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Abstract

Mercury (Hg) pollution has been investigated in the area of the Idrija mercury mine, Slovenia, where the
second largest mercury mine in the world operated for more then 500 years. Although the production of
mercury at the Idrija mercury mine stopped in 1994, centuries of mining and ore processing operations left
behind intense pollution of all environmental compartments, not only in the vicinity of the mine but also in
the wider Idrija area.
The overall objective of this study was to establish the main recent sources and sinks, fate and
distribution of mercury in different environmental compartments in the Idrijca River catchment.
Sources of mercury in the Idrijca River catchment were identified by measurements of its
concentrations in all environmental compartments including water, soils, river sediments and air. In the
river water samples of the Idrijca River and its major tributaries, mercury speciation analyses (THg, PHg,
DHg, RHg, DGM, MeHg) as well as general geochemical analysis (pH, O2, Cl-, SO4
2-) were performed in
order to determine the parameters that influence the chemistry of mercury in river water. The influence of
changing hydrological conditions on chemistry and transport of mercury was also investigated. In soil
samples, spatial and vertical distribution, binding and mobility of different mercury forms (THg, MeHg,
water soluble) was investigated based on the Hg speciation and fractionation analysis. In river sediment
samples, total Hg was measured in different size fractions to estimate the mercury pool available for further
aquatic transport and transformation processes. With the aim of establishing spatial distribution and major
sources of elemental mercury (Hg0) in the atmosphere, Hg0 geochemical mapping was used. To better
understand the fate and behavior of atmospheric mercury, different mercury species (RGM, TPM, GEM) in
air over Idrija were determined. In order to determine the rates of atmospheric mercury deposition,
concentrations of different mercury species (THg, PHg, DHg, RHg, DGM, MeHg) in precipitation were
measured. Furthermore, the magnitude and the influence of different environmental parameters
(temperature, moisture and solar radiation) on the mercury soil-atmosphere exchange were investigated
during the laboratory flux measurement system experiment.
Based on the experimental results, a mass-balance model of sources, sinks and mercury transport
process at the Idrijca River catchment was developed. The processes that were taken into account in the
model include erosion of contaminated soils, surface runoff, riverine transport, atmospheric deposition and
mercury emissions from the surface. The model is based upon mercury mass-balance calculations as a
combination of different approaches. Mercury loads due to the atmospheric deposition and riverine
transport were calculated based on the measurements of Hg in precipitation and river water. For the
calculation of mercury terrestrial loads to the water system, a WCS mercury tool (Dai and Manguerra,
2000) was used and adopted for site specific conditions. Sediment production was estimated by the Erosion
Potential Method (EPM) (Gavrilovic, 1988). Based on the results of the laboratory flux chamber
experiment Hg emission model was developed. The results of the mercury mass balance model revealed
that in the Idrijca River catchment erosion of mercury contaminated soils and surface runoff remain the
main inputs of mercury into the Idrijca River tributary system. Taking the calculated inputs and outputs of
mercury to/from the catchment into account, it can be concluded that without the suitable remediation
actions a reduction of mercury pollution in the area can not be expected.