Potentially toxic element gradients in remote, residential, urban and industrial areas, as highlighted by the analysis of Quercus ilex leaves

Reconstructing spatial and temporal pollution gradients in natural and anthropogenic areas is of paramount importance to undertake proper mitigation strategies. To this end, air biomonitoring based on chemical analysis of selected bioaccumulators, provides useful information not only on the pollutant concentration gradients, but also on their possible effects on biota and ecosystems. The analysis of 18 potentially toxic elements (PTEs), namely macronutrients (Ca, K, Mg, P, S), micronutrients (Co, Cr, Cu, Fe, Mn, Na, Ni, V, Zn) and non-essential elements (Al, As, Cd, Pb), in Quercus ilex leaves collected from 26 sites belonging to remote, residential, urban and industrial areas of Salerno, in the Mediterranean area, provided accurate information on spatial and temporal air pollution gradients, as well as on the plant nutritional status within the whole area. Despite the adequate nutritional status of plants in all the site typologies, several criticalities were highlighted. Specifically, on a natural background contamination by Na (due to the sea proximity), Al and V (due to the lithological characteristics) of the whole area, anthropogenic activities were responsible for relatively high concentrations of selected PTEs in the different site typologies. Remote sites were affected by high Cd concentrations, due to the transport of fine particulate from urban or industrial areas. Urban (and to a lesser extent residential) sites were affected by high concentrations of most PTEs, mainly released by diffuse sources, such as vehicular traffic. Exceedingly high concentrations of As, Mn, Ni and Pb were observed in industrial sites, in relation to local and specific emissions. Anyway, an overall decrease, consistent with the general temporal trends observed in Europe in the last years, was observed in several PTE concentrations for all the site typologies.