Metal detoxification

Sulfur dioxide is usefiil as a solvent for sulfur trioxide in sulfonation reactions for example, in the large-scale production of alkylbenzenesulfonate surfactant (329). A newer use for sulfur dioxide is in cyanide detoxification in connection with cyanide leaching of precious metals from mine dumps. 

Metallothioneins are a group of non-enzymatic, low-molecular mass (6-7 kDa) metal-binding proteins. They play an important role in the detoxification of a number (Zn, Cu, Cd, and Hg) of trace metals (Chassaigne and Lobinski 1998). 

FSM Sosnowiec manufactures automobile lamps, door locks, and window winders for the Polish-manufactured Fiat cars. The lamp bodies are made of zinc-aluminum alloy and then copper-nickel-chromium plated. The door locks and window winders are made of steel and then zinc plated. The wastestreams contain cyanide and the heavy metals chromium (VI), copper, zinc, and nickel. The company carries out the traditional treatments of detoxification, neutralization, and dewatering.29... 

It is not currently feasible to achieve a zero discharge of chemical pollutants from metal finishing operations. However, substantial reductions in the type and volume of hazardous chemicals wasted from most metal finishing operations are possible.8 Because end-of-pipe waste detoxification is costly for small- and medium-sized metal finishers, and the cost and liability of residuals disposal have increased for all metal finishers, management and production personnel may be more willing to consider production process modifications to reduce the amount of chemicals lost to waste. 

This section provides guidance for reducing waterborne wastes from metal finishing operations in order to avoid or reduce the need for waste detoxification and the subsequent off-site disposal of detoxification residuals. Waste reduction practices may take the form of5 ... 

There are a number of different mechanisms by which microorganisms resist metal toxicity (Table 11.1). Five mechanisms that microbes use to mediate metal toxicity have been proposed and they include (1) formation of a permeability barrier,21-24 (2) active transport,25-29 (3) sequestration,30-32 (4) enzymatic detoxification,33 34 and (5) reduction in sensitivity.35,36 Microbes may use one or more of these mechanisms to exclude nonessential metals and regulate internal concentrations of essential metals. 

Some metals can be converted to a less toxic form through enzyme detoxification. The most well-described example of this mechanism is the mercury resistance system, which occurs in S. aureus,43 Bacillus sp.,44 E. coli,45 Streptomyces lividans,46 and Thiobacillus ferrooxidans 47 The mer operon in these bacteria includes two different metal resistance mechanisms.48 MerA employs an enzyme detoxification approach as it encodes a mercury reductase, which converts the divalent mercury cation into elemental mercury 49 Elemental mercury is more stable and less toxic than the divalent cation. Other genes in the operon encode membrane proteins that are involved in the active transport of elemental mercury out of the cell.50 52... 

Adsorption is a physicochemical process whereby ionic and nonionic solutes become concentrated from solution at solid-liquid interfaces.3132 Adsorption and desorption are caused by interactions between and among molecules in solution and those in the structure of solid surfaces. Adsorption is a major mechanism affecting the mobility of heavy metals and toxic organic substances and is thus a major consideration when assessing transport. Because adsorption is usually fully or partly reversible (desorption), only rarely can it be considered a detoxification process for fate-assessment purposes. Although adsorption does not directly affect the toxicity of a substance, the substance may be rendered nontoxic by concurrent transformation processes such as hydrolysis and biodegradation. Many chemical and physical properties of both aqueous and solid phases affect adsorption, and the physical chemistry of the process itself is complex. For example, adsorption of one ion may result in desorption of another ion (known as ion exchange). 

Biosorption strategies consist of a group of applications involving the detoxification of hazardous substances such as heavy metals instead of transferring them from one medium to another by means of biosorbents, which may be either microbes or plants. Biosorption options are generally characterized as being less disruptive and may henceforth be carried out on-site, thereby eliminating the need to transport the toxic materials to treatment sites.12 Biosorption is a very cost-effective method... 

In a separate study, Igwe and Abia46 determined the equilibrium adsorption isotherms of Cd(II), Pb(II), and Zn(II) ions and detoxification of wastewater using unmodified and ethylenediamine tetraacetic acid (EDTA)-modified maize husks as a biosorbent. This study established that maize husks are excellent adsorbents for the removal of these metal ions, with the amount of metal ions adsorbed increasing as the initial concentrations increased. The study further established that EDTA modification of maize husks enhances the adsorption capacity of maize husks, which is attributed to the chelating ability of EDTA. Therefore, this study demonstrates that maize husks, which are generally considered as biomass waste, may be used as adsorbents for heavy metal removal from wastewater streams from various industries and would therefore find application in various parts of the world where development is closely tied to affordable cost as well as environmental cleanliness.46... 

Amiard JC, Amiard-Triquet C, Barka S, Pellerin J, Rainbow PS (2006) Metallothioneins in aquatic invertebrates their role in metal detoxification and their use as biomarkers. Aquat Toxicol 76(2) 160-202... 

Pullen, J.S.H. and P.S. Rainbow. 1991. The composition of pyrophosphate heavy metal detoxification granules in barnacles. Jour. Exper. Mar. Biol. Ecol. 150 249-266. 

Mason, A. Z. and Jenkins, K. D. (1995). Metal detoxification in aquatic organisms. In Metal Speciation and Bioavailability in Aquatic Systems, eds. Tessier, A. and Turner, D. R., Vol.3, IUPAC Series on Analytical and Physical Chemistry of Environmental Systems. Series eds. Buffle, J. and van Leeuwen, H. P., John Wiley Sons, Ltd, Chichester, pp. 479-608. 

When animals are fed experimental diets lacking copper or zinc, their copper or zinc status rapidly declines, suggesting that there is not a storage pool of these metals. Thus, while the small, cysteine-rich protein metallothionein (see below) can avidly bind zinc and copper, this may reflect its role in detoxification rather than as a specific storage form. This is reflected by the fact that metallothionein genes are typically expressed at a basal level, but their transcription is strongly induced by heavy metal load. 

In a simplified model, the metal ions equilibrate on the outside of the cell with biologically produced and excreted ligands l 2 or ligands on the cell surface L3 these reactions are followed by a slow transport step to the inside of the cell. In the cell, the metal ions may be used in biochemical processes or become trapped in inactive forms as a detoxification mechanism. (After Williams, 1983) (cf. Fig. 4.15a). (From Sigg, 1987)... 

E. Pelizzetti, C. Minero, Metal oxides as photocatalysts for environmental detoxification, Comments Inorg. Chem. 15 (1994) 297-337. 

Cobbett C. S., 2000, Phytochelatins and their role in heavy metal detoxification, Plant Physiol. 123 825-832. 

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