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Digesting toxic mining waste!

Posted by on February 11th 2013

from Guardian Weekly & Le Monde

The sprouting plants look like a market garden.  Come spring they will produce white, yellow and mauve flowers.  But these plants are not decorative, less still edible.  They grow on sterile clay soil full of toxic metals, at the bottom of a former tailing pond at Saint Laurent Le Minier in the Cevennes, where mining started in Roman times and only finally stopped in 1992.  The concentrations of zinc, lead and cadmium are between 500 and 850 times higher than European standards allow.

No normal vegetation can stand such levels, apart from three species that have developed an extraordinary survival strategy: sucking up the toxic substances through their roots and storing them in vacuoles in their leaves.

Scientists from the Functional and Evolutionary Biology (CEFE) at Montpellier University, affiliated with the French National Centre for Scientific Research (CNRS), are experimenting with environmentally friendly ways of decontaminating soil by phytoextraction.

“Intensive mining operations and industrial metal working cause severe soil pollution: heavy metals are one of the greatest hazards and are not biodegradable,” says Claude Grison, professor of chemistry at Montpellier 2 University and the head of the programme.  Farming is strictly forbidden on the land once it is occupied by the mines, but wind and rain still disperse the toxic dust.

Hence the hopes raised by the three varieties of metallophyte: Noccaea caerulescens [Alpine Penny cress], Anthyllis vulneraria (kidney vetch) and Iberis intermedia.  Absorbing up to 7% or 8% of their dry weight, they can trap phenomenal quantities of metallic elements.

Last summer the research team transplanted 7,000 plants that had started life in the glasshouses at Montpellier University.  Last autumn they tested direct sowing.  Over the next year they hope to cover the whole site, but Grison admits: “It will certainly take over 50 years to clean it completely.”

 

CEFE is takling part in research programmes in New Caledonia, China and soon Gabon.  But no one has found a way of disposing of the contaminated vegetable matter.

Yet the CEFE researchers have discovered that the metal stored in leaves can act as a catalyst in industrial applications, such as synthesising drugs.

At Saint LAurent Le Minier the population has dropped from 1,100 to 360.  Daniel Favas, the deputy mayor, hopes the shcme will enable the village to make a fresh start.  And countless other sites could benefit from this sort of herbal medicine.