Lead and mercury

Deposits. Selenium forms natural compounds with 16 other elements. It is a main constituent of 39 mineral species and a minor component of 37 others, chiefly sulfides. The minerals are finely disseminated and do not form a selenium ore. Because there are no deposits that can be worked for selenium recovery alone, there are no mine reserves. Nevertheless, the 1995 world reserves, chiefly in nonferrous metals sulfide deposits, are ca 70,000 metric tons and total resources are ca 130,000 t (24). The principal resources of the world are in the base metal sulfide deposits that are mined primarily for copper, zinc, nickel, and silver, and to a lesser extent, lead and mercury, where selenium recovery is secondary. 

Catalyst lifetimes are long in the absence of misoperation and are limited primarily by losses to fines, which are removed by periodic sieving. Excessive operating temperatures can cause degradation of the support and loss of surface area. Accumulation of refractory dusts and chemical poisons, such as compounds of lead and mercury, can result in catalyst deactivation. Usually, much of such contaminants are removed during sieving. The vanadium in these catalysts may be extracted and recycled when economic conditions permit. 

HEAVY METALS A gi oup of metals which are sometimes toxic and can be dangerous in high concentrations. The main heavy metals covered by legislation are cadmium, lead, and mercury. Industrial activities such as smelting, rubbish burning, waste disposal and adding lead to petrol increase the amount of toxic heavy metals in the environment. 

Paracelsus, a Swiss physician of the sixteenth century, stated that everything is toxic, it is just the dose that matters. This statement still holds true 500 years after Paracelsus developed it to defend the use of toxic compounds such as lead and mercury in the treatment of serious diseases such as syphilis. Chemical compounds cause their toxic effects by inducing changes in cell physiology and biochemistry, and an understanding of cellular biology is a prerequisite if one wishes to understand the nature of toxic reactions. 

EDTA also is used to treat lead and mercury poisoning, as it can lock up those metals so they can do no harm in the body. 

Sometimes we have to precipitate one ion of a sparingly soluble salt. For example, heavy metal ions such as lead and mercury can be removed from municipal waste-water by precipitating them as the hydroxides. However, because the ions are in dynamic equilibrium with the solid salt, some heavy metal ions remain in solution. How can we remove more of the ions ... 

Many years ago, geochemists recognized that whereas some metallic elements are found as sulfides in the Earth s crust, others are usually encountered as oxides, chlorides, or carbonates. Copper, lead, and mercury are most often found as sulfide ores Na and K are found as their chloride salts Mg and Ca exist as carbonates and Al, Ti, and Fe are all found as oxides. Today chemists understand the causes of this differentiation among metal compounds. The underlying principle is how tightly an atom binds its valence electrons. The strength with which an atom holds its valence electrons also determines the ability of that atom to act as a Lewis base, so we can use the Lewis acid-base model to describe many affinities that exist among elements. This notion not only explains the natural distribution of minerals, but also can be used to predict patterns of chemical reactivity. 

Heo Y, Lee WT, Lawrence DA. 1997. In vivo the environmental pollutants lead and mercury induce oligoclonal T cell responses skewed toward type-2 reactivities. Cell Immunol 179 185-195. 

Bettmer, J., Cammann, K., and Robecke, M., Determination of organic ionic lead and mercury species with high-performance liquid chromatography using sulphur reagents, /. Chromatogr., 654, 177, 1993. 

Thus films can be divided into two groups according to their morphology. Discontinuous films are porous, have a low resistance and are formed at potentials close to the equilibrium potential of the corresponding electrode of the second kind. They often have substantial thickness (up to 1 mm). Films of this kind include halide films on copper, silver, lead and mercury, sulphate films on lead, iron and nickel oxide films on cadmium, zinc and magnesium, etc. Because of their low resistance and the reversible electrode reactions of their formation and dissolution, these films are often very important for electrode systems in storage batteries. 

Heavy metals with no known biological function, such as aluminum, arsenic, lead, and mercury, are nonessential metals.4-5 These metals are toxic because they can irreversibly bind to enzymes that require metal cofactors. Toxic metals readily bind to sulfhydryl groups of proteins.6-7 In fact,... 

Henry, J.R., An Overview of the Phytoremediation of Lead and Mercury, National Network of Environmental Management Studies (NNEMS), U.S. EPA, Technology Innovation Office, Washington, 2000. 

Chemical reduction is used to transform a toxic substance with a higher valence to a nontoxic or less-toxic substance with lower valence. The most promising application is the reduction of hexava-lent chromium to trivalent chromium. This method is also applicable to other multivalent metals such as lead and mercury. Commonly used chemical agents for this purpose are sulfite salts, sulfur dioxide, and base metals (e.g., iron and aluminum).22 24... 

Waste halogen and sulfur content Waste lead and mercury content... 

Abadin HG, Hibbs BF, Pohl HR. 1997b. Breast-feeding exposure of infants to cadmium, lead, and mercury A public health viewpoint. Toxicol Ind Health 15(4) 1-24. 

Altmann L, Sveinsson K, Kraemer U, et al. 1998. Visual functions in 6-year-old children in relation to lead and mercury levels. Neurotoxicology and Teratology 20(1) 9-17. 

Ariza ME, Bijur GN, Williams MV. 1998. Lead and mercury mutagenesis Role of H202, superoxide dismutase, and xanthine oxidase. Environ Mol Mut 31 352-361. 

Pacyna J.M. Atmospheric emissions of arsenic, cadmium, lead and mercury from high temperature processes in power generation and industry. In Lead, Mercury, Cadmium and Arsenic in the Environment, T.C. Hutchinson, K.M. Meema, eds. SCOPE 1987 31 69-87. 

The authors studied the reduction of C02 at lead and mercury cathodes in DMF and monitored the distribution of products as a function of current, C02 concentration, water concentration and changing the solvent to DMSO. The product analysis was performed using standard quantitative analysis on the electrolyte and the gas phase above. 

Zinc, Manganese, Cobalt, Copper, Chromium, Nickel, Iron, Cadmium, Lead, and Mercury... 

In addition to the chemicals included on the other lists, the CDC also included heavy metals such as arsenic, lead, and mercury volatile solvents such as benzene, chloroform, and bromoform decomposition products such as dioxins and furans polychlorinated biphenyls (PCBs) flammable industrial gases and liquids such as gasoline and propane explosives and oxidizers and all persistent and nonpersistent pesticides. Agents included in this volume are limited to those that are most likely to pose an acute toxicity hazard. 

Tin is comparable in its toxicological behavior to lead and mercury. Bivalent tin compounds generally are more toxic than the tetravalent compounds. Furthermore, organic tin compounds are more toxic than inorganic ones and the trialkyl analogs (triethyltin, trimethyltin, tributyltin) are the most toxic. As the number of carbon atoms attached to tin increases, the toxicity of the organic tin compounds rapidly declines9,77. 

Schell, W. R., and Barnes, R. S., Lead and Mercury in the aquatic environment of Western Washington State, In Aqueous Environmental Chemistry of Metals, A. J. Rubin, ed., Ann Arbor Science, Ann Arbor, Michigan, 129-165 (1974). 

Borgmann, U., W.P. Norwood, and C. Clarke. 1993. Accumulation, regulation and toxicity of copper, zinc, lead and mercury in Hyalella azteca. Hydrobiol. 259 79-89. 

Khan, A.T., S.J. Thompson, and H.W. Mielke. 1995. Lead and mercury levels in raccoons from Macon County, Alabama. Bull. Environ. Contam. Toxicol. 54 812-816. 

Chigbo, F.E., R.W. Smith, and F.L. Shore. 1982. Uptake of arsenic, cadmium, lead and mercury from polluted waters by the water hyacinth Eichhomia crassipes. Environ. Pollut. 27A 31-36. 

In the environment, metals are common as a chemical species, and as usual the metal-organic species are more toxic. For example, the inorganic lead and mercury species are less toxic for living organisms than the organic ones (methyl mercury, tetraethyl lead). However inorganic arsenic compounds are more toxic than organic... 

Cadmium occurs naturally as sulfide co-deposited with zinc, copper, and lead sulfides. It is produced as a by-product in above-mentioned metal processing. Similar to lead and mercury, this heavy metal has no known biological functions in living organisms, and accordingly its accumulation in food and water leads to undesirable consequences to biota. Cadmium toxicology is related to dangerous influence to CNS and excretion systems, firstly, on kidney. 

Similar to other batteries and accumulators, the burying of cadmium batteries is a very great problem in every country, and Cd seepage from landfills and waste sites (in addition to fertilizers) is responsible for soil and water pollution and environmental risks to human and ecosystem health. The same is true for lead and mercury. 

Similar information is also available for lead and mercury, and not only for forests and arable lands, but also for other land-cover categories. This information is presented on the Internet [www.msceast.org]. 

Annual emissions of heavy metals from the anthropogenic sources of HELCOM countries significantly decreased during the period of 1990-2001. In particular, annual emissions of cadmium decreased by 45%, whereas lead and mercury emissions reduced by 60%. Following this reduction and also due to the changes of heavy metals emissions in other European countries the level of atmospheric depositions to the Baltic Sea has also significantly decreased (Figure 20). Compared to 1990... 

Hengge et al. reported the formation of Si-Si bond in the electrochemical reduction of chlorosilanes in DME without control of the applied potential. For the formation of the Si-Si bond the choice of electrode materials seems to be of great importance [81]. Lead and mercury have proved suitable as cathode materials. 

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