Metal toxicity arsenic

The term heavy metal refers to any metallic chemical element that has a relatively high density (nsnally specific density of more than 5 g/mL) and is toxic or poisonous at low concentrations. Examples of heavy metals include arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), lead (Pb), and thallium (Tl). The sources, uses, and environmental effects of several exemplary specific metals are discussed briefly here. 

Occupational and environmental poisoning with metals, metalloids, and metal compounds is a major health problem. Exposure in the workplace is found in many industries, and exposure in the home and elsewhere in the nonoccupational environment is widespread. The classic metal poisons (arsenic, lead, and mercury) continue to be widely used. (Treatment of their toxicities is discussed in Chapter 57.) Occupational exposure and poisoning due to beryllium, cadmium, manganese, and uranium are relatively new occupational problems, which present new and previously unaddressed problems. 

The Clean Air Act of 1990 has made trace metal content in fuels and wastes the final ash-related compositional characteristic of significance. Considerable attention is paid (ca 1993) to emissions of such metals as arsenic, cadmium, chromium, lead, mercury, silver, and zinc. The concentration of these metals in both grate ash and flyash is of significance as a result of federal and state requirements of particular importance is the mobility of metals. This mobility, and the consequent toxicity of the ash product, is determined by the Toxic Characteristic Leaching Procedure (tclp) test. Tables 8—10 present trace metal contents for wood wastes and agricultural wastes, municipal waste, and refuse-derived fuel, respectively. In Table 8, the specific concentration of various components in the RDF governs the expected average concentration of trace metals. 

Arsenic trioxide. Arsenic is a heavy metal that can exert toxic, poisonous effects. Therapeutic dosages of arsenic trioxide (Trisenox), however, may limit the growth of certain leukemias such as acute promyelo-cytic leukemia.11 However, because of its potential toxicity, arsenic trioxide is not usually an initial treatment, but is reserved for patients who relapse or who are resistant to other treatments. Although the exact mechanism of action is unclear, this drug apparently induces several cytotoxic effects by directly damaging DNA and proteins that regulate DNA synthesis and replication. 

Of the elements in the Periodic Table more than two thirds are metals. Although many of these metals are toxic, only some metals are major environmental pollutants, because of their widespread use. U S. EPA has classified 13 metals as priority pollutants aluminum, antimony, arsenic, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, and zinc. The Resource Conservation and Recovery Act has fisted eight metals whose mobility in the soil is measured to determine the characteristic of toxic wastes. These metals include arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver—all but one from the above list of priority pollutant metals. 

It is well known that a large number of chemical substances, including toxic metals and metalloids such as arsenic, cadmium, lead, and mercury, cause cell injury in the kidney. With metal-induced neurotoxicity, factors such as metal-binding proteins, inclusion bodies, and cell-specific receptor-like proteins seem to influence renal injury in animals and humans. It is of interest to note that certain renal cell populations become the targets for metal toxicity, while others do not. In fact, the target cell populations handle the organic and common inorganic nephrotoxicants differently. ... 

The principal ore of arsenic (5 x 10 % of earth s crust) is arsenical pyrites, FeAsS, but the element occurs commonly with nickel, copper and tin As40g is recovered from flue-dusts collected during the extraction of these metals. Sublimation in the presence of galena, which prevents the formation of arsenites, purifies the oxide this is reduced to arsenic with carbon in a cast iron retort. The element itself has few uses about 0.5% added to lead increases the surface tension of the molten metal and allows spherical lead-shot to be produced. The principal commercial form is the so-called white arsenic, As Og. Arsenic compounds are used mainly for their toxicity arsenical insecticides have been much used. 

It is more difficult to prepare III-V semiconductors than the II-VI. Two sonochemical investigations reported on the preparation of these materials. The first paper details a safe method for the preparation of transition metal arsenides, FeAs, NiAs, and CoAs [142]. At room temperature, well-crystallized and monodispersed arsenide particles were successfully obtained under high-intensity ultrasonic irradiation for 4 h from the reaction of transition metal chlorides (FeCla, NiCl2, and C0CI2), arsenic (which is the least toxic arsenic feedstock) and zinc in ethanol. Different characterization techniques show that the product powders consist of nanosize particles. The ultrasonic irradiation and the solvent are both important in the formation of the product. 

Several toxic metals, including arsenic, iron, lead, and mercury, are discussed in Chapters 30 and 35. Their measurement in urine, blood, and hair (in some cases) is valuable to help diagnose acute or chronic metal poisoning. Specific therapy for these toxins is listed in Table 34-1. Because the assessment of acute iron overdose requires emergency laboratory support, it is discussed in this chapter. 

Kotsanis, N. and J. Iliopoulou-Georgudaki. Arsenic induced liver hyperplasia and kidney fibrosis in rainbow trout Oncorhynchus mykiss) by microinjection technique a sensitive animal bioassay for environmental metal-toxicity. Bull. Environ. Contam. Toxicol. 62 169—178, 1999. 

Vesicants may be volatilized during a fire or be spread by efforts to extinguish the fire. Combustion of Arsenical Vesicants will produce volatile, toxic arsenic decomposition products. In addition. Arsenical Vesicants may react with steam or water during a fire to produce toxic, corrosive and/or flammable vapors. Hydrogen produced by the action of the corrosive vapors on metals or other corrodible materials may be present. 

Examples showing that metal speciation is important to metal toxicity include arsenic, copper, selenium, and chromium. While ionic copper (Cu2+) and CuClj are highly toxic, Q1CO3 and Cu-EDTA have low toxicity (Morrison et al, 1989). Toxicity tests show that As(III) is about 50 times more toxic than As(VI). Trivalent chromium is much less toxic than hexavalent chromium, probably because Cr(VI) is much smaller and the chemical structure of chromate is similar to sulfate. A special channel already exists in biomembranes for sulfate transport. While modeling metal speciation is not always possible, and redox equilibrium is not achieved in all natural waters, geochemical modeling of equilibrium species distribution remains one of the methods of discerning metal speciation. 

ARSENATE (7778-39-4) Reacts with strong acids, acid fumes, forming toxic arsenic fumes. Incompatible with alkalis, ammonia, amines, isocyanates, alkylene oxides, oxidizers, epichlorohydrin, vinyl acetate, amides. Weak acid slowly reacts with mild steel, galvanized metals, and brass,... 

Chemical Processes for Particulate Matter Formation Most chemical processes that produce particulates are combustion processes, as we have mentioned already. These processes include fossil fuel fired power plants, incinerators, home furnaces, fireplaces and stoves, cement kilns, internal combustion engines, forest, brush and grass fires, and active volcanoes. Particles from combustion sources tend to occur in a size < 1 fjtm. Such small particulates are particularly important because they are readily carried into the alveoli of lungs and are relatively enriched in more hazardous constituents, such as toxic heavy metals and arsenic. 

Graeme KA and Pollack CV Jr (1998) Heavy metal toxicity, part I Arsenic and mercury. J Emerg Med 16 45-56. 

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