A project was undertaken to examine reactions of metals with soils and soluble organics and to characterize plant uptake by cadmium (Cd). The project addressed three components of the sewage sludge-soil-plant system related to the bioavailability of Cd. These were the mechanisms controlling Cd activity in sludge-amended soil, the role of soluble organics in maintaining high solution levels of Cd, and factors affecting plant uptake of Cd at low, sustained levels of free Cd ion in solution. This information is necessary if plant uptake of Cd is to be simulated successfully with a solute transport model. A large part of the research involved methods development. Analytical procedures were developed and checked for metal analyses of plant tissue and soil extracts by inductively coupled plasma emission spectroscopy and graphite furnace atomic absorption. These procedures were used to develop methods for determining speciation of Cd and other metals in soil solutions and in soil suspensions. The methods were then used to study the effects of environmental variables on metal speciation.