Doctoral dissertation
Tracing mercury in the wider Idrija region using stable isotopes
Views: 8 | Downloads: 7
Abstract
Mercury, a toxic element, known for its physical and chemical properties, spreads
throughout the environment and is found in various ecosystems, including water, air, soil,
and biological systems. The natural mercury cycle begins beneath the earth's crust,
where it rises to the surface and is released into the air through volcanic activity.
Mercury completes its cycle by redepositing into the geosphere, where the cycle can begin
anew. Historically, mercury has been utilized as a fungicide, catalyst in various chemical
processes, and in amalgamation. Human activities significantly contribute to the presence
of mercury in the environment. The forms, quantities, causes, and pathways of mercury
during its cycle can vary and are the subject of numerous scientific investigations.
One key characteristic of mercury is its seven stable isotopes. These isotopes can
distribute differently among reactants and products during environmental conversions.
Due to different reactions in various environments, individual ecosystems or subsystems
can have their own isotopic signatures. This unique isotopic fingerprint allows for tracing
the origins of mercury and understanding conversion processes such as photochemical
induction or methylation.
The Idrija region is contaminated with mercury due to centuries-long mining activity.
Elevated levels of mercury extend all the way to the Gulf of Trieste. The challenge lies in
distinguishing the contributions of mining, natural sources, long-range transport, and
other sources that have contributed to this pollution to varying degrees. Research on
mercury isotopes in ore, soil, and lichens was conducted within the framework of this
task to understand the mercury cycle in the Idrija region.
The first part of the research focused on airborne mercury content using transplanted
and in-situ lichens at three locations in Slovenia: Idrija, an area historically polluted due
to mercury mining; Anhovo, which contains a cement plant, another source of mercury;
and Pokljuka, a natural park. The research aimed to understand the behavior of mercury
using lichens as bio-monitors, with a focus on measuring stable isotopes. The results
showed that the isotopic composition of mercury exhibits pronounced seasonal
fluctuations, with lighter isotopes prevailing in lichens during winter and heavier isotopes
during summer. Similar fluctuations to those in lichens were also observed in atmospheric
particles.
The second part of the research aimed to determine the isotopic fingerprint of
mercury in the Idrija mine. The results showed that the isotopic composition in the mine
is very wide primarily due to mass-dependent fractionations, with weak correlations
between different types of ore, ore bodies, or geological periods of origin. This indicates
that the formation of mercury ore in the mine is a complex process, making its tracing
challenging.
The complexity of mercury heterogeneity was also evident in soil analyses from Idrija
and downstream Anhovo. Idrija soils show a wide range of values, likely associated with
different ores exploited during different periods of mine operation, while this fingerprint
is much more homogeneous in floodplains in Anhovo. The soils from Anhovo floodplains
in contrast show a much more homogenous isotopic fingerprint.