This paper reviews key aspects of phytoremediation technology and the biological mechanisms underlying phytoremediation. Current knowledge regarding the application of phytoremediation in alleviating heavy metal toxicity is summarized highlighting the relative merits of different options. The results reveal a cutting edge application of emerging strategies and technologies to problems of heavy metals in soil. Progress in phytoremediation is hindered by a lack of understanding of complex interactions in the rhizosphere and plant based interactions which allow metal translocation and accumulation in plants. The evolution of physiological and molecular mechanisms of phytoremediation, together with recently-developed biological and engineering strategies, has helped to improve the performance of both heavy metal phytoextraction and phytostabilization. The results reveal that phytoremediation includes a variety of remediation techniques which include many treatment strategies leading to contaminant degradation, removal (through accumulation or dissipation), or immobilization. For each of these processes, we review what is known for metal pollutants, gaps in knowledge, and the practical implications for phytoremediation strategies.

Phytoremediation Technology: Hyper-accumulation Metals in Plants

The use of higher plants to remediate contaminated land is known as phytoremediation, a term coined 15 years ago Among green technologies addressed to metal pollution, phytoextraction has received increasing attention starting from the discovery of hyperaccumulator plants, which are able to concentrate high levels of specific metals in the above-ground harvestable biomass The small shoot and root growth of these plants and the absence of their commercially available seeds have stimulated study on biomass species, including herbaceous field crops We review here the results of a bibliographical survey from 1995 to 2009 in CAB abstracts on phytoremediation and heavy metals for crop species, citations of which have greatly increased, especially after 2001 Apart from the most frequently cited Brassica juncea (L) Czern, which is often referred to as an hyperaccumulator of various metals, studies mainly focus on Helianthus annuus L, Zea mays L and Brassica napus L, the last also having the greatest annual increase in number of citations Field crops may compensate their low metal concentration by a greater biomass yield, but available data from in situ experiments are currently very few The use of amendments or chelators is often tested in the field to improve metal recovery, allowing above-normal concentrations to be reached Values for Zn exceeding 1,000 mg kg−1 are found in Brassica spp, Phaseolus vulgaris L and Zea mays, and Cu higher than 500 mg kg−1 in Zea mays, Phaseolus vulgaris and Sorghum bicolor (L) Moench Lead greater than 1,000 mg kg−1 is measured in Festuca spp and various Fabaceae Arsenic has values higher than 200 mg kg−1 in sorghum and soybean, whereas Cd concentrations are generally lower than 50 mg kg−1 Assisted phytoextraction is currently facilitated by the availability of low-toxic and highly degradable chelators, such as EDDS and nitrilotriacetate Currently, several experimental attempts are being made to improve plant growth and metal uptake, and results are being achieved from the application of organic acids, auxins, humic acids and mycorrhization The phytoremediation efficiency of field crops is rarely high, but their greater growth potential compared with hyperaccumulators should be considered positively, in that they can establish a dense green canopy in polluted soil, improving the landscape and reducing the mobility of pollutants through water, wind erosion and water percolation

Field crops for phytoremediation of metal-contaminated land. A review

Characterization of heavy metal-resistant endophytic bacteria from rape (Brassica napus) roots and their potential in promoting the growth and lead accumulation of rape.

Increased soil pollution with heavy metals due to various human and natural activities has led to a growing need to address environmental contamination. Some remediation technologies have been developed to treat contaminated soil, but a biology-based technology, phytoremediation, is emerging. Phytoremediation includes phytovolatilization, phytostabilization, and phytoextraction using hyperaccumulator species or a chelate-enhancement strategy. To enhance phytoremediation as a viable strategy, microbiota from the rhizosphere can play an important role, but the use of genetic engineering can also increase the success of the technique. Here we review the key information on phytoremediation, addressing both potential and limitations, resulting from the research established on this topic.

Remediation of Heavy Metal Contaminated Soils: Phytoremediation as a Potentially Promising Clean-Up Technology

Isolation and characterization of a heavy metal-resistant Burkholderia sp. from heavy metal-contaminated paddy field soil and its potential in promoting plant growth and heavy metal accumulation in metal-polluted soil.

A. Argilla

Papers

Phytoextraction of metals from a multiply contaminated soil by Indian mustard.