Evaluation of the suitability of Tillandsia usneoides (L.) L. as biomonitor of airborne elements in an urban area of Italy, Mediterranean basin

The suitability of a rootless Bromeliad species (Tillandsia usneoides) as biomonitor of airborne trace elements in urban areas of the Mediterranean basin was evaluated. The study was performed at five sites of the city of Pisa (Tuscany, Central Italy) differing for land use, anthropogenic activities and/or proximity to emission sources. The elements investigated were Al, As, B, Ba, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sb, Sr, V and Zn. Unwashed and washed samples, collected after 36 days of exposure (May-June 2011), were analyzed by ICP-MS. Results showed significant differences among sampling sites for several elements. Concentrations of Al, Ba, Bi, Cd, Co, Cu, Pb, Sb and Zn were the highest in urban/traffic and/or suburban/traffic areas. Some of these elements e.g. Ba, Cu, Sb and Zn are commonly considered as traffic-related elements. In the industrial site, the main elements found were Mg, Sr and Zn. Iron, Mn, Na and V concentrations were much higher in rural/remote areas. Enrichment factors highlighted that T. usneoides showed: high resistance/tolerance to heavy metal toxicity, specificity, capability to well-definitely represent a sampling site, quantitative response to pollutant exposure. The results indicated that T. usneoides reflects the intrinsic characteristics of each sampling area and allows tracing back differences related to the various emission sources by factor analysis.