Mercury toxicity mechanism

Current work directed at elucidating the mechanism of mercury toxicity will be a fertile area of research into potential sub-organismal biomarkers. Techniques including... 

An intriguing problem about which we know very little is the mechanism of metal identification by the body that triggers Its response, as in the case of the huild-up of metallothioneins upon exposure to toxic metals. Perhaps the best understood of the metalloregulatory proteins is MerR that protects bacteria from mercurial toxicity. It is extremely sensitive to Hg, and distinguishes it from its congeners Zn and Cd. There is good evidence that the mercury receptor forms three-coordinate mercury(II) complexes (see Fig. 12.1c), making possible this specificity. ... 

Mercury, arsenic, and lead also provide examples of how differences in the form (valence, organic/inorganic, gas/aqueous, etc.) of a given element can result in strikingly different exposure pathways, absorption and transport mechanisms, toxicity mechanisms, metabohc processes, excre-tion/storage mechanisms, and the affected target organs (see Table 3). 

The mechanism of mercury toxicity is still largely unknown. It is not known whether there are unique mechanisms of action for the toxic effects in children that would require special consideration for treatment modalities, but at present it appears that target site is determined more by the pharmacokinetics (i.e., which tissues end up with the highest levels) than by a specific mechanism of action (e.g., a receptor binding-process initiating type of mechanism). 

Despite eoncems about mercury toxicity, amalgam is still the most-common posterior restorative material. As it is non-adhesive, it is retained in the cavity mechanically by... 

Kudo, A. (1983). Physical/chemical/biological removal mechanisms of mercury in a receiving stream. In Toxic Materials - Methods for Control" (N. E. Armstrong and A. Kudo, eds). The Center for Research in Water Resources, University of Texas at Austin, Austin, TX. 

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). 

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... 

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. 

Substitute (substitution) Use mechanical pump seals vs. packing Use welded pipe vs. flanged Use solvents that are less toxic Use mechanical gauges vs. mercury Use chemicals with higher flash points, boiling points, and other less hazardous properties Use water as a heat transfer fluid instead of hot oil... 

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