Date of Award

Spring 1997

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Geology

Committee Director

Joseph H. Rule

Committee Member

Frank Dudas

Committee Member

G. Richard Whittecar

Call Number for Print

Special Collections LD4331.G4 I67

Abstract

The large biomass of corn (Zea mays) and promising results from a previous experiment (Chlopecka and Adriano, 1995) concerning metal uptake by corn indicate that corn may be a good candidate for phytoremediation of trace metal contaminated soil. Appling soil (acid, thermic, typic paleudult) was treated with increasing levels of a metal rich flue dust based on Zn concentration (0, 150, 300, 600, 1200, and 2400 mg/kg). Four replicates at each Zn treatment level were either limed to pH 6.3-6.5 and covered with a two inch thick layer of organic matter rich topsoil (OM), unlimed and covered with OM, limed with no OM, or unlimed with no OM. Eight corn seeds were planted per pot and the pots randomly arranged on benches in a whitewashed greenhouse in early June. After a germination period of sixteen days, plants were removed from each pot leaving four plants per pot which grew for an additional five weeks. Acid digestions of plant tissue were analyzed for Cd, Cu, Fe, Ni, Mn, Pb, and Zn by Atomic Absorption Spectrophotometry (AAS). Soil samples from the start and end of the experiment were selectively extracted and analyzed for the same metals by AAS.

Trace metal concentrations for corn top tissues ranged from 30.0 - 6500.0 mg/kg Zn, 1.0 - 24.0 mg/kg Cd, 4.0 - 12.0 mg/kg Cu, 90.0 - 200.0 mg/kg Fe, 2.0 - 6.5 mg/kg Ni, 200.0 - 2000.0 mg/kg Mn, and 3.0 - 21.0 mg/kg Pb. Trace metal concentrations for corn root tissues ranged from 70.0 - 8450.0 mg/kg Zn, 1.0 - 107.0 mg/kg Cd, 3.0 - 63.0 mg/kg Cu, 1450.0 - 3500.0 mg/kg Fe, 3.0 - 14.0 mg/kg Ni, 175.0 - 1400.0 mg/kg Mn, and 5.0 - 320.0 mg/kg Pb. The total weight of trace metals removed from the soil by the corn plants (top and root tissue) was calculated and these data were extrapolated to fully grown corn plants. The results of this extrapolation suggest that corn may be an effective phytoremediator of soils moderately contaminated by Zn and/or Cd. Very broad time estimations were on the order of 5 to 20 growing seasons for decontamination of Zn and/or Cd depending on initial contamination level.

The OM rich topsoil amendment caused more rapid germination and increased dry biomass of the corn at all contamination levels. For every metal analyzed, the OM rich topsoil amendment decreased the amount of metal in the plant tissue grown in both the slightly acidic (6.3 & pH & 7.0) and acidic (4.0 & pH & 6.0) soils. While pH governs the overall mobility and speciation of trace metals, the results from this experiment suggest that organic matter may determine the amount of metal that ultimately becomes bioavailable.

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DOI

10.25777/tfq6-qs08

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