Plant - Vacuum Cleanser of Soils

Soils and sediments are known as the ultimate sink for many organic compounds and heavy metals. Heavy metals in soils can be taken up by roots of crops and therefore gets in food and harm people’s health. Heavy metals in contaminated soils could also leach into the groundwater and bio-accumulate in the food chain. Nowadays the soil contamination has raise concerns on environmental, agricultural, and human health problems worldwide. In a recent article, Phytoremediation: Using Plants To Clean Up Soils (http://www.ars.usda.gov/is/ar/archive/jun00/soil0600.htm), Kochian discusses how plants can help clean up soils contaminated with heavy and toxic metals.

Kochian’s “green” technology is very cost-effective compare to some current engineering-based technologies used to clean up soils such as the removal of contaminated topsoil for storage in landfills which is usually very costly. It is known as phytoremediation which uses plants to “vacuum” heavy metals form the soil through their roots and concentrate them in the stems, shoots, and leaves. And latter these plant tissues can be collected and stored for later use. One challenge of this technique is that the plants must be able to tolerate and survive from the high levels of heavy metals in soils which are usually toxic to plants. Recently Kochian’s team found that Thlaspi known as alpine pennycress is a potential vacuum cleaner since it can survive on soils having high levels of zinc and cadmium and is able to accumulate excessive amounts of heavy metals. By planting the plant, zinc and cadmium can be removed from contaminated soil, and by harvesting the plant’s shoots these metals can be extracted from them and recovered. Kochian also found that for cleaning up soils with high levels of uranium, adding the organic acid citrate to soils significantly increase the solubility of uranium and make it easier for plants to uptake and store them in their tissues.

One of the major goals for agricultural scientists is to increase food production to keep up with the rapid growing world population. As much of the best agricultural land has been used or is being contaminated, there is an increasing pressure for farmers to plant crops in the less arable lands such as acid soils that are not currently used for production. Kochian’s team is trying to find ways to grow crops on acid soils. However, in acid soils aluminum forms Al³⁺ which is soluble and very toxic to plant roots therefore limit the crop production. “Aluminum toxicity limits crop production on acid soils, which cover well over half of the world’s 8 billion acres of otherwise arable land, including about 86 million acres in the United States”, Kochian said. He and coworkers have identified the aluminum tolerant mutants in Arabidopsis, and their goal is to isolate this gene and use it to improve the tolerance of aluminum-sensitive crops such as barley.

The phytoremediation technique Kochian discussed in the article is an attractive alternative to current cleanup methods that are energy intensive and very expensive. This technique not only can remove heavy metals from the contaminated soils, but also can economically recover these metals elements by collecting the plants tissues and extracting from them. In addition, as more researches being done on studying crop genotypes that tolerate the suboptimal conditions of the marginal lands, it could become a very effective way to significantly increase the food production.