HOME
Phytoremediation is an
environmentally friendly, safe, cheap way to clean up contaminants. Early
estimates on the costs have shown that plants could do that same job as a group
of engineers for one tenth of the cost. The plants are also more pleasing to
look at than many such operations are. The soil or water need not be gathered in
and stored as hazardous waste, requiring large amounts of land,money, and
manpower. Plants can be planted, watered, and then harvested with less manpower.
If need be the storage of the harvested plants as hazardous waste would be a far
smaller amount. The main drawback on the use of technology is that it isn't good
for all sites. If the contamination runs too deep, or is too much the plants
alone can't handle it. Studies have been done though where the ground water is
pumped out and then treated. (www.oocities.org/College/park/Lab/961/phyto
1.html).
Phytoremediation can be used in combination with other cleanup approaches as a “finishing” or “polishing” step. Although some phytoremediation applications are slower than mechanical methods and are limited to the depths that are within the reach of the plant roots.
Generally, the use of phytoremediation is limited to sites with low to medium contaminant concentrations and contamination in shallow soils, streams, and ground water. Researchers are finding that the use of trees (rather than smaller plants) allows them to treat deeper contamination because tree roots penetrate more deeply into the ground. Pumping the water out of the ground and using plants to treat the contamination may treat very deep lying contaminated ground water. Further research is needed to study the effects on the food chain that could occur if insects and small rodents eat the plants that are collecting contaminants and are then eaten by larger mammals. Also, scientists still need to establish whether contaminants can collect in the leaves and wood of trees used for phytoremediation and be released when the leaves fall in the autumn or when firewood or mulch from the trees is used. (Soil Stabilization Action Team. April 1996, EPA 542-F-96-010d)
Phytoremediation has been
successfully tested in many locations, but full-scale applications are still
limited. In Maryland at a U.S. Army testing facility, hybrid poplar trees were
planted in a one-acre area over a shallow ground water plume contaminated with
organics from several toxic disposal pits. The poplar trees act as hydraulic
pumps to prevent the spread of contaminants to a nearby marsh. In addition to
hydraulic control, researchers have determined that phytovolatilization and
rhizofiltration are other mechanisms by which the system is treating the
contaminated plume. After the second growing season, the trees are successfully
containing the contaminated ground water plume with rates estimated at 2-10
gallons of water per day for each tree. In addition, preliminary results have
indicated that the poplar trees are degrading the contaminants in the ground
water plume. . (Soil Stabilization Action Team. April 1996, EPA
542-F-96-010d).