Mercury detoxification

A knowledge of physiology and pharmacokinetics is needed (Fanis et al. 1993 Monteiro and Furness 2001). Levels of mercuiy normally vary among internal tissues, and the time to equilibrate within each tissue varies. For example, blood mercury levels normally reflect veiy recent exposure, while brain and liver levels reflect longer-term exposure. Tissue-specific mechanisms of detoxification and seqnestration, among other processes, must be understood to define the bioactive moiety in observed tissue bmdens before a clear expression of toxicity can be derived (Woodetal. 1997). 

Caurant F, Navarro M, Amiard JC. 1996. Mercury in pilot whales possible limits to the detoxification process. Sci Total Environ 186 95-104. 

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... 

And finally, additional research is needed on mercury accumulation and detoxification in comparatively pristine ecosystems. Key uncertainties in understanding the process of mercury uptake in aquatic ecosystems, for example, include relations between water chemistry and respiratory uptake, quantitative estimates of intestinal tract methylation and depuration, and degree of seasonal variability in mercury speciation and methylation-demethylation processes (Post et al. 1996). 

Four courses of action now seem warranted. First, toxic mercurials in agriculture and industry should be replaced by less toxic substitutes. Second, controls should be applied at the point of origin to prevent the discharge of potentially harmful mercury wastes. Third, continued periodic monitoring of mercury in fish and wildlife is needed for identification of potential problem areas, and for evaluation of ongoing mercury curtailment programs. And fourth, additional research is merited on mechanisms of mercury accumulation and detoxification in comparatively pristine ecosystems. 

Robinson, J.B. and O.H. Touvinen. 1984. Mechanisms of microbial resistance and detoxification of mercury and organomercury compounds physiological, biochemical and genetic analysis. Microbiol. Rev. 48 95-124. 

Fig. 13.3 NMR structure of the mercury-bound form of merP, a72-residue protein from the bacterial mercury detoxification system. The merP protein resides between the inner and outer membranes of the cell in a region known as the periplasm. Mercury(ll) entering the cell is bound by merP in the periplasm, passed to the transport protein (merT) which moves it through the inner membrane where it is reduced...

Bizily, S. P., Kim, T., Kandasamy, M. K., and Meagher, R. B., 2003, Suhcellular targeting of methylmercury lyase enhances its specific activity for organic mercury detoxification in plants, Plant Physiol. 131 463-471. 

Not all agents can be readily metabolized. The toxic metals lead and mercury are elements that cannot be degraded but must still be removed from the body. Another important mechanism of detoxification is the attachment or binding of another compound to a toxic chemical to make it easier for the kidney to filter the compound out of the blood and excrete it in the urine. A primary purpose of the kidney is to screen the blood for waste products and concentrate them in the urine for excretion, as occurs, for example, with mercury. Caffeine is excreted in the urine at approximately the same concentration as the blood because the kidney cannot concentrate caffeine. Vitamins, however, are readily concentrated and excess quickly eliminated in the urine. 

Table 1 contains 1995 estimated materials costs for a single photo-thermal detoxification unit chamber fitted with six 15-kW medium-pressure mercury lamps. Labor and licensing costs were not included (D117317, p. 9). 

However chemical methods of mercury detoxification are far from adequate. It has become evident that mercury can be solubilized from HgS under conditions that could be present in a landfill. We have demonstrated chemical solubilization followed by volatilization with Fe2(S04)3, a product of oxidation of FeS04 (pyrite) by Thiobacillus ferrooxidans (data not shown). Other researchers have indicated that T. ferrooxidans can facilitate solubilization and volatilization of Hg° from HgS. Growth of T. ferrooxidans in the presence of cinnabar (mercury ore-contains HgS and some impurities) by Silver and Torma (1984) resulted in dissolved mercury concentration in the bioreactor of 64 mg/L (the form of Hg was not given). In similar experiments with T. ferrooxidans and cinnabar, Baldi and Olson (1987) did not... 

A biological process for detoxification of mercury in polluted water and sludges has been developed. Recovery of elemental mercury from the vapor phase for reuse is being studied and preliminary results show promise for the process. A full-scale process is under investigation for field/commercial application. 

Xu, H. J., C. L. Hansen, and G. S. Choudhury. 1987. Using dairy byproduct for mercury detoxification. Presented at Food Processing Waste Conference, Atlanta, Ga. 

The one exception is the capacity of some micro-organisms to methylate certain metals, e.g. arsenic, antimony and mercury, probably as a kind of detoxification mechanism. Methylcobal-amin is the only organometallic compound known to have a physiological function in life processes. 

Enzymatic detoxification or modification AGAC antibiotics /(-Lactams Chloramphenicol Erythromycin Tetracyclines Mercury compounds Formaldehyde Modification by acetyltransferases, adenylylases or phosphotransferases Inactivation (/(-lactamases) Inactivation (acetyltransferases) Esterases produce anhydroerythromycin Enzymatic inactivation Inactivation (hydrolases, lyases) Dehydrogenase... 

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