phytoremediation- wiki notes

introduction

• phytoremediation- using plants to take care of contamination
• to “contain, remove, or render harmless“ contaminants
• Cost-effective, BUT- not been shown to have significant change
• uses plant’s ability to “concentrate elements and compounds” and “detoxify various compounds“
  • comes from hyperaccumulators which bioaccumulate chemicals

background

• phytoremediation can be used on polluted soil or water
• used for soils with:
  • cadmium
  • lead
  • aluminium
  • arsenic
  • antimony
• such metals cause oxidative stress, break down cell membrane, cause many other negative effects etc.
• SUCCESSFUL:
  • abandoned mines- polychlorinated biphenyl dumpings- contaminated soil, water, and air
  • metal, peticides, solvents, explosives, crude oil
  • toxic waste mitigated: mustard plants, alpine pennycress, hemp, pigweed

Limitations

• limited by how extensive plant root systems are
• even with phytoremediation- groundwater can still be contaminated
• plants may, of course, die
• some metals are stuck to soil- plant can’t extract

Processes

• phytoextraction
  • takes contaminants- better for the plant- makes for a healthier plant- becomes a part of the plant
  • hyperaccumulators
  • can also be done with plants that have a low amt of pollutant capacity- but grow very fast- still remove a lot of pollutants
  • must be done with many different harvest cycles to ensure a fully clean area
  • Hyperaccumulators are metallophytes- plants that can withstand lots of heavy metals
  • list of toxins and plants that can accumulate
  • arsenic- sunflower, chinese brake fern
  • cadmium- willow ( additionally- willow was good at cadmium, zinc, copper, and can transport large amt, large biomass production, can also be used for BIO ENERGY in biomass power plants
  • cadmium and zinc- alpine pennycress, can accumulate a large amt, copper slows growth
  • chromium- tomatoes (some promise)
  • lead- indian mustard, ragweed, hemp dogbane, poplar
  • sodium chloride (for fields flooded with seawater)- barley, sugar beets
  • caesium-137, strontium-90,, sunflowers after chernobyl
  • mercury, selenium, PCBs- TRANSGENIC PLANTS- WITH GENES FOR BACTERIAL ENZYMES

phytostabilization

• “reduces mobility of substances in environment- less leakage or leaching
• fortifies “long-term stabilization”
• binds pollutants to soil-less available for organism uptake
• isolates toxins near roots but not in tissues- pollutants less available- reduces exposure
• plants can secrete subtance- triggers chem reaction, makes metal less toxic
• example:
  • vegetative cap- mine tailings
• can increase or decrease radio source mobility- specific grass used makes the difference

phytodegradation

• plants degrade organic pollutants in soil or in plant
• using enzymes secreted from roots, take in the polutants and transpire them
  • best with herbicides, trichloroethylene, methyl tert-butyl ether
• Chemical modification of environmental substances due to plant metabolism
  • inactivation, degradation, or immobillization
• orgtanic. pollutants- Cannas plant’s metabolism detoxifiys them
• plant roots+microorganisms - metabolize
• cant break down into basic molecules(water, co2 etc)
• structural change - not full breakdown

phytodegradation- metabolism

• Phase 1
  • uptake in xenobiotics
  • increase polarity of xenobiotics- by adding hydtoxyl groups
  • enzymes used: peroxidases, phenoloxidases, esterases, nitroreductases
• phase 2
  • biomolecules (glucose, amino acids), added to polarized xenobiotics- makes even more polar
• (increasing polarity- decreaseds toxicity)
• phase 3
  • xenobiotics create a structure “sequestered” - polymerize like a lignin
  • stored within the plant
  • can be toxic to animals that eat them

xenobiotic= foreign substance

phytostimulation

• making soil microbes better to degrade xenobiotics
  • uses roots mainly
• happens in rhizosphere- soil layer that surrounds roots
• plants release carbs and acids that create microbe activity- biodegrades- microoranisms can digest toxins
• effective in hydrocarbons, PCB, PAH
• can use aquatic plants- atrazine, hornwort

Phytovolatilization- turns into vapor

• removing substances from soil and water- release into air
• can be phytodegradation that resulted in less harmgul substances
• xenobiotics takes up and transpirated, gets evaporated in atmosphere
  • volatilization happens at stem and leaves
  • indirect volatilization- volatilized at roots
  • Se and Hg--- good phytovolatilization from soil qith poplar trees (high transpiration rate)

rhizofiltration

• water filtered through roots to remove xenobiotics
• substances remain in roots
• used to cleangroundwater- planting directly in site- or removedd and treated in a diff location

biological hydraulic containment

• when plants draw water from soil into roots and out of plant
• decreases downward mov ement of contaminants into water

phytodesalination

• halophytes (plants that can withstand salty soil)
  • used to remove salt from soil and improve quality for other plants

GENETICS!!!!!!

• breeding and GENETIC ENGINEERING are “powerful tools“ for phytoremediation
• genes can come from a microorganism or from another plant thats better suited for cleanup
• EG::: genes for nitroreductase from bacteria- put into tobacco- faster TNT removal- better resistance to TNT
• new discovery- mechanism in plants that lets them grow even when soil is toxic.
  • natural biodegradable compounds, eg. exogenous polyamines, lets plants withstand 500x higher amt of pollutants

hyperaccumulators and biotic interactions

• hyperaccumulator- concentrate toxins greater than or equal to set amount (amount varies by pollutant)
  • eg. >100mg/kg for nickel, >10,000mg/kg for zinc
• ability to accumulate- hypertolerance (just thru evolution and adaptations)

phytoscreening

• biosensors of subsurface contamination- toxins can be dealt with quickly
• extract part of plant to see if contaminated

Hyperaccumulators:

• can grow in high conc of metals
• can absorb metal through roots
• can store high amts of metal in tissues
• ability to hyperaccumulate due to different GENE EXPRESSION AND REGULATION of genes found in said species and related ones

physiological basis

• in normal plants- more metal in roots than shoots
• in HAs (hyperaccumulator) plants- more metal in leaves--- metals are brought to shoots to protect roots from toxins
• lack of knowledge on tolerance::::::::::
  • tolerance and accumulation are separate and moderated by genetics and physiological things
• species spec characgterists
  • alpine pennycress accumulates more zinc but when there is a low supply
• active accumulation
  • low concentration
• passive accumulation
  • very high concentration

genetic basis

• HA (hyperaccumulator) geenes foiund in 450+ species
• ability to hyperaccumulate if::::envifronmental expostre and expressiioin of ZIP gene framily
  • envtion exposure- only plants that are exposed to such metals have the opportunity to absorb such metal
  • but comes down to genes
  • can b inheritied
• ZIP family- encodes Cd, Mn, Fe, and Zn transporters, supplying ZN to metalloproteins
• ZTP and ZNT families- zinc transproters
• zinc transporters cant discrinimtate agaisnt speciici metal ions- can accumulate a wide variety of metals
  • hyperaccumulation happens with an overexpressed Zn transport system- plants cant differentiate between different kinds of metals

metal transporters

• another important trait: good translocation of metal to shoot.
• usually tolerated by plants that are native to metalliferous soils
• ways plants can tolerate
  • exclusion:
  • resist metal (bad)
  • absorbtion and sequestratioin (good for remediaton)- pass metal thru shoot and accumulate it
    • hyperaccumulators need this ^ and the ability to absorb 100x more metal than others

metallophyte

• plant that can tolerate high amounts of heavy metals
• Obligate metallophytes- can only survive with these metals
• facultative metallophytes- can tolerate them, but arent bound to them
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