Mercury in Terrestrial Food Webs of the Idrija Mining Area
295
During the year the composition of plant species in roe deer stomach varies
(Klotzli 1965; Adamic 1990). Also, the roe deer's energy consumption changes
considerably during the year. The energy consumption is the highest during the
summer-autumn period, is reduced drastically due to the lack of food in winter
and increases very little until late spring. Therefore, the summer composite
vegetation samples, collected to reflect roe deer food at that time, contained a
higher percentage of herbs and twigs of deciduous trees and a small percentage of
conifer twigs compared to the late autumn composite vegetation samples (Tables
1 and 2). The mercury contents in vegetation samples from different years were
compared. Plant species in roe deer diet were determined using analysis of the
stomach content, and hypothetical browsing preferences were determined for the
area around Idrija (Adamic 1990).
No significant differences of total and methyl mercury were found on
comparing air dried (clean room, 4 days, room temperature) and freeze-dried
plant samples. This observation is not in agreement with the observations of La
Fleur (1973), who claimed that lyophilization of certain biological samples
without sulphydryl groups may result in decomposition of up to 50% of Me-Hg
to inorganic mercury. In order to avoid possible contamination during air
drying, freeze drying was chosen.
The highest vegetation mercury concentrations occur in the heavily contaminated location of the smelter complex (I-Sm), where the true extent of the heavy
anthropogenic close-range contamination in the Idrija area is revealed. In this
location Hg values of 45 to 65 ~Lg/g d.w. in the composite plant samples and up to
900 ~lg/g d.w. in soils were found (see Fig. 3a). The extent of the heavy
anthropogenic close-range contamination is even more evident from the mercury
concentrations in soil profiles and grassland vegetation from the hill in the
immediate vicinity of the smelter chimney outlet, where T -Hg concentrations
reach 2500 to 3000 ~Lg/g d.w. (Gnamus et al. 1996). Me-Hg concentrations in soil
and grassland vegetation from the top of the hill in the immediate vicinity of the
smelter chimney outlet reach very high values of 400 to 600 ng/g d.w. in soil
samples, and about 300 to 400 ng/g d.w. in the grassland vegetation (Gnamus
et al. 1996).
4.2
Roe Deer as a Bioindicator of Mercury Contamination
in the Terrestrial Environment
Roe deer have a number of advantages, such as their defined food chain, high
abundance and wide distribution in Europe and Eurasia (see Fig. I, shaded area).
Each animal ranges over a restricted area and their distinctive territoriality is
expressed over the majority of their adult life. Their tissues are relatively easy to
obtain due to overpopulation caused by anthropogenic elimination of predators
such as the wolf and lynx in most European forests. Therefore, the population
density of roe deer in the monitored area is large enough that culling of a few
animals per year does not threaten the species with extinction (Gnamus et al.
1991). Their long life-time enables us to obtain chronological information about
295
During the year the composition of plant species in roe deer stomach varies
(Klotzli 1965; Adamic 1990). Also, the roe deer's energy consumption changes
considerably during the year. The energy consumption is the highest during the
summer-autumn period, is reduced drastically due to the lack of food in winter
and increases very little until late spring. Therefore, the summer composite
vegetation samples, collected to reflect roe deer food at that time, contained a
higher percentage of herbs and twigs of deciduous trees and a small percentage of
conifer twigs compared to the late autumn composite vegetation samples (Tables
1 and 2). The mercury contents in vegetation samples from different years were
compared. Plant species in roe deer diet were determined using analysis of the
stomach content, and hypothetical browsing preferences were determined for the
area around Idrija (Adamic 1990).
No significant differences of total and methyl mercury were found on
comparing air dried (clean room, 4 days, room temperature) and freeze-dried
plant samples. This observation is not in agreement with the observations of La
Fleur (1973), who claimed that lyophilization of certain biological samples
without sulphydryl groups may result in decomposition of up to 50% of Me-Hg
to inorganic mercury. In order to avoid possible contamination during air
drying, freeze drying was chosen.
The highest vegetation mercury concentrations occur in the heavily contaminated location of the smelter complex (I-Sm), where the true extent of the heavy
anthropogenic close-range contamination in the Idrija area is revealed. In this
location Hg values of 45 to 65 ~Lg/g d.w. in the composite plant samples and up to
900 ~lg/g d.w. in soils were found (see Fig. 3a). The extent of the heavy
anthropogenic close-range contamination is even more evident from the mercury
concentrations in soil profiles and grassland vegetation from the hill in the
immediate vicinity of the smelter chimney outlet, where T -Hg concentrations
reach 2500 to 3000 ~Lg/g d.w. (Gnamus et al. 1996). Me-Hg concentrations in soil
and grassland vegetation from the top of the hill in the immediate vicinity of the
smelter chimney outlet reach very high values of 400 to 600 ng/g d.w. in soil
samples, and about 300 to 400 ng/g d.w. in the grassland vegetation (Gnamus
et al. 1996).
4.2
Roe Deer as a Bioindicator of Mercury Contamination
in the Terrestrial Environment
Roe deer have a number of advantages, such as their defined food chain, high
abundance and wide distribution in Europe and Eurasia (see Fig. I, shaded area).
Each animal ranges over a restricted area and their distinctive territoriality is
expressed over the majority of their adult life. Their tissues are relatively easy to
obtain due to overpopulation caused by anthropogenic elimination of predators
such as the wolf and lynx in most European forests. Therefore, the population
density of roe deer in the monitored area is large enough that culling of a few
animals per year does not threaten the species with extinction (Gnamus et al.
1991). Their long life-time enables us to obtain chronological information about