Quercus ilex L. leaves as filters of air Cd, Cr, Cu, Ni and Pb.

The study of particulate matter pollution in urban areas is of great concern due its adverse effects on human health. Roadside vegetation, intercepting and filtering it, contributes to improve air quality. The aim of the research was to investigate the capability of Q. ilex leaves, already known good biomonitors of air quality, in filtering air metals. Besides, the main derivation (i.e. air or root uptake) of the investigated metals in leaf tissue was evaluated. The concentrations of Cd, Cr, Cu, Ni and Pb were measured in three groups of Q. ilex leaves (unwashed, water washed and chloroform washed). Besides, several leaf traits (i.e. length, width, petiole length, leaf area, leaf mass area and thickness) were evaluated. The findings highlighted that Cd, Cr, Cu, Ni and Pb in Q. ilex leaves exceeded the chemical fingerprint. In particular, Cd and Pb appeared the main contaminants of the investigated area as also after water washing of the leaves, their concentrations exceeded the chemical fingerprint. Ni, Cr and Pb appeared to be accumulated on leaf deposit; whereas, Cd appeared mainly adsorbed to leaf cuticle. Higher leaf width, lower leaf area and shorter petiole favoured leaf metal accumulation. Root uptake and translocation to leaves cannot be excluded for Cr and Ni; whereas, leaf Cu content would seem to depend on both leaf deposit and soil content. In conclusion, Q. ilex can be useful in filtering air metal pollution, especially for Ni, Cd, Cr and Pb, and improving air quality.