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Nerium oleander L. (Oleander) leaves grown in Palermo city (Sicily, Italy) were collected from six sampling sites representing either areas of high traffic and urbanisation density or areas far away from traffic (e.g. city gardens). Concentration of Al, Ba, Cr, Cu, Fe, Pb, Mg, Mn, and Zn were determined in leaf samples during two years. Multivariate analysis classified the sampling sites in four groups based on the metal content in vegetal leaves in agreement with traffic and human activity site. Many elements studied (Al, Ba, Fe, Mn Mg) arise from the soil composition and others such as Cr, Cu, Pb and Zn as pollutant of the soil. On the other hand, about 30% of Al, Fe Cr, Cu and Pb originate from aerial deposition on leaves. Although the results presented should be handled with caution N. oleander can be considered as a means of assessing dust contamination in the urban environment.

The influence of silicon on responses to copper excess was studied in plants of Erica andevalensis. Plantlets were grown in nutrient solutions containing two Cu (1 and 500 mM) and three Si concentrations (0, 0.5 and 1 mM). Plant growth, water content, and mineral nutrient concentration were determined. Plants grown with 500 mM Cu showed differences in growth and shoot water content depending on Si supply. The addition of 1 mM Si in high-Cu nutrient solutions significantly improved plant growth and reduced water loss preventing plant death related to Cu-excess. Silicon supply reduced significantly leaf Cu concentration (up to 32%) and increased Cu concentration in roots. Phytoliths isolated from leaves were analysed by scanning electron microscopy coupled with energydispersive X-ray spectroscopy. Such phytoliths consisted in silica deposits associated with Cu and other elements (K, Ca, P). Improvement by Si of Cu tolerance in E. andevalensis was clearly related to the inhibition of Cu upward transport. The leaf phytoliths formed in Si-treated plants might have some contribution to tolerance by Cu immobilisation and inactivation.