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Researchers at the Consejo Superior de Investigaciones Científicas (CSIC) have succeeded in modifying poplar for decontaminating soil and water with traces of TNT (trinitrotoluene). This explosive, highly toxic and difficult to eliminate, is in large parts of Europe and the United States as a result, above all, the various wars and the manufacture of armaments. During the study have been changed so that the poplars are more resistant to pollution and absorb more of it. The results were published in the American journal Environmental Science and Technology.

Plants to act as if they were a TNT green liver through which the pollutant is converted into a harmless substance and 'kidnapped' in the plant tissues. While all trees are enzymes that attack the contaminants, their efficiency is overcome by some organisms, the ability of the tree can be improved if you transferred them. So researchers at the Experimental Station of Zaidín (CSIC Granada) and the Research Institute agrobiological de Galicia (CSIC Santiago de Compostela) have joined the aspen PNRA gene from the bacterium Pseudomonas putida, which has a high rate of reduction TNT and other nitroaromatic compounds.

The results show that the modified poplars well tolerated up to 57mg per liter of TNT and more than 1.000mg per kg of soil before they stop their growth, compared to 500mg/kg of the plant 11mg/ly unchanged. In addition, show a greater absorption at high concentrations of contaminant. In conclusion, the incorporation of the gene of the bacteria from poplar improves ability to tolerate, to grow and remove TNT from contaminated waters and soils where the bioavailability of the contaminant is reduced. Furthermore, research has shown that, once absorbed by the roots, very little contaminant which is transported to the stem, the leaves fall or consumption by herbivores pose no risk.

The investigation, which concluded that it is most appropriate plants to use more than four months for the in situ bioremediation, was developed over five years.

The TNT is an explosive toxic to most living organisms, resistant to biological degradation and is present in soil and water in large areas in Europe and the United States, due to world wars and the presence of arms factories. Very difficult to remove, there is no one hundred percent effective method: "At the moment, using the excavation and incineration, and a little expensive for a benign environment," says Pieter van Dillewijn of the Experimental Station of Zaidín. "There Other cheaper methods such as composting, but its implementation is more limited and often without reliable data, "adds the researcher.

Bioremediation with trees, though still at an experimental stage, is considered a promising alternative. The trees have an intrinsic resistance to many pollutants, low nutritional requirements and a long life cycle. "Within the trees, poplars are particularly suitable because they have very deep roots can reach groundwater, high breathability allowing you to pump large amounts of water and pollutants, and rapid growth," says van Dillewijn.

They are also easy to transform genetically and female plants to be used, there is no risk of transgene spread by pollen. However, the method is not perfect: "One of the limitations of the use of phytoremediation is that it is a slow process that could take 5, 10 or more years. Moreover, there is a threshold of contamination of the plant and Furthermore, it is not entirely clear what happens to the derivatives of TNT once absorbed by the plant or when it dies, "says Dutch.

"We have shown that, once absorbed by the roots, a very small amount of pollutant that is transported to the stem, the leaves fall or consumption by herbivores does not pose a risk. However, it would be necessary to remove the plant mature, including much of its roots, so that TNT or its derivatives do not return to the ground, "concludes van Dillewijn. This could be burning the tree and thereby to generate energy.