Halophytes—An Emerging Trend in Phytoremediation

Abstract

Halophytic plants are of special interest because these plants are naturally present in environments characterized by an excess of toxic ions, mainly sodium and chloride. Several studies have revealed that these plants may also tolerate other stresses including heavy metals based on the findings that tolerance to salt and to heavy metals may, at least partly, rely on common physiological mechanisms. In addition, it has been shown that salt-tolerant plants may also be able to accumulate metals. Therefore, halophytes have been suggested to be naturally better adapted to cope with environmental stresses, including heavy metals compared to salt-sensitive crop plants commonly chosen for phytoextraction purposes. Thus, potentially halophytes are ideal candidates for phytoextraction or phytostabilization of heavy metal polluted soils and moreover of heavy metal polluted soils affected by salinity. Some halophytes use excretion processes in order to remove the excess of salt ions from their sensitive tissues and in some cases these glandular structures are not always specific to Na⁺ and Cl⁻ and other toxic elements such as cadmium, zinc, lead, or copper are accumulated and excreted by salt glands or trichomes on the surface of the leaves—a novel phytoremediation process called “phytoexcretion.” Finally, the use of halophytes has also been proposed for soil desalination through salt accumulation in the plant tissue or dissolution of soil calcite in the rhizosphere to provide Ca²⁺ that can be exchanged with Na⁺ at cation exchange sites.

KEY WORDS::

• phytoextraction
• phytostabilization
• phytoexcretion
• heavy metals
• salt tolerance

ACKNOWLEDGMENTS

The project was funded by the European Economic Area Financial Mechanism Grant EL-0075.