Research on the ability of urban trees to retain heavy metals. A silvicultural approach.

The purpose of the present research was to study the ability of urban trees’ leaves to retain heavy metals. Three major heavy traffic streets of Thessaloniki were chosen. Two tree species were studied: Ailanthus altissima (Mill.) Swingle and Catalpa bignonioides Walt. and 360 leaf samples were collected from 20 trees. The selection of the species was carried out according to their leaf morphology and silvicultural characteristics. Also, for each tree were measured: breast diameter, tree height, crown height, crown’s diameter and then crown volume was calculated. Two treatments were applied (washed and unwashed leaves). The following heavy metals were measured: iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), cadmium (Cd), cobalt (Co), chromium (Cr), nickel (Ni) and lead (Pb) and the metal concentration was determined with the use of ICP-OES inductively coupled plasma optical emission spectrometry. The concentrations of heavy metals were significantly related to the species for the heavy metals: iron (Fe), manganese (Mn), cobalt (Co), chromium (Cr), nickel (Ni), lead (Pb). Catalpa bignonioides captured the highest concentrations of heavy metals. Finally, the morphological characteristics of leaves and not the silvicultural characteristics of species are the factors that influence their ability to retain heavy metals.