Geogenic vs. Anthropogenic distribution of inorganic substances in environmental pollution: Case Histories by Tuscany sites

This PhD research project were focused on selected Case Histories regarding environmental pollution linked to inorganic substances in groundwater, soil and sediment of some Tuscany sites. Among the several case studies addressed during the PhD research, this work reports the most significant for scientific community. Cap.1 investigates serpentine soils and derived sediments from coastal Tuscany, far from anthropogenic pollution, that show high concentrations of geogenic Cr and Ni. The objective of cap.2 was to evaluate, using chemical Selective Sequential Extraction (SSE): a) The distribution of Cr and Ni in the geochemical phases containing Fe and Mn; b) the role of Fe and Mn oxides (crystalline and not-crystalline) into redox processes which lead to the formation of Cr (VI) during the serpentine soils weathering; c) the definition of a test for identify the potential risk of release of Cr (VI) in groundwater from serpentine and derived geomaterials. The mobility of Cr and Ni is related to their association with mineral phases easily weathered in the environment. Particularly, the Fe/Mn hydroxides, produced by the weathering of serpentinites, could be enriched by Cr and Ni that could be released in the environment by weakly acid solution or system with high redox potential. Data discussed in cap.3 point to a natural origin of Cr(VI), which likely derives from the interaction of rainwater with a mineral assemblage (mainly chlorite group) containing serpentinite rocks and/or their fragments. In cap.4 the Possera Creek basin and a stretch of the middle course of the Cecina River has been investigated in order to provide a sediment (alluvial deposits) quality characterization of these watercourses and to assess the spatial distribution of As, B, Hg and other metals of environmental relevance. Sediment samples from alluvial deposits of Possera creek, downstream of Larderello area show a distribution consistent with an overlap of antrophogenic and geogenic pollution. In cap.5 the pollution of mine deposits of Mt.Arsiccio and Valdicastello (Baccatoio basin, Alpi Apuane) were investigated and the contributions of the acid mine drainage (AMD) sources to the pollution load of groundwater, freshwater and stream sediments of Baccatoio Creek were determined. The dispersion of heavy metals associated with the primary mineralization has been traced through physical and chemical weathering and production of AMD, producing secondary dispersion into stream sediments, groundwater and surface water. In Cap.6 are reported the result of environmental characterization of surface and subsurface waters in the Pisan coastal plain. The investigations provide insights into the inland flow of seawater via surface water through the hydrographic network. Especially during the dry season, this flow leads to the loss of the hydrodynamic surface equilibrium between the groundwater table and the seawater level in surface water. This causes widespread salinisation of the phreatic aquifer starting from the hydrographic network, which carries seawater towards the inland plain.