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Natural processes may bring about highly
anomalous values of these elements at the Earth's
surface. Among these processes the most effective ones are those connected with hydrothermal
circulation in high heat flow areas. Hydrothermal
circulation supports geothermal fields at present
and supported minerogenetic processes in the
past. There is a logical link between these two
resources, which are related to each other, in
space and time. by geochemical, tectonic, and
structural features.
In the last years, the assessment of natural
risks has undergone a scientific revolution.
Among these risks, the geochemical one ranks
among the most severe. Italy is one of the coun1tIJ-eant
• :s; 0.2 ppm
• 0.2 - 0.4 ppm
• 0.4-1.0 ppm
• 1.0-5.0 ppm
• > 5.0ppm
o I
20Km
I
tries in the world most exposed to these risks.
Past and present natural processes, mainly due to
hydrothermal circulation, generate intense and
widespread anomalies in trace elements of toxicological concern at the Earth surface. (Dall' Aglio
and Marinelli 1994).
The geochemical risk may be defmed as the
health hazard originating by huge anomalies of
toxic elements at the Earth's surface interacting
with the biosphere. (Dall' Aglio 1996).
One of the most serious issues that mankind
has to face now, and especially in the near future,
concerns the anthropic change of the environment and, in particular, in the concentration of
elements in geochemical cycles and different
Fig. 1. Hg distribution in stream
sediments from Tuscany region