Phytoremediation

Phytoremediation

Phytoremediation is the use of plants and their associated microorganisms in order to remove, degrade or isolate toxic substances from contaminated soil, water or air.

Phytoremediation is useful by cleaning soil contaminated with:

- petroleum hydrocarbons (BTEX)

- pesticides and herbicides (atrazine, bentazone, chlorinated and nitroaromatic compounds)

- industrial organic wastes (PCPs, PAHs)

- metals (Pb, Zn, Cd, Cu, Ni, Hg)

- inorganic compounds (NO3- NH4+, PO43-)

- chlorinated solvents (TCE, PCE)

- metalloids (As, Sb)

- radioactive chemical elements (U, Cs, Sr)

- explosive substances (TNT, DNT)

The most important methods of phytoremediation:

- phytodegradation (phytotransformation);

- phytostabilization (phytoimmobilization);

- phytovolatilization;

- phytoextraction (phytoaccumulation, phytoabsorption or phytosequestration);

- phytofiltration;

- rhizodegradation (phytostimulation).

By phytodegradation organic contaminants are metabolized or mineralized inside plant cells by specific enzymes:

- nitroreductases

(degradation of nitroaromatic compounds);

- dehalogenases (degradation of pesticides and chlorinated solvents);

- laccases (degradation of anilines).

Plant-species:

- Populus species

- Myriophyllium spicatum

Phytostabilization is used to avoid mobilization of contaminants (binding of contaminants) and to limit their diffusion in the soil

Plant-species:

- Haumaniastrum

- Eragrostis

- Ascolepis

- Gladiolus

- Alyssum

Phytovolatilization use the ability of some plants to absorb and volatilize certain metals and / or metalloids into the atmosphere.

Plant-species:

- Astragalus bisulcatus and Stanleya pinnata(Se)

- transgenic plants (with bacterial genes) of Arabidopsis thaliana, Nicotiana tabacum, Liriodendron tulipifera or Brassica napus (Hg)

Phytoextraction is the use of plants to absorb, translocate and store toxic contaminants from soil into their root and shoot tissues. Useful by metals (Cd, Ni, Cu, Zn, Pb) but also other elements (Se, As) and organic compounds.

Hyperaccumulator plants species for Cu, Ni, Zn/Cd:

- Elsholtzia splendens, Alyssum bertolonii, Thlaspi caerulescens and Pteris vittata

Phytofiltration is the use of roots to uptake and store contaminants (e.g. heavy metals or radioactive elements) from an aqueous environment.

Plant-species:

- Helianthus annus

- Brassica juncea

- Phragmites australis

- Fontinalis antipyretica

- several species of Salix, Populus, Lemna and Callitriche

Rhizodegradation is the use of rhizospheric associations between plants and symbiotic soil microbes to degrade contaminants.

Plant-species:

- genus Pseudomonas

Advantages of phytoremediation:

- low cost;

- the plants can be easily monitored;

- the possibility of the recovery and re-use of valuable metals;

- passive technique;

- reduced impact;

- reduction in dispersal of dust / contaminats by wind.

Disadvantages of phytoremediation:

- phytoremediation is limited to the surface area and depth occupied by the roots;

- metal concentrations in soil can be toxic / lethal to plants;

- slow growth and low biomass require a long-term commitment;

- it is not possible to completely prevent the leaching of contaminants into the groundwater;

- bio-accumulation of contaminants, especially metals, into the plants which then pass into the food chain from primary level consumers.

Special characteristics of plants used by phytoremediation are:

- rapid growth;

- high biomass production;

- tolerance to high concentrations of metals;

- accumulate high concentrations in their aerial tissues;

- profuse root system;

- easy to cultivate and harvest.