Magnetic and chemical biomonitoring of particulate matter at cultural heritage sites: The Peggy Guggenheim Collection case study (Venice, Italy)

Cultural heritage (CH) is heavily threatened by air pollution, especially by airborne particulate matter (PM), that acts on the surfaces of fine arts, causing artistic loss. Therefore, the monitoring of air quality assumes a central role for the preventive conservation of CH. In this study, magnetic and chemical biomonitoring of PM was applied at the Peggy Guggenheim Collection, a contemporary and modern art museum in Venice, Italy. It is located in an aquatic context, where the PM sources are considerably different, with respect to the usual vehicular-dominated urban emissions. Lichen biomonitoring is a well-established technique for the assessment of air quality, especially where PM collecting devices cannot be operated for aesthetic and practical reasons. Samples of the lichen species Evernia prunastri were collected from a pristine area and exposed for three months (November 2022–February 2023) at increasing distances from the Grand Canal, planning an outdoor vs. indoor sampling design, for outlining the diffusion of airborne PM inside the museum. In combination with lichen exposure, the leaves of Pittosporum tobira hedges were sampled for determining their efficiency as bioaccumulators. The magnetic properties of lichens showed a moderate bioaccumulation of magnetite-like particles outdoors. Conversely, the magnetic properties of the indoor samples were like those of the unexposed ones, indicating a negligible accumulation of metallic particles indoors. Pittosporum tobira leaves mostly showed diamagnetic properties, resulting an ineffective species for preventing conservation purposes. Chemical analysis did not show any significant difference between unexposed, indoor and outdoor samples. A directional gradient of bioaccumulation was not evident, thus implying that the sources of metallic PM are distant or diffused, with respect to the site. The joint use of magnetic and chemical analyses was useful for evaluating the negligible impact of airborne particulate pollution arising from the Grand Canal towards the Halls of the Collection.