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
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