Mercury in Terrestrial Food Webs of the Idrija Mining Area
283
particularities. To reveal them and to enable comparisons with other heavily
polluted sites in the world, some efforts were made to describe the soil types and
the parameters controlling their metal capacity, the composition of parent
materials, as well as vegetation types in the area surveyed.
2
Mercury in the Study Area
The Idrija cinnabar ore deposit with an estimated thickness of 800 m is sited in
a Paleozoic and Trias fracture and covers an area of approx. 350000 m\ situated
beneath the town of Idrija and its surroundings. The Idrija mine is the world's
second largest mercury mine, with continuous mining, smelting and refining
operations for over 500 years. So far, over 12.7 million tons of Hg-ore were
excavated and the Idrija mercury mine contributed about 13% of the world Hg
stock - over 108 000 tons of commercial mercury, with a total of mined Hg of
over 145000 t (courtesy Idrija Mining Company). In the last 5 centuries, over
37000 t of Hg has been officially discharged to the environment due to the
inefficient smelting technology; the actual figures of Hg emissions must have
been much higher. Thus, the estimated average annual anthropogenic release
into the air from the Idrija mining region would be approx. 70 t of Hg, which
represents almost 2% of the annual amounts of Hg released on the global scale by
human activities, according to recent literature estimations (Nriagu and Pacyna
1988; Fitzgerald 1995). The mine's average annual production in the third quarter
of this century was between 400 and 500 t of commercial Hg/year, but was
reduced in the last few years from 1986 to only about 50 t of Hg per year. In 1990
the Idrija mine produced only about 25 t/year, production has been reduced even
more since and the mine is now being finally closed since the summer of 1996
(courtesy Idrija Mining Company). A geographical map of Slovenia showing the
origin of the samples is presented in Fig. 2. Approximately 40 km west of
Slovenian's capital of Ljubljana, Idrija is situated in a climatic transitional region
between the Alps, Karst and Adriatic with a prevailing continental temperate
climate and slight sub-Mediterranean and sub-montane influence. Geographically, Idrija is located in very heterogeneous terrain at an altitude of approx.
330 m in the relatively narrow valley of the river Idrijca, surrounded by hills of an
average altitude between 600 and 900 m (see Fig. 3a). The main Hg deposits,
mine and smelter are situated in the middle of the densely populated valley of the
town of Idrija and it is, therefore, subjected to natural and strong anthropogenic
Hg emissions. A semimillenium of mining resulted in a multilevel network of
together over 700 km of longitudinal shafts beneath the town's surface, down to
-38 m below sea level (courtesy Idrija Mining Company). The mine still
represents 12% of the world's Hg reserves, or around 4 million tons of cinnabar
ore containing 0.1 to 0.33% of Hg (Drovenik 1992). Idrija Hg-bearing minerals
contain 0.1 to 86.2% of Hg, but the richest Idrija ore deposits with average Hg
contents between 25 and 30% were excavated in the mine's early production in
the 16th century. Ancient mineral paragenesis in the Idrija ore deposit area
283
particularities. To reveal them and to enable comparisons with other heavily
polluted sites in the world, some efforts were made to describe the soil types and
the parameters controlling their metal capacity, the composition of parent
materials, as well as vegetation types in the area surveyed.
2
Mercury in the Study Area
The Idrija cinnabar ore deposit with an estimated thickness of 800 m is sited in
a Paleozoic and Trias fracture and covers an area of approx. 350000 m\ situated
beneath the town of Idrija and its surroundings. The Idrija mine is the world's
second largest mercury mine, with continuous mining, smelting and refining
operations for over 500 years. So far, over 12.7 million tons of Hg-ore were
excavated and the Idrija mercury mine contributed about 13% of the world Hg
stock - over 108 000 tons of commercial mercury, with a total of mined Hg of
over 145000 t (courtesy Idrija Mining Company). In the last 5 centuries, over
37000 t of Hg has been officially discharged to the environment due to the
inefficient smelting technology; the actual figures of Hg emissions must have
been much higher. Thus, the estimated average annual anthropogenic release
into the air from the Idrija mining region would be approx. 70 t of Hg, which
represents almost 2% of the annual amounts of Hg released on the global scale by
human activities, according to recent literature estimations (Nriagu and Pacyna
1988; Fitzgerald 1995). The mine's average annual production in the third quarter
of this century was between 400 and 500 t of commercial Hg/year, but was
reduced in the last few years from 1986 to only about 50 t of Hg per year. In 1990
the Idrija mine produced only about 25 t/year, production has been reduced even
more since and the mine is now being finally closed since the summer of 1996
(courtesy Idrija Mining Company). A geographical map of Slovenia showing the
origin of the samples is presented in Fig. 2. Approximately 40 km west of
Slovenian's capital of Ljubljana, Idrija is situated in a climatic transitional region
between the Alps, Karst and Adriatic with a prevailing continental temperate
climate and slight sub-Mediterranean and sub-montane influence. Geographically, Idrija is located in very heterogeneous terrain at an altitude of approx.
330 m in the relatively narrow valley of the river Idrijca, surrounded by hills of an
average altitude between 600 and 900 m (see Fig. 3a). The main Hg deposits,
mine and smelter are situated in the middle of the densely populated valley of the
town of Idrija and it is, therefore, subjected to natural and strong anthropogenic
Hg emissions. A semimillenium of mining resulted in a multilevel network of
together over 700 km of longitudinal shafts beneath the town's surface, down to
-38 m below sea level (courtesy Idrija Mining Company). The mine still
represents 12% of the world's Hg reserves, or around 4 million tons of cinnabar
ore containing 0.1 to 0.33% of Hg (Drovenik 1992). Idrija Hg-bearing minerals
contain 0.1 to 86.2% of Hg, but the richest Idrija ore deposits with average Hg
contents between 25 and 30% were excavated in the mine's early production in
the 16th century. Ancient mineral paragenesis in the Idrija ore deposit area