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