Phytoremediation

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Introduction:

In recent years it has become clear that some environmental chemicals can cause risks to the developing embryo and fetus. Evaluating the developmental toxicity of environmental chemicals is now a prominent public health concern. The suspected association between TCE and congenital cardiac malformations warrants special attention because TCE is a common drinking water contaminant that is detected in water supplies throughout the U.S. and the world. There is a lot of concern about the clean up of toxic pollutants from the environment.

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

Cleaning up contamination:

Phytoremediation is a novel, efficient, environmentally friendly, low-cost technology, which uses plants and trees to clean up soil and water contaminated with heavy metals and/or organic contaminants such as solvents, crude oil, polyaromatic hydrocarbons and other toxic compounds from contaminated environments. This technology is useful for soil and water remediation.

Mechanisms:

Phytoremediation uses one basic concept: the plant takes the pollutant through the roots. The pollutant can be stored in the plant (phytoextraction), volatized by the plant (phytovolatization), metabolized by the plant (phytodegradation), or any combination of the above.

Phytoextraction is the uptake and storage of pollutants in the plants stem or leaves. Some plants, called hyperaccumulators, draw pollutants through the roots. After the pollutants accumulate in the stem and leaves the plants are harvested. Then plants can be either burned or sold. Even if the plants cannot be used, incineration and disposal of the plants is still cheaper than traditional remediation methods. As a comparison, it is estimated a site containing 5000 tons of contaminated soil will produce only 20-30 tons of ash (Black, 1995). This method is particularly useful when remediating metals. Some metals are also being recycled from the ash.

Phytovolatization is the uptake and vaporization of pollutants by a plant. This mechanism takes a solid or liquid contaminant and transforms it to an airborne vapor. The vapor can either be the pure pollutant, or the plant can metabolize the pollutant before it is vaporized, as in the case of mercury, lead and selenium (Boyajian and Carriera, 1997; Black, 1995; Wantanbe, 1997).
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