AVAILABILITY OF APPLIED HEAVY METALS AS A FUNCTION OF TYPE OF SOIL MATERIAL AND METAL SOURCE

Abstract

The authors applied the heavy metals Cd, Cu, Ni, and Zn, as sulfate salts and as lime-stabilized, digested Washington, D.C., sewage sludge, to surface and subsurface horizon materials of six Maryland soils in the greenhouse. Rates of metal addition were equivalent to field rates of 224 metric tons (t)/ha of the sludge. Corn (Zea mays L.) was grown for 30 d, 13 mo after treatment application, and the tissue was analyzed for metals. Yields of plant material were generally enhanced by sludge and suppressed by metal salts. Tissue levels of both Cd and Zn were considerably elevated. In general the sludge did not elevate tissue Cu and Ni, whereas metal salts slightly elevated tissue Cu and Ni with some soil materials. An interaction between type of soil material and source of metal on plant tissue metal levels was observed. Essentially inert soil materials tended to produce tissue with the highest metal levels when metal-salt-treated, but with the lowest metal levels when sludged. Conversely, reactive soil materials, tended to produce tissue with relatively lower levels of metals than other materials when metal-salt-treated, but with relatively high levels when sludged.