Majeti Narasimha Vara Prasad* Helena Maria de Oliveira Freitas * Corresponding author Key words: Metalliferous soils, Rhizosphere,
Mycorrhizae, Genetic engineering, Metal sequesteration, Metal hyperaccumulators,
Metal tolerant plants
* MNVP is thankful to the Fundação para a Ciência e Tecnologia, Ministério da Ciencia de Tecnologia, Portugal for awarding visiting fellowship (December 1998 to February 1999).
Reclamation of
metalliferous areas is a priority field of biogeochemistry of trace elements.
Ultramafic outcrops rich in heavy metals have been mapped in different
parts of the world. Heavy metals are potentially cytotoxic, caricinogenic
and mutagenic. Environment protection agencies and legislations insisting
the mine operators to restore the mine spoils and tailings since the metal
leachates have serious implications in production of healthy agricultural
products. Hence, restoration of mine spoils, tailings and metalliferous
soils is a challenging task for the well being of Humans. Synthetic and
natural zeolites have been used as chelators for rapid mobility and uptake
of metals from contaminated soils by plants. Use of synthetic chelators
significantly increased Pb and Cd uptake and translocation from roots
to shoots facilitating phytoextraction of the metals from low grade ores.
Contrastingly, synthetic cross linked polyacrylates, hydrogels have protected
plant roots from heavy metals toxicity and prevented the entry of metals
into roots. However, application of these synthetics on large scale may
not be a practical solution due to exorbitant costs. Therefore, introduction
of metal tolerant wild plants to metalliferous soils, genetic engineering
of plants for enhanced synthesis and exudation of natural chelators into
the rhizosphere, improvement of the rhizosphere with the help of mycorrhiza
and integrated management of the metalliferous ecosystem following the
principles of phytoremediation are discussed in this paper. |
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