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University of the Aegena (2016)

Arsenic des nappes phréatiques de l’île de Lesbos : formes chimiques, conditions hydrogéologiques, facteurs physico-chimiques

Ζκέρη, Ειρήνη

Titre : Arsenic des nappes phréatiques de l’île de Lesbos : formes chimiques, conditions hydrogéologiques, facteurs physico-chimiques

Αρσενικό στα υπόγεια ύδατα στη νήσο Λέσβο : χημικές μορφές, υδρογεωλογικές συνθήκες, φυσικοχημικοί παράγοντες

Auteur : Ζκέρη, Ειρήνη

Etablissement de soutenance : University of the Aegena

Grade : Doctor of Philosophy (PhD) 2016

Résumé partiel
Arsenic (As) is a ubiquitous element in the earths crust known since antiquity for its toxicity on humans. Because of its high mobility under different geochemical conditions, groundwater concentrations of As in many areas around the world were found to exceed the legislation limits of 10 μg/L. It is estimated that millions of people around the world are exposed to water consumption with high As concentrations, where the most serious poisoning problems occur in Asia (Bangladesh and India) and in Latin America. Due to the intensity of the phenomenon, scientific research has primarily focused on those areas. This thesis explores the problem of elevated As in groundwater in a completely different geological setting, that of the Lesvos island, where high As concentrations in groundwater (exceeding the limit of 10 μg/L) occur mainly in acidic volcanic rock areas, where the Mediterranean climate, the volcanic substrate and the relatively high relief form a set of environmental conditions under which the geochemistry of As is poorly understood. In the international literature the investigations of the geochemistry of As in areas with volcanic rocks are focused on areas in Latin America, especially in Argentina, a region that differs from the study area of this thesis in terms of climatic conditions, topography and hydrogeology. Furthermore, the seasonal variation of As concentrations in groundwater and the investigation of the factors that lead to temporal changes, although they have received more attention recently, they focus on Indian sites and Bangladesh. There are only few studies in areas with volcanic rocks which often only indicate the existence or not of seasonal changes. It is clear that the exploration of the factors that influence and lead to these variations, will enhance the existing knowledge on this important problem. The main objectives of this thesis are to a) record the spatial distribution of As in groundwater of Lesvos island, b) explain the processes and the mechanisms responsible for As release in groundwater from selected areas of Lesvos, where high As concentrations were observed in groundwater, c) investigate the factors and mechanisms that contribute to the seasonal variation of the element in the groundwater, and d) to explore and propose possible management practices so as to address the problem with optimal risk - cost - benefit relationship. Groundwater from two different geological regions (volcanic and metamorphic) on Lesvos Island was examined in order to explore the processes responsible for As occurrence and release in groundwater. A total of seven sampling campaigns were conducted between October 2010 and October 2011 at 2 month intervals, including 65 samples from wells and springs from two study areas : a) the volcanic area of Mandamados and b) the metamorphic area of Tarti. The concentrations of As exceeded the 10 μg/L limit in 46% of the samples collected from the volcanic area of Mandamados (67% and 31% for the coastal wells and the inland wells, respectively), whereas all waters from the metamorphic area of Tarti were below this limit. The predominant As species was As(V), indicating that As is mobilized under oxidizing conditions. In Mandamados, where the major concern about public health regarding As stems, silicate weathering and ion exchange due to increased EC have been identified as factors of major importance in enhancing As mobility in groundwater

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