Metal heavy

Heavy metals in PVC compoimds, including tin from stabilisers or biocides, have also attracted attention. The implications for heat stabilisers have already been discussed. A decision was made by the Emopean Stabilisers Producers Association to phase out lead stabilisers by 2015. The central issues in the medium-term future are likely to be (a) the rate at which lead is phased out and (b) the future attitude of regulatory authorities to organotin. Organotin stabilisers represented 9% of the Emopean stabiliser market in 2002. (Greenpeace opposes organotin compoimds in PVC products intended for children, as well as lead.) 

The European Union has legislated to reduce the permitted lead contents in potable water. Denmark banned lead in certain PVC applications, including pipes, from the end of 2003, and the UK banned lead in potable water pipes by the same date. Wire and cable insulation materials for use in vehicles has had to be lead-free in Europe since 2003. Sweden implemented a ban on lead stabilisers from January 2002. The Netherlands has followed a voluntary coiuse, with Norway expected to ban lead by 2010. In practice not much lead stabiliser is used in Scandinavia, but other parts of Europe still depend on this type of product. 

Japan banned lead based stabilisers from water pipes as long ago as 1993, replacing them by organotin, and may soon even replace existing pipes that contain lead stabilisers, as well as encouraging the voluntary phase out of lead from sewerage pipes. 

In February 2004 Denmark revoked a tax targeted at PVC products containing phthalates or certain rigid PVC products used in building. It was explained that the industry had improved its record on health and safety since the tax was imposed in 2000, and need no longer be regarded as a special problem. 

The use of PVC in cable in Europe may be affected if the EU s Fire Regulatory Committee incorporates an optional provision for an acid fume test in its construction products directive, as mged by Sweden. 

Salts of some heavy metals such as gold and platinum are used pharmacologically as immimomodulators to treat rheumatoid arthritis and as anti-neoplastic drugs, respectively. Most heavy metal salts inhibit mitogenicity. 

Pollution caused by heavy metals is now a worldwide phenomenon. Among the many heavy metals, lead (Pb), mercury (Hg), cadmium (Cd), arsenic (As), chromium (Cr), zinc (Zn), and copper (Cu) are of most concern, although the last three metals are essential nutrients in animal and human nutrition. These metals are widely used in industry, particularly in metal-working or metalplating, and in such products as batteries and electronics. They are also used in the production of jewelry, paint pigments, pottery glazes, inks, dyes, rubber, plastics, pesticides, and even in medicines. These metals enter the environment wherever they are produced, used, and ultimately discarded. 

Heavy metals are very toxic because, as ions or in compound forms, they are soluble in water and may be readily absorbed into living organisms. After absorption, these metals can bind to vital cellular components such as structural proteins, enzymes, and nucleic acids, and interfere with their functioning. In humans, some of these metals, even in small amounts, can cause severe physiological and health effects. 

In this chapter, we will consider Pb, Cd, and Hg, the three heavy metals widely recognized as the most toxic in our environment. 

Lead (Pb) is one of the ancient metals and has been used by humans for several thousand years. Lead plays an important role in the economy of all industrialized countries in the world. In the U.S., the industrial consumption of Pb is estimated to be about 1.3 million tons per year, with a concomitant annual emission of about 600,000 tons of Pb into the environment (NAS 1980). Additional amounts are added through mining, smelting, manufacturing, disposal, and recycling processes. Furthermore, until recently, huge amounts of Pb and its compounds had been emitted into the atmosphere as a result of leaded gasoline combustion. Consequently, lead is ubiquitous in our environment. 

Because Pb is toxic to humans at high doses, levels of exposure encountered by some members of the population constitute a serious public health problem (NAS 1980). The importance of Pb as an environmental pollutant is 

Humans have been exposed more and more to metallic contaminants in the environment, mostly from the products of industry. There are three main sources of metals in the environment. The most obvious are the processes of extraction and purification mining, smelting, and refining. Another is the release of metals from fossil fuels (e.g., coal, oil), when these are burned. Cadmium, lead, mercury, nickel, vanadium, chromium, and copper are all present in these fuels, and considerable amounts enter the air or are deposited in ash. The third and most diverse source is the production and use of industrial products containing metals, which is increasing as new applications are found. The modem chemical industry, for example, uses many metals or metal compounds as catalysts metal compounds are used as stabilizers in the production of many plastics, and metals are added to lubricants, which then find their way into the environment.21 

Mercury is an especially dangerous compound. Mercury levels have changed relatively little over the past two decades. Mercury is now used, in increasing quantities, in parts of the Amazon basin where prospectors pan for gold along small streams and tributaries. Atmospheric deposition is now a major source of mercury as well in the Great Lakes ecosystem. 

All newborn infants have an increased concentration of copper in the liver, and a decreased concentration of a specific plasma copper-protein, ceruloplasmin, in comparison to individuals over one year of age (1 ). The rare infant who has inherited a pair of the specific autosomal recessive gene that causes Wilson s disease exhibits an excess of hepatic copper and a deficiency of ceruloplasmin for life. 

ACS Symposium Series American Chemical Society Washington, DC, 1980. 

Protein Organ or tissue Source Molecular Weight X 10 copper content (atoms/ molecule] Color 1 Biochemical function Physiological function Hereditary defect Comments 

Ceruloplasmin (EC 1.12.3.1) Plasma 132 6 Blue Polyamine oxidase ferroxidase Unkno m Deficient or absent in Wilson s disease. and in Menkes syndrome Glycoprotein 

Dopamine -mono-oxy-genase (EC 1.14.17.1) Plasma Cerebrospinal fluid Pheochromo- cytoma of adrenal 290 4 Colorless Dopamine -hydroxylase Biosynthesis of noradrenaline Glycoprotein 

Identify the clinically useful chelators and know their indications and their adverse effects. Describe the major clinical features and treatment of acute and chronic lead poisoning. Describe the major clinical features and treatment of arsenic poisoning. 

Leam the definitions that follow. Table 58-1. Definitions.  

Chelating agent A molecule with two or mote electronegative groups that can fomn stable coordinate complexes with multivalent cationic metal atoms 

Erethism Syndrome resulting from mercury poisoning characterized by insomnia, memory loss, excitability, and delirium 

Ion chromatography has been applied to the determination of cobalt, nickel, copper, zinc and cadmium as their EDTA complexes using anion separation and suppressor columns and 0.03pm so um bicarbonate-0.03pm sodium carbonate [28] eluant and a conductiometric detector. 

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Once the life-cycle inventory has been quantified, we can attempt to characterize and assess the eflfects of the environmental emissions in a life-cycle impact analysis. While the life-cycle inventory can, in principle at least, be readily assessed, the resulting impact is far from straightforward to assess. Environmental impacts are usually not directly comparable. For example, how do we compare the production of a kilogram of heavy metal sludge waste with the production of a ton of contaminated aqueous waste A comparision of two life cycles is required to pick the preferred life cycle. 

Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

Reverse osmosis is a high-pressure membrane separation process (20 to 100 bar) which can be used to reject dissolved inorganic salt or heavy metals. The concentrated waste material produced by membrane process should be recycled if possible but might require further treatment or disposal. 

Soaps of heavy metals have been used but cationic surface-active agents have proved more suitable, notably organic amines of relatively high molecular weight. 

Dissolves in alkaline solutions to give purple-red solutions which are precipitated as lakes by heavy metal salts. Occurs naturally as a glucoside in madder but produced synthetically by fusing anthraquinone-2-sulphonic acid with NaOH and some KCIO3. Applied to the mordanted fibre. Al(OH)3 gives a bright red lake, Cr(OH)3 a red lake, FefOH) ... 

Inorganic amides contain the ion NH2". They are formed by the action of ammonia on metals or by the ammonolysis of nitrides. The heavy metal amides are prepared by meta-thetical reactions in liquid ammonia, e.g. 

The alkali amides are stable, crystalline salts the heavy metal amides are often explosive. The amides are the bases of the ammonia system. 

M.p. —80°C, b.p. 37°C. Prepared from sodium azide and acid or (N2Hj) plus nitrous acid, HNO2. Heavy-metal salts, azides, are used as detonators, alkali metal salts are stable and azides are used synthetically in organic chemistry. 

In organic chemistry the term refers to compounds containing the NH2 ion or the > NH group. These are prepared by the action of heat on amides or by metathetica reactions in liquid ammonia. The heavy metal imides are explosive. 

The phthalocyanine molecule is remarkably stable to heat and chemical reagents. The metal-free and heavy metal compounds sublime practically unchanged at 550-580 C. 

Finally, micellar systems are useful in separation methods. Micelles may bind heavy-metal ions, or, through solubilization, organic impurities. Ultrafiltration, chromatography, or solvent extraction may then be used to separate out such contaminants [220-222]. 

Anodic-stripping voltaimnetry (ASV) is used for the analysis of cations in solution, particularly to detemiine trace heavy metals. It involves pre-concentrating the metals at the electrode surface by reducmg the dissolved metal species in the sample to the zero oxidation state, where they tend to fomi amalgams with Hg. Subsequently, the potential is swept anodically resulting in the dissolution of tire metal species back into solution at their respective fomial potential values. The detemiination step often utilizes a square-wave scan (SWASV), since it increases the rapidity of tlie analysis, avoiding interference from oxygen in solution, and improves the sensitivity. This teclmique has been shown to enable the simultaneous detemiination of four to six trace metals at concentrations down to fractional parts per billion and has found widespread use in seawater analysis. 

At potentials positive to the bulk metal deposition, a metal monolayer-or in some cases a bilayer-of one metal can be electrodeposited on another metal surface this phenomenon is referred to as underiDotential deposition (upd) in the literature. Many investigations of several different metal adsorbate/substrate systems have been published to date. In general, two different classes of surface stmetures can be classified (a) simple superstmetures with small packing densities and (b) close-packed (bulklike) or even compressed stmetures, which are observed for deposition of the heavy metal ions Tl, Hg and Pb on Ag, Au, Cu or Pt (see, e.g., [63, 64, 65, 66, 62, 68, 69 and 70]). In case (a), the metal adsorbate is very often stabilized by coadsorbed anions typical representatives of this type are Cu/Au (111) (e.g. [44, 45, 21, 22 and 25]) or Cu/Pt(l 11) (e.g. [46, 74, 75, and 26 ]) It has to be mentioned that the two dimensional ordering of the Cu adatoms is significantly affected by the presence of coadsorbed anions, for example, for the upd of Cu on Au(l 11), the onset of underiDotential deposition shifts to more positive potentials from 80"to Br and CE [72]. 

It is thought that the function of the glue or gelatin is to combine with very slight traces of heavy metal cations, for example Cu, which are known to catalyse the nitrogen-forming reaction. 

Nitrogen dioxide is prepared by heating the nitrate of a heavy metal, usually that of lead(ll) ... 

Hence dinitrogen tetroxide (sometimes mixed with an organic solvent) can be used to prepare anhydrous metal nitrates (many heavy metal nitrates are hydrated when prepared in aqueous solution, and they cannot be dehydrated without decomposition). 

Both the acid and its salts are powerful reducing agents. They reduce, for example, halogens to halides, and heavy metal cations to the metal. Copper(H) ion is reduced further to give copper(I) hydride, a red-brown precipitate ... 

Selenium and tellurium occur naturally in sulphide ores, usually as an impurity in the sulphide of a heavy metal. They are recovered from the flue dust produced when the heavy metal sulphide is roasted. 

Generally the solubility of a given metal halate decreases from chlorate(V) to iodatef and many heavy metal iodates(V) are quantitatively insoluble. Like their parent acids, the halates(V) are strong oxidising agents, especially in acid solution their standard electrode potentials are given below (in volts) ... 

The principle of this test is as follows The liquid suspected of containing urea is treated with dilute acid or alkali until its pH is about 7. A solution of the enzyme is also made and its pH adjusted to 7. The two solutions are mixed and the resulting conversion of urea to ammonium carbonate causes the pH of the solution to rise to over 8 this change is noted by the use of a suitable indicator, phenol-red being the one usually employed. Proteins do not interfere with the test, but the reaction is inhibited by traces of heavy metals. 

Aminodiacetate exchangers have the —N(CH2COOH)2 group which has an unusually high preference for copper, iron, and other heavy metal cations and, to a lesser extent, for alkaline earth... 

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