Wednesday, 21 November 2007

Plants that eat up toxic elements


Published in Deccan Chronicle/The Asian Age
Problem: Waterways and public drinking sources can contain deposits of heavy metals that can cause serious health problems. These contaminants are very difficult to remove using conventional methods.
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Solution: Certain plants that thrive in watery environments can absorb these pollutants as they grow.
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By Syed Akbar
Pineapple, sunflower and amaranthus, the popular leafy vegetable of the Indian kitchen, can suck up pollution from the soil, water and air, researchers at the University of Hyderabad have reported.
These plants accumulate the pollutants in their roots, stems and leaves and leave the substratum clean.
These plants clean up pollutants that cannot otherwise be removed through the normal chemical processes. As with all things natural, these plants do not despoil nature.
A study by University of Hyderabad researchers has revealed that these and other ornamental and horticultural plant species are capable of removing pollutants even from sewage.
The study was conducted on the bed of the highly polluted Musi river that passes through Hyderabad. Leafy vegetables like Amaranthus spinosus, Alternanthera philoxeroides [alligator weed] and Alternanthera sessiles [khakiweed]were grown on the sewage sludge of the river.
The researchers measured the metal content in the soil and in the fully grown plants after harvesting them.
The team found that the plants had sucked up a variety of metal pollutants.
The concentration of these metals was invariably high in leaf tissue. The transfer factor and content of cadmium, zinc and ferrous in plant parts of these species showed their ability to bioconcentrate these in their tissues.
"It is possible to use these species to restore the biosolid and sewage sludge contaminated sites, while exercising caution on human consumption. Alternanthera philoxeroides was used for removal of lead and mercury from polluted waters," the study reported.
"It is possible to supplement the dietary requirement of human food with zinc and ferrous as these are essential nutrients and the plant species are edible. However, there is a need to monitor the metal transfer factor through the food chain," the study said.
What the study is warning of is leafy vegetables grown in polluted beds. Since the leafy vegetables suck up pollution, people eating them may ingest the metals which can be harmful in large quantities.
Scientists call this ability to suck harmful metals as "hyperaccumulation". Plants with this ability can decontaminate metalliferous substrates in environment. Species belonging to families like Poaceae [a family of common grass], Asteraceae [the sunflower family], Euphobiaceae [the castor family], Caryophyllaceae [the family of ornamental flowers including campion], Fabaceae [legumes] and Brassicacea [the mustard family] simply suck up metals like nickel, zinc and lead.
In the process of using hyperaccumulators to clean up sewage or river beds, the plants are grown on the polluted area. They absorb and concentrate the metals in their roots and shoots. After they become saturated with metal contaminants, roots or whole plants are harvested and disposed.
Heavy metals can be removed from water through hyacinth, pennywort and duckweed. The mustard plant can remove uranium and caesium.
This leads to permanent removal of metals from the polluted area.

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