Aruta, Antonio (2022) Development of new methods for the geospatial analysis of geochemical data for the assessment and prioritization of environmental risk at local and regional levels in areas with significant anthropogenic pressure. [Tesi di dottorato]

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This thesis explains the results of environmental geochemistry studies at local and regional scales. The main focus has been determining the distribution of potentially toxic elements in the environment, understanding the probable sources and assessing their health impact on the exposed population. Briefly, the data were analyzed with classical methodologies, compositional data analysis, spatial analysis (such as multifractal and probabilistic methods) and stochastic human health risk modelling. The entire activity was divided into three main phases concerning the assessment of the risk associated with environmental exposure in Naples (Italy), Santiago (Chile) and Yerevan (Armenia). The cities are in different geographical contexts, but they share similar urban and structural characteristics with a high degree of urbanization and continuously changing land-use patterns. Regarding the study on Santiago city, the geochemistry of urban soils is regulated by both natural and anthropic factors. The effort to consider the degree and complexity of contamination at the urban scale generated significant results. Multivariate analysis (PCA) following data transformation (to consider the compositional nature of the dataset) enabled discrimination of geochemical sources. The isometric log-ratio coordinates, generated by considering the principal component influencing the widest fraction of total variability, revealed the existence of secondary contamination processes that are normally difficult to constrain. Finally, the results of stochastic human health risk analysis showed that adults and children are exposed to different levels of risk. Ingestion represents an important exposure pathway for children, especially for non-carcinogenic adverse effects to some organs such as kidneys. In Yerevan city, multifractal and spectral separation techniques were implemented for the first time to determine background/baseline values for non-strictly geochemical data. The applied methods did not fail in the aim of spatially defining the distribution of background/baseline values of both NORs and technogenic Cs-137 and provide a valuable tool to assess the impact of future diffuse contaminating events or local processes (i.e., quarrying/mining activity) in the study area. Furthermore, the stochastic assessment of the ELCR provides valuable information, including in the uncertainty process. Regarding the study in Naples, the spatial distribution maps of the ambient equivalent dose rate at different altitudes are useful to understand where to intervene to reduce exposure to low-level ionizing radiation due to the activity of natural or artificial materials. Empirical Bayesian Kriging seems to be an effective interpolation method because it facilitates the understanding and analysis of the data. Areas where the road pavement is covered with non-geological material, have lower ADER values. This appears to be a demonstration that in general, the use of non-geological materials in road pavements can reduce exposure to the gamma dose produced by the materials of other origins. As demonstrated in this study, other materials of geological origin (e.g., Etnean material) can also reduce the risk. However, the choice of material should be made following a study aimed at identifying the background value of the environmental equivalent dose. The ELCR values estimated in this study were found to be relatively high, both for the outdoor and indoor evaluation, always exceeding the world average reference value (2.9E-04).

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