Effects of PM deposition on vegetation in urban environment: chemical characterization and oxidative potential assays on Quercus ilex L. leaves

Particulate matter (PM) pollution is a serious global problem especially in urban and industrialized areas (Xu et al., 2019), threatening both human health and vegetation. Urban and peri-urban forests as well as street trees are natural receptors of PM and they have been widely applied as a passive sampler for monitoring air quality (Kardel et al., 2018). However, PM can affect functionality of vegetation by impairing its capacity to provide regulating ecosystem services. This work aims to evaluate the oxidative potential of PM on Quercus ilex L. (hoak olm) leaves to investigate potential negative impacts of PM on plant functionality. Q. ilex was selected as a target species for its widespread use in the urban green of Mediterranean regions (Fusaro et al., 2015). Leaves of Q. ilex were sampled in eight sites of the metropolitan area of Rome (Italy), characterized by different exposure to vehicular traffic, by considering different Green Infrastructure elements and by including control sites. The leaves were collected and then extracted in water. Thus, dithiothreitol (OPDTT), ascorbic acid (OPAA) and 2′,7′-dichlorofluorescin (OPDCFH) oxidative potential assays were immediately performed on aqueous extracts to provide a proxy of the oxidative capability of PM (Simonetti et al., 2018a, 2018b). Then, the same samples were chemically analyzed by using inductively coupled plasma mass spectrometry (ICPMS) to identify the contribution of the main anthropogenic emission sources to PM deposition. OPAA values were strongly correlated (R 2 > 0.8) with tracers of brake dust abrasion (Cu, Mo, Sb, Sn), confirming the high sensitivity of the AA assay towards non-emissive traffic contribution (Simonetti et al., 2018a). Conversely, OPDTT and OPDCFH showed lower correlation with the analyzed elements, probably because of the prominent role of organic compounds on OP values obtained by these assays. Even though the study still needs further investigations, the results suggest that the use of tree leaves as passive PM samplers may be a valid and cheap alternative for the evaluation of OP in urban environment.