A new hope for environment clean up 
By M.Faisal Siddiqui

Environment is a treasure of all types of resources. It provides energy in the form of sunlight, a suitable temperature and nutrients for living organisms. In a properly manage ecosystem there is some sort of balance between living organisms and the environment. Disturbance in any component of environment is likely to have harmful effects on living organisms which is becoming more dangerous with every passing day. It is difficult and expensive to treat soil and water pollution .

Traditional methods for cleaning up contaminated sites such as dig and haul, pump and treat, soil venting and sparging are generally harmful. Some methods strip the soil of vital nutrients and microorganisms, so nothing can grow on the site, even if it has been decontaminated. These mechanical methods are also very expensive, relatively inefficient and generate a lot of waste to be disposed of.

Phytoremediation is an emerging technology in which plants are used for the degradation and removal of contaminants from soil and water. It is difficult to treat the soil and ground water by other methods. Plants can play a best role in the removal of wastes from soil and ground water. Specially selected or engineered plants are used for this purpose. Sites that have shallow, low level of contaminants are the best candidates for phytoremediation .Plants can degrade or remove organic and metal contaminants. This technology can be used at the polluted sites having pollutants like metals, pesticides, solvents, explosives, radionuclide, crude oils etc.

After the nuclear accident at Chernobyl, Ukraine, in 1986 Phytotech began using plants to decontaminate water and soil. This was to be the proving ground for the new technology. Iowa City used tree farms to clean landfills in 1989, after results of the Phytotech experiments were published. In 1990 phytoremediation was adopted as the method of choice to control Nitrogen contaminated aquifers in New Jersey. The first Living Machine was designed and constructed in Europe during 1995, which lead to researching genetic engineering applications. Research proved that specific plants were capable of removing toxins of certain metals. The Department of Defense and EPA joined forces to develop plant-based cleanup approaches to large scale cleanup projects.


HOW DOES IT WORK?

This technology presents several different ways in which plants can be used to clean up contaminated soil and water like phtytotransformation, rhizosphere bioremediation, phytostabilization, phytoextaction and rhizofilteration.Currently most advanced and effective phytoremediation technology is phytoextraction of heavy metals from soil using hyperaccumulating plants. Aquatic plants also hold great promise to rid contaminated water of heavy metal contaminants. Plants are selected and grown in contaminated area for a required growth period .Plants transform contaminants or absorb the pollutants through root system and accumulate the water and nutrients essential for growth as well as other components .Then plants are harvested, processed and disposed off.

Different plants have been used in various applications:

* Poplar, willow, grasses, alfalfa are used for the remediation of contaminants like herbicides, nutrients and ammunition wastes.

* Mulbury, rye for pesticides.

* Sunflower and barley for metals.

* Aquatic plants like bulrush, duckweed, algae for metals and radionuclide.

SOME AREAS STUDIED

Phytoremediation applies to all biological, chemical and physical processes that are influenced by plants and that aid in clean up of contaminated substances. Recent studies in Florida identified plants that accumulated arsenic in leaves and roots at concentration 20 to 2900 times greater than those in control plants. At the Naval Air Station Joint Reserve Base Fort Worth,phytoremediation is being used to clean up Trichloroethylene(TCE).Cottonwoods(trees)are being used .After one year ,the trees are beginning to show signs of taking the TCE(Betts,1997).

GENETIC MODIOFICATION

Genetic modification offers a new hope for phytoremediation, as GM approaches can be used to over express the enzymes involved in the existing plant metabolic pathways or to introduce new pathways into plants. Future Biotechnological strategies for enhancing phytoremediation include enlarging root mass to increase adsorption area, using agrobacteriun rhizogenes (bacteria) to altered the root morphology. The genes of plants could be altered so that the plant could take up certain contaminants, if genetically altered plants can be engineered to take up new kind of contaminants, it would allow a wider use of phytoremediation.

BNEFITS OF PHYTOREMEDIATION

Although phytoremediation can be used on every site, it is growing in popularity because of the many benefits it presents.Phytoremediation is a low cost, solar energy driven clean up technique. In many cases phytoremediation has been found to be less than half the price of alternative methods. It is most useful at sites with low level of contaminants. This technology can be used for a wide variety of environmental pollutants.Phytoremediation is long term applicable up to 95% TCE present in water could be remove by simply planting trees and letting them grow. After plants are introduced, wildlife is able to flourish at once uninhabitable site. There is no need of disposal sites. It is more likely to be accepted by the public as it is aesthetically pleasing than traditional methods. It has potential to treat sites polluted with more than one type of pollutant. It can stimulate the degradation and the removal of contaminants in the soil closely associated with plant root. Planting vegetation on site also reduces erosion by wind and water.Phytoremediation can leave usable top soil intact with minimal environmental disturbance.

LIMITATIONS OF PHYTOREMEDIATION

However phytoremediation is not without its faults, it is dependent on the depth of roots and the tolerance of plant to contaminants. Exposure of animals to plants which acts as hyperaccumulators, can also be a concern to environmentalists as herbivorous animals may accumulate contaminated particles in their cells which could in turn affect a whole food web.Phytoremediation is limited to sites with lower contaminants concentration(USEPA:1996).It is dependent on growing conditions (climate,altitude,temperature etc) required by the plant.Contaiminants collected in the tissues ( cells ) of plants may be released back into the environment ,if not disposed properly. It is slower process than other technologies. The air could be contaminated by the burning of leaves containing dangerous chemicals.


As we know that phtoremediation is a very new topic in the field of science. Phytoremediation processes hold great promise as means to clean up polluted soil and water. It is firmly believed by researchers of phytoremediation that the contaminants of metals and organic wastes by plants will provide not only effective removal of wastes from soil, but that the plants can be harvested and disposed in a safe way. It is a promising area of new research both for its low cost and great benefits to society in the clean retrieval of contaminated sites. International efforts are needed to solve it before this earth is laid waste and barren. Phytoremediation is a new hope for the environment clean up.

MUHAMMAD FAISAL SIDDIQUI
BIOTECHNOLOGIST.
CENTRE OF BIOTECHNOLOGY UNIVERSITY OF PESHAWAR