Magnetic Emissions from Brake Wear are the Major Source of Airborne Particulate Matter Bioaccumulated by Lichens Exposed in Milan (Italy)

Abstract

The concentration of selected trace elements and the magnetic properties of samples of the lichen Evernia prunastri exposed for 3 months in Milan (Italy) were investigated to test if magnetic properties can be used as a proxy for the bioaccumulation of chemical elements in airborne particulate matter. Magnetic analysis showed intense properties driven by magnetite-like minerals, leading to significant correlations between magnetic susceptibility and the concentration of Fe, Cr, Cu, and Sb. Selected magnetic particles were characterized by Scanning Electron Microscope and Energy Dispersion System microanalyses, and their composition, morphology and grain size supported their anthropogenic, non-exhaust origin. The overall combination of chemical, morphoscopic and magnetic analyses strongly suggested that brake abrasion from vehicles is the main source of the airborne particles accumulated by lichens. It is concluded that magnetic susceptibility is an excellent parameter for a simple, rapid and cost-effective characterization of atmospheric trace metal pollution using lichens.

Negative correlation between concentration of iron oxides and particulate matter in atmospheric dust: case study at industrial site during smoggy period

“…Magnetic properties of tree leaves as biocarriers of the deposited atmospheric dust have been investigated in relation to air pollution by many authors [5][6][7][8][9][10][11][12][13][14][15][16][17]. There are also numerous studies on magnetic properties of tree needles [18][19][20], tree barks, rings or branches [21][22][23][24][25][26], lichens, in situ or transplanted [27][28][29][30][31][32][33][34], and moss and transplanted moss bags [32,[35][36][37][38][39][40][41][42]. High sensitivity of magnetic methods enabled even examination of magnetic properties of spider webs [43].…”

Trace Element Concentrations Measured in a Biomonitor (Tree Bark) for Assessing Mortality and Morbidity of Urban Population: A New Promising Approach for Exploiting the Potential of Public Health Data

“…However, the results of the present study, although preliminary, point out the feasibility of an investigation that would permit obtaining information on the health status of urban populations, combining high spatial density and low cost. Furthermore, recent investigations on other types of bioindicators have shown that there are measurements able to provide information on atmospheric metal pollution by means of other analytical techniques, even simpler and cheaper than atomic emission spectrometry, such as X-ray fluorescence [42][43][44] and magnetic analysis [45][46][47][48][49]. This would make the approach accessible to a large number of laboratories in terms of purchase and operating costs of equipment.…”

Geochemical and Mineralogical Characteristics of Airborne Particulate Matter in Relation to Human Health Risk

“…Mn, Cd and Ni may be associated with exhaust emissions [74][75][76]. Furthermore, such elements as Pb, Zn, Cu, Cd, Cr and Ni in TSP and PM1 are the markers of diesel engine exhaust, oil combustion, tire and brake abrasion, brake wear debris and burning of lubricating oil [77][78][79]. Simultaneously, Al along with Ti (and also Fe and Mn) are considered as crustal metals and their enhanced concentration can be an effect of road dust re-suspension and the local geology/soil composition [71,72].…”

“…Mn, Cd and Ni may be associated with exhaust emissions [74][75][76]. Furthermore, such elements as Pb, Zn, Cu, Cd, Cr and Ni in TSP and PM1 are the markers of diesel engine exhaust, oil combustion, tire and brake abrasion, brake wear debris and burning of lubricating oil [77][78][79].…”