The use of lichen biomonitoring techniques for Environmental Justice assessment and the risk perception assessment in a typical European city (Milan, Italy)

Aim of this thesis is to investigate the application of lichen biomonitoring techniques in the study of environmental justice and risk perception of air pollution at urban scale. Lichen biomonitoring can, in fact, fill the void that several authors claim when talking about environmental justice assessment, i.e., the lack of high spatial resolution data of air quality, that is crucial when the goal is to match the socio-economic status with air quality. The area selected for the study is Milan municipality (N Italy) as an example of a typical European big city. In this area, a lichen biomonitoring survey was firstly carried out through transplants of lichen bags of the species Evernia prunastri, previously collected in a pristine area (Siena, C Italy). The exposure lasted three months during the winter period. To assess the biological effects of air pollution, analysis on the physiological status of the samples were conducted, in particular the photosynthetic efficiency of the photobiont, and damage to cell membranes and the antiradical activity of the mycobiont were measured. The bioaccumulation of trace elements Al, As, Cd, Cr, Cu, Fe, Sb, Pb and Zn was quantified and an overall contamination index (CI) was elaborated on the basis of the bioaccumulated elements. The use of a geographic information system support (QGIS 3.8) allowed to visualize the distribution of the contamination over the area, elaborated through an IDW interpolation algorithm. A deeper insight on the contamination of the area was obtained through the analysis of source apportionment, i.e., the research of the main emission sources. A theoretical approach was followed through the statistical method of Positive Matrix Factorization (PMF). Through this method, the overall contamination was de-structured in “factors” that, based on trace elements correlation, provided different “contamination profiles”, ascribable to different emission sources. The spatial distribution of the profiles, combined with their elemental composition, suggested both the type of emission sources and their magnitude in the study area. An empirical approach for source apportionment was also followed: the grain size, shape and magnetic behaviour of bioaccumulated particles was studied and compared with those of known emission sources. The results of the biomonitoring survey showed a general stress on the lichen physiology due to air pollution, but not so severe to compromise the general vitality of samples. Bioaccumulated elements were Cr, Cu, Fe, Sb and Pb and the Contamination Index showed generally high values over the whole area, even if central areas of the city were more polluted. Source apportionment analysis highlighted three main pollution profiles, ascribable to the industrial activity, brake abrasion from railways and cars, and soil resuspension. The magnetic behaviour of particles was in line with brake abrasion of vehicles, suggesting the vehicular traffic the most responsible of trace element contamination in Milan municipality. For the assessment of environmental justice, the air contamination was matched with the socio-economic characteristics of the citizens. An index of socio-economic deprivation (SDI) was calculated on the basis of the socio economic information provided by the national statistics institute (ISTAT), at the smallest spatial unit available, the census unit. Results showed that peripheral areas experience less air pollution but more socio-economic deprivation, however, the census units closer to main emission sources were generally more deprived than average. The last part of the study was dedicated to the evaluation of the risk perception of the citizens about air pollution. A questionnaire was elaborated and administrated randomly in the city of Milan to ca. 300 respondents. Main results showed a generally high attention for the air pollution issue in the city, as well as a high risk perception, regardless of gender, age or education level of the participants.