Nutrient and trace element dynamics in blended topsoils containing spent foundry sand and compost

Spent foundry sand (SFS) could be used with compost to produce blended synthetic topsoil material but many environmental agencies restrict such use out of concern for leaching and plant uptake of contaminants in SFS. A 3 yr field experiment assessed the potential for contaminant leaching and plant uptake from natural soils and blended synthetic topsoils made with three SFSs and three composts. Plots were instrumented with lysimeters and planted with perennial ryegrass (Lolium perenne L.). Growth was better on blended soils than natural soils and tissue content of most nutrients and trace elements remained within normal ranges in plants grown on both blended and natural soils, though concentrations of N, P, K, S, B, Cu, Mo, and Zn were larger from some of the blended soils. Blended soils leached more P and K than natural soils and blended soil made with low C/N ratio compost leached more NH₄ than the natural soil. All blended soils leached more Cu, and some leached more As, Mo, and Zn than natural soils. With the exception of As in leachates from one blended soil no trace elements exceeded drinking water standards. None of the 13 polyaromatic hydrocarbons or 11 phenolics analyzed was detected in the leachates. We conclude use of SFS in blended soils presents low risk from trace metal or organic contaminants in SFS. Blended soils with SFS and compost perform well as topsoil substitutes and the greatest environmental risk is N and P leaching from use of low C/N ratio or immature composts.