Introduction to Phytoremediation - CLU-IN

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ardous waste problems. The RTDF has grown to include partners from industry, several government agencies, and academia who share the common goal of developing more effective, less-costly hazardous waste characterization and treatment technologies. There are currently seven RTDF Action Teams, including the “Phytoremediation of Organics Action Team.” This Action Team was formed in early 1997, and is currently comprised of three working groups that are concerned with phytoremediation of three separate pollution/matrix situations: petroleum compounds in shallow soils, chlorinated solvents in near-surface groundwater, and the use of vegetation with high transpiration rates as an alternative cap for hydraulic containment and/ or degradation of various pollutants. The Action Team has held several meetings, and has regular conference calls to select and implement field testing projects. Current co-chairs in the subcommittees include representatives from Chevron, Exxon, the Air Force, and Union Carbide. To access meeting and teleconference minutes, bibliographic information on phytoremediation, and other information, refer to http://www.rtdf.org. The Technology Innovation Office (TIO) within OSWER supports RTDF activities, as well as other efforts aimed at bringing innovative site characterization and treatment technologies to commercialization. Further information on the Technology Innovation Office and resources generated by TIO can be found at http://www.clu-in.org. 13 In addition to EPA efforts, other Federal agencies, universities, consultants, and remediation contractors have research underway in phytoremediation. All these projects expand the knowledge base of what plants can be expected to do consistently, and make the application of innovative technologies more acceptable to regulators and consumers. Continuing research and policy discussions in the related areas of determining possible risk-based alternative endpoints for cleanups, and measuring the intrinsic remediative capacity of a site (natural attenuation) will impact the applicability of many biological-based technologies, including plant-based systems. Enhancements to the various phytoremediation processes are continuing. Some applied research is directed at selecting and breeding plants that have more of an attractive quality such as hyperaccumulation of metal, production of certain enzymes, and affinity or tolerance for contaminants. Research continues in genetic engineering of plants to combine positive traits, alter enzyme systems, or increase a plant’s natural range. An engineering approach could be pursued by using existing plant traits as only a part of a remediation system of combined planted systems and mechanical, thermal, or chemical systems in treatment trains. Suggested combinations include electrokinetics, bioventing, and surfactant addition.
This chapter presents a literature review and evaluation of the major phytoremediation processes or technologies. The technologies presented represent the major, significant, or widely studied forms of phytoremediation. This chapter is divided into subsections that present definitions, mechanisms, site characteristics, applicable media, contaminants amenable to each process, and the associated concentrations where available. The advantages, disadvantages, and current status of each process are also discussed. Finally, an annotated reference list is included at the end of the discussion of each process to provide more detailed, specific information. The purpose of this chapter is to provide site managers with an overview of the various phytoremediation processes as well as what can be expected from the process and its limitations. Therefore, information on applicable contaminants/concentrations is included even though the information may not be complete. Table 3-1 presents a summary of the various phytoremediation processes. 3.1 Phytoextraction 3.1.1 Definition/Mechanism Phytoextraction is the uptake of contaminants by plant roots and translocation within the plants. Contaminants are generally removed by harvesting the plants. This concentration technology leaves a much smaller mass to be disposed of than does excavation of the soil or other media. This technology is most often applied to metal-contaminated soil as shown in Figure 3-1. 3.1.2 Media Phytoextraction is primarily used in the treatment of soil, sediments, and sludges. It can be used to a lesser extent for treatment of contaminated water. 3.1.3 Advantages Chapter 3 Evaluation of Phytoremediation Technologies The plant biomass containing the extracted contaminant can be a resource. For example, biomass that contains selenium (Se), an essential nutrient, has been transported to areas that are deficient in Se and used for animal feed (Bañuelos 1997a). 3.1.4 Disadvantages Phytoextraction has the following disadvantages: 14 • Metal hyperaccumulators are generally slow-growing with a small biomass and shallow root systems. • Plant biomass must be harvested and removed, followed by metal reclamation or proper disposal of the biomass. Hyperaccumulators may accumulate significant metal concentrations — e.g., Thlaspi rotundifolium grown in a lead-zinc mine area contained 8,200 g/g Pb (0.82%) and 17,300 g/g zinc (Zn) (1.73%), and Armeria maritima var. halleri contained 1,300 g/g Pb, dry weight basis (Reeves and Brooks 1983). • Metals may have a phytotoxic effect (Nanda Kumar et al. 1995). • Phytoextraction studies conducted using hydroponicallygrown plants, with the contaminant added in solution, may not reflect actual conditions and results occurring in soil. Phytoextraction coefficients measured under field conditions are likely to be less than those determined in the laboratory (Nanda Kumar et al. 1995). 3.1.5 Applicable Contaminants/ Concentrations 3.1.5.1 Applicable Contaminants Constituents amenable to phytoextraction include: • Metals: Ag, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Zn The relative degree of uptake of different metals will vary. Experimentally-determined phytoextraction coefficients [ratio of g metal/g dry weight (DW) of shoot to g metal/g DW of soil] for B. juncea (Nanda Kumar et al. 1995) indicate, for example, that lead was much more difficult to take up than cadmium: Metal Phytoextraction Coefficient Cr 6+ 58 Cd 2+ 52 Ni 2+ 31 Cu 2+ 7 Pb 2+ 1.7 Cr 3+ 0.1 Zn 2+ 17 • Metalloids: As, Se
Page 1 and 2: Introduction to Phytoremediation Na
Page 3 and 4: Foreword The U.S. Environmental Pro
Page 5 and 6: Table of Contents Foreword ........
Page 7 and 8: Figures Figure 2-1. Mechanisms for
Page 9 and 10: Acronyms AAP Army Ammunition Plant
Page 11 and 12: Acknowledgements This Introduction
Page 13 and 14: • Chapter 3 provides a literature
Page 15 and 16: Figure 2-1. Mechanisms for phytorem
Page 17 and 18: Table 2-2. Root Depth for Selected
Page 19 and 20: Table 2-3. Phytoremediation at Supe
Page 21 and 22: egulated by the requirement. The Ma
Page 23: site. Plants and animals recolonize
Page 27 and 28: Figure 3-1. Phytoextraction. The fo
Page 29 and 30: In this literature review of resear
Page 31 and 32: Rhizofiltration has not been evalua
Page 33 and 34: sion of metals and metal concentrat
Page 35 and 36: Figure 3-2. Rhizodegradation. • L
Page 37 and 38: - PCP at 400 to 4100 mg/kg (in soil
Page 39 and 40: This paper introduces the important
Page 41 and 42: - A qualitative study indicated tha
Page 43 and 44: Figure 3-4. Phytovolatilization. 3.
Page 45 and 46: Newman, L. A., C. Bod, N. Choe, R.
Page 47 and 48: 3.8 Vegetative Cover Systems 3.8.1
Page 49 and 50: also be used in the treatment of so
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Page 57 and 58: Table 4-2. (continued) • Sterile/
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Page 61 and 62: arrier to block other site activiti
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Page 71 and 72: mum concentration of 640 ppb of 112
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6.2.6 Contacts Greg Harvey US Air F
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Figure 6-4. Sampling Grid Edward Se
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gravel drainage layer, and compacte
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variety had only a 54% survival rat
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surements are being taken to produc
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Phytoaccumulation: The uptake and c
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Project Name/ Size Primary Media an
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Adler, T. 1996. Botanical Cleanup C
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Ferro, A. M., L. Stacishin, W. J. D
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Newman, L. A., S. E. Strand, D. Dom
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Appendix D Common and Scientific Na
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Scientific Name Listed First Scient
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