Using plants to remove hazardous materials from soils is an alternative technique to costly traditional methods. For this, horticultural and forage plant species are usually used, which, being edible, increase the risk of contaminants entering the trophic webs. For this reason, a study by the Faculty of Agronomy of the University of Buenos Aires (FAUBA) evaluated the behavior of an ornamental species, the Busy Lizzy (Impatiens walleriana), as a remedy for lead-contaminated soils (Pb). The results indicate that it would have a good aptitude for this function, since it managed to retain significant amounts of this heavy metal in its roots. They discuss the many advantages of using them in urban settings.

“The idea was to investigate Impatiens walleriana as a phytoremediator of lead-contaminated soils. From the bibliography, we already knew that Busy Lizzy is a very aesthetically beautiful species and that it has characteristics that would make it good at capturing heavy metals from the soil ”, explained Mercedes Ramacieri, recent graduate of the Degree in Environmental Sciences (LiCiA- FAUBA), under the direction of Johanna Chirkes, professor of the Edaphology chair of that Faculty and Doctor in Veterinary Sciences (UBA).

Ramacieri, who teaches Bioindicators and Chemistry of Pollution and Toxicology —both from LiCiA— commented that although there is information on soil contamination with lead in Argentina, it is scarce. “This type of environmental problem is usually associated with foundries and metallurgical industries, the existence of illegal garbage dumps and also the circulation of vehicles. That is why it becomes more acute around large cities, and since lead is a heavy metal, it persists in the environment as long as the soil is not remedied ”.

“In my undergraduate thesis I carried out an experiment under controlled conditions in a greenhouse of the Juan O. Hall Gardening School, of FAUBA. I grew Busy Lizzy plants in pots containing a substrate very rich in organic matter. At the beginning of the study, a single dose of lead was applied to each pot, at a rate of 0; 500; 1,000 and 1,500 milligrams of lead per liter of water. From then on, for seven weeks it was only watered with water and the content of this metal was measured in three parts: the plant organs, the substrate and the liquid that flowed through the bottom of each pot after each irrigation ”, explained Mercedes .

"My results show that I. walleriana can work well as a remedial for lead soils," said the teacher, "since of the total of this metal measured in the three parts, the roots managed to retain up to 46% in the treatment of 500 mg. lead / L. For its part, the substrate retained even more: up to 83% when 1000 mg of lead / L were applied. Lastly, the leached liquids contained a minimal percentage, although significant, up to 1% in the treatment of 1000 mg of lead / L ”.

And she added that the Pb content that she detected in the roots of I. walleriana was very high in relation to that registered in the aerial organs. “This means that the lead that the plants took up was mainly retained in the roots. The fact that there was little lead in the leaves and flowers makes the Busy Lizzy ideal for cleaning floors with this heavy metal. Otherwise, with the renewal of foliage and flowering, the lead could return to the soil ”.

The ornamental ones, with advantage

“The good thing about ornamental plants as phytoremediators is that they have the added bonus of aesthetic beauty, which in urban areas would also help improve the psychological state of many people. They even have advantages over plants that are traditionally used in remediation, such as vegetables, corn, alfalfa or mustard. On the one hand, there is no possibility that people or animals will consume them and then the metal will enter and move through the food webs. On the other hand, its final disposal as hazardous waste would be avoided in the short term, something that does happen with traditional species ”, Ramacieri highlighted.

According to the researcher, there is a great variety of decorative plants that can potentially serve to sanitize the environment, from herbaceous to woody, native or exotic, more or less tolerant of saline, perennial or annual, rustic or delicate soils. There are even new transgenic species on the market, generated within the framework of the ornamental industry. For Mercedes, the range of options is immense and with a wide panorama in environmental terms.

“The use of showy plants to remediate contaminated soils is a known technique,” ​​Ramacieri said, adding that “in the world, it is still under development on a small scale. Asian countries are pioneers, but work is also being done in some Latin American countries such as Colombia and Brazil. The ornamentals have different phytoremediation mechanisms, so it is useful to know which one can be used in each situation. In this sense, we could say that our work opens a path in Argentina ”.

Future studies with lead and silicon

Johanna Chirkes pointed out that, at present, the FAUBA chair of Edaphology is not investigating the problem of contamination with heavy metals. For this reason, the work that she began with Mercedes Ramacieri in the framework of the Hall School - directed by the Agronomist Ernesto Giardina - is a new line that the two researchers wish to deepen.

“During my doctoral studies I investigated the effects of silicon as a reliever of different biotic and abiotic stresses. My idea, then, is to put both lines together: to build on Mercedes' results and incorporate silicon into future experiments. Our plans include working under natural conditions to analyze the interaction of lead with organic matter in the soil, also using native ornamental plants ”, said Johanna.

“We need to continue generating solid information to accompany that obtained by working with Impatiens walleriana, especially considering that the Busy Lizzy has been used very little as a phytoremediate, compared to geranium or damascene, for example. The only thing we have to consider is that laboratory testing for lead is expensive, so we are looking at a way to fix that so we can continue, "concluded Chirkes.