The aquatic geochemistry of arsenic in volcanic groundwaters from southern Italy |
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| Institution: | 1. DiSTeM, Università di Palermo, Via Archirafi 36, 90123 Palermo, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy;3. Dipartimento di Scienze dell''Ambiente e della Terra, Università di Milano Bicocca, Piazza della Scienza 4, 20126 Milano, Italy;4. Instituto Tecnológico y de Energías Renovables, S.A. (ITER, S.A.), Granadilla de Abona, Tenerife, Canary Islands, Spain;5. Instituto Volcanológico de Canarias (INVOLCAN), San Cristóbal de La Laguna, Tenerife, Canary Islands, Spain;1. Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria, 53, 56126 Pisa, Italy;2. Dipartimento di Scienze della Terra, Università di Firenze, via La Pira, 4, 50121 Firenze, Italy;3. School of Earth Sciences, University of Bristol, BS8 1RJ Bristol, United Kingdom;1. Dipartimento di Scienze della Terra, Università di Firenze, Via G. La Pira 4, 50121 Firenze, Italy;2. Istituto di Geoscienze e Georisorse (IGG), Consiglio Nazionale delle Ricerche (CNR), Via G. La Pira 4, 50121 Firenze, Italy;3. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione Palermo, Via Ugo La Malfa 153, 90146 Palermo, Italy;4. Dipartimento di Scienze Biologiche, Geologiche ed Ambientali, Università di Bologna, Porta S. Donato 1, 40127 Bologna, Italy;1. Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania – Osservatorio Etneo, P.zza Roma 2, 95123 Catania, Italy;2. Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Napoli - Osservatorio Vesuviano, Via Diocleziano, 328, 80124 Napoli, Italy |
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| Abstract: | This paper discusses the abundance, speciation and mobility of As in groundwater systems from active volcanic areas in Italy. Using literature data and new additional determinations, the main geochemical processes controlling the fate of As during gas–water–rock interaction in these systems are examined. Arsenic concentrations in the fluids range from 0.1 to 6940 μg/l, with wide differences observed among the different volcanoes and within each area. The dependence of As content on water temperature, pH, redox potential and major ions is investigated. Results demonstrate that As concentrations are highest where active hydrothermal circulation takes place at shallow levels, i.e. at Vulcano Island and the Phlegrean Fields. In both areas the dissolution of As-bearing sulphides is likely to be the main source of As. Mature Cl-rich groundwaters, representative of the discharge from the deep thermal reservoirs, are typically enriched in As with respect to SO4-rich “steam heated groundwaters”. In the HCO3? groundwaters recovered at Vesuvius and Etna, aqueous As cycling is limited by the absence of high-temperature interactions and by high-Fe content of the host rocks, resulting in oxidative As adsorption. Thermodynamic modelling suggests that reducing H2S-rich groundwaters are in equilibrium with realgar, whereas in oxidising environments over-saturation with respect to Fe oxy-hydroxides is indicated. Under these oxidising conditions, As solubility decreases controlled by As co-precipitation with, or adsorption on, Fe oxy-hydroxides. Consistent with thermodynamic considerations, As mobility in the studied areas is enhanced in intermediate redox environments, where both sulphides and Fe hydroxides are unstable. |
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