[LUM#6] Flowers at the planet's bedside

[LUM Magazine] - Published on September 19, 2017 in Science-Society

To clean up contaminated soil and polluted water, Claude Grison and his ChimEco laboratory ChimEco are harnessing the forces of nature. Healing the planet with plants: the idea is in full bloom.

It is 2007, and Claude Grison, a chemist, is not yet an ecologist when four of her students in a preparatory class for the grandes écoles suggest an original topic for study: "Can plants be used to clean up polluted soil?" To help them, she immerses herself in the existing literature."I discovered plants in a new light," she recalls. " In a polluted environment, they can't run away! They have only two options: adapt or disappear."

Industrial pollution

And those that have had the misfortune of being established on former mining sites have to contend with the worst kind of pollutants: heavy metals. " These pollutants are inorganic and therefore non-biodegradable. If nothing is done, they will remain there, in the soil or contaminated effluents, forever," summarizes the chemist.

In Saint-Laurent-le-Minier, in the Gard department, Claude Grison discovered during his research the sad legacy of decades of industrial activity: soil poisoned with cadmium and lead, two residues from zinc extraction. The mines have now disappeared from the landscape. Unfortunately, so have the plants: here, the lead content in the soil is 800 times higher than normal. With no vegetation to hold it down, the metal particles are easily carried away by rain or wind, contaminating the region within a radius of more than 50 km.

Plant follies

Yet, on these arid slopes, a few plants grow their timid corollas toward the sun. How do they survive? These "hyperaccumulators," called Noccaea caerulescens, Anthyllis vulneraria or Iberis intermedia, demonstrate an astonishing adaptation strategy: they trap metal particles in their leaves, where they store them. Claude Grison, who uses them to decontaminate the soil in Saint-Laurent-le-Minier, charmingly refers to them as "plant follies" (Plants for decontaminating soil and water, 2016).

Since then, the method has been hugely successful, and his ChimEco laboratory has planted similar plants in Crete, Gabon, China, and New Caledonia. Everywhere, these valuable allies help stabilize severely degraded soils while capturing the metal dust they contain through "phytoextraction": zinc, lead, cadmium, copper, manganese, nickel, and even palladium. Some of these metals are precious: all that remains is to recover them from the leaves of these extraordinary plants, using a 100% eco-friendly thermal and chemical treatment ( La chimie du futur passe par les plantes, 2017).

Claude Grison's laboratory is now turning its attention to a new field of research: water pollution. Certain aquatic plants have the same hyperaccumulation capabilities as their terrestrial cousins. "This isa particularly crucial issue, " the researcherpoints out . " Drinking water is becoming a scarce resource, and we must preserve it. It has become one of humanity's major challenges."

Keywords: Chemistry, LUM#6, LUM Magazine, Research, Health, Science