Person of the Year for 2019 according to the US magazine "Time", the very young Swedish activist Greta Thunberg is the contemporary symbol par excellence of the fight against pollution and climate change. His catchphrase “Skolstrejk för climatet” managed to unite under one aegis kids from every corner of the world to ask the powerful of the planet to reverse course and finally start dealing with the environment in a systematic and productive way.
But what is the current state of our knowledge on the damage deriving, for example, from fine particles? The World Health Organization has estimated that these particulates, which are usually classified as PM10 and PM2.5, based on their aerodynamic diameter, cause about two million victims every year worldwide, of which 400.000 in Europe alone. Therefore, there is a growing general interest in making increasingly specific survey methods that can help monitor PM and mitigate its effects, in order to adopt appropriate strategies that help to counter its diffusion and accumulation.
INGV has been engaged for many years in the study of the characteristics and nature of fine particles, using original laboratory techniques usually linked to the magnetism of rocks. Recently, a team of researchers from the Institute, with an article published in the journal “Science of the Total Environment”, presented the results of an innovative research which, through the magnetic biomonitoring of lichens, made it possible to outline the air pollution in a particularly complex area on the outskirts of Rome.
We talked about it with Aldo Winkler, INGV's first technologist and head of the Institute's paleomagnetism laboratory.
Aldo, your study is based on analytical methods typical of rock magnetism: what is it about?
Let's start by saying that rocks can have magnetic properties linked to the minerals that compose them.
In particular, in the thematic sector of paleomagnetism, which we deal with in our laboratory, we are interested in rocks that have intense and stable magnetic properties over time, as they contain minerals, usually iron oxides, which give them "ferromagnetism" characteristics. The best known and most suitable magnetic mineral for palaeomagnetic research is magnetite, an extremely widespread iron oxide which, especially when it is present in rocks in very small dimensions, of the order of hundredths of a micrometre, can keep a record of the Earth's magnetic field even for billions of years. Rocks containing magnetite have allowed us, for example, to know the reversals of our planet's magnetic field, or to reconstruct the position of continents in the geological past.
In this context, our Lab has developed and expanded its instrumental and analytical equipment to investigate the magnetic behavior of matter, with applications in all those sectors in which, starting from the magnetic properties - not only of rocks, but also of biological media, technological or artifacts - it is possible to understand something more about their general characteristics and the magnetic fractions that constitute them, without having to resort to complex and costly optical and chemical investigations. We therefore come to magnetism applied to environmental sciences, where magnetic minerals are interesting indicators of air pollution.
So how did the field of study of magnetic monitoring of air pollution come into being?
Almost twenty years ago, as part of a European project on rock magnetism, Barbara Maher of the University of Lancaster promoted the idea of applying magnetic methods to the study of air pollution and fine particles. We therefore took care of studying the magnetic properties of the leaves of Rome, dividing ourselves into teams and sampling different types of trees in various areas of the city. Thus we were able to complete the first magnetic biomonitoring of air pollution in Rome, demonstrating the feasibility of using the magnetic properties of leaves as an indicator of the concentration of metal particles due to city traffic.
What has changed in these twenty years?
The thematic, and underlying principles, have remained quite similar; in the meantime, also thanks to these studies, the instrumental equipment of the laboratory has considerably improved, above all since we have an instrument for carrying out hysteresis cycles, i.e. the curves which describe how the magnetisation of a body changes when the magnetic field varies applied. In these 20 years increasingly complex and refined analytical techniques have been developed, which now touch the structure and magnetic foundations of matter. Yet, the basic principle of magnetic biomonitoring has always remained the same: biological means, in general, have characteristics of "diamagnetism", i.e. extremely weak and non-lasting magnetism. The intense magnetic properties of the leaves sampled near roads and areas with intense anthropic characterization depend on the accumulation of metal particles emitted by brakes and exhaust pipes, as regards cars, or from industrial sources and landfills.
Over time, our investigations have become so refined as to be able to distinguish, based on the magnetic properties, whether the accumulated particulates derive from brakes, exhausted from diesel or petrol fuels.
Furthermore, at an international level, these techniques have had a particular resonance thanks to some studies that have linked ultrafine magnetic powders from air pollution, smaller than 30 nanometers, to heart problems and Alzheimer's disease. We are therefore beginning to understand, also at an epidemiological level, the connection between fine particles and the damage they cause to human beings.
How did we arrive at the use of lichens for biomonitoring in Rome?
In this case, the fundamental step was to collaborate with the Departments of Life Sciences of the Universities of Siena and Trieste, which introduced us to environmental bioindication with lichens, making our research interdisciplinary and, above all, completing it with the biological part. In fact, lichens are biological indicators of air pollution known for their ability to adapt even in extreme areas. Furthermore, clean samples, coming from unpolluted areas, can be transplanted in areas where it is interesting to evaluate the effect, over time, of their exposure to atmospheric pollution, evaluating the variation of their chemical, magnetic and functional properties.
After having achieved interesting scientific results, measuring the magnetic properties of lichens exposed in industrial areas in Northern Italy and Slovakia, in 2017 a scientific agreement was signed with ARPA Lazio - the Regional Agency for Environmental Protection - to contribute to the characterization of the air pollution in areas of particular environmental impact. We have selected, as a study area, the eastern suburbs of Rome, in the via di Salone area, due to the recurring fraudulent activities of open combustion, operated near Roma camps, aimed at obtaining metals, in particular copper, from waste accumulated in spontaneous landfills.
How did the investigation take place?
In July 2017 we carried out a first exploratory campaign to obtain so-called "pilot" lichen samples, aimed at verifying the feasibility of the study. The area turned out to be particularly complex, from an environmental point of view, due to the simultaneous presence of various emission sources, linked to traffic and industrial and manufacturing activities of various kinds.
We have found few sites with viable lichens, also due to the particularly hot summer, so we have extended the investigation area to an area with similar problems, near Tivoli, to then further enrich the set with transplanted specimens originating from Terminillo, and exposed for about 4 months. The magnetic characteristics were intense and indicative of a large accumulation of magnetic particles of presumable anthropic origin.
How did you arrive at these results?
The first very rapid magnetic analyses, consist in measuring the magnetic susceptibility of the lichens, i.e. their ability to become magnetised, indicative of the concentration of magnetic minerals present in the samples under examination. The measured values immediately proved the important accumulation of magnetic particles.
Subsequently, for each sample, the hysteresis cycles were obtained, which allowed us to understand that the magnetic minerals bioaccumulated by the lichens can be traced back to magnetite, of which we are also able to give a granulometric estimate, a fundamental aspect from the point of view from an environmental point of view.
What were the main results you achieved?
First of all, we realized how powerful, and fundamental, interdisciplinary methods are for characterizing air pollution, allowing for the integration of classic data based on the use of automatic control units, moreover not available in the area under examination.
By integrating the chemical analyzes on lichens, carried out by ARPA, the magnetic type analyzes and the electron microscopy ones, carried out at the HP-HT laboratory of INGV, we were able to characterize the chemical composition and morphology of the accumulated magnetic minerals from lichens, demonstrating the relationship between the concentration of iron oxides and that of heavy metals such as copper, chromium, lead and zinc, whose environmental impact is known.
The greatest emotion I felt during this study was when I saw at the SEM - the scanning electron microscope - the magnetic particles whose presence we had deduced thanks to magnetic and chemical analyses, incorporated in the lichen and spherical-shaped tissues, just as expected for combustion products.
As a further consideration, flocks of sheep grazing on the grass were common during sampling; this can give an idea of what the danger is associated with the diffusion of polluting dust, even for the part not inhaled or breathed in which, falling back into the ground, ends up in the food cycle.
What are the differences in the use of leaves and lichens?
They are two very different types of specimens, in terms of biological and display characteristics: for example, lichens can live for many years, while leaves, especially in urban environments, can be seasonal or annual. The lichen can therefore provide even a long-term indication of the conditions of accumulation and pollution in a given area. I would say that the preference basically depends on the type of context. In the city, it is easier and more representative to use leaves; those of holm oak and plane tree, for example, are widespread throughout the city of Rome.
It is necessary to resort to lichens when it is necessary to study non-vegetative areas, or in which it is necessary to carry out monitoring with particular characteristics of regularity of the points of exposure, using the transplanting technique.
What application are these results likely to have in the planning and management of anti-pollution plans in our cities?
The main tool for detecting air pollution inevitably remains the control unit, mainly for regulatory reasons, which identify, starting from the concentrations of PM10 and PM2.5, the thresholds not to be exceeded in order not to incur penalties. Lichens, as bioindicators, are arousing great interest also from the point of view of forensic botany, for the identification of pollutants and their biological effects in complex environmental areas. From a regulatory point of view, it is important to proceed in the awareness that the monitoring of air pollution must increasingly acquire multidisciplinary connotations, for example to favor the so-called "speciation" of dust, aimed at recognizing and distinguishing the emission sources through the analytical interpretation of the different compositional and granulometric characteristics. Finally, especially as regards leaves, urban furniture designs have been underway for several years which contemplate the widespread presence of trees and hedges as accumulators of the particulate matter, intercepted, I would like to say, on our behalf.
Over the years, INGV has joined numerous school-work alternation projects to bring young people closer to the subjects studied at the Institute: have any of these also concerned biomonitoring?
Yes, we have activated several projects in this area, and we should soon start another one, along the new lines of the PCTOs: all the cycles concerned the methods for characterizing atmospheric pollution with magnetic techniques. The boys have been an active part in all phases of the work, from sampling to laboratory experiences. After three experiments on the leaves, a survey of fine particles was carried out in schools, to understand which areas were most subject to pollution indoor, sampling the dust deposited in different areas of the schools (near the photocopier, in the gym, and so on) and identifying the dispersion of the dust in the school environment.
The most relevant scientific results were achieved in Ariccia, in Via della Cancelliera, where the students were able to verify the effects of a fire in an industrial warehouse on the magnetic properties of the leaves sampled in neighboring trees.
The new project, currently being planned, will concern theindoor automotive, through the study of air conditioning filters, to outline the importance of environmental protection devices even inside our machines.
What will be INGV's next steps in biomonitoring with magnetic techniques?
For some time we have been pursuing an innovative collaboration with the Department of Environmental Biology of the "La Sapienza" University of Rome, aimed at an integrated approach for monitoring the environmental quality of the city of Rome. The study aims to demonstrate how magnetic characteristics are an indicator of functional deterioration of leaves exposed in busy areas. These studies have already been the subject of three degree theses, of which I was co-supervisor.
Collaborations with the University of Siena are continuing, through an integrated study with biological and magnetic methods on transplanted lichens in Milan, to determine the main directions of bioaccumulation of fine particles in the Lombard capital; this study will be the subject of an invited talk at the next international conference on air quality in Thessaloniki.
Finally, as a result of the fruitful collaboration established with regard to via di Salone, the scientific collaboration with ARPA Lazio has been renewed and an agreement is being studied which could contribute to the environmental remediation plan promoted by the Lazio Region, with the precious contribution of the Department of Chemistry of the University "La Sapienza" of Rome. This time, as has already happened in the past, on the occasion of an agreement stipulated with the Lazio Region, for our analyses, we will use the PM10 and PM2.5 filters that ARPA Lazio manages on the regional territory. It will be an interesting study aimed at defining the polluting sources in some areas considered crucial due to their environmental impact.