With industrialization, many toxic substances have contaminated land, water and air. Such contamination can have an adverse affects on the health of the living organism and subsequently on that of the ecosystem as a whole. Among the many techniques that have been developed to reduce or remove the contaminants, the cheapest technique is the use of living organism- plants and micro-organisms. When living organisms are used to reduce or remove the contaminants it is called bioremediation. When plants are used for the removal of the contaminants, it is called Phytoremediation.

Technologies used:
The role of plants is not just limited to purifying air by absorbing pollutants like carbon-dioxide, bad odour etc but they can also be used for removing certain pollutants from the land.  It can be done by any of the following methods:

Phyto-extraction: Some plants are able to tolerate certain toxic substances like metals and radionuclide. So depending upon the contaminants present in the soil, different types of plants are cultivated in the polluted area. These roots of the plants take up the contaminants and pass it to the different parts of the plants above the ground. When the plants grow, they are harvested and taken away. This process is continued till the level of the contaminants is reduced to a permissible limit. If the soil contained some precious metals than, after harvesting the plants it is further processed to extract the metal by the process called phyto-mining.

Phyto-stabilization: The main objective of phyto-stabilization is to reduce the spreading of metal to other areas through erosion, leaching etc. Sometimes soil amendments like compost manure, yard manure, debris etc are also added to the soil. The plants can affect the bioavailability of the contaminants by releasing certain chemicals which changes the soil condition thus affecting the mobility of the contaminants like metals. The roots of the plants may also absorb and accumulate the metals or cause it to precipitate it around the roots zone. This prevents the contaminants from leaching to the ground water or getting exposed to agents of erosion like wind, rain etc.

Phyto degradation: This technique is usually employed for removing the organic pollutants. The plants absorb the pollutants which then react with the plant’s enzymes and are changed to less harmful compounds inside its tissues. The newly formed compound is then used by the plant during its growth.

Phyto- volatilization: plants absorb the pollutants which are soluble in water. When transpiration takes place in plants the pollutants are also releases in the atmosphere. Some of the pollutants are changed on the way up. Many people do not prefer to employ this technique as the pollutants are only being transferred from land to the air. So, they are likely to return back to the ecosystem.

Plants commonly used for Phytoremediation:
Many of the ornamental plants and vegetables can extract metals present in the soil. Bracken fern can extracts arsenic from the soil and store it in its leaves. Hydrangeas an ornamental plant with large clumps of colourful flowers can extract aluminum.  Vegetables like mustard and broccoli can extract lead from the soil. Water hyacinth which is a common water plant is known for its ability to absorb many pollutants like pesticides and various metals like chromium, zinc, mercury etc. Sunflower has also been used for cleaning up the areas affected by Chernobyl disaster. Among trees, poplar, juniper, alfalfa and mulberry are generally used for removing pollutants.

Significance of Phytoremediation:
Apart from being cost effective, Phytoremediation is preferred as it does not gives out any secondary waste materials. Moreover, if an area is contaminated by different kinds of pollutants it can be easily removed while adding to the scenic beauty of the place. However, such techniques require intensive management. If the leaves are allowed to fall down in the ground or the plants after harvesting is left as such, then the pollutants would be returned back to the soil. Care should also be taken not to allow the animals to feed on these plants as it would be toxic to them.