Metal contaminated soil

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

U.S. EPA, Recent Developments for In Situ Treatment of Metal Contaminated Soils, EPA-542-R-97-004, Technology Innovation Office, Washington, 1997. 

U.S. EPA, Recent developments for in-situ treatment of metal contaminated soils, U.S. EPA, Office of Solid Waste and Emergency Response, Technology Innovation Office, EPA Contract No. 68-W5-006, 1997, pp. 1-47. 

There is some uncertainty about the potential presence of metal in the TCE-contaminated soil of Area 2. If metal concentrations of concern are present, only Alternatives 2 and 5 would protect against direct contact and further groundwater contamination through a cap and incineration, respectively. Incineration of metal-contaminated soil may result in a hazardous waste residue, which would have to be disposed of in a hazardous waste landfill. Alternatives 3 and 4 rely on vapor extraction and would not lower risks from metal to human health or the environment. 

Ahnstrom and Parker (2001) studied Cd reactivity in metal-contaminated soils using a coupled stable isotope dilution-sequential extraction procedure. They found that in uncontaminated arid soil and in... 

Ahnstrom Z.A.S., Parker D.R. Cadmium Reactivity in Metal-Contaminated Soils Using a Coupled Stable Isotope Dilution-Sequential Extraction Procedure. Environ Sci... 

Mench M.J., Didier V.L., Loftier M., Gomez A., Masson P. A mimicked in-situ remediation study of metal-contaminated soils with emphasis on cadmium and lead. J Environ Qual 1994 23 58-63. 

Role of Bacteria and Bacteria-Soil Composites in Metal Biosorption and Remediating Toxic Metal-Contaminated Soil Systems... 

Lebeau et al. (2002) investigated the sorption of cadmium by viable microbial cells that were free or immobilized in alginate beads by incubating the bacteria in a liquid soil extract medium at pH 5 7 and Cd concentrations of 1 to 10 mg L-1. The percentage of Cd biosorbed reached a maximum (69%) at low Cd concentrations and neutral pH. Thus, the effectiveness of bacteria, inoculated into metal-contaminated soils, would largely depend on the concentration of the metal and its distribution between the biomass and the medium. 

Bacteria and their composites with soil minerals or organic matter are capable of taking up a wide range and variety of toxic metals in soil environments. Research done over the last decade or so has greatly improved our understanding of the mechanisms on biosorption of metals and bacte-ria-metal-soil component interactions. However, more studies from molecular level are needed in order to enhance the ability of bacteria and their association with soil components to remediate toxic metals-contaminated soils. The focus of future investigations should be on the mechanisms by which metals are sorbed and bound by bacterial cell surfaces and bacteria-soil/mineral composites. In this connection, X-ray absorption spectroscopy (XAS) is a promising technique because it can provide information about... 

Roane TM, Kellogg ST (1996) Characterization of bacterial communities in heavy metal contaminated soils. Can J Microbiol 42 593-603 Sahunalu P, Dhanmanonda P (1995) Structure and dynamics of dry dipterocarp forest, Sakaerat, northeastern Thailand. In Box EO, Peet RK, Masuzawa E,... 

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. 

Asphaltic metals stabilization is a stabilization technology for metal-contaminated soils in which the soils are combined with predetermined amounts of aggregates and asphalt emulsions to... 

The MRU technology is not applicable to heavy-metal-contaminated soils nor to radioactive waste contamination. The one exception to heavy-metals remediation is mercury. The vaporization temperature for mercury is well within the operating range of the MRU, and because of closed chamber construction, it is ideally suited for the removal and reclamation of mercury from contaminated soil. 

Direct pyrometallurgical processing of heavy-metals-contaminated soils, sands, and dust is often better suited for materials with higher levels of contamination however, it can be effective for low-level contamination as well. The technology is also well suited to process-concentrated heavy metals that have been generated by on-site screening or soil washing (personal communication, M. Thomas, The Doe Run Company, 10/97). 

This is an ex situ anaerobic bioremediation technology for metal-contaminated soils, sludges, and sediments. While metals are the primary pollutant treated, the biological system also degrades and removes organics such as hydrocarbons. 

TABLE 1 ChemTech Estimated Total Cleanup Costs for a Metals-Contaminated Soil"... 

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). 

A new phytoremediation technology is being developed for treating heavy-metal-contaminated soils. Researchers at the University of Georgia have modified two bacterial genes, merA and merB, and inserted them into the deoxyribonucleic acid (DNA) of certain plants, enabling them... 

Hodson, M. E., Valsami-Jones, E. Cotter-Howells, J. D. 2000. Bonemeal additions as a remediation treatment for metal contaminated soil. Environmental Science Technology, 34, 3501-3507. 

Soil washing with acidic solutions is one way to facilitate metal removal. Under acidic conditions, sorbed metals are released as the increase in hydrogen ions causes competition for available phosphate and results in formation of phosphoric acid. The released metals have increased solubility and thus are more easily removed from the system during treatment. For example, Tuin Tels (1991) describe the use of concentrated acid or phosphate solutions to wash metal-contaminated soil. 

Gieger,G.,Federer,P. Sticher, H.(1993). Reclamation of heavy metal-contaminated soils field studies and germination experiments. Journal of Environmental Quality, 22,201—7. 

Miller, R.M. (1995a). Biosurfactant-facilitated remediation of metal-contaminated soils. 

Otte, M. L. (1991). Contamination of coastal wetlands with heavy metals factors affecting uptake of heavy metals by salt marsh plants. In Ecological Responses to Environmental Stresses, ed. J. Rozema J. A. C. Verkleij, pp. 126-33. London Kluwer Academic. Peters, R. W. Shem, L. (1992). Use of chelating agents for remediation of heavy metal contaminated soil. In Environmental Remediation, ed. American Chemical Society, pp. 70-84. Washington, D.C. American Chemical Society. 

Roane, T. M. (1994). Microbial community analyses in heavy metal contaminated soil (thesis). Moscow, Idaho University of Idaho. 

Chemical Fixation of Heavy Metal-Contaminated Soils... 

The treatment of heavy metal contaminated soil has become an important issue in the past few years. Nearly one-third of the sites on the Superfund National Priorities List (NPL) possess lead concentrations significantly higher than normal background levels.(U The difficulties in treating heavy metal contamination stems from the fact that they cannot be destroyed or biodegraded. 

Currently there is a variety of treatment technologies available for heavy-metal contaminated soils (both bench and pilot scales). P. S. Puglionesi et al. 5) conducted an evaluation of various treatment technologies chosen through extensive literature research and personal contacts. 

P. S. Puglionesi et al. 1987, "Treatment Technologies For Heavy Metal Contaminated Soils" American Defense Preparedness Association s 15th Environmental Symposium Proceedings. April 28-30, 1987. 

Mulligan, C.N., Yong, R.N. and Gibbs, B.F. (2001) Remediation technologies for metal-contaminated soils and ground-water an evaluation. Engineering Geology, 60(1-4), 193-207. 

Reynolds [25] has reviewed digestion procedures for the analysis of metal-contaminated soils. 

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