Abstract. For analysing karst hydrogeological systems, observations of karst springs and cave drips are considered indispensable. In addition to hydrometric observations, knowing the oxygen and hydrogen stable isotope ratios has improved the understanding of vadose zone and aquifer dynamics, likewise supporting system characterisation and modelling. However, limited accessibility and high costs of the analysis of stable isotopes in karst aquifers have hindered progress in karst research and impeded the accurate understanding of karst processes especially when it comes to comparative or large-scale studies. In this study, we present our workflow to compile the WoKaS-Iso database, the first extensive collection of time series data for Oxygen-18 and Deuterium isotopes in karst springs and cave drip water from diverse sources, encompassing publications, theses, reports, online archives, and collaborative initiatives worldwide. The database incorporates data sourced from 236 springs and 74 caves, comprising in total 997 time series (379 time series for the springs and 618 time series for the cave drip water). These datasets provide coverage across significant karst regions globally, spanning China, the USA, Europe, the Middle East, and Australia. Within datasets, 79% for springs and 68% for cave drip water exhibit resolutions finer than monthly intervals. In addition, by integrating isotopic records with ancillary environmental variables including spring discharge, cave drip rate, precipitation, and rainwater isotopes, the database offers a more comprehensive perspective on hydrological behaviours in karst aquifers, hence advancing hydrogeological characterisation and modelling. The WoKaS-Iso database not only deepens the understanding of the complex systems but also promotes sustainable water resource management as well as the potential to foster collaborative research. The database can be accessed at: https://doi.org/10.25532/OPARA-909.

Active biomonitoring of mercury (Hg) using non-indigenous moss bags was performed for the first time within and around the former Hg mining area of Abbadia San Salvatore (Mt. Amiata, central Italy). The purpose was to discern the Hg spatial distribution, identify the most polluted areas, and evaluate the impacts of dry and wet deposition on mosses. The exposed moss bags consisted of a mixture of Sphagnum fuscum and Sphagnum tenellum from an external uncontaminated area. In each site, two different types of moss bags, one uncovered (to account for the wet + dry deposition) and one covered (to evaluate the dry deposition), were exposed. The behavior of arsenic (As) and antimony (Sb) in the mosses was investigated to assess the potential relationship with Hg. GEM (Gaseous Elemental Mercury) concentrations were also measured at the same sites where the mosses were exposed, although only as a reference in the initial stages of biomonitoring. The results revealed that the main Hg emissions sources were associated with the former mining area of Abbadia San Salvatore, in agreement with the measured GEM concentrations, while arsenic and antimony were related to soil enriched in As-Sb waste material. The three elements registered higher concentrations in uncovered mosses with respect to the covered ones, i.e., wet deposition was the key factor for their accumulation on the uncovered mosses, while dry deposition was especially important for the covered samples in the mining area. Hg was accumulated in the mosses via GEM adsorption, uptake of particulate Hg, and precipitation via raindrops/snowfall, with almost no loss and without post-deposition volatilization. The results testified that the chosen biomonitoring technique was an extremely useful tool for understanding Hg transport and fate in a contaminated area.

Within the framework of SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, three oceanographic cruises were performed in December 2022 and June and October 2023, with the research vessels PHILIA and AEGAEO of the HCMR at the submarine volcano Kolumbo, 7 km NE of Santorini. Kolumbo is considered to be one of the most active submarine volcanic complexes in the Eastern Mediterranean Sea, while being easily accessible from land.. The oceanographic surveys were mainly aimed at the deployment of a new generation observatory along with several multiple innovative sensors such as temperature sensors, inclinometers, pressure gauges, optical cameras, multispectral and stereo camera, radioactivity sensor gSniffer and the γ-radiation imager. During the surveys, several water column profiles were also performed in order to collect seawater samples for chemical analysis. At the bottom of the Kolumbo crater (500m depth), acidic and slightly reducing conditions prevail, due to the presence of several active hydrothermal vents. This agrees with previous studies and with the data recorded by the deployed observatory. Collected samples have been analyzed for the chemical and isotope (carbon, helium and argon) composition of the dissolved gases as well as for the major, minor and trace element concentrations. The results indicate that the morphology of the crater allows the buildup of persistent anomalies that extend from the bottom up to the lowest crater-rim level at about 250-meter depth. We will discuss the temporal variability of the Kolumbo venting dynamics and the explore in detail the resulting vertical gradients in the crater funnel.

The isotopic compositions of boron (δ11B‰) and strontium (87Sr/86Sr) were measured, for the first time, in 10 rainwater samples from Mt. Etna, Italy. The samples were collected during the paroxysmal sequence of 2021-2022. The chemical composition was determined using an ICP-MS, while the isotopic ratios of B and Sr were measured using a mass spectrometer MC-ICP-MS (Neptune Plus™), after specific pre-concentration procedures in clean rooms (class 100 - 1000). In the analysed rainwater samples, the concentrations of B and Sr were between 4.6 µg L-1 and 42.2 µg L-1, and between 9.7 µg L-1 and 541 µg L-1, respectively. Overall, the isotopic composition of B ranging from +1.29‰ ± 0.30‰ to +42.9‰ ± 0.20‰, with a median value of +22.0‰ ± 0.19‰. The lowest δ11B‰ values were measured in the site closest to the main active craters (3.6 km), with a median value of +11.4‰ ± 0.21‰; the highest was measured in the site close to the Ionian Sea (Zafferana Etnea), with a median value of +38.1‰ ± 0.21‰. Strontium (87Sr/86Sr) ratios were between 0.703728 ± 0.000008 and 0.710363 ± 0.000006, with a median of 0.707328 ± 0.000007. The highest and the lowest 87Sr/86Sr ratios were measured in the sites most and less affected by the contribution of the volcanic emissions, with median values of 0.704339 ± 0.000007 and 0.709583 ± 0.000007, respectively. Although exists few data of isotopic ratios of boron and strontium on fluids in volcanic systems (δ11B‰ between -9.3 to 21.4‰), there are no studies on rainwater influenced by volcanic emissions. Nevertheless, the data available in the literature are sufficient to attribute Etna's volcanic source as the major contributor to B and Sr emissions in the atmospheres of this area. The rainwater chemistry of the Zafferana Etnea site was partly influenced by the volcanic source, but the measured isotopic ratios at this site showed a strong contribution from the marine source. The results provide the first comprehensive study of B and Sr isotopes in Mt. Etna rainwater. Two main sources of atmospheric emissions of B and Sr were recognised: sea-salt aerosols and volcanic gases. This research also adds to the potential for the use of B and Sr isotopes as volcanic emissions contribution tracers.

Volcanic eruptions stand as formidable threats to adjacent communities, unleashing a spectrum of hazards such as earthquakes, tsunamis, pyroclastic flows, and toxic gases. The imperative for proactive management of volcanic risks cannot be overstated, particularly in densely populated areas where the potential for widespread devastation looms large. Kolumbo, an active submerged volcano located approximately 7 kilometers northeast of Santorini Island in Greece at 500m depth, serves a pertinent case. Its historical record is marred by an eruption in 1650 AD which triggered a relentless tsunami. The aftermath witnessed havoc on neighboring islands, coupled with casualties stemming from noxious gases in Santorini. Eyewitness accounts mention maximum water run-up heights of 20m on the southern coast of Ios, a staggering 240m inundation on Sikinos, and a disconcerting flooding of up to 2km² of land on the eastern coast of Santorini.Recent studies suggest that a potential future explosive eruption of Kolumbo poses a substantial hazard to the northern and eastern coasts of Santorini. Unfortunately, the absence of a concrete management protocol, leaves these areas vulnerable to an impending threat that demands immediate attention. Therefore, it is recommended that a comprehensive approach be adopted, involving scientific research (active monitoring, hazard maps), community engagement, preparedness planning with government agencies, and the development of timely response strategies to reduce the associated risks, prevent casualties, and mitigate the consequences on the region's economy and infrastructure. Our team has multidisciplinary data from past oceanographic expeditions that will help us to understand Kolumbo’s behavior. These include a) High-resolution multibeam bathymetry data and optical data., b) a dense network of sub-seafloor seismic reflection profiles, c) a series of the seafloor and sub-seafloor samples of microbial mat and sediments, d) CTD data, e) several polymetallic (Au, Ag, As, Sb, Pb, Hg, Mo, Zn, Cu, Tl) CO2 diffuser chimney samples and f) tephra in marine sediment cores. Despite the current knowledge that we managed to obtain, monitoring is needed to efficiently assess potential hazards and create early warning systems and management protocols for an imminent eruption from Kolumbo. In the current context, advanced sensors have been deployed to monitor Kolumbo's active hydrothermal field as part of the SANTORY project. The SANTORY project aims to create innovative communication tools and establish interregional monitoring protocols, providing the scientific community, policymakers, and stakeholders with the means to assess hazard warning codes effectively.

The underwater volcanic activity associated with deep-seated mantle processes represents a primary driver of the chemical and biogeochemical evolution of the global oceans. Hydrothermal activity is often a manifestation of submarine volcanism, where fluxes of heat and magmatic volatiles confer both potential hazard and opportunities of resource exploitation. Despite this, research on shallow submarine arc volcanoes is still in an early stage and only a few continuous seafloor observing infrastructures have been developed until now. The Kolumbo underwater volcano, located in the Aegean Sea, hosts one of the most active and dynamic hydrothermal vent fields, marking it - along with the proximity to the world-known Santorini island - a severe geohazard for a combination of reasons. Within the framework of the SANTORY (SANTORini’s seafloor volcanic observatorY) project, funded by the Hellenic Foundation for Research and Innovation and with the financial support of the Municipality of Thira, between 2022 and 2023, three oceanographic cruises were performed on submarine Kolumbo volcano. The oceanographic surveys were mainly aimed at the deployment of integrated operating sensors of state-of-the-art technology, for in situ monitoring. A new-generation stand-alone multiparametric observatory has been developed at INGV Palermo and deployed at the bottom of the crater (500 meters depth) for the first time in December 2022. The battery powered module has been able to operate autonomously for a 10-month-long period, collecting a dense, heterogeneous dataset able to describe the activity of the hydrothermal reservoir, highlighting its intense dynamic along the time.In June 2023, the observatory was recovered and re-deployed after brief maintenance operations including battery charging and data downloading. Finally, in October 2023, the observatory was definitely recovered.Here we present for the first time a mid-term-long chemical-physical data series acquired (pH, temperature, hydrostatic pressure, turbidity, conductivity, dissolved methane) along with passive acoustic and the preliminary findings of the system evolution within the observing window. A variety of local VT events likely sourced in the deeper portion of the plumbing system, together with several other minor seismic events related to fluid dynamics inside “fluid-filled” cracks and conduits has been revealed by passive acoustic data. Moreover the acoustic sensor recorded all the signals generated by the bubbles along the water column. The obtained results gave back an up to date picture of the ongoing Kolumbo degassing dynamics, hydrothermal and seismic activity.

Nyiragongo (D.R. Congo) is an active volcano known for its impressive persistent lava lake within its crater, and it is recognized as one of the most dangerous volcanoes in the world because more than two million people live on its slopes. Suddenly, on 22 May 2021, Nyiragongo produced three different lateral lava flows from the southern lower flanks, and significant amounts of volcanic gas and ash were emitted from the summit crater following the collapse of the crater floor. For a few weeks, the ash fallout impacted the main city of Goma and the numerous villages located in the vicinity of the volcano. 22 samples of volcanic ashes and 135 samples of drinking water (springs, rivers, rainwater, roof runoff) were collected before, during and after the eruption. From the leaching of the ashes and their direct observation through a field emission scanning electron microscope (FE-SEM), large quantities of soluble salts (e.g. sulphates, chlorides) on their surface were identified. The results showed that most of the drinking waters collected in the downwind villages (like Rusayo, Kingi, Sake) were heavily contaminated by volcanic emissions. In fact, fluoride, chloride, sulphur, and many potentially toxic elements (PTEs), including Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Pb, Sb, Se, Te, Tl, and V, exceeded the suggested World Health Organization (WHO) drinking water limits during the eruptive period, exposing the population living in villages downwind of the preferential direction of the volcanic plume, to high health risks.

In Palermo, (Sicily, Italy), a year-long study was conducted to analyse the chemical composition of atmospheric deposition samples. The research was carried out at four urban sites and one semi-rural site. The atmospheric deposition samples were analysed both for major ions and trace elements. Abundances of major ions, on meq L-1 basis, followed the sequence Cl- > HCO3- > NO3- > SO42- > F- > Br- for anions, and Na+ > Ca2+ > NH4+ > Mg2+ > K+ for cations. The statistical technique of Confirmatory Factor Analysis (CFA) was used to identify the main sources of origin of some of the main species and trace elements studied. Ions such as Cl-, Na+, Br and I were attributed to the marine source, whilst NH4+ and NO3- to the anthropogenic source, as well as Mo, Cd, Cu, As, Pb, Sb and V among the trace elements. On the other hand, Ca2+, K+, Li, Fe, Al, and Sr were mainly of crustal origin. The seawater fractions of Mg2+ and SO42- were of marine origin, whereas the non-seawater fractions of the same ions were of crustal and anthropogenic origin, respectively. Anthropogenic sources, such as internal-combustion vehicle, domestic heating, and plant emissions, must be considered for Cu, Cr, Ba, Mo, Sb, Zn, As, Ni, and V. This study produced a previously unpublished dataset on the chemical composition of atmospheric deposition that made it possible to identify the main sources influencing air quality in the metropolitan area of Palermo (Italy).

SANTORY is a state-of-the-art project dedicated to advancing submarine volcanic hazard monitoring and risk mitigation in the Aegean Sea. Located in Kolumbo submarine volcano, northeast of Santorini Island, this groundbreaking observatory employs advanced imaging, geophysical and geochemical measurements, and real-time monitoring technologies to address one of the most significant volcanic threats in the region.Over the past two years, SANTORY has provided unparalleled insights into Kolumbo’s geological dynamics and processes and potential hazards. High-resolution 3D mapping has identified steep slopes, mass-wasting deposits, and hydrothermal vent fields, crucial for assessing seafloor instability and the risks associated with eruptions and submarine landslides. Novel hyperspectral imaging and autonomous video systems have documented persistent hydrothermal venting, bubbling plumes, and environmental changes, offering a comprehensive baseline for tracking volcanic activity and geohazard precursors.Autonomous sensors on the crater floor have continuously monitored hydrothermal outflow temperature, pressure, and fluid chemistry, capturing variations driven by tides and magmatic activity. These continuous datasets are critical for identifying precursor signals of volcanic unrest, such as changes in subsurface permeability and magmatic degassing. Chemical and isotopic analyses of hydrothermal fluids have confirmed the degassing of CO2-rich fluids with a mantle-like 3He/4He signature, underscoring Kolumbo’s potential for hazardous eruptions and its significance as a high-risk volcanic system.SANTORY goes beyond scientific exploration; it is a transformative initiative aimed at improving volcanic hazard assessment and developing mitigation protocols. By integrating cutting-edge technologies and multidisciplinary expertise, the project delivers actionable insights to enhance early warning systems and protect vulnerable coastal communities.

Volcanoes are an important source of gas and particles into the atmosphere, during the eruptive periods or even during passive degassing activity. The study of volcanic gases is a robust geochemical tool to understand, monitor and predict the behaviour of volcano activity, but it is also important to evaluate the effects of volcanic emission on a local and regional scale. The study of the chemistry of atmospheric deposition can provide important information in this regard. Vulcano Island is a stratovolcano located in the southernmost sector of the Aeolian archipelago (Sicily). Since the last eruption occurred in 1888-1890, volcanic emissions are characterized by intense fumarolic activity localized on the northeastern rim of La Fossa crater. Several episodes of volcanic unrest have occurred over the past 130 years, and the most recent period of crisis was between 2021 and 2022. It was characterised by the increasing fumarole temperatures and gas fluxes, shallow long-period seismicity, and diffuse soil degassing around the main crater. This study reports on the chemical composition of rainwater samples collected from November 2021 to January 2023, during the last unrest period of Vulcano Island. Fifteen rainwater samples were collected through a network of three bulk collectors; two of them were placed inside the fumarolic field, and the last one was located near Vulcano Porto. Rainwater samples were analysed for major and trace element contents, and physicochemical parameters were also measured. The pH of rainwater collected near the summit area reaches very low pH values (min 1.63), with a mean value of 2.29, which is significantly lower respect to the mean value at Vulcano Porto (5.7). The concentrations of dissolved solutes in rainfall (expressed as Total Dissolved Solids) are inversely proportional to pH and reach extremely high values in the most acidic samples (up to 1133 mg/L). The most influenced samples by the volcanic emissions are strongly enriched in sulphate, chlorine and fluorine as a direct result of the dissolution of acid gases in rainwater. In addition to the major species, high concentrations of potentially toxic trace elements (Al, As, B, Cd, Fe, Pb, Sb, Te, Ti, Tl, and REE) were found. At the most distal site (Vulcano Porto) the impact of volcanic emissions on rainfall is much less pronounced and the dominant source is mainly related to marine aerosol. These preliminary results on trace element concentrations in rainfall at Vulcano highlight the importance of these studies to fully evaluate the potential impact of volcanic emissions on rainwater and consequently on other environmental matrices (e.g. soils and plants), especially during a period of intense outgassing.

The system of Domuyo Volcanic Complex is one of the most promising geothermal fields of Patagonia (Argentina). In this paper, we present a geochemical model of the Domuyo geothermal system based on previous studies and integrated with the systematic characterization of trace elements, thus adding a new piece to the puzzle of one of the most impressive geothermal systems in Argentina. A total of 38 water samples were collected from 17 different sampling sites, during three field-campaigns from 2013 to 2016, and analysed for 28 trace elements (Li, Be, B, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Y, Zr, Mo, Cd, Sb, Cs, Ba, Tl, Pb, Th and U). Sampling sites included the main river (Varvarco), its tributaries which cross the geothermal area, and thermal and cold springs. The investigation was focused on the origin, behaviour and estimation of mass fluxes of trace elements. Computing mass fluxes of trace elements transported by rivers is an important tool in the estimation of both the impact of potentially toxic elements and the exploitation of economically valuable elements. Among others, the mass fluxes of trace elements originating from the Domuyo geothermal system transported by rivers range from 45 to 278 t y(-1) for As, B, Cs, Li, Sr and Rb; such contributions flow to the Varvarco river, where the concentrations and mass fluxes of these elements increase by one to two orders of magnitude in the site downstream of the geothermal area with respect to that upstream.

This study explores the distribution of 16 trace elements between soluble and insoluble fractions of atmospheric deposition in Sicily, Italy, based on EU protocols for monitoring pollutants. Using a standardised deposimeter, we collected 149 atmospheric deposition samples over two years. Additionally, we analysed the rinse solution of the deposimeter separately. Higher deposition values for elements like Sr, B, Ba, Zn, As, and Cu were found in the soluble fraction, whereas Fe, Ti, Al, Cr, Co, Li, Mn, V, Ni, and Pb were prevalent in the insoluble fraction. The rinse fraction typically accounted for lower deposition values (from 1 % to 19 %), except for Pb and B, which accounted for 42 % and 31 % of the total deposition. We compared trace element distribution during a "dry period" and a "wet period." During the dry period, the insoluble fraction represented up to 97 % for elements like Ti and Fe, while the rinse fraction was notable for B (similar to 51 %) and Pb (similar to 33 %). In the wet period, insoluble contributions were higher for Li, Al, Ti, Cr, Fe, Co, and Pb, and soluble contributions increased for B, V, Mn, Zn, As, Sr, Ba, and Cu. While soluble elements were affected by temporal precipitation distribution, less soluble elements like Ti, Fe, and Al showed no significant differences between periods. Overall, the study highlights varying degrees of solubility among trace elements. Although the rinse fraction was generally negligible for most elements, overlooking it could lead to underestimating total atmospheric deposition for some elements, especially after extended dry periods.

Tectonic structures such as faults and fractures act as preferential pathways for gas ascent and their consequent release into the atmosphere. Magma-derived gases are widespread throughout the western Eger Rift (Czech Republic), an intraplate region without active volcanism but with the occurrence of mid-crustal earthquake swarms. Geogenic CO2 discharges from the Počatky–Plesná fault zone (PPZ), Mariánské Lázně Fault (MLF), Bad Brambach (BB), and a deep local fault (DLF) have been sampled since 2021. Gases were analysed for their chemical (CO2, N2, O2, Ar, He, CH4, and H2) and isotopic contents (noble gases, CO2, and CH4). Results showed that CO2 is the dominant gas species (concentrations > 99.4%), with the remaining gases being present in minor amounts. The He isotopic composition for gas samples from the PPZ and MLF is typical for the subcontinental lithospheric mantle (SCLM - with 3He/4He ratios between 5 and 6 RA), while gases from BB and the DLF show a lower mantle input (3He/4He is 3.2 and 2.4 RA, respectively). δ13CCO2 data reflect a SCLM CO2 signature (-4 to -1 ‰ vs. V-PDB). First CH4 isotopic data present values between -52.0 and -47.1 ‰ vs. V-PDB for δ13CCH4 and between -307 and -284 ‰ vs. V-SMOW for δ2HCH4. With the exception of samples collected from the MLF that show a clear thermogenic CH4 origin, all the other samples present isotopic values and CH4/(C2H6+C3H8) ratios that suggest a likely biogenic origin, with secondary processes playing a crucial role on the gases’ isotopic signature. It should be noted that low CH4concentrations (

Santorini Island (Greece) is an active volcano which has alternated between dormant and active periods over the last 650,000 years with the latest volcanic unrest occurring in 2011–2012. Here we report a geochemical survey of fumarolic gases collected at Nea Kameni islet located in the center of the caldera over the period 2015–2022 in order to study the activity of the volcano and changes in hydrothermal conditions. This period is marked by the absence of significant geochemical anomalies compared to the unrest of 2011–2012, implying that no new magma upwelling has occurred. This is evident from the low CO2/CH4 ratio and H2 concentration of fumaroles. An increase of the atmospheric contribution in gases after the 2011–2012 unrest suggests a decrease of the deep gas flow and the chemical and C-He-isotope compositions are compatible with a model of Rayleigh fractionation in which CO2 dissolves in water at decreasing temperatures over time. These results are consistent with temperature estimates obtained using the H2/N2 geothermometer, seismic and geodetic evidences. This implies a slowing of the degassing of the hydrothermal/volcanic system and a cooling of the magma injected at shallow depth in 2011–2012. All these conclusions support a quiescent state of the Santorini volcano over the period 2015–2022.

This study presents the first data on REY (Rare Earth Elements plus Yttrium) in the aquifer of Mount Etna (Sicily, Italy). Patterns normalized to chondrites indicate strong water–rock interaction, facilitated by a slightly acidic pH resulting from the dissolution of magma-derived CO2. REY patterns provide insights into the processes of both mineral dissolution and the formation of secondary phases. The relative abundance of light to heavy rare earth elements is compatible with the prevailing dissolution of ferromagnesian minerals (e.g., olivine or clinopyroxenes), reinforced by its strong correlation with other proxies of mineral dissolution (e.g., Mg contents). Pronounced negative Ce anomalies and positive Y anomalies demonstrate an oxidizing environment with continuous formation of secondary iron and/or manganese oxides and hydroxides. The Y/Ho fractionation is strongly influenced by metal complexation with bicarbonate complexes, a common process in C-rich waters. In the studied system, the measured REY contents are always below the limits proposed by Sneller et al. (2000, RIVM report, Issue 601,501, p. 66) for surface water and ensure a very low daily intake from drinking water.

Natural thermal and mineral waters are widely distributed along the Hellenic region and are related to the geodynamic regime of the country. The diverse lithological and tectonic settings they are found in reflect the great variability in their chemical and isotopic composition. The current study presents 276 (published and unpublished) trace element water data and discusses the sources and processes affecting the water by taking into consideration the framework of their geographic distribution. The dataset is divided in groups using temperature- and pH-related criteria. Results yield a wide range of concentrations, often related to the solubility properties of the individual elements and the factors impacting them (i.e. temperature, acidity, redox conditions and salinity). Many elements (e.g. alkalis, Ti, Sr, As and Tl) present a good correlation with temperature, which is in cases impacted by water rock interactions, while others (e.g. Be, Al, Cu, Se, Cd) exhibit either no relation or an inverse correlation with T possibly because they become oversaturated at higher temperatures in solid phases. A moderately constant inverse correlation is noticed for the vast majority of trace elements and pH, whereas no relationship between trace element concentrations and Eh was found. Seawater contamination and water-rock interaction seem to be the main natural processes that influence both salinity and elemental content. All in all, Greek thermomineral waters exceed occasionally the accepted limits representing in such cases serious harm to the environment and probably indirectly (through the water cycle) to human health.

The concentrations of trace elements in atmospheric bulk depositions (wet plus dry) were investigated from two highly industrialised areas of Sicily (southern Italy) from June 2018 to July 2019, in order to recognise the main natural and anthropogenic sources. A side objective of this study was to improve the common sampling procedures and analytical methods used for monitoring trace elements in atmospheric deposition. The trace element VWM (Volume-Weighted Mean) concentrations ranged from less than 0.01 μg L−1 for trace elements such as Cs, Tl, and U, up to 24 μg L−1 for minor elements (Al, Zn, Sr), in the filtered aliquot, while they reached concentrations up to 144 μg L−1 for the same elements, in the unfiltered aliquot. Therefore, significant differences in concentrations between these two aliquots were found, particularly for Al, Fe, Ti, Zn, Cr, Pb, Se, Cs, and U. This implies that filtering operations may produce a consistent underestimation of concentrations of certain ‘constituents’ of the atmospheric deposition. Natural (marine spray, local and regional geogenic input, volcanic emanations) and anthropogenic sources (industrial emissions, auto vehicular traffic, and diffuse background pollution) which influence rainwater chemistry were identified. Enrichment factors (EFs), with respect to the upper crust composition, provided clear evidence of the different sources above mentioned: Ti, Fe, Al, Cs, Cr, Rb, and Co have low EFs (<1), and are referable to the (local and/or regional) geogenic input, while Se, Sb, Zn, B, Cd, Cu, Mo, Sr, As, with high EFs (>10), highlight the influence of marine and/or industrial sources. The study produced a novel dataset on the atmospheric deposition rate of several trace elements, which had never been studied in the investigated areas. Finally, a comparison of trace element deposition rates in the studied areas with the atmospheric deposition reported for 53 different sites, belonging to 20 different European nations, was made. The comparison showed that some elements, such as Al, V, Zn, and Mo had higher median deposition fluxes in the Sicilian sites than in European monitoring sites.

The Caviahue-Copahue Volcanic Complex is one of the most studied active volcanic systems in the South American Andean range, and yet little research has focused on trace and rare-earth elements of waters, especially during an eruptive cycle. In this study, we sampled and investigated natural waters from 23 sites (involving the crater lake, hot springs, streams, rivers, and bubbling pools) in two campaigns in 2017 and 2018, using physicochemical parameters, major, trace and rare-earth elements concentrations. With this novel dataset, it was possible to identify, characterize and compare three groups of waters with distinctive hydrofacies. Indeed, the normalization of water compositions against host rock concentrations showed a particular trace element pattern for each group of waters. Although the absolute concentrations of the elements in each sampling site changed from 2017 to 2018, the normalized patterns did not. Boron, As, Cd, Tl, Se, and Te, commonly recognized as volatile, are the main trace elements that magmatic gases supply to the system headwaters, whereas elements such as Ca, K, and Ba are affected by precipitation of secondary minerals (gypsum, anhydrite, barite, jarosite, and alunite). Furthermore, the main river draining the summit volcano shows a steep decrease in As, Cr, and V concentrations correlated to the precipitation of Fe and Al hydroxysulfates (schwertmannite and basaluminite, respectively). Moreover, it is the first time that a comparison between the different water groups is made using the patterns of the rare-earth elements, allowing us to identify and separate depletion patterns due to dilution processes from those due to precipitation processes.