Concentrations of five metals (cadmium, chromium, copper, nickel and lead) were determined in tree leaves collected from 13 areas of the Attica basin and Athens city, Greece. Geographical distribution patterns were investigated, and factors affecting toxic element accumulation in trees were discussed. The mean heavy metal content in the tree leaves is described in the descending order of copper>lead>nickel>chromium>cadmium. Generally, the most damaged areas have been proved to be those near the city center and in the vicinity of the Attica highway. The geomorphological relief of the area plays an important role in the dispersion of airborne particles from pollution sources to the surrounding area. Areas on the NE region are also polluted mainly due to wind directions. In Citrus aurantium leaves, with relatively impermeable cuticle, high chromium, copper and nickel concentration would be possibly caused only by significant stomatal uptake. The conifer tree Pinus brutia providing a rough leaf surface also showed elevated concentrations, especially of cadmium and lead. The thick waxy cuticle of the sclerophyllous broad-leaved Olea europaea forms a smooth sheet increasing the barrier properties of the leaf epidermis and causing a reduction in leaf permeability. The dense trichomes of the abaxial epidermis of Olea europaea also act as a pollution screen keeping away the air particles from the epidermis stomata. The presence of a certain metal within the leaf cells could reduce the uptake or toxicity of some others.

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Metal concentrations in plants, soil and sediment were evaluated in the vicinity of a former iron/nickel enriching factory at Pogradec, near Ohrid Lake in Albania. Metal levels were significantly higher in soil samples than in the corresponding plants. Iron concentrations in both soil and plants were much higher than the nickel ones. Lower plants (lichens, mosses and fungi) had a higher uptake and accumulation of nickel, followed by water plants and non-cultivated (wild) plants. Iron levels were very high in mosses and lichens and relatively lower values in fungi. Water plants showed increased iron concentrations followed by trees and shrubs and non-cultivated plants. In the edible parts of the cultivated plants Capsicum annuum, Lycopersicon esulentum and Zea mays, nickel levels were generally lower ranging from 11 to 29 mg/kg, whereas the nickel concentration in the soil was 925 mg/kg. Iron concentrations in the edible parts of the above mentioned plants were also lower, ranging from 67 mg/kg (Zea mays) to 205 mg/kg (Capsicum annuum) in comparison to other plant organs. In the case of nickel, roots showed generally greater metal concentrations than leaves while stems showed the lowest concentrations. In cultivated plants fruits were less contaminated, but a little bit more than the stems. Seeds of Alyssum murale showed remarkably higher nickel concentrations than other plant organs. In the case of iron the root was more contaminated in tree, shrub and cultivated plant samples but in noncultivated and aquatic plants the leaves showed the highest iron values.