Fractionation of heavy metals and evaluation of the environmental risk for the alkaline soils of the Thriassio plain: a residential, agricultural, and industrial area in Greece

The purpose of the present study is to test metals’ accumulation and behavior in surface soils of Thriassio plain, Attica, an area registered as probably the most polluted in Greece. Avoiding sampling close to obvious specific pollution sources, 50 surface soil samples were collected and the Tessier fractionation scheme was applied to determine the chemical partitioning of Pb, Cu, Zn, Ni and Cr. Five chemical fractions of the studied metals were defined: exchangeable ( F 1), acid-soluble ( F 2), reducible ( F 3), oxidizable ( F 4) and residual ( F 5). The highest Cu, Ni and Cr concentrations were measured in the residual fraction, while the highest Zn and Pb concentrations were found in the reducible fraction. However, F 3 Cr and Ni concentrations were also high. These increased amounts of Zn and Pb and to a lesser extent those of Cr and Ni found in the reducible fraction indicate a potential hazard of metals’ mobilization under flooding and anaerobic conditions due to excess irrigation or rain water. Concentration of Pb in F 1 was high suggesting recent pollution episodes. Principal component analysis (PCA) showed that the exchangeable fraction of Zn, Pb, Cr and Ni is strongly related to the soil clay content and the oxidizable fraction of Cr and Ni to organic matter content. According to PCA results, no other clear relation between the extracted metal fractions and the soil components (i.e. CaCO 3 eq., organic matter, clay and amorphous iron oxides) was observed. The weak relation of CaCO 3 eq., content with many metal fractions suggests that carbonates affect the chemical partitioning of metals in alkaline soils with high CaCO 3 eq., content. The high values of mobility factor for Pb, Cu, Ni and Zn point to a considerable risk since these metals may accumulate in soil biota and plants.