Phytoextraction, metals

DTPA-extractability) of PTMs was high, Brassica juncea feasibility for metal phytoextraction was too low for efficient soil remediation (Clemente el al, 2005). 

Keller, C., Hammer, D., Kayser, A., Richner, W., Brodbeck, M., and Ennhauser, M. (2003). Root development and heavy metal phytoextraction efficiency Comparison of different plant species. Plant Soil 249, 67-81. 

Increasing attention has been given to the potential of mycorrhizal associations for reforestation and clean-up of metal-contaminated areas (Van der Lelie et al. 2001). Mycorrhizas may enhance metal phytoextraction by host plants by increasing plant biomass and increasing metal... 

Sapundjieva K, Kouzmanova J, Vassilev A, Kartalska Y, Krastev S (2003) Metal phytoextraction on carbonate rich soils a... 

Box 1. Heavy metal phytoextraction from contaminated waters (after Sen and Mondal, 1990 and Shrivastava and Rao, 1997)... 

Angle JS, Linacre NA. (2005). Metal phytoextraction A survey of potential risks. International Journal of Phytoremediation 7 241-257. 

Many natural hyperaccumulators, i.e., plants that actively accumulate several percent of heavy metals in the dry mass of their above-ground parts, have a good potential to be used for phytoremediation, i.e., to extract and remove heavy metals from anthropogenically contaminated soils, which was first proposed by Chaney [132]. Some of them even allow for commercially profitable phytomining, i.e., the extraction of metals from naturally heavy metal rich soils (that are not directly usable as metal ores) with subsequent burning of the plants, the ash of which can be used as a metal ore (first proposed by Baker, Brooks, and Reeves [133]). These applications of metal phytoextraction have been a subject to extensive research (for reviews see [3,31,132,134-141]. 

In the past, removing metal and metalloid contaminants from soil has been impossible, and site clean-up has meant excavation and disposal in a secure landfill. An exciting new approach to this problem is phytoextraction, where plants are used to extract contaminants from the soil and harvested. Immobilization and Toxicity-Minimization. 

Phytoextraction is mainly carried out by certain plants called hyperaccumulators, which absorb unusually large amounts of metals compared to other plants. A hyperaccumulator is a plant species capable of accumulating 100 times more metal than a common nonaccumulating plant. Therefore, a hyperaccumulator will concentrate more than 1000 mg/kg or 0.1% (dry weight) of Co, Cu, Cr, or Pb, or 10,000 mg/kg (1%) of Zn and Ni (dry matter).43-44 Similarly, halophytes are plants that can tolerate and, in many cases, accumulate large amounts of salt (typically sodium chloride but also Ca and Mg chlorides). Hyperaccumulators and halophytes may be selected and planted at a site based on the type of metals or salts present, the concentrations of these constituents, and other site conditions. 

Phytoextraction Soils, sediments Metals (Ag, Au, Cd, Co, Cr, Cu, Hg, Mn, Mo, Ni, Pb, Zn) Radionuclides (90Sr, 137Cs, 239Pu, 234JJ 238JJ) Sunflowers Indian mustard Rape seed plants Barley, hops Crucifers Serpentine plants Nettles, dandelions... 

Higher phytoextraction coefficients indicate higher metal uptake. The effectiveness of phytoextraction can be limited by the sorption of metals to soil particles and the low solubility of the metals however, metals can be solubilized through the addition of acids or chelating agents and so allow uptake of the contaminant by the plant. Ethylene diamine tetra-acetic acid (EDTA), citric acid, and ammonium nitrate have been reported to help in the solubilization of lead, uranium, and cesium... 

Source Kumar, P.B.A.N., Dushenkov, V., Motto, H. and Raskin, I., Phytoextraction The use of plants to remove heavy metals from soils, Environ. Sci. Technol., 29, 1232-1238, 1995. With permission. 

Phytoextraction has several advantages. The contaminants are permanently removed from the soil and the quantity of the waste material produced is substantially decreased. In some cases, the contaminant can be recycled from the contaminated biomass. However, the use of hyperaccumul-ating plants is limited by their slow growth, shallow root systems, and small biomass production. In order for this remediation scheme to be feasible, plants must tolerate high metal concentrations, extract large concentrations of heavy metals into their roots, translocate them into the surface biomass, and produce a large quantity of plant biomass. 

Equations 14.24 to 14.27 can be applied to most sites where soil cleanup regulations are known for metals or organic contaminants. Two examples follow, one for TCE treatment by phytotransformation and another for lead removal by phytoextraction, which demonstrate the use of the design equations. 

Blaylock M.J., Huang J.W. Phytoextraction of metals. In Phytoremediation of Toxic Metals Using Plants to Clean Up the Environment, Raskin I., Ensley B.D., eds. New York, NY John Wiley Sons, Inc., 2000. 

Chaney R. L., Angle J. S., Wang A. S., McIntosh M.S., Broadhurst L., and Reeves R. D., 2005, Phytoextraction of soil Cd, Ni and Zn using hyperaccumulator plants to alleviate risks of metal contaminated soils requiring remediation. International Workshop Current developments in remediation of contaminated lands p. 39, 27-29 October 2005. Pulawy, Poland. 

Cost estimates for phytoremediation vary widely. One estimate for phytoextraction included 10,000 per acre for planting, with total remediation costs estimated at 60,000 to 100,000 per acre. Total costs included expenses associated with maintenance, monitoring, and verification testing. Another estimate placed phytoremediation costs at 80/yd of contaminated soil (D131431). Cleanup costs for an acre of metal-contaminated soil were estimated to range from 60,000 to 100,000. This estimate assumes remediation to a depth of 50 cm. In contrast, excavation and disposal storage without treatment for a comparable site would cost at least 400,000 (D16482T). 

TABLE 3 Cost Comparison between Phytoextraction of Metals and Other Treatment Options... 

Mertens, J., S. Luyssaert, and K. Verheyen. 2005. Use and abuse of trace metal concentrations in plant tissue for biomonitoring and phytoextraction. Environ. Pollut. 138 1 4. 

Phytoextraction is the best approach to remove the contamination primarily from soil and isolate it, without substantially alternating the soil structure and fertility. It is also referred as phytoaccumulation. As the plant absorbs, concentrates, and accumulates toxic metals and radionuclides from contaminated soils and waters into plant tissues, it is best suited for the remediation of diffusely polluted areas, where pollutants occur only at relatively low concentrations and superficial distribution in soil (Rulkens et al., 1998). Several approaches have been studied to enhance the effectiveness of phytoextraction, including the use of chelators to increase the bioavailability and plant uptake of metal contaminants. In order to make this... 

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