Phytoavailability and fractionation of lead and manganese in a contaminated soil after application of three amendments

Studies were conducted to determine the best management practice for immobilisation of toxic Pb and Mn in soil and the interaction of these metal contaminants with the associated plants. The research protocol comprises addition of soil amendments to accelerate physico-chemically driven sorption processes and growth of appropriate plant species to reduce physiologically driven uptake of Pb and Mn. Lolium perenne L (perennial rye grass), Festuca rubra L (creeping red fescue) and Poa pratensis L (Kentucky blue grass) were tested in the presence of soil amendments (lime, phosphate and compost, both individually and in combination). The effectiveness of treatments in stabilizing metals was assessed on the basis of metal speciation in soil, partitioning of metals in plants, and metal uptake. Significant partitioning of Pb in immobile forms was noticed by the growth of P. pratensis and Mn by the growth of L. perenne. Lime application lowered plant Pb and Mn, while phosphate decreased plant Pb and increased plant Mn. Combined amendment addition resulted in a significant decrease in the exchangeable (mobile) metal fraction in soils growing Poa for Pb and in soils growing Lolium for Mn. ECroot (ratio of root concentration to soil concentration) and ECshoot (ratio of shoot concentration to soil concentration) for Pb in Poa decreased by 72% and 60% with combined application of amendments, while the corresponding decreases for Mn in Lolium were 48% and 43%.