Magnetic particle monitoring on leaves in winter: a pilot study on a highly polluted location in the Po plain (Northern Italy)

Environmental monitoring in Northern Italy, one of the most polluted areas in Europe, is of paramount importance. Leaf monitoring throughout magnetic and scanning electron microscopy (SEM–EDS) analysis could be considered a good complementary analysis to sampling stations, but the lack of evergreen plants in the northern Italy towns may hinder magnetic leaf analysis in the winter season. Therefore, we tested three species of urban vegetation, which are evergreen and commonly found in urban environment, namely Hedera helix L., Parietaria officinalis L. and Rubus caesius L. Magnetic susceptibility, chosen as a simple parameter suitable for monitoring, was measured in seven stations, during the period 25 January 2019 to 8 March 2019 at a weekly step, in the cities of Torino and Parma in the same days. P. officinalis and R. caesius showed the best response, but also H. helix was suitable to detect highly polluted areas. In Torino, the magnetic susceptibility decreased in the last sampling, together with PM10, whereas in Parma it increased, likely for the beginning of the academic period in the University Campus. SEM–EDS analysis was done comparing leaves from the same plant sampled in February 2019, in highly polluted conditions, and in May 2020, after 2 months of very limited traffic, due to national lockdown. Silicate grains of natural minerals, sized between 10 and 20 µm, are present in both samples, whereas Fe oxides, about one micron size, possibly coming from car brake consumption, are prominent in the February 2019 sample. Magnetic susceptibility of leaves form the examined species looks promising to spot urban sites with high metal pollution.