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659 water samples from springs and wells in the Sabatini and Vicano-Cimino Volcanic Districts (central Italy) were analyzed for arsenic (As), fluoride (F−) and radon (222Rn) concentrations. Waters mostly sourced from a shallow and cold aquifer hosted within volcanic rocks, which represents the main public drinking water supply. Cold waters from perched aquifers within sedimentary formations and thermal waters related to a deep hydrothermal reservoir were also analyzed. The highest concentrations of As and F− were measured in the thermal waters and attributed to their enhanced mobility during water-rock interaction processes at hydrothermal temperatures. Relatively high concentrations of As and F− were also recorded in those springs and wells discharging from the volcanic aquifer, whereas waters hosted in the sedimentary units showed significantly lower contents. About 60% (As) and 25% (F−) of cold waters from the volcanic aquifer exceeded the maximum allowable concentrations for human consumption. Such anomalously high levels of geogenic pollutants were caused by mixing with fluids upwelling through faulted zones from the hydrothermal reservoir. Chemical weathering of volcanic rocks and groundwater flow path were also considered to contribute to the observed concentrations. Cold waters from the volcanic aquifer showed the highest 222Rn concentrations, resulting from the high contents of Rn-generating radionuclides in the volcanic units. Approximately 22% of these waters exceeded the recommended value for human consumption. A specific Quality Index (QI), comprised between 1 (very low) and 4 (very high), was computed for each water on the basis of As, F− and 222Rn concentrations and visualized through a spatial distribution map processed by means of geostatistical techniques. This map and the specific As, F− and 222Rn maps can be regarded as useful tools for water management by local authorities to both improve intervention plans in contaminated sectors and identify new water resources suitable for human consumption. Image 1 • Volcanic-sedimentary aquifers from Central Italy were analyzed for As, F− and 222Rn. • Water-rock interaction and input of thermal fluids are sources of geogenic pollutants. • High contents of geogenic pollutants were pertaining to the volcanic aquifers. • Quality Indexes (QIs) were obtained by combining the As, F− and 222Rn concentrations. • QI distribution maps can be used for water management in geogenically polluted areas. Spatial distribution maps of geogenic pollutants (As, F− and 222Rn) and quality indexes for water resources were determined in volcanic-sedimentary aquifers of central Italy for water management. [ABSTRACT FROM AUTHOR]

In a volcanic-sedimentary aquifer in central Italy, we investigate the co-existence of arsenic and fluoride in groundwater, aiming at identifying the most probable processes deductible at regional/groundwater body scale leading to the observed co-contamination in groundwater. Further, the areas at risk for human health where high concentrations can produce a significant risk to human health have been investigated. The study area is located in Latium (Central Italy) where silica-undersaturated alkali-potassic formations of Plio-Pleistocene age largely outcrop above marine and continental sand and clay deposits (Neogene) and continental alluvial deposits (Lower Pleistocene–Middle Pleistocene). Geochemical data from groundwater at 322 wells and 76 springs have been analyzed through statistical methods including clustering/PCA and geostatistical analysis. The results show exceedances of the drinking water standards for F (1.5 mg/L) and As (10.0 μg/L) in 29% and 55% of the sampled groundwater, respectively. Multivariate statistics suggest a widespread process of water-rock interaction with the K-alkaline volcanic formations releasing As, F, K, Si, V, Rb and PO 4 to the groundwater. As and F show a good correlation (Pearson's r = 0.61, Spearman's r s = 0.59) and define a separate PCA component, confirming that their background in groundwater might be governed by a common process. Kriging interpolations have been used to study the spatial distribution of the two parameters, identifying areas with the highest concentrations and highest probability of exceeding the standards for human consumption. Moreover, by resampling the As-F data with the jackknife technique it was possible to identify the variations of their correlation index in the study area, due to specific As or F anomalies. While in the peripheral areas of the volcanic districts, dominated by sedimentary deposits, the As-F correlation index does not present important fluctuations, Indicator Kriging shows specific As or F correlation anomalies within the volcanic groundwater bodies and along the Tyrrhenian coastline. These anomalies seem to correspond to the zones with the highest thermal flux and/or are located near important structural lineaments. Fluoride correlation anomalies close to mining sites (fluorite) have also been observed. We hypothesize that, unlike the regional co-contamination, these local anomalies are related to the upwelling of geothermal fluids along fracture/fault systems that mix with cold groundwater, or to the interaction with mineral deposits particularly enriched of these elements. • Arsenic-fluoride correlation in a volcanic-sedimentary aquifer in Italy is analyzed. • Water-rock interaction produces the As-F background and maintains their correlation. • Anomalies appear linked to interaction with geothermal fluids and/or mineral deposits. • Indicator kriging indicates the most suitable areas for drinking water exploitation. [ABSTRACT FROM AUTHOR]

This study explores the co-existence of arsenic and fluoride in a volcanic-sedimentary aquifer in central Italy, aiming at identifying the risk areas for human health and the most likely processes deductible at regional/groundwater body scale leading to the observed co-contamination in groundwater.The study area is located in Latium (Central Italy) where undersaturated alkali-potassic formations largely outcrop, belonging to three different volcanic apparatus of Plio-Pleistocene age.Geochemical data from groundwater at 398 wells or springs are analyzed through statistical methods including clustering/PCA and geostatistical analysis. 29% of the sampled groundwaters exceeds the drinking water standard for F (1.5 mg/L), while 55% exceeds that for As (10.0 µg/L). Multivariate statistics suggest a widespread process of water-rock interaction with the K-alkaline volcanic formations releasing As, F, K, Si, V, Rb and PO4 to the groundwater. As and F show a good correlation (Pearson's r = 0.61) and define a separate component, suggesting that their background in groundwater might be governed by a common process.While in the peripheral areas of the volcanic districts, dominated by sedimentary deposits, the As-F correlation index does not present important fluctuations, Indicator Kriging shows specific As or F anomalies within the volcanic groundwater bodies and along the Tyrrhenian coastline. These anomalies seem to correspond to the zones with the highest thermal flux and/or are located near important structural lineaments. Fluoride anomalies close to mining sites (fluorite) have also been observed. We hypothesize that, unlike the regional co-contamination, these local anomalies are related to the upwelling of geothermal fluids along fracture/fault systems that mix with cold groundwater, or to the interaction with mineral deposits particularly enriched of these elements. [ABSTRACT FROM AUTHOR]

Excess of arsenic in groundwater is a worldwide problem threatening the health of the millions of people directly exposed to As-rich water intake. The problem is particularly acute in naturally occurring unconsolidated aquifers where As-rich groundwater is an easily accessible resource of drinking water, such as in India, Bangladesh and Vietnam. Naturally occurring high concentrations of As in groundwater also notoriously mark the Venetian Alluvial Plain (VAP) in Italy, affecting in particular the shallower aquifers. The VAP is characterized by a patchy As distribution with variable extensions and concentrations. Although empirical evidences exist about the relationship between As occurrence and other factors, several aspects regarding the physical and geochemical processes controlling As in the VAP aquifers remain unclear. This study aims to elucidate the geochemical conditions that control As mobilization in the VAP, in order to improve the knowledge about As-controlling processes in the study area and use them as a proxy to evaluate occurrence of As in other world regions characterized by a similar hydrogeological and geochemical settings, such as the Bengal Delta Plain. To this end, we focused in detail on an agricultural zone nearby the Venice lagoon, affected by As contamination (called "Aree Agricole West", AAW). The available data, collected by several hydrogeological surveys, show a spatial and temporal variability of As concentration, which can be associated to a variety of hydro-geochemical processes such as redox variations, sorption or reductive dissolution of As-rich iron oxy-hydroxides. In order to point out the consistency and the importance of these processes, we combined an advance exploration analysis with a PHREEQC 0D reactive model. The former part, performed by mean of Self-Organized Maps (SOM) algorithm, allows for identification of the main geochemical relationships within the study aquifer and the associated geochemical processes. The latter, instead, allows us for testing whether the supposed processes are able to fit the geochemical conditions of the study system. The results highlighted a strong effect of oxy-reductive potential on arsenic mobility, and it seems to be strictly correlated to organic matter degradation. The uprising of reduced condition, then, affects other mechanism such as reductive dissolution of iron hydroxides, ion exchange and sorption processes, causing arsenic mobilization. Moreover, this study shaded light on the existence of oxygen ingress as function of local water recharge events, which seems to be responsible of space/time redox variation. Thanks to the 0D model, it was possible to explain, in a semi-quantitative way, the effect of the oxygen ingress on the redox aquifer condition, and so to explain the arsenic variation. This study has to be intended as a first step toward a more detailed study, which will account for a 2D/3D reactive transport model aiming at elucidating arsenic mobility, including influence of recharge due to agricultural activities. [ABSTRACT FROM AUTHOR]