Urban multifunctional Nature-based Solutions (NbS). A combined nano-assisted phytoremediation approach

Urban soil contamination by metal(loid)s represents a significant challenge for the development of resilient and sustainable cities. In this context, Nature-based Solutions (NbS) are increasingly recognized as multifunctional strategies that can address environmental issues while providing ecological and societal co-benefits. Among these, phytoremediation is a well-established, environmentally friendly, and cost-effective solution for soil decontamination. Nevertheless, its application in urban settings remains limited due to a lack of public acceptance, which is closely associated with the demand for aesthetic landscape enhancement during the remediation process. Furthermore, its efficiency in urban environments is frequently limited by slow plant growth, low biomass production, and metal-induced phytotoxicity, particularly in multi-contaminated soils. To overcome the operational constraints in urban settings, ornamental plants emerge as a viable alternative for landscape restoration and aesthetic enhancement. Simultaneously, recent advances in nanotechnology suggest that nanoparticles (NPs) can enhance the physiological response of plants by promoting growth and increasing metal uptake efficiency. Nevertheless, the integration of nanoremediation with phytoremediation, especially through sustainable delivery strategies and the use of ornamental plant species, remains poorly investigated. This PhD project addresses this knowledge gap by exploring the synergy between phytoremediation and nanoremediation within a multifunctional urban NbS framework. The research followed a stepwise approach combining bibliographic analysis and experimental investigation. First, a systematic literature review was conducted to identify ornamental plant species distributed in Europe with documented phytoremediation potential. This analysis led to the identification of 64 ornamental species with remediation abilities and highlighted Calendula officinalis L. as a particularly promising candidate due to its wide distribution, ornamental value, biomass production, and tolerance to metal-contaminated soils. Based on these findings, C. officinalis was selected as the model species for subsequent experimental trials. Exploratory in vitro assays and pot experiments were then performed using multi-contaminated soils, comparing different conjugated polymeric NP delivery strategies to evaluate their effects on plant growth and metal accumulation. Specifically, as these nanoparticles are semiconductors with distinct optoelectronic properties, they are highly suitable for interaction with plant systems due to their biocompatibility and biosafety profile. The results confirmed that ornamental plants represent a viable alternative to traditionally used phytoremediation species. Among the nanoremediation approaches tested, seed nanopriming proved to be the most effective delivery strategy, significantly enhancing root length, biomass production, and leaf area in marigold plants cultivated in contaminated soils. Statistical analyses further demonstrated that NP-treated plants in contaminated soil exhibited an increase in root and leaf biomass of up to 63% and 41%, respectively, compared to reference treatment. Furthermore, total Pb accumulation ranged between 16% and 27%, driven primarily by higher concentrations in the roots. Overall, this research highlights the potential of nano-assisted phytoremediation as an innovative and multifunctional strategy for urban soil management. Beyond improving soil decontamination efficiency, this approach can support urban biodiversity, climate change mitigation, and public well-being through aesthetic enhancement. Although regulatory gaps and the need for field-scale validation remain, the integration of polymer nanoparticles into urban NbS provides a solid scientific framework for the development of sustainable urban landscape management strategies.