Dr Jean-Paul Schwitzguébel, Sylvie Marcacci
SDC (Indo-Swiss Collaboration in Biotechnology)
November 2000 – February 2004
Prof Rainer Schulin, ETHZ, Zürich, Switzerland; Dr Muriel Raveton, Université Joseph Fourier, Grenoble, France; Dr Kishore Paknikar, Agharkar Research Institute, Pune, India; Dr Kantadai Raghu, Jai Research Foundation, Vapi, India.
Phytoremediation has been defined as the use of green plants and their associated micro-organisms, soil amendments and agronomic techniques to remove, contain or render harmless environmental contaminants. Plants can either accumulate and metabolise organic pollutants (phytodegradation) or stimulate appropriate rhizospheric micro-organisms (phytostimulation). Both approaches have been studied to efficiently remove atrazine (herbicide) or lindane (insecticide) from contaminated environment.
The ability of vetiver (Chrysopogon zizanioides) to act as a natural barrier against soil erosion makes the plant a major, simple and low cost tool for soil conservation on hill slopes in tropical developing countries. Since vetiver is known to be resistant to atrazine, we have evaluated its actual ability to take up and metabolise the herbicide. Vetiver is indeed able to accumulate and metabolize atrazine: small amounts of dealkylated products are detected in roots and leaves, whereas conjugated atrazine is found mainly in leaves. Under transpiring conditions, conjugation to glutathione in leaves is important, but under non-transpiring conditions, atrazine is also trapped in roots oil according to the partition-diffusion law. Lindane-degrading micro-organisms have been isolated from different contaminated soils. On the other hand, plant roots can release a vast range of organic compounds into the rhizosphere. Bacteria able to use these chemicals as carbon and/or energy sources often have enzymes that can (co-)metabolise pollutants with similar structures. Thus, the degradation of several hydrophobic chlorinated pesticides has been reported to be higher in a vegetated soil than a non-vegetated soil. Phytostimulation of bacteria present or added in soil thus seems the most promising approach to remove lindane from contaminated sites.