Signorini, Linda (2026) Green Barriers as Nature-Based Solutions and Soilless Systems for Reducing Human Exposure to Environmental Contaminants in Urban Areas. [Tesi di dottorato]

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Abstract

Urbanization and intensive agriculture have increased human and environmental exposure to multiple forms of anthropogenic pollution, including airborne particulate matter, airborne microplastics, and soil contamination by potentially toxic elements. This thesis investigates strategies to reduce contaminant exposure in urban and agricultural systems, focusing on mitigation approaches tailored to the specific environmental context and dominant exposure pathways. In urban environments, Nature-based Solutions (NbS) in the form of multi-species green barriers composed of Platanus × hispanica and Nerium oleander were evaluated over two years for their capacity to reduce airborne particulate matter. A combination of leaf biomonitoring, washing experiments, and real-time particle number measurements across different particle size fractions was used to assess barrier performance. Particulate matter concentrations were higher and more variable at street locations than in the urban park, while foliar analyses revealed the accumulation of traffic-related metals, confirming the filtering role of vegetation. Seasonal biomonitoring indicated reduced interception efficiency during autumn, associated with leaf senescence and surface saturation. Species-specific patterns emerged, with Nerium oleander showing higher metal accumulation under drier conditions and Platanus × hispanica exhibiting greater particle retention during wetter periods, highlighting the influence of species-specific leaf traits and canopy structure on particulate matter interception. The same green infrastructure was also investigated for its capacity to retain airborne microplastics (AMPs). Vertical sampling revealed that retention varied with both particle shape and canopy height: fibers were retained more efficiently at higher canopy levels, whereas fragments showed greater retention at lower heights. Overall, reductions of up to approximately 50% in AMP abundance were observed between positions inside and outside the barriers. Polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE) were identified as the dominant polymers. The observed retention patterns further highlighted the role of barrier design and canopy architecture in mitigating airborne microplastic dispersion in densely trafficked urban areas. In agricultural settings affected by soil contamination by potentially toxic elements, sustainable soilless cultivation systems were investigated as a strategy to maintain crop productivity while preventing contaminant uptake. Lemon basil (Ocimum × citriodorum) was cultivated in two sequential experiments comparing growing substrates and nutrient solution management. Coconut fiber–perlite mixtures enhanced germination and early growth compared to rock wool, while decoupled aquaponic nutrient solutions increased flavonoid content and improved calcium and magnesium uptake relative to hydroponics. These results demonstrate that soilless cultivation can effectively decouple crop production from contaminated soils, supporting food safety, crop quality, and resource-efficient agricultural practices. Overall, this thesis highlights how context-specific interventions can mitigate human exposure to anthropogenic contamination. Urban multi-species green barriers demonstrate how species selection and canopy structure can be leveraged to modulate the interception of airborne pollutants and microplastics. At the same time, soilless cultivation systems enable the safe production of crops on contaminated soils using optimized substrates and recycled nutrient solutions.

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