Phytoremediation, the technique to purify the environment with plants
Some plants are able to accumulate and tolerate heavy metals in their organs at concentrations that are toxic to other organisms. This topic is at the centre of the research activities of two young scholars from the Department of Agriculture, Food, Environment and Forestry.
Plants and the microorganisms associated with them may be used to eliminate, contain or detoxify the substances present in contaminated soils and waters. Phytoremediation is the subject matter at the centre of the work of Elisa Azzarello and Werther Guidi Nissim, two Florentine researchers who work under the scientific supervision of Professor Stefano Mancuso of the Department of Agriculture, Food, Environment and Forestry (DAGRI).
“Terrestrial plants appeared about 470 million years ago,” explain Dr. Azzarello and Dr. Guidi Nissim. “In the course of evolution, they developed adaptive mechanisms necessary for survival in difficult environmental conditions, to the point that some of them today are able to accumulate and tolerate, inside their organs, certain heavy metals at concentrations that are toxic to other organisms. These initial observations suggested the potential of using plants to clean up contaminated land and water.”
The Florentine team has developed two projects funded by the Ministry of Defence under the National Military Research Plan. The first, entitled “Vegetal System for Pollution Avoidance”, concerned the reclamation of a site contaminated by heavy metals and was carried out inside the Maritime Military Arsenal of Taranto. The survey showed that in the first two years of testing, poplar and willow absorb and translocate to the aboveground organs between sixty and seventy-five per cent of the zinc available in the soil and that fibre hemp is highly suited for the absorption of lead. The results of this research have recently been published in the journal Environmental Science and Pollution Research (https://doi.org/10.1007/s11356-018-1197-x)
The second project, entitled “Innovative Plant Environmental Remediation”, is still in progress and is related to the reclamation of a highly contaminated site at the Maritime Military Arsenal of La Spezia. The purpose of this current project is to demonstrate the effectiveness of phytoremediation even in presence of high environmental contamination (higher than in the previous study at Taranto), and “although the data collection campaign is ongoing”, the two researchers explain, “the initial results are very encouraging”.
In a third study, the two young scholars have instead dealt with the functionality of the phytoremediation for the purification of sewage sludge. The survey showed that plants have a high potential for the purification of water of different contaminants and, in particular, it showed a high chromium removal capacity. Willow, in particular, has shown the capacity to remove a number of organic pollutants from the mud. The results of the study were published in the journal “Environmental Research” (https://doi.org/10.1016/j.envres.2018.03.009).
“Phytoremediation”, the Florentine researchers continue, “is a technique that involves much lower costs than conventional remediation techniques. Furthermore, it presents a high ecological-aesthetic value and a high level of social acceptability. Its main limits are represented by the fact that its application is restricted to the environments in which the plants can actually live and by reclamation times, which are generally longer than those of the classical techniques. It is, nonetheless, a promising technology because phytoremediation is characterised by high ecological and economic sustainability, but many aspects linked to its efficiency still need to be carefully evaluated before it will be widely utilised.”
