Phytoremediation Of Metals: An Overview

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Phytoremediation Of MetalsAn Overview

• Kirk Cammarata

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Metal Pollution

• Fe, Zn, Cu, Ni, Cd, As, Hg, U, Mo, Be, Se, etc
• Anthropogenic Activities
• Excessive levels in sensitive places
• Toxicity
• Arises from interactions w/ protein
• Competition for functional metals
• Disrupt protein structure
• Oxidative stress

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Metal Pollution

• HEAVY METAL !

• Regulatory levels typically lt100 PPM
• Big Problem Persistence

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Phytoremediation of Metals

• Phytoremediation of Metals

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Phytoremediation of Metals

• Phytoremediation Disadvantages
• Slower
• Less Effective (Surface Soils Only)
• Phytoremediation Advantages
• Semi-passive Cheaper (5 - 80 of traditional)
• Aesthetically Pleasing
• Suited for milder contamination, abandoned
  sites
• Less site disturbance

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Mechanisms of Phytoremediation

• DNAPL/LNAPL

• Hyperaccumulation
• Rhizofiltration

• Bacteria
• Mycorrhizae
• Wetlands

• Precipitation, Sequestration

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Phytoremediation Wetlands

• Trap metals
• Bind C AVS

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Plant Responses To Metals

• Peripheral Accumulation
• Binding to root mass

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Plant Responses To Metals

• Metal (As) hyperaccumulation requires chelators
  within the cell

• Schoger et al., 2000
• (Rauvolfia, Silene)

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Phytoremediation

• The Engineered Use of Plants To Render
  Environmental Pollutants Less Harmful

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Zn Compartmentation

• Lasat etal., (1998)

• Kupper etal., (1999)

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Plant Responses To Metals

• Hyperaccumulation
• Accumulation within plant cells
• Concentration of metal above solution levels
• Metal transported into shoots

• Edenspace

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SUMMARY

• Hypothesis Plants can remedial metal pollution
• Methods Put metal on plants and see what happens
• Conclusion Plants will solve all of the worlds
  pollution problems

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Ni Transport in Xylem

• Kramer etal., (1996)

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Mercury Reduction and Volatilization

• Rugh et al., 2000

10 mg arabidopsis seedlings 5 uM Hg2
(sublethal)
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Growth of Transgenic Arabidopsis Plants on
Organomercurials

• Rugh et al., 2000

Key merA Hg2 --gt Hg0 merB R-CH2-Hg --gt
Hg2 and Hg2 --gt Hg0 RLD normal control
plants A no mercury _at_ 4 wks B 2 uM PMA_at_ 4
wks C 2 uM PMA _at_ 6 wks D no mercury _at_ 5
wks E 0.5 uM MM _at_ 5 wks F 2 uM MM _at_ 5 wks G
2 uM MM _at_ 8 wks H no mercury _at_ 3 wks I 1 uM
PMA _at_ 3 wks (B1-8 transgenic lines)
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Future Directions For Phytoremediation of Mercury

• Engineer plants more practical for contaminated
  environments
• Poplar Trees
• Wetland Plants
• Problem
• Volatilization to atmosphere
• Want to localize in plant
• Mining Gold, Platinum, etc

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• Heavy Metal

• HEAVY METAL !

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Metal Pollution Sources

• Industrial Activities
• Smelting, Electroplating
• Magic Marker
• Military
• Includes Brownfields - Abandoned Sites

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Abandoned Zn Smelter Site
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Metal Pollution Sources

• Mining Activities
• Precious Metals
• Oil and Gas
• Coal
• Acid Mine Drainage (AMD)

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AMD From Coal Mining
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AMD From Coal Mining
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AMD From Coal Mining
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AMD From Coal Mining
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AMD From Coal Mining
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Metal Pollution Sources

• Atmospheric Deposition
• Automobiles Pb
• Coal Burning Hg, As

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Metal Pollution Other Sources

• Highways
• Urban Highway Runoff Zn, Cd, Pb, Cu
• Autos Tires, Brakes, Trim, Exhaust
• Maintenance Guardrails, Bridges, Herbicides,
  Salt and Cinders
• NPDES permits may be required
• Agricultural
• Landfills
• Shooting Ranges

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Mechanisms of Phytoremediation

• Natural adaptations to metal stress
• Some species tolerant of high metals
• Hyperaccumulators gt 0.1 dry weight as metal
• Some accumulate gt 3 dry wt as metal
• Alyssum, Thlaspi, Brassica
• Tolerant non-tolerant species of each
• Indicator species for mineral prospecting

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Phytoremediation Wetlands

• Aqueous waste streams
• Landfill Leachates, Polishing Treated Sewage
• Aerobic vs Anaerobic processes

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Plant Responses To Metals

• Toxicity Growth inhibition or death
• Tolerance Exclusion
• Tolerance Hyperaccumulate

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Remediation of Metals

• Change form, concentration, distribution
• Traditional Treatment
• Water Chemical Treatment
• Soil Wash, Landfill, Solidify, Cover
• Expensive

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Plant Responses To Metals

• Metal hyperaccumulation requires transport to
  shoots
• Metal must traverse cells (membranes)
• Transporters required

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Water and Mineral Transport in Plants

• Uno, Storey, Moore (2000)

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Water and Mineral Transport in Plants

• Stern (1994)

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Plant Responses To Metals

• Metal transport to shoots
• Plants transporting metals have high levels of
  chelators in their xylem sap
• Organic acids malate, citrate, acetate
• Amino acids histidine
• Root cells must actively secrete

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Genetic Engineering

• Potential to improve upon limitations of
  naturally tolerant plants
• Create plants for special situations

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Strategy For Phytoremediation Of Mercury

• Some bacteria grow in Hg-contaminated
  environments
• Human gut
• can convert toxic forms to harmless forms
• evolved enzymes and genes encoding them
• merA Hg2 --gt Hg0
• merB R-CH2-Hg --gt Hg2
• Strategy
• Genetically engineer bacterial genes into plants

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Plant Responses To Metals

• Tolerance by Exclusion
• Keep metals out or unavailable
• Secrete organic acids citrate, malate, oxalate
• Precipitate by Root OxidationPhytostabilization

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• Continuous Extraction

• Induced Extraction

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Morphology of Plants Exposed to Ionic Mercury or
Gold
merA -
merA -
merA -
A
B
Au2
Hg2
-

• Rugh et al., 2000

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Phytoremediation

• Metal Pollution Toxicity and Examples
• Mechanisms of Plant Responses to Metals
• Examples of Phytoremediation
• Genetic Engineering Hg Phytoremediation

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AMD From Coal Mining