Assessment of lead speciation by organic ligands using speciation models

The biogeochemical behaviour of lead (Pb) in ecosystems greatly depends on its chemical species. Organic ligands strongly influence Pb species and mobility in soil solution. In the present study, two metal speciation models, Windermere Humic Aqueous Model (WHAM) and Visual Minteq are used to compute Pb speciation in nutrient solution in the presence and absence of organic ligands. The three organic ligands used include ethylenediamine tetraacetic acid (EDTA), citric acid (CA) and fulvic acid (FA). The results show that in the absence of organic ligands, Pb2+ is the dominant form under acidic conditions and Pb-OH under alkaline conditions. The presence of organic ligands strongly influences Pb speciation. EDTA is more effective than are CA and FA concerning its influence on Pb speciation due to high Pb binding capacity. The results also indicate that Pb binding capacity of organic ligands varies with solution pH.