Effects of mycoremediation on element mobility in contaminated soils

This thesis is within the context of the goals of Spoke 5 “Urban Biodiversity”–Activity 6 “Ecological and environmental restoration” – Task 6.2 “Urban Mycoremediation” of the National Biodiversity Future Center (NBFC), whose aims are the development of strategies and guidelines to realize suitable solutions to restore and/or improve the functional components of urban biodiversity. The study of this PhD thesis advances the understanding of non-exhaust emissions (NEEs) within the transport sector, with a specific focus on those generated by railway traffic. The aims are: A. to carry out the chemical characterization of brake wear particles (brake dust; BD) produced by vehicular and rail traffic and evaluate their contribution to urban soil contamination through the analysis of deposition gradients (paper A; https://doi.org/10.3390/atmos17010114); B. to study the ability of different species, commonly used as biomonitors, to retain BD particles on their surfaces (paper B, under submission); C. to examine the role of specific fungal strains in influencing the mobility of potentially toxic elements (PTEs) derived from BD in the framework of mycoremediation strategies. A part of this study, in particular for the achievement of objectives (A) and (B), was carried out in the city of Terni. This site represents a particularly suitable case study, as its specific orographic and meteorological conditions favor atmospheric stability and the consequent accumulation of atmospheric pollutants. Furthermore, previous air quality monitoring studies have highlighted that the presence of the railway line constitutes a significant source of NEEs, making Terni an ideal context for analyzing the contribution of brake wear particles to urban contamination. Two sites representative of railway and vehicular traffic were therefore selected. Soils were sampled along transects orthogonal to the emission sources at increasing distances. ICP-MS analyses and magnetic susceptibility measurements allowed the characterization of soil chemical profiles and the comparative evaluation of the impact of the two emission types. In parallel, different species commonly used as biomonitors were employed to assess the interception capacity of BD particles on surfaces within the context of Nature-based Solutions (NbS). Based on chemical characterization, realistic exposure concentrations of BD were defined for the subsequent experimental phase (C). Several fungal strains were isolated from HCH-contaminated soils of two selected plots within the National Priority Site (NPS) “Bacino del Fiume Sacco” and screened to evaluate their tolerance and interactions with BD. Interactions between BD and two strains belonging to the genus Fusarium, selected from the best siderophore producing ones, were tested to understand the influence of fungal activity on element mobility, analyzing the partitioning of PTEs into different fractions (soluble, insoluble, and bioaccumulated). Overall, this study highlights the role of NEEs as a pressure factor in urban soils and underscores the importance of railway-related NEEs as a source of PTEs in urban soils, particularly in proximity to railway lines. Furthermore, the findings contribute to the understanding of the mechanisms involved in determining the bioaccessible fraction of these contaminants within the context of mycoremediation.