Interaction Between High Levels of Applied Heavy Metals and Indigenous Soil Manganese

Abstract

AbstractThe importance of indigenous soil Mn level on plant Mn uptake from metal salt or sewage sludge amended soils was investigated. Twelve soil materials, six surface and six subsurface, were amended with either varying rates of a composite of Cd, Cu, Ni, and Zn sulfate salts, equivalent to the total of these metals present in a digested sewage sludge (Washington, D.C.) at rates of 0–896 dry metric tons/ha or with the sludge itself, at 224 dry metric tons/ha. Corn (Zea mays L.) was grown in the greenhouse for 30 days, 1 year after amendment application. Two pH levels of about 5.5 and 6.5 were maintained during the experiment on the metal salt amended soil materials.Plant tissue Mn levels increased with the application of Cd, Cu, Ni, and Zn (in combination) as metal salts or as sewage sludge over the range of soil materials used. The amount of increase with a given increase in applied metals was greater for the unlimed than for the limed metal salt treatments. Elevated tissue Mn concentrations were positively and significantly correlated with the indigenous levels of soil Mn. A tissue Mn level of over 3,000 µg/g was observed with unlimed metal salts equivalent to 896 dry metric tons/ha of sludge with Manor Ap horizon soil material. Studies by others suggest that elevation of tissue Mn levels may be related to replacement of Mn from Mn “oxides” by the applied heavy metals.The interaction between applied heavy metals and indigenous soil Mn may affect guidelines for disposition of metal‐bearing wastes on soils. Soils regarded as acceptable for waste disposition, but which have high native Mn levels, may produce higher plant tissue Mn levels than similar soils with lower native Mn.