Ebrahimi, Pooria (2022) Geochemical study of different environmental media for characterization of the hydrothermal system and the subaerial environment of Phlegrean Fields, and the surrounding areas. [Tesi di dottorato]

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The Phlegrean Fields are located in southern Italy and the latest volcanic eruption in this area goes back to 1538 CE. In the last decades, the bradysismic crises were sometimes followed by evacuation orders from the authorities to manage an emergency. On the other hand, the study area is highly populated and urbanization, industries together with agricultural practices may pose a threat to the ecosystem and human health. The main objective of this thesis is to use some recently developed data treatment approaches (i.e. compositional data analysis and spatial analysis) for highlighting the dominant processes controlling geochemical composition of different environmental compartments. The groundwater samples could be categorized in four groups: (1) the bicarbonate-rich groundwater mainly derived from poor-arsenic meteoric water; (2) the chlorine-rich groundwater with significant thermal/seawater contribution; (3) the sulfate-rich groundwater generated by the interaction of bicarbonate-rich groundwater and hydrothermal vapors around Solfatara volcano; and (4) the mixed groundwater observed where the three groundwater groups undergo a mixing process. Based on another prospecting campaign for determination of the dissolved radon and carbon dioxide (in addition to the major ions, lithium, arsenic, boron and physicochemical parameters), two geochemical associations are identified using multivariate statistics: (1) Ca^(2+), Mg^(2+), K^+, SO_4^(2-), HCO_3^-+CO_2 and pH; and (2) Na^+, Cl^-, As, B, Li, Rn, TDS and T. It highlights that the groundwater composition is generally influenced by: (1) meteoric water, which is modified by the CO2‒rich magmatic gas in some cases; and (2) hydrothermal fluid and/or seawater. Regarding Naples tap water, seasonal variation is observed in chemistry of the water exploited from the nearby aquifers and well fields. It stresses the importance of interconnections between urban water reservoirs for adjusting water quality, being complicated in cities like Naples with an old distribution network. Thus, the compositional nature of data is considered in hierarchical clustering to study water transfer between urban water reservoirs. The proposed method potentially defined the source of tap water in each city area based on chemical data and provided an overview of the relationships between different components of the network for encouraging advanced simulations. The eastern sector of Pozzuoli Bay is divided into the proximal and distal zones for conducting research on the spatial distribution and source of elements in the marine sediment. In front of the former industrial site (i.e. the proximal zone), Hg, Cd, Cu, Pb and Zn are positively correlated with mud and organic matter. Concentrations of these metals decrease along the cores and in the distal zone. Nevertheless, Al, As, V, Fe, Cr, Ni and sand form an association along the coast which strengthens with increasing distance from fumaroles in the proximal zone. It suggests that the pyroclastic deposits of Phlegrean Fields and some of the seepages with a hydrothermal component are related to this group of elements. Soil geochemistry indicates that higher Pb, Zn, Cd, Cr, Hg, Ni and Sb levels correspond to the urban area, but greater As, Tl, Co, Cu, Se and V quantities occur in other parts of the study area. The Pb‒Zn‒Hg‒Cd‒Sb‒Cr‒Ni association probably highlights anthropogenic activities in the urbanized area while the Al‒Fe‒Mn‒Ti‒Tl‒V‒Co‒As‒U‒Th association mostly reveals the contribution of pyroclastic deposits. The Na‒K‒B association feasibly indicates the weathering degree, being lower in the Neapolitan Yellow Tuff caldera. The probabilistic health risk assessment for the children under 6 years old shows negligible non-carcinogenic risk for exposure to Pb and Zn through soil ingestion (certainty > 95%). Unexpected Pb carcinogenic risk through the ingestion route is detected for all age groups (CR ≤ 1E-06 with above 99% certainty). However, for the inhalation pathway, there is a 90% chance of acceptable (i.e. between 1E-6 and 1E-4) Pb carcinogenic health risk for the children aged <1 year old and a 25-45% chance for those between 1 and 6 years old. Overall, the underground water is mainly influenced by the hyrothermal system although the sediment and soil geochemistry is affected by both natural and anthropogenic activities. The effectiveness of compositional data analysis for investigating groundwater hydrogeochemistry in the volcanic aquifer of Phlegrean Fields indicates that this technique deserves further attention for developing new tools and identifying promising precursors of volcanic eruption worldwide. The number of magnetic resonance imaging centers administering contrast agents for diagnostic imaging in the study area highlights that gadolinium contamination in water resources is a question to be answered in Phlegrean Field and the immediate surroundings. This line of research might also be advantageous in hydrogeological studies. Considering the environmental aspects, the results in this thesis should not be overlooked because Naples is a heavily populated metropolis under high environmental pressure and previous studies reported the increased Pb and Zn in soil over a 26-year timespan. In addition, the Bagnoli industrial site is still a source of pollution. Implementing a combination of spatial analysis, multifractal analysis, compositional data analysis and probabilistic health risk modeling helped to characterize the environmental status in detail.

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