Preliminary study on geogenic degassing through the big karstic aquifers of Greece

Non-volcanic degassing contributes to the C-cycle by providing on a global scale a significant amount of CO2 emitted through diffuse earth degassing processes (Kerrick et al 1995). Due to the elevated solubility of the CO2 in water, in the areas where high CO2 fluxes directly affect regional aquifers, most of it can be dissolved, transported and released by groundwaters. Therefore, quantification of this contribution to the atmosphere has a substantial implication for modeling the global carbon cycle. According to Chiodini et al. (2000), total dissolved inorganic carbon (TDIC) concentrations and δ13CTDIC values of groundwaters are useful tools to both quantify the geogenic degassing and distinguish the different carbon sources. This approach was proved to be valid for central Italy and can possibly work for continental Greece; due to similar geodynamic history. Greece is considered one of the most geodynamically active regions and is characterized by intense geogenic degassing. The main source of degassing in the Hellenic area is concentrated on hydrothermal and volcanic environments (Daskalopoulou et al., 2019), however, the impact of geogenic CO2 released by tectonically active areas shouldn’t be disregarded. Aim of this work is to quantify the CO2 degassing through aquifers hosted in the carbonate successions in the Hellenic region. 95 karst, thermal and cold waters were collected in the northern and central part of Greece with some of which being characterized by bubbling of CO2-rich gases. Results show that karst waters have a typical Ca-HCO3 composition. Thermal and cold waters show two different compositions: some samples are characterized by Ca-HCO3 composition suggesting the presence of a carbonate basement, whilst others have a prevailing Na-HCO3 composition. On the basis of TDIC concentrations and δ13CTDIC values, the springs are divided into two groups. The first group includes karst waters and some of thermal waters and is characterized by low TDIC concentrations and negative δ13CTDIC values. This group shows no evidence of deep CO2 contributions, whereas the carbon of these waters derives from dissolution of carbonate minerals by organic derived CO2. Remaining samples belong to the second group and present intermediate to high TDIC concentrations and δ13CTDIC values, indicating a possible input of inorganic CO2. Some of these springs are characterized by gas bubbling at discharge, suggesting an extensive degassing

Impact of Etna’s volcanic emission on major ions and trace elements composition of the atmospheric deposition

Mt. Etna, on the eastern coast of Sicily (Italy), is one of the most active volcanoes on the planet and it is widely recognized as a big source of volcanic gases (e.g., CO2 and SO2), halogens, and a lot of trace elements, to the atmosphere in the Mediterranean region. Especially during eruptive periods, Etna’s emissions can be dispersed over long distances and cover wide areas. A group of trace elements has been recently brought to attention for their possible environmental and human health impacts, the Technology-critical elements. The current knowledge about their geochemical cycles is still scarce, nevertheless, recent studies (Brugnone et al., 2020) evidenced a contribution from the volcanic activity for some of them (Te, Tl, and REE). In 2021, in the framework of the research project “Pianeta Dinamico”, by INGV, a network of 10 bulk collectors was implemented to collect, monthly, atmospheric deposition samples. Four of these collectors are located on the flanks of Mt. Etna, other two are in the urban area of Catania and three are in the industrial area of Priolo, all most of the time downwind of the main craters. The last one, close to Cesarò (Nebrodi Regional Park), represents the regional background. The research aims to produce a database on major ions and trace element compositions of the bulk deposition and here we report the values of the main physical-chemical parameters and the deposition fluxes of major ions and trace elements from the first year of research. The pH ranged from 3.1 to 7.7, with a mean value of 5.6, in samples from the Etna area, while it ranged between 5.2 and 7.6, with a mean value of 6.4, in samples from the other study areas. The EC showed values ranging from 5 to 1032 μS cm-1, with a mean value of 65 μS cm-1. The most abundant ions were Cl- and SO42- for anions, Na+ and Ca+ for cations, whose mean deposition fluxes, considering all sampling sites, were 16.6, 6.8, 8.4, and 6.0 mg m-2 d, respectively. The highest deposition fluxes of volcanic refractory elements, such as Al, Fe, and Ti, were measured in the Etna’s sites, with mean values of 948, 464, and 34.3 μg m-2 d-1, respectively, higher than those detected in the other sampling sites, further away from the volcanic source (26.2, 12.4, 0.5 μg m-2 d-1, respectively). The same trend was also observed for volatile elements of prevailing volcanic origin, such as Tl (0.49 μg m-2 d-1), Te (0.07 μg m-2 d-1), As (0.95 μg m-2 d-1), Se (1.92 μg m-2 d-1), and Cd (0.39 μg m-2 d-1). Our preliminary results show that, close to a volcanic area, volcanic emissions must be considered among the major contributors of ions and trace elements to the atmosphere. Their deposition may significantly impact the pedosphere, hydrosphere, and biosphere and directly or indirectly human health

Impact of geogenic degassing on C-isotopic composition of dissolved carbon in karst systems of Greece

The Earth C-cycle is complex, where endogenic and exogenic sources are interconnected, operating in a multiple spatial and temporal scale (Lee et al., 2019). Non-volcanic CO2 degassing from active tectonic structures is one of the less defined components of this cycle (Frondini et al., 2019). Carbon mass-balance (Chiodini et al., 2000) is a useful tool to quantify the geogenic carbon output from regional karst hydrosystems. This approach has been demonstrated for central Italy and may be valid also for Greece, due to the similar geodynamic settings. Deep degassing in Greece has been ascertained mainly at hydrothermal and volcanic areas, but the impact of geogenic CO2 released by active tectonic areas has not yet been quantified. The main aim of this research is to investigate the possible deep degassing through the big karst aquifers of Greece. Since 2016, 156 karst springs were sampled along most of the Greek territory. To discriminate the sources of carbon, the analysis of the isotopic composition of carbon was carried out. δ13CTDIC values vary from -16.61 to -0.91‰ and can be subdivided into two groups characterized by (a) low δ13CTDIC, and (b) intermediate to high δ13CTDIC with a threshold value of -6.55‰. The composition of the first group can be related to the mixing of organic-derived CO2 and the dissolution of marine carbonates. Springs of the second group, mostly located close to Quaternary volcanic areas, are linked to possible carbon input from deep sources

Etna International Training School of Geochemistry. Science meets Practice

Also this year, the “Etna International Training School of Geochemistry. Science meets practice” took place at Mt. Etna, now in its fourth edition. The school was hosted in the historical Volcanological Observatory “Pizzi Deneri”, one of the most important sites of the INGV - Osservatorio Etneo for geochemical and geophysical monitoring. Mount Etna, located in eastern Sicily, is the largest active volcano in Europe and one of the most intensely degassing volcanoes of the world [Allard et al., 1991; Gerlach, 1991]. Mt Etna emits about 1.6 % of global H2O fluxes from arc volcanism [Aiuppa et al., 2008] and 10 % of global average volcanic emission of CO2 and SO2 [D’Alessandro et al., 1997; Caltabiano et al., 2004; Aiuppa et al., 2008; Carn et al., 2017]. Furthermore, Gauthier and Le Cloarec, [1998] underscored that Mt. Etna is an important source of volcanic particles, having a mass flux of particle passively released from the volcano during non-eruptive period estimated between 7 to 23 tons/day [Martin et al., 2008; Calabrese et al., 2011]. In general, Etna is considered to be still under evolution and rather ‘friendly’, which, along with the above, makes it a favorable natural laboratory to study volcanic geochemistry. The Observatory Pizzi Deneri was sponsored by Haroun Tazieff, and it was built in 1978 by the CNR - International Institute of Volcanology under the direction of Prof. Letterio Villari. It is located at the base of the North-East crater (2,850 m a.s.l.), near the Valle del Leone and it was built on the rim of the Ellittico caldera. A picturesque building, consisting of two characteristics domes in front of the breath-taking panorama of the summit craters. Even though it is quite spartan as an accommodation facility, the dormitories, kitchen, seminar room and laboratory are well equipped. In other words, the Pizzi Deneri observatory is a unique place close to the top of the most active volcano of Europe. The observatory lies in a strategic location making it one of the most important sites for monitoring, research and dissemination of the scientific culture. After six field multidisciplinary campaigns (2010-2015) organized by a group of researchers of several institutions (INGV of Palermo, Catania, Naples, Bologna; Universities of Palermo, Florence, Mainz, Heidelberg), the idea of sharing and passing on the experience to the new generation of students has materialized, and the “Etna International Training School of Geochemistry. Science meets practice” was born in 2016. The four editions of the school were partially funded by INGV of Palermo and Catania, European Geoscience Union (EGU), Società Geochimica Italiana (SoGeI) and Associazione Naturalistica Geode. The conceptual idea of the school is to share scientific knowledge and experiences in the geochemical community, using local resources with a low-cost organization in order to allow as many students as possible access to the school. The “Etna International Training School of Geochemistry. Science meets practice” is addressed to senior graduate students, postdoctoral researchers, fellows, and newly appointed assistant professors, aiming to bring together the next generation of researchers active in studies concerning the geochemistry and the budget of volcanic gases. Introduce the participants with innovative direct sampling and remote sensing techniques. Furthermore, it gives young scientists an opportunity to experiment and evaluate new protocols and techniques to be used on volcanic fluid emissions covering a broad variety of methods. The teaching approach includes theoretical sessions (lectures), practical demonstrations and field applications, conducted by international recognized geochemists. We thank all the teachers who helped to make the school possible, among these: Tobias Fischer (University of New Mexico Albuquerque), Jens Fiebig (Institut für Geowissenschaften Goethe-Universität Frankfurt am Main), Andri Stefansson (University of Iceland, Institute of Earth Sciences), Mike Burton (University of Manchester), Nicole Bobrowski (Universität Heidelberg Institute of Environmental Physics and Max Planck Institute for Chemistry), Alessandro Aiuppa (Università di Palermo), Franco Tassi (Università di Firenze), Walter D’Alessandro (INGV of Palermo), Fatima Viveiros (University of the Azores). Direct sampling of high-to-low temperature fumaroles, plume measurement techniques (using CO2/SO2 sensors such as Multi-GAS instruments, MAX-DOAS instruments and UV SO2 cameras, alkaline traps and particle filters), measurement of diffuse soil gas fluxes of endogenous gases (CO2, Hg0, CH4 and light hydrocarbons), sampling of mud volcanoes, groundwaters and bubbling gases. Sampling sites include the active summit craters, eruptive fractures and peripheral areas. The students have shown an active participation both to the lessons and the fieldworks. Most of them describe the school as formative and useful experience for their future researches. Their enthusiasm is the real engine of this school

Etna International Training School of Geochemistry. Science meets Practice

Also this year, the \u201cEtna International Training School of Geochemistry. Science meets practice\u201d took place at Mt. Etna, now in its fourth edition. The school was hosted in the historical Volcanological Observatory \u201cPizzi Deneri\u201d, one of the most important sites of the INGV - Osservatorio Etneo for geochemical and geophysical monitoring. Mount Etna, located in eastern Sicily, is the largest active volcano in Europe and one of the most intensely degassing volcanoes of the world [Allard et al., 1991; Gerlach, 1991]. Mt Etna emits about 1.6 % of global H2O fluxes from arc volcanism [Aiuppa et al., 2008] and 10 % of global average volcanic emission of CO2 and SO2 [D\u2019Alessandro et al., 1997; Caltabiano et al., 2004; Aiuppa et al., 2008; Carn et al., 2017]. Furthermore, Gauthier and Le Cloarec, [1998] underscored that Mt. Etna is an important source of volcanic particles, having a mass flux of particle passively released from the volcano during non-eruptive period estimated between 7 to 23 tons/day [Martin et al., 2008; Calabrese et al., 2011]. In general, Etna is considered to be still under evolution and rather \u2018friendly\u2019, which, along with the above, makes it a favorable natural laboratory to study volcanic geochemistry. The Observatory Pizzi Deneri was sponsored by Haroun Tazieff, and it was built in 1978 by the CNR - International Institute of Volcanology under the direction of Prof. Letterio Villari. It is located at the base of the North-East crater (2,850 m a.s.l.), near the Valle del Leone and it was built on the rim of the Ellittico caldera. A picturesque building, consisting of two characteristics domes in front of the breath-taking panorama of the summit craters. Even though it is quite spartan as an accommodation facility, the dormitories, kitchen, seminar room and laboratory are well equipped. In other words, the Pizzi Deneri observatory is a unique place close to the top of the most active volcano of Europe. The observatory lies in a strategic location making it one of the most important sites for monitoring, research and dissemination of the scientific culture. After six field multidisciplinary campaigns (2010-2015) organized by a group of researchers of several institutions (INGV of Palermo, Catania, Naples, Bologna; Universities of Palermo, Florence, Mainz, Heidelberg), the idea of sharing and passing on the experience to the new generation of students has materialized, and the \u201cEtna International Training School of Geochemistry. Science meets practice\u201d was born in 2016. The four editions of the school were partially funded by INGV of Palermo and Catania, European Geoscience Union (EGU), Societ\ue0 Geochimica Italiana (SoGeI) and Associazione Naturalistica Geode. The conceptual idea of the school is to share scientific knowledge and experiences in the geochemical community, using local resources with a low-cost organization in order to allow as many students as possible access to the school. The \u201cEtna International Training School of Geochemistry. Science meets practice\u201d is addressed to senior graduate students, postdoctoral researchers, fellows, and newly appointed assistant professors, aiming to bring together the next generation of researchers active in studies concerning the geochemistry and the budget of volcanic gases. Introduce the participants with innovative direct sampling and remote sensing techniques. Furthermore, it gives young scientists an opportunity to experiment and evaluate new protocols and techniques to be used on volcanic fluid emissions covering a broad variety of methods. The teaching approach includes theoretical sessions (lectures), practical demonstrations and field applications, conducted by international recognized geochemists. We thank all the teachers who helped to make the school possible, among these: Tobias Fischer (University of New Mexico Albuquerque), Jens Fiebig (Institut f\ufcr Geowissenschaften Goethe-Universit\ue4t Frankfurt am Main), Andri Stefansson (University of Iceland, Institute of Earth Sciences), Mike Burton (University of Manchester), Nicole Bobrowski (Universit\ue4t Heidelberg Institute of Environmental Physics and Max Planck Institute for Chemistry), Alessandro Aiuppa (Universit\ue0 di Palermo), Franco Tassi (Universit\ue0 di Firenze), Walter D\u2019Alessandro (INGV of Palermo), Fatima Viveiros (University of the Azores). Direct sampling of high-to-low temperature fumaroles, plume measurement techniques (using CO2/SO2 sensors such as Multi-GAS instruments, MAX-DOAS instruments and UV SO2 cameras, alkaline traps and particle filters), measurement of diffuse soil gas fluxes of endogenous gases (CO2, Hg0, CH4 and light hydrocarbons), sampling of mud volcanoes, groundwaters and bubbling gases. Sampling sites include the active summit craters, eruptive fractures and peripheral areas. The students have shown an active participation both to the lessons and the fieldworks. Most of them describe the school as formative and useful experience for their future researches. Their enthusiasm is the real engine of this school

Signature of the 24th December 2018 eruption of Mt. Etna on the chemical composition of bulk deposition in the Siracusa area (Italy)

Mt. Etna, in the eastern coast of Sicily (Italy), is one of the most active and most intensely monitored volcanoes of the planet. It is widely recognized as a big source of volcanic gases, such as CO2, SO2 and halogens, to the troposphere in the Mediterranean basin, and its gas emissions account for a significant percentage respect to the worldwide average volcanic budget. The SO2 flux from Mt. Etna’s plume has been routinely measured by the INGV since 1987. SO2 flux ranges between 600 to 25000 Mg/d; fluxes greater than 100000 Mg/d were prevalently measured during eruptive events. During eruptive periods, Etna’s emissions can be dispersed over long distances and cover wide areas of the Mediterranean region. Mt. Etna is also considered a huge source of many trace elements to the atmosphere on regional and global scale. On the morning of December 24th 2018, a moderate lateral eruption of the Mt. Etna started. This eruption was related to an intrusion of a magmatic dike on the high eastern flank of the volcano, through a 2 kilometres long fracture in the NNW SSE direction. At the same time, the summit craters produced a continuous strombolian activity generating a very dense ash plume, dispersed by the wind into the S/SE direction. From June 2018 to June 2019, atmospheric precipitations were collected in the area of Siracusa, a city on the east coast of Sicily, about 80 km SSE of Mt. Etna, and in the area of Milazzo, a city on the northern coast of Sicily. Atmospheric precipitations were monthly collected through a network of 12 pluviometers; the collectors were open during the entire exposure time, receiving both wet and dry deposition (bulk collectors). All the collected water samples were analysed for major ion contents and for a large number of trace elements by ICPOES and ICPMS. During the eruptive period (from 24th to 27th December 2018), the prevailing winds blew from the North direction and there were light rainfalls in the monitored sites (between 0.2 mm in Siracusa and Augusta, and 1.6 mm in Palazzolo Acreide). As a consequence, gases and particles of Etna’s plume were carried for long distance from the emission point, and they were deposited as dry and wet deposition also in the area of Siracusa. During the eruption event and in the following days, the plume reached distances of more than 300 km from the emission point (island of Malta). The samples collected in the study area of Siracusa during the period straddling the eruptive event are characterized by high concentrations of some major ions, such as Fluoride (up to 0.88 mg/l), Chloride (up to 124 mg/l) and Sulphate (23.1 mg/l). These ions derive mainly from the emitted volcanic gases (HF, HCl and SO2). The effect of the described eruption is also visible in the high concentrations of some trace elements, such as Aluminium, Thallium and Tellurium. The mean concentrations of the selected trace elements in the samples collected in the area of Siracusa, in the period before the eruptive event, are: 18.2 μg/l for Aluminium, 0.009 μg/l for Thallium, while Tellurium was always under the detection limit (0.004 μg/l); the concentrations of the same elements in the samples collected during the eruptive event reach 152 μg/l for Aluminium, 0.16 Âg/l for Thallium and 0.025 μg/l for Tellurium, therefore showing a strong enrichment. While Thallium and Tellurium are highly volatile elements typically enriched in volcanic emissions, Aluminium is a refractory element that was probably released by the dissolution of the related volcanic ashes. The study area of Milazzo, due to the prevailing winds from the North direction during the period of the eruption, has not been affected by the plume and therefore the signature of the eruption is not visible in the samples collected in that area, as shown by the mean values of the selected trace elements: 24.2 μg/l, 0.026 μg/l and < 0.004 μg/l for Aluminum, Thallium and Tellurium respectively. In conclusion, close to active volcanic areas, volcanic emissions have to be considered among the major contributors to the chemistry of rainwater, especially during eruptive periods

The precious "scientific heritage" of Mariano Valenza: the unknown history of Ludovico Sicardi and the birth of the modern volcanology

Mariano Valenza was an important scientific figure of the geochemical community and a person characterized by his great intellect, diplomacy and human qualities. Sadly, he passed away in July of 2018, leaving a great void. He left us a precious treasure for all the geochemists involved in volcanology: the story and the memory of Ludovico Sicardi. Indeed, Valenza carefully preserved in his office, for a long time, four boxes containing the scientific material belonged to Ludovico Sicardi. As often happens, a little by chance, the precious material returned to light thirty-five years later, on the 20th of April 2018, and was donated to the Museum of Mineralogy of Palermo. It is nowadays subject of study and cataloging by the volunteers of the Associazione Naturalistica Geode. The “scientific treasure” consists of the personal field-equipment of Sicardi, glassware, copies of the scientific articles, many old maps of volcanic areas, several historical photos of Vulcano and Solfatara. Among all these findings, several manuscript notes and three important unpublished researches about Vulcano, Vesuvio and Campi Flegrei. Who was Ludovico Sicardi? Sicardi was a chemist and a pharmacist, who was passionate about volcanoes and, in particular, enraptured by the island of Vulcano (Eolie - Sicily). During his several field trips in Vulcano, he observed and described the fumarolic field on systematic basis, measuring the temperatures and recording their variations over time (Sicardi, 1973). He was the first to perform chemical analysis of fluids emitted by fumaroles in Vulcano Island and Solfatara. Furthermore, he was the former to suppose the coexistence of SO2 and H2S in fumarolic discharges, which by that time was considered to be impossible. Also, he succeeded in measuring their ratio by developing an in situ method that chemically separate the S-gaseous species. This method was based on the sampling of fumarolic fluids using a glass flask that contained a NH4OHAgNO 3solution, with the aim to absorb the soluble acid gases (CO2, SO2 and HCl) and precipitate H2S as an insoluble Ag2S (Sicardi, 1955). Based on his remarkable scientific production, Sicardi can be considered as a precursor of the modern Volcanology and a pioneer of the volcanic monitoring techniques.We are extremely grateful to Mariano Valenza for giving us this fascinating story

Geochemical characterization of trace elements in thermomineral waters of Greece

Trace elements have a fundamental role in natural and anthropogenic systems. In waters, they present a great variability of concentrations that mostly depends on the degree of gaswaterrock interactions and geochemical conditions such as pH, temperature, redox and/or exchange reactions, etc. Even though, they are present in very low contents in hostrocks, elevated concentrations in ground or surface waters may have a hazardous impact on human and animal health and thus, it is important to both quantify and try to understand their behaviour in natural systems. Here we present the results of about 300 cold and thermal mineral waters collected along the entire Hellenic territory. Physicochemical parameters (temperature, pH, electrical conductivity and Eh) were measured in situ, whilst samples were analysed by Ionic Chromatography (IC) and Inductively Coupled Plasma Mass Spectrometry (ICPMS) for their major and trace elements’ content. The great variability in hydrogeological settings justifies the wide range of temperatures (6.5 98° C) and pH (1.96 11.98). Total Dissolved Solids (TDS) values also covered a wide range, from 0.06 to 43 g/L. Based on the combination of pH, T and TDS, samples were subdivided into 5 classes: i) thermal waters; ii) thermal waters affected by sea water contamination; iii) cold CO2rich waters; iv) hyperalkaline waters; and v) acidic waters. The great variability in chemical composition of the sampled waters is reflected in the large range of trace element contents (four to five orders of magnitude). Thermal waters affected by seawater contamination show the strongest enrichments in Li (up to 17,600 μg/L), B (up to 38,200 μg/L), Sr (up to 80,000 μg/L) and Rb (up to 9230 μg/L), mostly deriving from waterrock interaction. Cold CO2rich waters display elevated concentrations of Mn (up to 3970 μg/L), Ni (up to 111 μg/L) and Fe (up to 218,000 μg/L), whilst at the water outflow an extensive precipitation of iron oxihydroxides is observed. Hyperalkaline waters are generally strongly depleted in trace elements due to the precipitation of secondary minerals, however they are enriched in Al (up to 421 μg/L). Aluminium becomes soluble at extreme pH conditions and therefore also acidic waters present enhanced concentrations (up to 100,000 μg/L). Acidic waters show also enrichments in Fe (up to 58,400 μg/L), Mn (up to 15,600 μg/L) and Ni (up to 101 μg/L). In some cases, the maximum contaminant levels (MCLs) fixed by the Directive 98/83/EC for drinking water (and subsequent updates), are strongly exceeded in the under investigation waters. Such elevated concentrations of harmful elements may create hazards to human health either via direct consumption of cold mineral waters or through mixing of highly mineralized waters even in small proportions with shallow groundwater. For instance, As (MCL 10 μg/L) in the sampled waters reaches concentrations up to 1820 μg/L that derive from high temperature waterrock interaction within the hydrothermal circuit

The impact of Mt. Etna's ash plume on the chemical composition of meteoric deposition

Mt. Etna, in eastern coast of Sicily (Italy), is one of the most active and most intensely monitored volcanoes of the planet. It is the biggest volcanic point source of volcanic gases and particles to the troposphere in the Mediterranean basin. On the morning of December 24th 2018, a new lateral eruption of the Mount Etna started. This eruption was related to an intrusion of a magmatic dike on the high eastern flank of the volcano, which a two kilometers long fracture in the NNW - SSE direction. At the same time, the summit craters also produced a continuous strombolian activity generating a very dense dark ash plume, dispersed by the wind into the southeastern direction. This volcanic event well record from the atmospheric precipitations. During the period from June 2018 to May 2019, atmospheric precipitations were collected in the area of Priolo, eighty kilometer far SSE from Mt. Etna. The sampling and analytical protocols were chosen following the guidelines published by the main international agency involved in the monitoring of atmospheric precipitation. The rain gauges were open during the entire exposure time, collecting both wet and dry deposition (bulk collectors). All the collected water samples were analysed for major ion contents and for a large number of trace elements. The atmospheric precipitation of the period straddling the eruptive event is characterized by high concentration of major ions, such as Fluoride (up to 0.88 mg/l), Chloride (up to 124 mg/l) and Sulphate (23.1 mg/l). These derive mainly from the emitted volcanic gases (HF, HCl and SO2). On the another hand, an enrichment of some trace elements is also presented, such as Aluminum (up to 152 μg/l), Thallium (0.16 μg/l), Tellurium (0.025 μg/l). While Tl and Te are highly volatile elements typically enriched in volcanic emissions, Al is a refractory element that is probably correlated to the dissolution of the emitted volcanic ashes