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Phosphate-Induced Pb Immobilization in a Contaminated Soil

Explore the effectiveness of phosphorous application methods and plant presence in immobilizing Pb in contaminated soil. Assess metal accumulation in plants grown on a contaminated site.

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Phosphate-Induced Pb Immobilization in a Contaminated Soil

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  1. Phosphate-Induced Pb Immobilization in a Contaminated Soil Joon ki Yoon Department of Soil and Water Science University of Florida

  2. RATIONALE • Soil contamination by heavy metals from abandoned disposal and industrial sites is environmental concern • A total of 1,208 Pb contaminated sites are currently listed on the EPA National Priority List • Toxicity and bioaccumulation in food chain make it necessary to remediate Pb contaminated sites

  3. OBJECTIVES • Examine the effectiveness of various phosphorous application methods on Pb immobilization in soil • Evaluate the effects of plants on phosphate induced Pb immobilization in soil • Explore metal accumulation in plants growing on a contaminated soil

  4. The study site in Jacksonville • Located in a urban area of Northwest Jacksonville • Occupies approximately 1 acre • Covered with vegetation • Used to be gas station, salvage yard, and discharging area

  5. Experiment 1-Application method • OBJECTIVE Examine the effectiveness of various phosphorous application methods on Pb immobilization in soil

  6. Effects of Phosphorous on Pb immobilization • Ca9.5(PO4)5CO3FOH +10H+ 9.5Ca2+ + 5H2PO4- + CO32- + F- + OH- (dissolution) 9.5Pb2+ + 5H2PO4- + CO32- + F- + OH- Pb9.5(PO4)5CO3FOH + 10H+ (precipitation) • In situ Pb stabilization using phosphorous is sustainable and cost-effective.

  7. Column leaching test • 45 cm x 3.5 cm • PVC column • 18 columns ( 3 rep) • Phosphoric acid (PA) • Phosphate rock (PR)

  8. Column leaching test • P/Pb ratio: 4 • 1st 20-cm filled with contaminated soil (Total Pb 5012 ppm) 2nd 20-cm with clean soil (Total Pb 77 ppm) to simulate field condition • Column incubated for 6 weeks after P application • Leaching test was conducted twice (after 1wk and 5 wks)

  9. W M Ctd-soil (0-20 cm) L Clean soil (20-40 cm) Five P treatments • Rphosphate Rock • Aphosphoric Acid • MMixing • LLayer • WWeek • SSimultaneous • 11time • 22times • ½ PR + ½ PA RLAS1 RMAS1 RMAW1 • ½ PR + ¼ PA + ¼ PA RLAW2 RMAW2

  10. Parameters determined • Chemical - Soil pH - Soluble P and Pb concentrations in soil - Distribution of Pb in soil column - Toxicity Characteristic Leaching Procedure (TCLP) • Biological - Physiologically-Based bioavailibiity test (PBET) • Mineralogical (not shown) - X-ray diffraction (XRD) - Scanning Electron Microscopy (SEM)

  11. Effects of phosphoric acid addition on soil pH R:Phosphate rock M: Mixing W:Week 1: 1 time A: Phosphoric acid L:Layer S:Simultaneous 2: 2 time

  12. Leachate Pb (ppb) in soil column R:Phosphate rock M: Mixing W:Week 1: 1 time A: Phosphoric acid L:Layer S:Simultaneous 2: 2 time

  13. Leachate P (ppm) in soil column R:Phosphate rock M: Mixing W:Week 1: 1 time A: Phosphoric acid L:Layer S:Simultaneous 2: 2 time

  14. Distribution of Pb in column a b c c a b ab c b ab R:Phosphate rock M: Mixing W:Week 1: 1 time A: Phosphoric acid L:Layer S:Simultaneous 2: 2 time R:Phosphate rock A: Phosphoric acid M: Mixing L:Layer W:Week S:Simultaneous 1: 1 time 2: 2 time

  15. TCLP analysis ab a ab ab b b a b b c R:Phosphate rock M: Mixing W:Week 1: 1 time A: Phosphoric acid L:Layer S:Simultaneous 2: 2 time

  16. Pb bioavailability-PBET (mg/L) PBET Pb(mg/l) PBET Pb(mg/l) R:Phosphate rock M: Mixing W:Week 1: 1 time A: Phosphoric acid L:Layer S:Simultaneous 2: 2 time R

  17. SUMMARY 1 • Application of PA reduced soil pH by 1 unit, within Florida soil range • Applying mixture of PA and PR effectively reduced TCLP-Pb (<95%), bioavailable Pb (<42%) and vertical Pb migration (<80%)in soil • Application of phosphate rock as a layer was effective in Pb migration reduction • RMAS1was overall the most effective in Pb immobilization

  18. Experiment 2-Plant effect • OBJECTIVE - To determine the effects of plants on phosphate induced Pb immobilization

  19. Methods • 3 plant species - Agrostis capillaris - Lolium rigidum - Brassica napus • 2 phosphorous application methods - PR - ½ PR + ½ PA • Plants grown in a Pb-contaminated soil(Total Pb 5012ppm) for 4 wks • Plant and soil samples were characterized - PBET - SEM

  20. Treatments • Control 1: Soil + PR • Control 2: Soil + ½ PR + ½ PA • Treatment 1: Soil + PR + Plant • Treatment 2: Soil + ½ PR + ½ PA + Plant

  21. Effects on bioavailable Pb-PBET PBET Pb(mg/l)

  22. Scanning electron microscopy elemental dot map of Agrostis capillarisroots(PR only) P Si Pb Ca

  23. Scanning electron microscopy elemental dot map of Lolium rigidum roots (PR only) Al Si Pb Ca P

  24. Scanning electron microscopy elemental dot map of Brassica napus roots (PR only) Al Si Ca P Pb

  25. SUMMARY 2 • The presence of plant enhanced Pb immobilization when applied with PR but not with PR+PA • Reduction in Pb bioavailability in rhizosphere may be due to formation of Pb phosphate

  26. Experiment 3-metal accumulation • OBJECTIVES - Determine the concentrations of Pb, Cu and Zn in plant biomass - Compare metals concentrations in the aboveground biomass to those in roots and in soils - Assess the feasibility to use these plants for phytoremediation purpose

  27. Experiment 3-metal accumulation • Sampling date: 12-2002 • Plant sampling • Coverage at the site • 36 samples of 18 species from 10 locations • Divided into roots/shoots • Air dried and ground • Soil sampling • Surface soil: 0-20 cm • Air dried and sieved (2-mm) • Digested using the hot-block procedure (US EPA Method 3050) • Analyzed for total Pb, Zn, Cu using atomic absorption spectrophotometry

  28. Sampling locations

  29. Site characteristics

  30. Criteria for hyperaccumulator • Total metal concentration in plant • >1,000 mg kg-1 of As, Cu, Co, Cr, Ni or Pb • >10,000 mg kg-1 of Mn or Zn • Bioconcentration factor (BCF) > 1 • Elemental concentration ratio of plant to soil • Ability to accumulate elements from soils • Translocation factor (TF) > 1 • Elemental concentration ratio of shoot to root • Ability to translocate elements from root to shoot

  31. Metal concentrations in plants • Pb concentrations 5 to 1,183 mgkg-1 • Cu concentrations 4 to 460 mg kg-1 • Zn concentrations 17 to 598 mg kg-1 • Maximum value found in the roots of Phyla nodiflora

  32. Plants with high BCF and TF

  33. SUMMARY 3 • No plant species were identified as metal hyperaccumulators • Gentiana pennelliana was most effective in taking up all three metals, with BCFs ranging from 0.54-22 • Cyperus esculentus was most effective in translocating all three metals ranging from 1.0-2.8

  34. CONCLUSIONS • Application of phosphoric acid and phosphate rock mixture was effective in reducing soluble, bioavailable, and TCLP Pb as well as Pb migration in soil • The presence of plant enhanced Pb immobilization in soil when applied with PR but not with PR+PA • No Pb hyperaccumulator was identified from plants growing on a contaminated-site in Jacksonville.

  35. ACKNOWLEDGEMENT Advisor: Dr. Lena Q. Ma Committee: Dr. Jean-Claude Bonzongo Dr. Willie G. Harris Trace Metal Biogeochemistry lab group

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