Heavy metal toxicity cadmium

The salts of the heavy metals beryllium, cadmium, chromium, copper, lead, mercury, nickel and zinc are all of high eco-toxicity. For example, the toxicity of some heavy metals to rainbow trout is demonstrated in Table 16.13 coarse fish are somewhat more resistant. 

Nanoparticles such as those of the heavy metals, like cadmium selenide, cadmium sulfide, lead sulfide, and cadmium telluride are potentially toxic [14,15]. The possible mechanisms by which nanoparticles cause toxicity inside cells are schematically shown in Fig. 2. They need to be coated or capped with low toxicity or nontoxic organic molecules or polymers (e.g., PEG) or with inorganic layers (e.g., ZnS and silica) for most of the biomedical applications. In fact, many biomedical imaging and detection applications of QDs encapsulated by complex molecules do not exhibit noticeable toxic effects [16]. One report shows that the tumor cells labeled with QDs survived in circulation and extravasated into tissues... 

Devi, V.U. 1987. Heavy metal toxicity to fiddler crabs, Uca annulipes LatreiUe and Uca triangularis (Milne Edwards) tolerance to copper, mercury, cadmium, and zinc. Bull. Environ. Contam. Toxicol. 39 1020-1027. Devi, V.U. and Y.R Rao. 1989. Heavy metal toxicity to fiddler crabs, Uca annulipes Latreille and Uca triangularis (Milne Edwards) respiration on exposure to copper, mercury, cadmium, and zinc. Bull. 

Heavy metal toxicity in plants is infrequent (143). In many cases, metal concentrations in plant parts show poor correlation with soil concentrations of the element (147). Plants tend to exclude certain elements and readily accept or concentrate others. Lisk (148) reported natural plant soil concentration ratios of 0.05 or less for As, Be, Cr, Ga, Hg, Ni, and V. Cadmium appears to be actively concentrated and selenium appears to be easily exchangeable. Indicator plants are capable of markedly concentrating specific elements, e.g., Astragalus spp. for selenium (138) and Hybanthus floribundus for nickel (149). Plants growing on mine wastes have been shown to evolve populations which exhibit metal-specific tolerances (150). 

The metals of most concern are the heavy metals, especially cadmium, lead, and mercury. Although it is a metalloid with characteristics of both metals and nonmetals, arsenic is commonly classified as a heavy metal for a discussion of its toxicity. Though not particularly toxic, zinc is abundant and may reach toxic levels in some cases. For example, zinc accumulates in sewage sludge and crop productivity has been lowered on land fertilized with sludge because of zinc accumulation. Copper may be toxic to plants. Aluminum, a natural constituent of soil, may be leached from soil by polluted acidic rainwater and reach levels that are toxic to plants. Other metals that may be of concern because of their toxicides include chromium, cobalt, iron, nickel, and vanadium. Radium, a radioactive alpha particle-emitting metal, can be very toxic at even very low levels in water or food. 

Zinc efflux is mediated by a zinc exporter known as ZntA (Zn + transport or tolerance), a membrane protein which was identified through studies of bacterial strains that were hypersensitive to zinc and cadmium. Sequence inspection revealed that ZntA was a member of the family of cation transport P-type ATPases, a major family of ion-translocating membrane proteins in which ATPase activity in one portion of the protein is used to phophorylate an aspartate within a highly conserved amino acid sequence, DKTG, in another portion of the protein. The cysteine rich N-terminus of these soft metal transport proteins contains several metal-binding sites. How the chemical energy released by ATP hydrolysis results in metal ion transport is not yet known, in part because there is only partial information about the structures of these proteins. The bacterial zinc exporter also pumps cadmium and lead and is therefore also involved in protection from heavy metal toxicity (see Metal Ion Toxicity). 

More specifically, a 1000-MWe coal plant with optimal pollution abatement equipment will annually emit into the atmosphere 900 tonnes of SOj, 4500 tonnes of NO,j, 1300 tonnes of particulates, and 6.5 million tonnes of CO2. Depending on the quality of the coal, up to 1 million tonnes of ashes containing hundreds of tonnes of toxic heavy metals (arsenic, cadmium, lead, and mercury) will have to be disposed of. 

Selectivity of adsorbants vis a vis mercury. Attempts to remove toxic heavy metal ions, cadmium and lead, were made in order to check the specificity of modified corn--stick powder. 

The mechanisms by which metals induce toxic effects or diseases are not well understood. The most toxic heavy metal ions, cadmium, lead, mercury, are potent enzyme inhibitors because the ions are readily polarizable and bind to donor groups in the enzyme, the binding strengths decreasing in the electron-donor element order S > N > O. In-vivo, phosphate and chloride ions are ubiquitous and these may lead to the formation of insoluble species such as lead hydroxophosphate or only slightly soluble mercuric chloride. 

Van Assche F, Cardinaels C and Clijsters H (1988) Induction of enzyme capacity in plants as a result of heavy metal toxicity dose—response relations in Phaseolus vulgaris L, treated with zinc and cadmium. Environ Pollut 52 103-115. 

Suppose that you want to construct a galvanic cell firom nickel and cadmium for a chemistry project. You take all the precautions necessary to deal with a toxic heavy metal like cadmium, and you decide to use a 0.01 M solution of cadmium nitrate... 

Purity control limits contamination with pathogenic bacteria Staphylococcus aureus, Escherichia coli. Salmonella-species, Pseudomonas aeruginosa, Clostridium-species and others), yeasts, moulds, microbial toxins (aflatoxins, endotoxins), toxic heavy metals (lead, cadmium, mercury, arsenic e.g. from industrial emission), pesticide and herbicide residues, fumigants (ethylene oxide, methyl bromide, phosphine) and radionuclides. Furthermore, impurities with other plants parts ( foreign organic matter ) are limited. Moist levels must be below a certain maximum to avoid deterioration by microorganisms. Excreta of animals and dead insects must be absent. The ash value and acid-insoluble ash limits the amount of inorganic impurities (soil, sand). 

Various proposals have been presented to explain the interaction of selenium with heavy metals. However, no single one appears to explain the mechanism of interaction with all heavy metals. It appears that there are several mechanisms involved in this interaction and that more than one could be involved with a particular metal. It is clear that selenium does not protect animals against heavy metal toxicity by increasing their excretion instead, it causes an increased retention of metals (Parizek et al, 1971 Wagner et al., 1975 Diplock, 1976 Ganther, 1978 Whanger, 1981). A summary of the proposed interactions of selenium with cadmium, mercury, and silver is presented in Fig. 1. 

Of the heavy metals, lead, cadmium, tin and iron, the first two are toxic, the last two are not. We accept tin as a metal coating in contact with foodstuffs, and iron is even vital for human beings and mammals. The difference is due to the fact that lead and cadmium are markedly chalcophilic l (occur as sulfides in nature) while tin and iron are HthophiHc (occur mainly as oxides in nature). like all chalcophilic elements, lead has a strong tendency to bind sulfur. That is the reason for its toxicity. 

The heavy metals lead, cadmium and mercury are toxic because they combine with sulfur in proteins. They can occupy sites where no metal is normally present, a serious disturbance, or they can push vital metals such as iron out of their positions. The liver prepares a remarkable protein, metallothionein, especially rich in cysteine groups, which can act as a scavenging substance, taking care of toxic elements up to a certain level. Even essential elements, copper for instance, may be removed if present in too high, toxic concentrations. 

The development of probes for the toxic heavy metals mercury, cadmium and lead in biological systems is of special interest In this context, selectivity is particularly important since alkali and alkaline earth metals (e.g. Na", K", ... 

Currently, waterborne toxic chemicals pose the greatest threat to the safety of water supplies in industrialized nations. This is particularly true of groundwater in the U.S., which exceeds in volume the flow of all U.S. rivers, lakes, and streams. In some areas, the quality of groundwater is subject to a number of chemical threats. There are many possible sources of chemical contamination. These include wastes from industrial chemical production, metal-plating operations, and pesticide runoff from agricultural lands. Some specific pollutants include industrial chemicals such as chlorinated hydrocarbons heavy metals, including cadmium, lead, and mercury saline water bacteria, particularly coliforms and general municipal and industrial wastes. 

As the carbonate content of the ore increases, the substitution of carbonate in the francolite tends to increase. It is common for trace quantities of heavy metals, toxic elements such as cadmium, and radionuclides such as uranium to exist in phosphate rock owing to substitution in the crystal lattice (see Table 10.5). Usually the quantities of these elements are insufficient to be of concern. 

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. 

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