Trace element behaviour at the root–soil interface: Implications in phytoremediation

We are just beginning to understand the metabolism of heavy metals and to use their metabolic functions in biotechnology, although heavy metals comprise the major part of the elements in the periodic table. Because they can form complex compounds, some heavy metal ions are essential trace elements, but, essential or not, most heavy metals are toxic at higher concentrations. This review describes the workings of known metal-resistance systems in microorganisms. After an account of the basic principles of homoeostasis for all heavy-metal ions, the transport of the 17 most important (heavy metal) elements is compared.

Phytoremediation, the use of plants and their associated microbes for environmental cleanup, has gained acceptance in the past 10 years as a cost-effective, noninvasive alternative or complementary technology for engineering-based remediation methods. Plants can be used for pollutant stabilization, extraction, degradation, or volatilization. These different phytoremediation technologies are reviewed here, including their applicability for various organic and inorganic pollutants, and most suitable plant species. To further enhance the efficiency of phytoremediation, there is a need for better knowledge of the processes that affect pollutant availability, rhizosphere processes, pollutant uptake, translocation, chelation, degradation, and volatilization. For each of these processes I review what is known so far for inorganic and organic pollutants, the remaining gaps in our knowledge, and the practical implications for designing phytoremediation strategies. Transgenic approaches to enhance these processes are also reviewed and discussed.