Wednesday, 14 December 2011

Just more than the calories and vitamins: Scientists find plants that clean up environment and polluted soils

By Syed Akbar
Pineapple, sunflower and Amaranthus, the popular leafy vegetable of Indian kitchen, have more to give than just calories and vitamins. Scientists have now found that these simple sources of nutrition and health also play a major role in keeping our environment clean.
These plant species clean up the soil, water and air of harmful pollutants including heavy metals and keep the environment clean. They simply suck the harmful elements and accumulate themselves in their roots, stem and or leaves.
What is interesting is that these plants clean up pollutants that cannot otherwise be removed through normal chemical processes. A study by a team of researchers in the University of Hyderabad has revealed that these and other ornamental and horticultural plant species are capable of removing pollutants even from sewage waters.
The study was conducted on the river bed of highly polluted Musi river that passes through Hyderabad. Leafy vegetables like Amaranthus spinosus, Alternanthera philoxeroides and Alternanthera sessiles were grown on the sewage sludge of the river. The researchers calculated the metal content in the plants and in the soil. The transfer factor and metal content Cadmium, Zinc and Ferrous in plant parts of these species showed their ability to bioconcentrate in their tissues. The concentration of these metals is invariably high in leaf tissue.

"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. It is also possible to supplement the dietary requirement of human food with Zinc and Ferrous as these being essential nutrients and the plant species are edible. However, there is a need to monitor the metal transfer factor through food chain," the study pointed out.
Scientists call this ability to suck harmful metals from soil and water as "hyperaccumulation". Plants with this ability can decontaminate metalliferous substrates in environment. Species belonging to families like Poaceae, Asteraceae, Flacourtiaceae, Euphobiaceae, Caryophyllaceae, Fabaceae and Brassicacea simply suck up metals like nickel, zinc and lead.
Plants are simply grown on metal-polluted waters. They absorb and concentrate the metals in their roots and shoots. As they become saturated with the metal contaminants, roots or whole plants are harvested for disposal. 
Even heavy metals can be removed from water through water hyachinth, pennywort and duckweed. Indian mustard removes even uranium and caesium.
After sufficient vegetative growth and metal accumulation, parts of the plant over the soil (stem and leaves) are harvested and removed. This leads to permanent removal of metals from the polluted area. These plants play a vital role in protection of environment as unlike many organic contaminants, most metals and radionuclides cannot be eliminated from the environment by chemical or biological transformation. Only these simply plants do.

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