Assessment of sequential extraction methods for the prediction of bioavailability of elements in plants grown on agricultural soils near to boron mines in Turkey

Two sequential extraction methods (BCR sequential extraction method and a newly proposed sequential extraction method) were used to evaluate the bioavailability of the elements from the contaminated soils to different plants. The concentrations of As, B, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn in acid digests from different plants collected from the fields near to boron mines in Turkey were determined using ICP-MS. The levels of the elements in some plants exceeded the limits of maximum and guideline levels for As, Cd and Pb; Tolerable Upper Intake Levels (ULs) for Ni and B; Adequate Intakes (AIs) for Cr and Mn and Recommended Dietary Allowances (RDAs) for Cu, Fe and Zn. The average Transfer Factor values for elements were in the order of B > Ni > Zn > Cu > Cr > Co > Fe > Mn > Cd > Pb > As. In most cases, Principal Component Analysis and correlation analysis showed that these methods gave similar results. However, the newly proposed sequential extraction method is a more detailed method, capable of separating metals associated with manganese oxides and iron as amorphous and crystalline fractions. Three different fractions are produced for these environmental phases instead of the BCR sequential extraction procedure in which they are represented together in the second fraction. The new method therefore specifically fractionates bioavailable manganese and iron to plants.