The plant's only role in this case to maintain soil

Users of the Parisian station Magenta (RER E) breathe fresh air for a few weeks. SNCF erected them a wall vegetated 70 m, which overlooks and brightens the great hall of grey concrete home. The device, installed by the Lyon SME Canevaflor, weighs 18 tonnes and mobilizes 3,000 plants of 31 species such as philodendron, fern, Ivy. The station air is sucked by a pump and crosses the substrate on which grow plants. SNCF ensures that air is from the dépollué wall, while recognizing that the current measures will have to demonstrate a real effectiveness of this technique. A lecture this week by the public body OQAI (Observatory of indoor air quality) gave a first guarantee of credibility in this kind of installation, to the detriment of other products more accessible, but totally ineffective: "dépolluantes plants. "Potted plants sold in many garden centres are a scam", do not hesitate to say Jean-Pierre Garrec, laboratory air pollution at the Inra of Nancy.

National program Phytair, researchers can better understand the phenomenon of plant remediation, highlighted by a researcher at Nasa in the 1980s. They rely on one hundred scientific publications, including a third focused on the araceae, the star of dépolluantes plants. They confirm that some plants confined in a small volume and dives in high concentration can reduce some harmful gases. But recent tests show that, in more realistic conditions, the effect disappears. The laboratory of Damien Cuny, Faculty of pharmaceutical and biological science of Lille, a mesuré that 12 plants placed in a cube of 8 m with input and output of air have virtually no effect on pollution.

"We know today that passive pollution based on the leaf system is not sufficiently effective." "However, the active all soil-plant systems appear most promising, in any case on organic gaseous pollutants", says Damien Cuny.

The plant's only role in this case to maintain soil. This technique of biofiltration has already led to products such as filter coffee percolator Darlington, which reduces formaldehyde of 90 or 20 benzene. Commercial products in VGbox or Phytorestore to reproduce the principle. But these ventilated systems pose other issues, as their energy consumption, Joëlle Collosio, responsible of the Ademe air Department. They have not shown nor visible effects on other pollutants of indoor air: (deadly) carbon monoxide, mushrooms, volatile organic compounds, bacteria, particules And you don't know their effectiveness on several substances at a time.

The Phytair program must test the effect of active systems by 2011 in real conditions. Damien Cuny stressed the fact that Phytair has defined a test protocol, which allows to compare the performance of different plant-based systems. "None will treat all pollution, be expected to adapt the processing solutions for every building", warns the biologist. The OQAI reminds him that the treatment of air should intervene in that third line in the fight against the pollution of indoor air, after the limitation of the pollutant and ventilation of buildings.

Plants, however, retain supporters in the Interior: a few studies have shown that their presence in offices improves the sense of well-being of employees.