moderate winds in the upper air layers of the Idrija
area flow predominantly from the south-southeast, and also periodically from the
north (Petkovsek 1980), causing the highest Hg deposition rates in the prevailing
wind directions.
However, the Idrija Hg deposits with the mine-smelter complex represent one
of the biggest point source contributions of Hg to the atmosphere. The area of
the town and surrounding hills is densely covered with numerous tailing sites
from the past. According to some estimates, an area of approx. 90 km 2 out of
425 km
2
of the Idrija community has been used for deposition of waste ignition
residues from smelting. It is also subjected to severe contamination by airborne
Hg from the mercury mine ventilation shafts, and periodically by flue gases from
the smelting works. Since the mine with its ventilation shafts, smelting complex
and neighbouring tailings sites, as well as the area especially rich in geological Hg
deposits (i.e. Hg-bearing rocks) named Pront, are all positioned in a relatively
closed valley separated by less than 1 km, the area may be regarded as a uniform
point source of pollution. These characteristics and a high rate of the ground Hg
contamination distinguish the whole area as a unique natural laboratory for the
investigation of biogeo transformations and food-chain transfer of mercury in the
terrestrial environment.
3
Experimental
3.1
Sample Collection and Sampling Procedures
Collection of samples in the Idrija district started in 1990 as part of a long-term
complex study using environmental and biota samples to reveal the extent of
contamination and transformations of Hg deposited in the area heavily affected
by naturally and anthropogenically increased Hg concentrations. In this
biogeochemical and ecological survey the wider mine and smelter area was taken
into consideration. To evaluate contamination with mercury in the heavily
polluted natural terrestrial environment, forest soil profiles, composite plant
samples and tissues of animals that graze on selected plant species were selected.
Since it is planned that the mine and smelter will be permanently closed within the
next few years, the opportunity has been chosen to determine the consequences of
a semi-millenium of continual mercury ore processing. One of the aims of our
survey was to record the ultimate state as regards contamination of the
surrounding environment with the objective of observing the following restoration processes in the affected area. In addition, our objective was to estimate the
fate and significance of Hg accumulated in the soils based on the bed- rock parent
characteristics and individual soil types, and to determine the factors that
influence the transfer of Hg to plants. For comparison with the heavily polluted