Nature-based solutions for monitoring the impact of vehicular particulate matter and for the preventive conservation of the Palatine Hill archaeological site in Rome, Italy.

Magnetic and chemical biomonitoring methodologies were applied to the southern slopes of the Palatine Hill archaeological area in Rome, Italy. Plant leaves and lichen transplants were respectively sampled and exposed between July 2022 and June 2023 to assess the impact of vehicular particulate matter from Via dei Cerchi, a trafficked road coasting Circus Maximus, towards the archaeological area upon the Palatine Hill. The magnetic properties of leaves and lichens, inferred from magnetic susceptibility, hysteresis loops and first order reversal curves, were combined with the concentration of trace elements. It was demonstrated that the bioaccumulation of magnetite-like particles, associated with tracers of vehicular emissions, such as Ba and Sb, decreased with longitudinal distance from the road, without any important influence of elevation from the ground. Lichens demonstrated to be more efficient biomonitors of airborne PM than leaves, irrespective of the plant species. Conversely, leaves intercepted and accumulated all PM fractions, including road dusts and resuspended soil particles. Thus, plant leaves are suitable for providing preventive conservation services that limit the impact of particulate pollution on cultural heritage sites within busy metropolitan contexts.

Robinia pseudoacacia L. (Black Locust) Leaflets as Biomonitors of Airborne Microplastics.

Here we investigate the suitability of Robinia pseudoacacia L. (black locust) leaflets as a novel biomonitor of airborne microplastics (MPs) including tyre wear particles (TWPs). Leaflets were collected from rural roadside locations (ROs, n = 5) and urban parks (UPs, n = 5) in Siena, Italy. MPs were removed by washing, identified by stereomicroscope, and analysed for polymer type by Fourier transform infrared spectroscopy. Daily MP deposition was estimated from leaf area. The mass magnetic susceptibility and the bioaccumulation of traffic-related potentially toxic elements (PTEs) were also analysed. The total number of MPs at ROs was significantly higher at 2962, dominated by TWPs, compared with 193 in UPs, where TWPs were not found. In contrast, total microfibres were significantly higher in UPs compared with ROs (185 vs. 86). Daily MP deposition was estimated to range from 4.2 to 5.1 MPs/m2/d across UPs and 29.9-457.6 MPs/m2/d across ROs. The polymer types at ROs were dominated by rubber (80%) from TWPs, followed by 15% polyamide (PA) and 5% polysulfone (PES), while in UPs the proportion of PES (44%) was higher than PA (22%) and polyacrylonitrile (11%). The mean mass magnetic susceptibility, a proxy of the bioaccumulation of traffic-related metallic particles, was higher at ROs (0.62 ± 0.01 10-8 m3/kg) than at UPs (-0.50 ± 0.03 10-8 m3/kg). The content of PTEs was similar across sites, except for significantly higher concentrations of Sb, a tracer of vehicle brake wear, at ROs (0.308 ± 0.008 µg/g) compared with UPs (0.054 ± 0.006 µg/g). Our results suggest that the waxy leaflets and easy determination of surface area make Robinia an effective biomonitor for airborne MPs including TWPs.