Phytoremediation

Dr. Tini Surtiningsih, Ir., DEA

PhytoremediationPhytoremediation is the use of plants,

trees and herbaceous species to eliminate or degrade contaminants or reduce their bioavailability in both water and soil.

Many chemical species that can be treated with phytoremediation techniques, which compriseheavy metalsorganic compounds such as pesticides,

solvents, and other persistent pollutants (PCB´s)

Phytoremediation can be applied as long as the concentration of the pollutant is within an appropriate concentration range, which shall not be too high, since it may cause phytotoxicity to the plant

Phytoremediation can be performed following different methods:

Phytoextraction: Uptake and concentration of pollutants from the environment into the plant biomass.

Phytostabilization: Reduction of the mobility of the contaminants in the environment.

Phytotransformation: Chemical modification of the environmental substances as a direct result of the plant metabolism.

Phytostimulation: Enhancement of the native soil microbial activity for the degradation of contaminants.

Phytovolatilization: Removal of substances from soil or water with release into the air.

Rhizofiltration: Filtering water through a mass of roots to remove toxic substances or excess nutrients.

Regarding the rhizosphere, there are other techniques besides the rhizofiltration.

The roots can be used as stimulator of the micro-organisms living there due to the exudates that plants expulse in this medium.

This can increase the amount of organisms in 2 or 3 orders of magnitude.

Within remediation, one of the most important factors to take into account is the tolerance of the plant.

The same chemical species may produce different effects at the same concentration in different plants.

For this reason, it is important to know about the background levels in the polluted area: Sites with natural high concentration of some

pollutant may lead to an increased presence of tolerant species.

These species are of big interest for phytoremediation and hence many are used for remediation purposes.

These plants are able to accumulate due to different detoxifying mechanisms such as the chelation of heavy metals or the storage of the contaminants in vacuoles or the cellular wall

Plants which are able to accumulate extremely high concentrations in their tissues are considered hiperaccumulator species. Although their ability of accumulating high concentrations of metals is highly interesting, these species normally only show low growth rates and hence are not suitable for extracting high amounts of pollutants from the soil.

However there are plants which are able to accumulate lower concentrations of metal but present higher growth rates. For this reason, these species showed to be more suitable for phytoextraction processes.

The low accumulation capacity of these species may be highly improved by the addition of synthetic chelates, which increase the solubility of metal in the soil, making them more bioavailable for the plant and hence increasing the uptake rate of metals by the plant

. Examples of chelating agents are EDTA, NTA or weak organic acids, such as citric acid. Chelates, however, have to be used with caution, since they may increase the mobility of pollutants, posing a risk of contamination of underlying groundwaters

They may also provoke negative effects for the native microbial community of the soil. In particular, EDTA has recently been banned as a chelating agent, due to its toxicity for the soil microbiota and its high persistence.

These plants are able to accumulate due to different detoxifying mechanisms such as the chelation of heavy metals or the storage of the contaminants in vacuoles or the cellular wall

Plants which are able to accumulate extremely high concentrations in their tissues are considered hiperaccumulator species. Although their ability of accumulating high concentrations of metals is highly interesting, these species normally only show low growth rates and hence are not suitable for extracting high amounts of pollutants from the soil.

However there are plants which are able to accumulate lower concentrations of metal but present higher growth rates. For this reason, these species showed to be more suitable for phytoextraction processes.

The low accumulation capacity of these species may be highly improved by the addition of synthetic chelates, which increase the solubility of metal in the soil, making them more bioavailable for the plant and hence increasing the uptake rate of metals by the plant

Examples of chelating agents are EDTA, NTA or weak organic acids, such as citric acid. Chelates, however, have to be used with caution, since they may increase the mobility of pollutants, posing a risk of contamination of underlying groundwaters

They may also provoke negative effects for the native microbial community of the soil. In particular, EDTA has recently been banned as a chelating agent, due to its toxicity for the soil microbiota and its high persistence.

To improve the effectiveness of these technologies, genetic manipulation of some organisms can be used.

For example, tobacco plant was inoculated with bacterial genes encoding a nitroreductase enzyme.

Genetically engineered tobacco plant showed a significantly faster degradation of TNT and an enhanced resistance to the toxic effect of the explosive.

Regarding the economical aspects of these technologies, some studies suggest that when a phytoremediation process is used instead the conventional processes, the costs may be reduced up to 50-60%. However, the effectiveness of the process has

to be taken into account. Although the price is significantly lower, the time needed for the remediation may be

much longer.

No specific regulatory standards have been developed for phytoremediation processes, so that installations must be approved on a case by case basis. There are several regulatory issues which will need to be addressed on most sites

Several methods exist for the disposal of the harvested pollutant-rich crop after a phytoextraction process: Pre-treatment processes aim to reduce the volume of biomass to be treated, by strongly reducing its water content. Composting, compactation and pyrolisis are the most important ones. After the pre-treatments, the final disposal of vegetal material takes places.

Although the only technique used in praxis is the incineration (in combination with filtering mechanisms to clean the gas effluent), other techniques exist, such as the direct disposal in a deponie.

Other techniques also are being developed at a laboratory scale, such as the ashing or the liquid extraction techniques. However they still lack the required technology for its on-field application

Phytoremediation is an emerging and promising technology which permits a low cost alternative to other remediation processes.

However, the mechanisms behind the remediation process still need to be better understood, so that the best species-pollutant combination can be chosen.

Other problems such as contaminant migration need to be focused in further studies to minimize the drawback of this new technology.

TERIMA KASIH ATAS PERHATIANNYA

Wassalamu’alaikum Wr. Wb.

FitoremediasiFitoekstraksi/fitoakumulasiRhizofiltrasiFitostabilisasi, mobilisasi logam Fitodegradasi/fitotransformasi,

menguraikan/menghancurkan log beratFitovolatilasiRhizodegradasi, mikroba rhizosfir

Kelebihan fitoremediasiMemanfaatkan cahaya matahariBiaya murahMudah diterima masyarakat

Bioremediasi EXSITU, mahalBioremediasi INSITU, lebih murah

Keterbatasan fitoremediasiTerbatas pada air dan tanahCara kerja lambatMeracuni tnamanPotensi racun masuk makananRacun sulit diketahui jenisnyaHanya untuk lingkungan tanah dan air

Jenis tanaman fitoremediasiBunga matahari/ Heliantus anuus :

mendegradasi UraniumPopulas trichocarpa, P.deltaritas Famili

sacnaceae : mendegradasi TCE (Trichloroethylene)

Najar graminae (tumbuhan air) : menyerap Co, Pb,Ni

Vetiver grass (Vetiveria zizonaides), akar wangi : mendegradasi Pb, Zn

Tanaman air fitoremediasiMenyerap/mengakumulasi logam berat pada

semua jaringanKangkung airTerataiEceng gondok

Bioremediasi dengan mikrobaDengan 2 caraOxidasi, bersamaan pertumbuhan mikrobaReduksi, elektron akseptor

Akumulasi logam pada dinding selAkumulasi logam dalam vakuola selMenghasilkan enzim pendegradasi logam,

eksoenzim diluar sel, endoenzim dalam sel

Mikroba bioremediasi logamBakteri mentransformasi Fe : Thiobacillus, Leptothrix, Crenothrix,Sulfolobus, Gallionela

Bakteri mentransformasi Mn :Arthrobacter, Leptothrix, SphaerotillusHg : Pseudomonas, Bacillus