Phyto-what?

by Helen M. Scott
Tuesday, May 22, 2007 2:16 PM MDT

Phytoremediation, according to references available, is the use of green plants to remove pollutants from the environment or render them harmless.

There are sunflowers that capture uranium, ferns that thrive on arsenic, alpine herbs that hoard zinc and clovers that eat oil, or so they say.

Several different types of phytoremediation, as technically defined by references found, are as follows:

Rhizosphere bio-degradation n- a process by which the plant releases natural substances through its roots, supplying nutrients to microorganisms in the soil. The microorganisms enhance degrading.

Phyto-stabilization n- a process in which chemical compounds produced by the plant immobilize contaminants rather than degrade them. Plants are allowed to grow and take in the chemicals and afterwards be destroyed or recycled if metals stored in the plants can be reused.

Phyto-accumulation n- in this process, the plant roots take in the contaminants along with other nutrients and water. The contaminated mass is not destroyed, but ends up in the plant shoots and leaves.

Phyto-volatilization n- a process wherein plants take up water containing contaminants and release the contaminants into the air through their leaves.

Phyto-degradation n- plants actually destroy contaminants within the plant tissues.

Hydraulic control n- trees indirectly remediate by controlling groundwater movement.

On the up side, it is widely known that plant roots evolved as extremely efficient at pulling nutrients, water and minerals out of the ground; however, the process that pulls pollutants into roots and then stashes them harmlessly in plant tissue remain somewhat of a mystery.

Numerous studies have been made on alpine pennycress trying to discover the underlying process that enables the plant to accumulate excessive amounts of heavy metals. According to information available, these studies supposedly found that the plants possess genes that regulate the amount of metals taken up by roots.

These genes govern processes that can increase the solubility of metals in the soil surrounding the roots as well as the ability to move the metals into root cells. Even though some of the physiology and chemistry remain somewhat murky, phytoremediation as a method of environmental cleanup seems to be proving its worth.

On the down side, according to information available, there is more to phytoremediation than merely placing plants in the ground and letting them do the work. Cleanup areas have to be engineered to prevent flooding and erosion. Phytoremediation isn’t necessarily chemical free either, as certain chemical agents that will free metals and other contaminants from soil particles to allow them to be taken up by the plants, will be needed in some cases.

In addition, studies are needed to determine whether plants grown to clean up pollution can be harmful to people, insects and foraging animals. Phytoremediation seems to be an emerging technology for contaminated sites that is attractive due to its low cost and versatility; however, the information available claims it can take years to clean up sites using this process and hundreds of hours of careful monitoring.

It is by no means a panacea for hazardous waste problems, but shows tremendous potential in treatment of contamination existing in shallow depths.

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