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Plants Help Clean Contamination in Mining Areas

March 11, 2010

When conditions become complicated, there is no choice but to adapt to them. Plants have to do the same. Some of them growing in mining areas have unusual strengths, accustomed as they are to living in a toxic environment and knowing how to deal with this. Based on this capacity to adapt, researcher Ms Lur Epelde used these plants as medicinal herbs for contaminated soils.

The current level of contamination in the soil, caused by human intervention – is highly worrying. Nevertheless, more than the contamination as such, Ms Epelde was more interested in the effect these plants have on the health of the soil. The researcher puts forward phytoremediation as a means for confronting this problem; i.e. treating poor environments with these plants, without the need to excavate soil. Moreover, the idea is based on the microbiological properties of the soil itself to measure this technique: the mass of its microbian community, its activity and its biodiversity. The title of her PhD thesis is Evaluation of the efficiency of metal phytoremediation processes with microbiological indicators of soil health.

Technique adapted to each condition

Ms Epelde investigated, above all, pseudometalophyte plants – which grow in mining environments -, and the reaction they have to metals. To begin with, she linked Lanestosa of the thlaspi caerulescens species with zinc and cadmium. Lanestosa is a traditional mining town in the Encartaciones region near Bilbao and its namesake plant has optimum conditions for continuous phytoextraction (a process for differentiating metal from the rest of the elements). According to the research, it is capable of withstanding great concentrations of metal and also of accumulating considerable quantities of zinc and cadmium in its tissues that are in contact with the air. As with hyperaccumulator species such as this, large-sized plants are also effective. For example, sorghum has great potential for phytoextracting zinc and cadmium.

On the other hand, to phytoextract soils contaminated by lead, Ms Epelde opted for combining plants and chemistry, on the one hand using thistle (a plant of large dimensions) and, on the other, a chelating agent. She tested them with two chelating substances: EDTA and EDDS and concluded that, while EDTA is more effective for phytoextraction and less toxic for thistle plants, EDDS is less toxic for the soil microbian community and biodegrades rapidly.

In highly contaminated soils (zinc, cadmium and lead), Ms Epelde, instead of extraction, opted for stabilisation with grass crops, to this end using lolium perenne (ryegrass) and fertiliser. Particularly effective is cattle purine as it enhances the properties of the mining soils and reduces the toxicity of metals.

Finally, Ms Epelde combined three species of plants with different strategies for tolerance to metals, in order to see how they worked together. The three were thlaspi caerulescens (Alpine pennycress), rumex acetosa (sorrel) and festuca rubra (red fescue). It was shown that this technique has a great future. In fact, the thlaspi caerulescens causes the growth of the other two species and the rumex acetosa extracts more zinc when operating in conjunction with the thlaspi caerulescens.

Microbiological properties as indicator
 
Ms Epelde has shown that microbiological properties are effective for measuring phytoremediation. Microbiological properties are bioindicators of great value, given their sensitivity, speed of response and comprehensive character.

Helped by this technique, she concluded that the key is phytoremediation plants, rather than phytoremediation itself. Just the presence of these plants improves the health of the soil and, moreover, does so in a very short time, through increase in activity and functionality of the microbian community in the soil. However, more time is needed for the phytoremediation to clean up the contamination left by metals in the soil. In any case, as the most important thing is to recover the health of the soil, the aim is accomplished.

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