Sequential fractionation of lead in contaminated and non-contaminated soils

The purpose of this study was to determine the effect of soil properties and Cd or Pb addition on the transformations of Pb in soils and its distribution between different fractions determined according to Tessier et al. The study was carried out in model pots filled with mineral or organic soils taken from the surface soil layer. The soils showed either acidic or neutral reactions. The mineral soil (Haplic Podzols) has the granulometric composition of light loamy sand. The soils were altered with the addition of: 0 mg kg -1 of Cd or Pb (control sample); 10 mg kg -1 of Cd in the form of Cd(NO3)2; 100 mg kg -1 of Pb in the form of Pb(NO3)2. Speciation data indicate that in non-adjusted mineral soil, lead was associated mainly with Fe-Mn oxide and residual fractions (near 80% of total Pb), and relatively small amounts of Pb with others forms. In non-adjusted organic neutral soil, the dominant fractions of Pb were Fe-Mn oxide bound (56%) and organic (24%), while in organic acidic soil: organic (42%), exchangeable (21%) and Fe-Mn oxide bound (19%) fractions. Introducing 100 mg kg -1 of Pb into the mineral soil changed the Pb distribution pattern among the particular fractions, while for organic soils it did not change the Pb distribution in comparison to that of uncontaminated soils. The addition of Pb to mineral and organic soils caused an increase in Pb bound to Fe-Mn oxides and in organic neutral soil also to the organic bound fraction. In the mineral soil, significant amounts of Pb were also present in the carbonate form. A significant amount of Pb associated with the non-residual fraction (> 65%) indicates that Pb in these soils may be easily available for plants.