Phytoremediation describes the treatment of environmental problems (bioremediation) through the use of plants which mitigate the environmental problem without the need to excavate the contaminant material and dispose of it elsewhere.
The word's etymology comes from the Greek plant, and Latin « remedium » = restoring balance, or remediation. Phytoremediation consists in mitigating pollutant concentrations in contaminated soils, water or air with plants able to contain, degrade or eliminate metals, pesticides, solvents, explosives, crude oil and its derivatives, and various other contaminants, from the media that contain them.
Brassica juncea, also known as mustard greens, Indian mustard and leaf mustard, is a species of mustard plant. Sub-varieties include Southern Giant Curled Mustard, which resembles a headless cabbage such as Kale, but with a distinct horseradish-mustard flavor. It is also known as green mustard cabbage.
This plant is used to remove heavy metals from the soil in hazardous waste sites because it has a higher tolerance for these substances and stores the heavy metals in its cells. The plant is then harvested and disposed of properly. This method is easier and less expensive than traditional methods for the removal of heavy metals.It also prevents erosion of soil from these sites preventing further contamination.
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)
For more information (background, pictures, experiments and references): Phytoremediation