De Filippis, LF; Hakeem, KR; Sabir, M; Ozturk, M; Mermut, AR
Phytoremediation is the technology that uses living plants for in situ remediation of contaminated soils, sediments, tailings and groundwaters, through the removal, containment or degradation of toxic wastes. Growing plants on a contaminated site is a sunlight-driven and energy-efficient technique that is capable of cleaning up an area with low to moderate levels of contamination, and additionally can be ecologically and aesthetically suited to the landscape. Phytoremediation can be used alone or in combination with mechanical (engineering) clean-up methods. Plant-based methods can be used to remove metals, pesticides, solvents, explosives, crude oil, polycyclic aromatic hydrocarbons and radionuclides in landfills (and associated soils and tailings). Phytoremediation has been studied extensively and research is advanced, especially in small-scale operations; however, large-scale applications are currently limited in technology, knowledge and success. Phytoremediation has not been used so far in commercial or industrial decontamination of radioactive sites; however, it has been successfully tested, and some of these advances in radioactive remediation are described. Selection of possible remediation methods used on radioactive wastes primarily depends on the nature of the radioactive isotopes present, and the first part of the chapter covers the types and nature of radioisotope contamination resulting from mining, industry, medicine, accidents and the uranium energy cycle. Innovative new methodologies have been initiated to treat radioactive waste, and some of the most promising are those that rely on phytoremediation. However, it is clear that not all categories of radioactive waste are suitable for phytoremediation. The second part of the review addresses and discusses the different categories of phytoremediation techniques, and which of these may treat and control radioactive contaminated waste. Several different approaches and different plant species are already in the testing and development phase for application to radionuclide wastes. Phytoremediation approaches have the objective of partly restoring the waste sites for eventual use of native plants and animals, and to curtail or eliminate the off-site movement and leaching of the radioactive entities. The performance of phytoremediation, compared to physical methods of remediating radioactive soils depends on several factors, including the composition of soils, the toxicity level of the contaminant, the degree to which plant species fit natural local growth conditions and the type and concentration of the radionuclides both outside and within plants. Nevertheless, phytoremediation has opened up the prospect for a less costly, practical and environmentally sound approach to clean-up low-level radiation waste sites. Detailed discussion of plant species that are capable of phytoextracting and. /. or rhizofiltering harmful radioactive elements from contaminated soils and water is presented, and where such processes are being proposed for use on mine tailings. To a lesser extent, the review addresses contaminants that are derived from existing low- to middle-level radionuclide waste that may need to be stored securely for many years. © 2015 Elsevier Inc. All rights reserved.