The magnetic properties of leaves and lichens provide information on the accumulation and composition of fine atmospheric polluting particles. With a multidisciplinary study, the relationship between the magnetic properties of lichens and the concentration of heavy metals sampled in a highly anthropized area of the eastern Roman periphery was highlighted
A team of researchers from the National Institute of Geophysics and Volcanology (INGV) and the Regional Agency for Environmental Protection of the Lazio Region (ARPA Lazio) analyzed the lichens sampled in Rome in 2017 in via di Salone, an area characterized by multiple sources of air pollution, including frequent illegal burning outdoors. The research, published in the Elsevier group's journal Science of the Total Environment, highlighted the properties of lichens as receptors and accumulators of fine dust.
“Fine particles”, explains INGV technologist Aldo Winkler, “are made up of micrometric substances suspended in the air, present in the atmosphere due to natural or anthropic causes. Usually, when we talk about fine particulate matter, we refer to the so-called PM10, consisting of particles with a diameter equal to or less than 10 thousandths of a millimeter. Today, attention is paid to even smaller particles, PM2.5, and even nanometric, the most dangerous. In this study, autochthonous and transplanted lichens were analyzed in the studied area, interpreting them - in fact - as PM receptors and accumulators".
Considering the impact of these particles on the health and well-being of the population, innovative methods of research and analysis on PM have spread in recent years, including those used in this study, which are complementary to the use of monitoring stations.
"PM can include a magnetic fraction deriving from combustion processes - for example in the case of industrial and vehicular emissions - and from abrasion, such as for brakes and rails", continues the expert. "Biomonitoring with magnetic methods consists in considering leaves and lichens as collectors of atmospheric particulate which significantly modifies their magnetic properties, thus providing a rapid indication of atmospheric pollution by fine particles and allowing the differentiation between PM deriving from natural sources from that deriving from anthropogenic sources. The comparison between magnetic properties, chemical analyzes and electron microscope observations" continues Aldo Winkler, "has made it possible to outline, in the sampled lichens, the important accumulation of micrometric magnetic particulates, similar in composition to magnetite, linked to the presence of heavy metals such as copper, zinc, nickel, chromium and lead. These results reaffirm the high degree of anthropization of the studied area, characterized by multiple sources of pollution”, concludes the expert.
The measurements of environmental magnetism, carried out at the Paleomagnetism Laboratory of the INGV, are rapid and at low cost; in urban areas, focusing on traffic, research continues in collaboration with the Department of Environmental Biology of the Sapienza University of Rome, relating the magnetic measurements to the functional traits of holm oak leaves sampled in urban areas subject to intense traffic convey.
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Photo 1 - Waste combustion residues accumulated in via di Salone, Rome.
Photo 2 - Scanning electron microscope image, spherical particle rich in iron, incorporated in lichen structures.
Photo 3 - Magnetic measurements of leaves and rock samples at the Paleomagnetism and Environmental Magnetism Laboratory of INGV.