Heavy metals in soils from Tirana (Albania)

This study was aimed to establish background and reference values of total heavy metals in soils from a representative area of Albania (Tirana). Thirty-eight soil samples collected from genetic horizons of major soil types of Tirana were analyzed for important physicochemical properties by standard methods and for total contents of Cd, Cr, Ni, Pb, Zn, and Cu by atomic absorption spectrometer, after extraction with aqua regia. The results showed that the total contents of Cd, Cr, Ni, Pb, Zn, and Cu in surface horizons varied widely with respective mean values of 0.3 (± 0.6), 174.2 (± 63.7), 305.9 (± 133.0), 19.7 (± 12.4), 95.5 (± 26.3), and 42.7 (± 6.8) mg/kg. The highest metal contents were found in two soils developed in limestone. The depth distribution of metals showed a tendency for accumulation of Cd and Pb in the surface horizons of three soils, suggesting that these metals partially come from anthropogenic inputs. Correlation analysis indicated that the metal contents of soils were controlled by soil properties, including pH, CaCO₃, clay, organic matter, cation exchange capacity, and Fe oxides. The background values (given as the 90th percentile) were much higher than those reported in the literature, showing that the levels of respective metals were naturally higher. The total metal contents of some soils were above background levels, suggesting metal pollution. The reference values for all the analyzed metals were quite consistent with those of the Dutch system. The proposed background and reference values can be used to evaluate the soil pollution with these elements.