Leaves of Quercus ilex as Indicators of Airborne Trace Element Distribution in Lucca (Central Italy)

Ambient air has always contained particles, ranging from sub-micrometric aerosols to clearly visible dust and sand grains. Plants have evolved to maximise light interception and CO2 assimilation and, as a consequence, they are also highly efficient receptors of airborne pollutants. The use of plant tissues has since long been shown to be an effective indicator of metal air pollution. Leaves of the evergreen species Quercus ilex were used as a passive sampler to describe the distribution of selected elements in the area around the walls of Lucca (Central Italy). Unwashed healthy mature leaves collected in June 2006 from 16 sampling sites were analysed by ICP-MS for Al, Ba, Be, Bi, Br, Ca, Cd, Cl, Co, Cr, Cs, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Si, Ti, V and Zn. Values were normalised by subtracting baseline concentrations of biologically essential elements coming from Q. ilex plants collected into Botanical Garden of Lucca. Enrichment factors (EF) were calculated taking Al as crustal reference element. Cd, Cu and Zn exhibited the highest EF, with values ranging between 100 and 1000. Varimax rotated factor analysis allowed identifying three main source groups of elements, namely crustal components, sea-salt spray and anthropogenic sources (vehicular traffic, industrial activities). The factor one (crustal components) explained 48.3% of the total variance. Common high loadings for this factor were Al, Bi, Br, Co, Cu, Fe, Si, V, and Zn, which indicate a predominant soil contribution. Results are discussed with emphasis on the potential role of vegetation for the removal of particulate pollution.