Metal toxicity chromium

Some heavy metals and semi-metals are quite toxic (chromium, lead, and antimony) and expensive care is needed to prevent them from being dispersed in the environment. Lead in gasoline and paint has been... 

Many studies have reported the effects of metals on general soil microbiological processes. Metals including cadmium, chromium, copper, lead, mercury, nickel, and zinc have been reported to inhibit many of the microbial processes listed above. Metal toxicity in the environment ultimately decreases litter decomposition, which can be measured by the rate of mass loss. Both copper (0.5 mg Cu g4 soil) and zinc (1.0 mg Zn g 1 soil) were shown to decrease the rate of decomposition of unpolluted Scots pine needle litter near a brass mill in Sweden.61 Duarte et al.63 also determined that copper and zinc toxicity reduced leaf decomposition rates and fungal reproduction. Other metals, such as cadmium, nickel, and lead, have also been reported to decrease litter decomposition.77... 

Toxic pollutants found in the mercury cell wastewater stream include mercury and some heavy metals like chromium and others stated in Table 22.8, some of them are corrosion products of reactions between chlorine and the plant materials of construction. Virtually, most of these pollutants are generally removed by sulfide precipitation followed by settling or filtration. Prior to treatment, sodium hydrosulfide is used to precipitate mercury sulfide, which is removed through filtration process in the wastewater stream. The tail gas scrubber water is often recycled as brine make-up water. Reduction, adsorption on activated carbon, ion exchange, and some chemical treatments are some of the processes employed in the treatment of wastewater in this cell. Sodium salts such as sodium bisulfite, sodium hydrosulfite, sodium sulfide, and sodium borohydride are also employed in the treatment of the wastewater in this cell28 (Figure 22.5). 

Srinath T, Verma T, Ramteke PW, Garg SK (2002) Chromium biosorption and bioaccumulation by chromate resistant bacteria. Chemosphere 48 427-435 Stephen JR, Macnaughton SJ (1999) Developments in terrestrial bacterial remediation of metals. Curr Opinion Biotechnol 10 230-233 Tabak HH, Lens P, van Hullebusch ED, Dejonghe W (2005) Developments in bioremediation of soils and sediments polluted with metals and radionuclides 1. Microbial processes and mechanisms affecting bioremediation of metal contamination and influencing metal toxicity and transport. Rev Environ Sci Bio/Technol. 4 115-156... 

Hexavalent chromium is a known human carcinogen, however, and its commercial use is strictly regulated and highly discouraged by environmental authorities. An alternative metal to chromium in premetallized azo dyes would have to have the same color and fastness properties as chromium but without the toxicity. It has been found that iron, which is essentially nontoxic, often imparts the same desirable qualities as chromium when used in azo dyes [82,83]. This is exemplified in comparing azo dyes 44 and 45. Dyestuff 45 has the same color and fastness as 44, but does not contain chromium. Other examples of dyestuffs that use iron rather than chromium are available [82, 83]. 

An interesting finding regarding potentially toxic chromium (and cobalt) in the body is elevated blood and urine levels of these metals in patients who have undergone total hip replacement.5 The conclusion of the study was that devices such as prosthetic hips that involve metal-to-metal contact may result in potentially toxic levels of metals in biological fluids. 

Chromium in the +6 oxidation state, Cr(VI), is a very important and effective oxidant in the organic laboratory. The major drawback to the use of reagents based on this species is that the product, Cr(III), is toxic. Chromium is just one example of a toxic heavy metal that requires quite expensive disposal procedures... 

Fly ash from municipal waste and industrial waste incinerators contains polychlorinated dibenzo-p-dioxins (PCDDs), including tetrachlorodibenzo-/j-dioxin (TCDD) and polychlorinated dibenzofurans (PCDFs), which are lipophiles, and heavy metals, including chromium, copper, manganese, vanadium, and lead, which are hydrophilesJ29-31 These chemicals have multiple toxicities and are known to impact the human liver, immune system, respiratory system, thyroid, male reproductive function, and CNS J32 34l Several are human carcinogensJ32 35 Enhanced toxic effects are observed in the mixtures of some of theseJ21,22 36 The mixtures of toxicants present in fly ash are complex and the mechanisms for their action on the human body are largely unknown. It is known that occupational exposure to fly... 

In addition to the above-mentioned metals, essential or not for human life, mention should also be made of toxic metals like chromium, silver, selenium, barium, aluminium (if their concentration goes beyond the permissible exposure limit). 

The search is on for catalysts to replace those containing toxic heavy metals. The addition of hydrogen chloride to acetylene to form vinyl chloride is catalyzed by mercuric chloride. Rhodium (III) chloride on activated carbon works just as well and is much less toxic 97 It should be tried also in other addition reactions of acetylene as well as in trans-esteriflcation reactions of vinyl acetate. The reduction of 2 ethyl-2-hexenal to 2-ethylhexanol can be catalyzed by a mixture of copper, zinc, manganese, and aluminum oxides in 100% yield.98 This is said to be a replacement for carcinogenic copper chromite. In Reaction 4.15, the amount of toxic chromium(II) chloride has been reduced from stoichiometric to catalytic (9-15 mol% chromium(II) chloride) by the addition of manganese metal.99... 

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. 

Simultaneous removal of heavy metals and nitrate. In addition to denitrification, the above series of columns were also used for the removal of heavy metals. A decrease in the denitrification capacity of the column was used as an index of the critical heavy metal concentrations causing toxicity to the P. aeruginosa. The toxic effect of metals (lead, chromium, copper, cadmium and zinc) was examined in a separate study (unpublished data). Of these metals copper proved to have the highest toxicity as it fully prevented denitrification in a very short time at a concentration of 10 ppm. Regarding their toxic effect the next in order was lead, followed by cadmium, zinc, and chromium. 

Only a few general remarks The organic film can be a thicker film of paint or a very thin film not distorting the geometry of the parts. In the latter case, a thin wax film (10-100 nm) is applied to the surface. The film is hydrophobic and keeps moisture away from the surface. The film can also prevent direct contact of the metal deposited with the human sldn. This is important with toxic or problematic metals like chromium and nickel. 

The automobile is also an indirect source of another heavy metal contaminant, chromium. Chromium compounds (such as Cr04 ) are used in chrome plating for bumpers and grills. This plating also requires the use of the cyanide ion (CN), another major pollutant. These contaminants used to be discharged directly into streams, but now they re either pretreated to reduce to a less-toxic form or precipitated (formed into a solid) and disposed of in landfills. 

A specific heavy-metals contamination (chromium) was detected in collagen hydrolysates prepared from trimming/cuttings of chromium-tanned hides up to 100 ppm of chromium was found in samples of powdered collagen hydrolysates on the market at the end of the 1970s (135). The oxidation state of chromium was not determined, but probably it was Cr ", less toxic than Cr, as in the tanning industry only basic salts of Cr " are used. 

Metal Toxicity Inhibition of microbial activity by certain metals— including arsenic, barium, cadmium, chromium, lead, mercury, and nickel—that interact with cellular proteins in complex ways. Microclimate Small but distinct climate zone within a larger climate area slight differences in landscape climates (frequently due to shade trees or mountains and valleys) allow for variegated and unusual species to occupy a common terrain. Micrometeorology Study of the atmosphere just above the ground. 

Chromium is a steel-gray, lustrous, hard metaL It is an essential trace element and has a role in glucose metabolism. Compounds of hexavalent chromium are toxic. Chromium is a very important alloying element for steel. More than 12% Cr makes steel stainless. 

Industrial Applications Detecting/quantifying/ measuring metals (beryllium, chromium, lead) Safety/Toxicity No data available... 

Some metals used as metallic coatings are considered nontoxic, such as aluminum, magnesium, iron, tin, indium, molybdenum, tungsten, titanium, tantalum, niobium, bismuth, and the precious metals such as gold, platinum, rhodium, and palladium. However, some of the most important poUutants are metallic contaminants of these metals. Metals that can be bioconcentrated to harmful levels, especially in predators at the top of the food chain, such as mercury, cadmium, and lead are especially problematic. Other metals such as silver, copper, nickel, zinc, and chromium in the hexavalent oxidation state are highly toxic to aquatic Hfe (37,57—60). 

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