Kotnik, Joze

We monitored the soil gas emission of CO2 from selected sites of Mt. Etna volcano during the period February 2009 to December 2010 by measuring periodically the soil CO2 ef- flux together with the associated stable carbon isotope com- position of CO2. Correlation between the two parameters showed distinct behaviors depending on the sites as a re- flection of the different interactions between crustal and sub-crustal fluids. Where deep CO2 interacted with shallow cold ground water and/or with shallow biogenic CO2, a positive correlation between soil CO2 effluxes and carbon isotopes was evident and it depended strongly on the veloc- ity of gas through the soil. In these cases, the highest CO2 effluxes corresponded to δ13CCO2 values similar to those of the deep magmatic CO2 emitted from the crater and peri- crateric gas emissions at the summit. In areas where a shal- low hydrothermal system was presumed, then a similar correlation was less evident or even absent, suggesting strong control on C isotopes arising from the interactions between CO2 gas and dissolved HCO3- that occur in aquifers at T>120 °C. Marked temporal variations were observed in both parameters at all sites. No significant effect of me- teorological parameters was found, so the observed changes were reasonably attributed to variations in volcanic activity of Mt. Etna. In particular, the variations were attributed to increased degassing of CO2 from incoming new magma, possibly coupled with increased hydrothermal activity in at least some of the shallow aquifers of the volcano. The largest anomalies in the monitored parameters preceded the opening of the New Southeast Crater in late 2009 and there- fore they could represent a key to unveiling the dynamics of the volcano.

Mercury is transported globally in the atmosphere mostly in gaseous elemental form (GEM, Hg0 gas), but still few worldwide studies taking into account different and contrasted environmental settings are available in a single publication. This work presents and discusses data from Argentina, Bolivia, Bosnia and Herzegovina, Brazil, Chile, China, Croatia, Finland, Italy, Russia, South Africa, Spain, Slovenia and Venezuela. We classified the information in four groups: (1) mining districts where this contaminant poses or has posed a risk for human populations and/or ecosystems; (2) cities, where the concentration ofatmospheric mercury could be higher than normal due to the burning of fossil fuels and industrial activities; (3) areas with natural emissions from volcanoes; and (4) pristine areas where no anthropogenic influence was apparent. All the surveys were performed using portable LUMEX RA-915 series atomic absorption spectrometers. The results for cities fall within a low GEM concentration range that rarely exceeds 30 ng m-3, that is, 6.6 times lower than the restrictive ATSDR threshold (200 ng m-3) for chronic exposure to this pollutant. We also observed this behavior in the former mercury mining districts, where few data were above 200 ng m-3.We noted that high concentrations of GEM are localized phenomena that fade away in short distances. However, this does not imply that they do not pose a risk for those working in close proximity to the source. This is the case of the artisanal gold miners that heat the Au–Hg amalgam to vaporize mercury. In this respect, while GEM can be truly regarded as a hazard, because of possible physical–chemical transformations into other species, it is only under these localized conditions, implying exposure to high GEM concentrations, which it becomes a direct risk for humans.

Beside anthropogenic influences, mercury in the environment can also be of natural origin. Among geologic sources, volcanic activity has been of main interest so far. Modern estimations of global natural emissions are between 2000 and 5200 tonnes per year. However, these estimates are very uncertain, thus more detailed and systematic research on natural sources of mercury is necessary. Tectonic activity is connected to certain phenomena such as degassing of Hg and other gases from active faults, geothermal activity, volcanoes, etc., especially on tectonic plate margins. Elemental mercury concentrations in air, soil gases and fluxes, as well as its speciation, in connection to tectonic activity, were studied in different environments such are karst cave (Postojna Cave), active volcano areas (Mt. Etna, Italy), and active tectonic areas in the Mediterranean Basin on Africa-Adriatic tectonic plate margin. Postojna Cave is characterized by elevated Hg (up to 150 ng m-3) air concentrations at certain areas in vicinity of active faults; however the concentrations showed also strong seasonal variations. Mt. Etna on Sicily is the largest and most active Mediterranean volcano. Concentrations of mercury in air in the vicinity of the volcano are relatively high (between 4 and 30 ng m-3) and rise towards the summit crater (65 to 130 ng m-3). Concentrations in sulphatare and fumaroles gases on the summit of the volcano can reach very high values (even up to 60 μg m-3). The Mediterranean Basin is characterized by strong tectonic activity as a consequence of subduction of African plate under the Eurasian plate. A possible source of DGM (dissolved gaseous mercury in sea water) in deeper and bottom waters could be intensive tectonic activity of the seafloor, since higher concentrations and portions of DGM were found near the bottom at locations with strong tectonic activity (Alboran Sea, Strait of Sicily, Tyrrhenian Sea, Ionian Sea). Distribution of different mercury species in sediment and water of the Mediterranean Sea showed that the main source of mercury is geotectonic activity and its accompanying phenomena.

Mercury is a global pollutant that can be found in different forms and different ecosystems. Special attention has recently been devoted to mercury due to its high chemical reactivity, its global spreading, its biogeochemical cycling, its transformations in the environment, its ability for biomagnification and its high toxicity. Beside anthropogenic sources, mercury can also be of natural origin. Among natural Hg sources, volcanoes can be important. Volcanic gas emissions may be rich in elemental gaseous mercury (Hg0), reactive gaseous mercury (HgII) and other mercury forms. Mt. Etna (Sicily, Italy) is one of the most active volcanoes in the world and one of the largest contributors of magmatic volatiles to the environment; consequently, we tried to estimate its contribution to regional and global Hg budgets and tested the eligibility of Hg as a tool for volcano monitoring. Mercury concentrations have been measured on Mt. Etna during several campaigns carried out between 2004 and 2007 in fumaroles, mofettes and diffuse degassing areas, as well as in the air inside and across the volcanic plume. In addition, Hg fluxes have been measured by flux chamber technique. Mercury concentrations measured in air below the volcanic plume in November 2004 ranged between 4 and 30 ng m-3 at low altitude, and between 65 and 132 ng m-3 close to the summit craters. A profile of Hg in the air below the volcanic plume carried out on helicopter on November 2006 showed Hg concentrations up to 60 ng m-3. Hg contents in fumarole gases reached 64,200 ng m-3, and soil gas Hg showed temporal variations that reached the highest values (up to 240 ng m-3) in fall 2005. The highest Hg fluxes were measured in bubbling gas from mud volcanoes at the SW foot of Etna, reaching 1300 ng m-2 h-1. Mercury contents were found highly correlated both with water/mud temperature at mud volcanoes and with concurrent soil CO2 effluxes. In the latter case, hydrothermal gases showed higher values and a higher correlation than “cold”gases. Our results, therefore, look promising for the use of mercury in geochemical monitoring of volcanic activity.