Lead

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This article is about the metal. For other uses, see Lead (disambiguation).
thallium ← lead → bismuth
Sn
↑
Pb
↓
Uuq
Appearance
Metallic gray
General properties
Name, symbol, number lead, Pb, 82
Pronunciation /ˈlɛd/ LED
Element category post-transition metal
Group, period, block 14, 6, p
Standard atomic weight 207.2
Electron configuration [Xe] 4f14 5d10 6s2 6p2
Electrons per shell 2, 8, 18, 32, 18, 4 (Image)
Physical properties
Phase solid
Density (near r.t.) 11.34 g·cm−3
Liquid density at m.p. 10.66 g·cm−3
Melting point 600.61 K, 327.46 °C, 621.43 °F
Boiling point 2022 K, 1749 °C, 3180 °F
Heat of fusion 4.77 kJ·mol−1
Heat of vaporization 179.5 kJ·mol−1
Molar heat capacity 26.650 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 978 1088 1229 1412 1660 2027
Atomic properties
Oxidation states 4, 2 (Amphoteric oxide)
Electronegativity 2.33 (Pauling scale)
Ionization energies 1st: 715.6 kJ·mol−1
2nd: 1450.5 kJ·mol−1
3rd: 3081.5 kJ·mol−1
Atomic radius 175 pm
Covalent radius 146±5 pm
Van der Waals radius 202 pm
Miscellanea
Crystal structure face-centered cubic
Magnetic ordering diamagnetic
Electrical resistivity (20 °C) 208 nΩ·m
Thermal conductivity 35.3 W·m−1·K−1
Thermal expansion (25 °C) 28.9 µm·m−1·K−1
Young's modulus 16 GPa
Shear modulus 5.6 GPa
Bulk modulus 46 GPa
Poisson ratio 0.44
Mohs hardness 1.5
Brinell hardness 38.3 MPa
CAS registry number 7439-92-1
Most stable isotopes
Main article: Isotopes of lead
iso NA half-life DM DE (MeV) DP
204Pb 1.4% >1.4×1017 y α 2.186 200Hg
205Pb syn 1.53×107 y ε 0.051 205Tl
206Pb 24.1% 206Pb is stable with 124 neutrons
207Pb 22.1% 207Pb is stable with 125 neutrons
208Pb 52.4% 208Pb is stable with 126 neutrons
210Pb trace 22.3 y α 3.792 206Hg
β 0.064 210Bi
· r

Lead (play /ˈlɛd/) is a main-group element in the carbon group with the symbol Pb (from Latin: plumbum) and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid.

Lead is used in building construction, lead-acid batteries, bullets and shots, weights, as part of solders, pewters, fusible alloys and as a radiation shield. Lead has the highest atomic number of all of the stable elements, although the next higher element, bismuth, has a half-life that is so long (much longer than the age of the universe) that it can be considered stable. Its four stable isotopes have 82 protons, a magic number in the nuclear shell model of atomic nuclei.

Lead, at certain exposure levels, is a poisonous substance to animals as well as for human beings. It damages the nervous system and causes brain disorders. Excessive lead also causes blood disorders in mammals. Like the element mercury, another heavy metal, lead is a neurotoxin that accumulates both in soft tissues and the bones. Lead poisoning has been documented from ancient Rome, ancient Greece, and ancient China.

Contents

Characteristics

A sample of recently solidified lead (from a molten state)

Lead is a bright and silvery (with a very slight shade of blue[1]) metal in a dry atmosphere; upon contact with air, it begins to tarnish. It has a few characteristic properties: high density, softness, ductility and malleability, poor electrical conductivity (compared to other metals), high resistance to corrosion, and ability to react with organic chemicals.[1]

Various traces of other metals change its properties significantly: addition of small amounts of antimony or copper increases hardness and improves the corrosion reflection from sulfuric acid for lead.[1] A few other metals also improve only hardness and fight the metal fatigue, such as cadmium, tin, or tellurium; metals like sodium or calcium also have this ability, but they weaken the chemical stability.[1] Finally, zinc and bismuth simply impair the corrosion resistance (0.1% bismuth content prevent lead from the industrial usage).[1] In return, lead impurities mostly worsen the quality of industrial materials, although there are exceptions: for example, small amounts of lead improve the ductility of steel.[1]

Lead has only one common allotrope, which is face-centered cubic, with the lead–lead distance being 349 pm.[2] At 327.5 °C (621.5 °F),[3] lead melts; the melting point is above that of tin (232 °C, 449.5 °F),[3] but significantly below that of germanium (938 °C, 1721 °F).[4] The boiling point of lead is 1749 °C (3180 °F),[5] which is below than those of both tin (2602 °C, 4716 °F)[3] and germanium (2833 °C, 5131 °F).[4] Densities get simply bigger down the group: the Ge and Sn values (5.23[6] and 7.29 g·cm−3,[7] respectively) are significantly below that of lead: 11.32 g·cm−3.[6]

A lead atom has 82 electrons, having an electronic configuration of [Xe]4f145d106s26p2. In its compounds, lead (unlike the other group 14 elements) most commonly loses its two and not four outermost electrons, becoming lead(II) ions, Pb2+. Such unusual behavior is rationalized by considering the inert pair effect, which occurs because of the stabilization of 6s-orbital due to relativistic effects, which are stronger closer to the bottom of the periodic table.[8] Tin shows a weaker such effect: tin(II) is still a reducer.[8]

The figures for electrode potential show that lead is only slightly easier to oxidize than hydrogen. Lead thus can dissolve in acids, but this is often impossible due to specific problems (such as insoluble salts formation).[9] Powdered lead burns with a bluish-white flame. As with many metals, finely divided powdered lead exhibits pyrophoricity.[10] Toxic fumes are released when lead is burned.

Isotopes

Main article: Isotopes of lead

Lead occurs naturally on Earth exclusively in the form of four isotopes: lead-204, -206, -207, and -208.[11] All four can be radioactive as the hypothetical alpha decay of any would release energy, but the lower half-life limit has been put only for lead-204: over 1.4×1017 years.[12] This effect is, however, so weak that natural lead makes no radiation hazard. Three of them are also found in three of the four major decay chains: lead-206, -207 and -208 are final decay products of uranium-238, uranium-235, and thorium-232, respectively. Since the amounts of them in nature depend also on other elements' presence, the isotopic composition of natural lead varies by sample: in particular, the relative amount of lead-206 varies between 20.84% and 27.78%.[11]

Aside from the stable ones, thirty-four radioisotopes have been synthesized: they have the mass numbers of 178–215.[12] Lead-205 is the most stable radioisotope of lead, with a half-life of over 107 years. 47 nuclear isomers (long-lived excited nuclear states), corresponding to 24 lead isotopes, have been characterized. The most long-lived is lead-204m2 (half-life of about 1.1 hours).[12]

Chemical reactivity

Lead is chemically a post-transition metal and belongs to the group 14 of the periodic table. It shows two main oxidation states, which are +2 and +4. The former is more stable, while the +4 oxidation state, favored for the rest of the group, is an oxidizer; lead(IV) ions exist only in highly acidic solutions.[8]

Cold thoroughly crushed lead may ignite in the air, as it is attacked by oxygen in it; compact lead only form a protective oxide layer. Melted lead is oxidized in the air to become lead monoxide. At 430 °C (810 °F), it is further oxidized to become trilead tetroxide, which decomposes at 550 °C (1020 °F) to turn back into PbO. All chalcogens oxidize lead upon heating; during the reaction with sulfur, the metal may be heated to get red.[13]

Fluorine does not oxidize cold lead. Hot lead can be oxidized, but the formation on a protective halide layer lowers the intensity of the reaction above 100 °C (210 °F). The reaction with chlorine is similar: thanks to the chloride layer, lead persistence against chlorine surpasses those of copper or steel up to 300 °C (570 °F).[13]

Water in presence of oxygen attacks lead to start an accelerating reaction. Presence of carbonates or sulfates lead to formation of insoluble lead salts, which prevent the metal from corrosion. So does carbon dioxide, as the insoluble lead carbonate is formed; however, excess of the gas leads to the formation of the soluble bicarbonate; this dangers the usage of lead pipes.[9] Lead dissolves in organic acids (in presence of oxygen) and concentrated (≥80%) sulfuric acid thanks to complexation; however, it is only weakly affected by hydrochloric acid and is stable against hydrofluoric acid, as the corresponding halides are weakly soluble. Lead also dissolves in quite concentrated alkalis (≥10%) thanks to the amphoteric character and solubility of plumbites.[9]

Compounds

Main article: Compounds of lead

Oxides and sulfide

There are three oxides known: PbO, Pb3O4 (sometimes called "minium"), and PbO2. The former has two allotropes: α-PbO and β-PbO, both with layer structure and tetracoordinated lead. The alpha allotrope is red-colored and has the Pb–O distance of 230 pm; the beta allotrope is yellow-colored and has the Pb–O distance of 221 and 249 pm (due to asymmetry).[14] Thanks to the similarity, both allotropes can exist under standard conditions (beta with small (10-5 relative) impurities, such as Si, Ge, Mo, etc.). PbO reacts with acids to form salts, and with alkalies to give plumbites, [Pb(OH)3]- or [Pb(OH)4]2-.[15]

The dioxide may be prepared by, for example, halogenization of lead(II) salts. Regardless the allotrope, it has a black-brown color. The alpha allotrope is rhombohedral, and the beta allotrope is tetragonal.[15] Both allotropes are black-brown in color and always contain some water, which cannot be removed, as heating also causes decomposition (to PbO and Pb3O4). The dioxide is a powerful oxidizer: it can oxidize hydrochloric and sulfuric acids. It does not reacts with alkaline solution, but reacts with solid alkalies to give hydroxyplumbates, or with basic oxides to give plumbates.[15]

Reaction of lead with sulfur or hydrogen sulfide yields lead sulfide. The solid has the NaCl-like striucture (simple cubic), which it keeps up to the melting point, 1114 °C (2037 °F). If the heating occurs in presence of air, the compounds decomposes to give the monoxide and the sulfate.[16] The compounds is almost insoluble in water, weak acids, and (NH4)2S/(NH4)2S2 solution is the key for separation of lead from analythical groups I to III elements, tin, arsenic, and antimony. The compounds, however, dissolves in nitric and hydrochloric acids, to give elemental sulfur and hydrogen sulfide, respectively.[16] Heating a mixture of the monoxide and the sulfide heated together forms the metal.[17]

2 PbO + PbS → 3 Pb + SO2↑

Halides and other salts

Heating lead carbonate with hydrogen fluoride yields the hydrofluoride, which decomposes to the difluoride when melts. This white crystalline powder is more soluble than the diiodide, but less than the dibromide and the dichloride. No coordinated lead fluorides exist (except the unstable PbF+ cation).[18] The tetrafluoride, a yellow crystalline powder, is unstable.

Other dihalides are received upon heating lead(II) salts with the halides of other metals; lead dihalides precipitate to give white orthorhombic crystals (diiodide form yellow hexagonal crystals). They can also be obtained by direct elements reaction at temperature exceeding melting points of dihalides. Their solubility increases with temperature; adding more halides first decreases the solubility, but then increases due to complexation, with the maximum coordination number being 6. The complexation depends on halide ion numbers, atomic number of the alkali metal, the halide of which is added, temperature and solution ionic strength.[19] The tetrachloride is obtained upon dissolving the dioxide in hydrochloric acid; to prevent the exothermic decomposition, it is kept under concentrated sulfuric acid. The tetrabromide may not, and the tetraiodide definitely does not exist.[20] The diastatide has also been prepared.[21]

The metal is not attacked by sulfuric or hydrochloric acids. It dissolves in nitric acid with the evolution of nitric oxide gas to form dissolved Pb(NO3)2.[18] It is a well-soluble solid in water; it is thus a key to receive the precipitates of halide, sulfate, chromate, carbonate, and basic carbonate Pb3(OH)2(CO3)2 salts of lead.[22]

Organolead

Main article: Organolead compound

The best-known compounds are the two simplest plumbane deratives: tetramethyllead (TML) and tetraethyllead (TEL); however, the homologs of these, as well as hexaethyldilead (HEDL), are of lesser stability. The tetralkyl deratives contain lead(IV); the Pb–C bonds are covalent. They thus resemble typical organic compounds.[23]

Lead readily forms an equimolar alloy with sodium metal that reacts with alkyl halides to form organometallic compounds of lead such as tetraethyllead.[24] The Pb–C bongs energies in TML and TEL are only 167 and 145 kJ/mol; the compounds thus decompose upon heating, with first signs of TEL composition seen at 100 °C (210 °F). The pyrolisis yields of elemental lead and alkyl radicals; their interreaction causes the synthesis of HEDL.[23] They also decompose upon sunlight or UV-light.[25] In presence of chlorine, the alkyls begin to be replaced with chlorides; the R2PbCl2 in the presence of HCl (a by-product of the previous reaction) leads to the complete mineralization to give PbCl2. Reaction with bromine follows the same principle.[25]

History

World lead production peaking in the Roman period and the rising Industrial Revolution[26]
Lead ingots from Roman Britain on display at the Wells and Mendip Museum
Lead mining in the upper Mississippi River region of the U.S., 1865.

Lead has been commonly used for thousands of years because it is widespread, easy to extract and easy to work with. It is highly malleable and ductile as well as easy to smelt. Metallic lead beads dating back to 6400 BCE have been found in Çatalhöyük in modern-day Turkey.[27] In the early Bronze Age, lead was used with antimony and arsenic.

The largest preindustrial producer of lead was the Roman economy, with an estimated output per annum of 80,000 t, which was typically won as a by-product of extensive silver smelting.[26][28][29] Roman mining activities occurred in Central Europe, Roman Britain, the Balkans, Greece, Asia Minor; Hispania alone accounted for 40% of world production.[26]

Roman lead pipes often bore the insignia of Roman emperors (see Roman lead pipe inscriptions). Lead plumbing in the Latin West may have been continued beyond the age of Theoderic the Great into the medieval period.[30] Many Roman "pigs" (ingots) of lead figure in Derbyshire lead mining history and in the history of the industry in other English centers. The Romans also used lead in molten form to secure iron pins that held together large limestone blocks in certain monumental buildings. In alchemy, lead was thought to be the oldest metal and was associated with the planet Saturn. Alchemists accordingly used Saturn's symbol (the scythe, ♄) to refer to lead.

Up to the 17th century, tin was often not differed from lead: lead was called plumbum nigrum (literally, "black plumbum"), while tin was called plumbum candidum (literally, "bright plumbum").[31] Their inherence through history can be seen in other languages: the word "olovo" stands for lead in Czech, but in Russian it ("олово") stands for tin. Lead's symbol Pb is an abbreviation of its Latin name plumbum for soft metals; the English words "plumbing", "plumber", "plumb", and "plumb-bob" also derive from this Latin root.

Occurrence

Lead and zinc bearing carbonate and clastic deposits. Source: USGS

Metallic lead does occur in nature, but it is rare. Lead is usually found in ore with zinc, silver and (most abundantly) copper, and is extracted together with these metals. The main lead mineral is galena (PbS), which contains 86.6 % lead by weight. Other common varieties are cerussite (PbCO3) and anglesite (PbSO4).

Ore processing

Galena, lead ore

Most ores contain less than 10% lead, and ores containing as little as 3% lead can be economically exploited. Ores are crushed and concentrated by froth flotation typically to 70% or more. Sulfide ores are roasted, producing primarily lead oxide and a mixture of sulfates and silicates of lead and other metals contained in the ore.[32]

Lead oxide from the roasting process is reduced in a coke-fired blast furnace.[33] This converts most of the lead to its metallic form. Three additional layers separate in the process and float to the top of the metallic lead. These are slag (silicates containing 1.5% lead), matte (sulfides containing 15% lead), and speiss (arsenides of iron and copper). These wastes contain concentrations of copper, zinc, cadmium, and bismuth that can be recovered economically, as can their content of unreduced lead.[32]

Metallic lead that results from the roasting and blast furnace processes still contains significant contaminants of arsenic, antimony, bismuth, zinc, copper, silver, and gold. The melt is treated in a reverberatory furnace with air, steam, and sulfur, which oxidizes the contaminants except silver, gold, and bismuth. The oxidized contaminants are removed by drossing, where they float to the top and are skimmed off.[32][34]

Most lead ores contain significant concentrations of silver, resulting in the smelted metal also containing silver as a contaminant. Metallic silver as well as gold is removed and recovered economically by means of the Parkes process.[17][32][34]

Desilvered lead is freed of bismuth according to the Betterton-Kroll process by treating it with metallic calcium and magnesium, which forms a bismuth dross that can be skimmed off.[32][34]

Very pure lead can be obtained by processing smelted lead electrolytically by means of the Betts process. The process uses anodes of impure lead and cathodes of pure lead in an electrolyte of silica fluoride.[32][34]

Production and recycling

Production and consumption of lead is increasing worldwide. Total annual production is about 8 million tonnes; about half is produced from recycled scrap. The top lead producing countries, as of 2008, are Australia, China, USA, Peru, Canada, Mexico, Sweden, Morocco, South Africa and North Korea.[35] Australia, China and the United States account for more than half of primary production.[36]

In 2010, 9.6 million tonnes of lead were produced, of which 4.1 million tonnes came from mining.[37]

At current use rates, the supply of lead is estimated to run out in 42 years.[38] Environmental analyst Lester Brown has suggested lead could run out within 18 years based on an extrapolation of 2% growth per year.[39] This may need to be reviewed to take account of renewed interest in recycling, and rapid progress in fuel cell technology. According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of lead in use in society is 8 kg. Much of this is in more-developed countries (20–150 kg per capita) rather than less-developed countries (1–4 kg per capita).

Applications

Elemental form

Lead bricks are commonly used as radiation shielding.

Because of its high density and resistance from corrosion, lead is used for the ballast keel of sailboats. Its high density allows it to counterbalance the heeling effect of wind on the sails while at the same time occupying a small volume and thus offering the least underwater resistance. For the same reason it is used in scuba diving weight belts to counteract the diver's natural buoyancy and that of his equipment. It does not have the weight-to-volume ratio of many heavy metals, but its low cost increases its use in these and other applications.

Roman lead water pipes with taps
Lead pipe in Roman baths
Multicolor lead-glazing in a sancai ceramic cup, Tang dynasty, China, 8th century CE.

Lead is used in applications where its low melting point, ductility and high density is an advantage. The low melting point makes casting of lead easy, and therefore small arms ammunition and shotgun pellets can be cast with minimal technical equipment. It is also inexpensive and denser than other common metals.[40] The hot metal typesetting uses a lead based alloy to produce the types for printing directly before printing.

Its corrosion resistance makes it suitable for outdoor applications when in contact with water.

More than half of the worldwide lead production (at least 1.15 million metric tons) is used for automobiles, mostly as electrodes in the lead–acid battery, used extensively as a car battery.[41]

Cathode (reduction)

PbO2 + 4 H+ + SO42– + 2e– → PbSO4 + 2 H2O

Anode (oxidation)

Pb + SO42– → PbSO4 + 2e–[42][43]

Lead is used as electrodes in the process of electrolysis. Lead is used in solder for electronics, although this usage is being phased out by some countries to reduce the amount of environmentally hazardous waste. Lead is used in high voltage power cables as sheathing material to prevent water diffusion into insulation.

Lead is one of three metals used in the Oddy test for museum materials, helping detect organic acids, aldehydes, and acidic gases.

Lead is used as shielding from radiation (e.g., in X-ray rooms).[44] Molten lead is used as a coolant (e.g., for lead cooled fast reactors).[45]

Lead is added to brass to reduce machine tool wear. Lead, in the form of strips, or tape, is used for the customization of tennis rackets. Tennis rackets of the past sometimes had lead added to them by the manufacturer to increase weight.[46]

Lead is used to form glazing bars for stained glass or other multi-lit windows. The practice has become less common, not for danger but for stylistic reasons. Lead, or sheet-lead, is used as a sound deadening layer in some areas in wall, floor and ceiling design in sound studios where levels of airborne and mechanically produced sound are targeted for reduction or virtual elimination.[47][48]

Lead is the traditional base metal of organ pipes, mixed with varying amounts of tin to control the tone of the pipe.[49][50]

Lead has many uses in the construction industry (e.g., lead sheets are used as architectural metals in roofing material, cladding, flashing, gutters and gutter joints, and on roof parapets). Detailed lead moldings are used as decorative motifs used to fix lead sheet. Lead is still widely used in statues and sculptures. Lead is often used to balance the wheels of a car; this use is being phased out in favor of other materials for environmental reasons.

Due to its half-life of 22.2 years, the radioactive isotope 210Pb is used for dating material from marine sediment cores byradiometric methods.[citation needed]


Compounds

Lead compounds are used as a coloring element in ceramic glazes, notably in the colors red and yellow.[51] Lead is frequently used in polyvinyl chloride (PVC) plastic, which coats electrical cords.[52][53]

Lead is used in some candles to treat the wick to ensure a longer, more even burn. Because of the dangers, European and North American manufacturers use more expensive alternatives such as zinc.[54][55] Lead glass is composed of 12–28% lead oxide. It changes the optical characteristics of the glass and reduces the transmission of radiation.[56]

Some artists using oil-based paints continue to use lead carbonate white, citing its properties in comparison with the alternatives. Tetra-ethyl lead is used as an anti-knock additive for aviation fuel in piston-driven aircraft. Lead-based semiconductors, such as lead telluride, lead selenide and lead antimonide are finding applications in photovoltaic (solar energy) cells and infrared detectors.[57]

Former applications

Lead pigments were used in lead paint for white as well as yellow, orange, and red. Most uses have been discontinued due of the dangers of lead poisoning. Beginning April 22, 2010, US federal law requires that contractors performing renovation, repair, and painting projects that disturb more than six square feet of paint in homes, child care facilities, and schools built before 1978 must be certified and trained to follow specific work practices to prevent lead contamination. Lead chromate is still in industrial use. Lead carbonate (white) is the traditional pigment for the priming medium for oil painting, but it has been largely displaced by the zinc and titanium oxide pigments. It was also quickly replaced in water-based painting mediums. Lead carbonate white was used by the Japanese geisha and in the West for face-whitening make-up, which was detrimental to health.[58][59][60]

Lead is the hot metal that was used in hot metal typesetting. It was used for plumbing (hence the name) as well as a preservative for food and drink in Ancient Rome. Until the early 1970s, lead was used for joining cast iron water pipes and used as a material for small diameter water pipes.[61]

Tetraethyllead was used in leaded fuels to reduce engine knocking, but this practice has been phased out across many countries of the world in efforts to reduce toxic pollution that affected humans and the environment.[62][63][64][65]

Lead was used to make bullets for slings. Lead was used for shotgun pellets in the US until about 1992 when it was outlawed (for waterfowl hunting only) and replaced by non-toxic shot, primarily steel pellets. In the Netherlands, the use of lead shot for hunting and sport shooting was banned in 1993, which caused a large drop in lead emission, from 230 ton in 1990 to 47.5 ton in 1995, two years after the ban.[66]

Lead was a component of the paint used on children's toys – now restricted in the United States and across Europe (ROHS Directive). Lead was used in car body filler, which was used in many custom cars in the 1940s–60s. Hence the term Leadsled. Lead is a superconductor at 7.2 K and IBM tried to make a Josephson effect computer out of lead-alloy.[67]

Lead was also used in pesticides before the 1950s, when fruit orchards were treated (ATSDR). A lead cylinder attached to a long line was used by sailors for the vital navigational task of determining water depth by heaving the lead at regular internals. A soft tallow insert at its base allowed the nature of the sea bed to be determined, further aiding position finding. Contrary to popular belief, pencil leads in wooden pencils have never been made from lead. The term comes from the Roman stylus, called the penicillus, which was made of lead without a wooden holder.[68] When the pencil originated as a wrapped graphite writing tool, the particular type of graphite being used was named plumbago (lit. act for lead, or lead mockup).

Health effects

Main article: Lead poisoning

Lead is highly poisonous metal (regardless if inhaled or swallowed), affecting almost every organ and system in the body. The main target for lead toxicity is the nervous system, both in adults and children. Long-term exposure of adults can result in decreased performance in some tests that measure functions of the nervous system. Long-term exposure to lead or its salts (especially soluble salts or the strong oxidant PbO2) can cause nephropathy, and colic-like abdominal pains. It may also cause weakness in fingers, wrists, or ankles. Lead exposure also causes small increases in blood pressure, particularly in middle-aged and older people and can cause anemia. Exposure to high lead levels can severely damage the brain and kidneys in adults or children and ultimately cause death. In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure have shown to reduce fertility in males.[69] Lead also damages nervous connections (especially in young children) and cause blood and brain disorders. Lead poisoning typically results from ingestion of food or water contaminated with lead; but may also occur after accidental ingestion of contaminated soil, dust, or lead-based paint.[70] It is rapidly absorbed into the bloodstream and is believed to have adverse effects on the central nervous system, the cardiovascular system, kidneys, and the immune system.[71] The component limit of lead (1.0 μg/g) is a test benchmark for pharmaceuticals, representing the maximum daily intake an individual should have. However, even at this low level, a prolonged intake can be hazardous to human beings.[72][73] The treatment for lead poisoning consists of dimercaprol and succimer.[74]

NFPA 704
NFPA 704.svg
Fire diamond for lead granules

The concern about lead's role in cognitive deficits in children has brought about widespread reduction in its use (lead exposure has been linked to learning disabilities).[75] Most cases of adult elevated blood lead levels are workplace-related.[76] High blood levels are associated with delayed puberty in girls.[77] Lead has been shown many times to permanently reduce the cognitive capacity of children at extremely low levels of exposure.[78]

During the 20th century, the use of lead in paint pigments was sharply reduced because of the danger of lead poisoning, especially to children.[79][80] By the mid-1980s, a significant shift in lead end-use patterns had taken place. Much of this shift was a result of the U.S. lead consumers' compliance with environmental regulations that significantly reduced or eliminated the use of lead in non-battery products, including gasoline, paints, solders, and water systems. Lead use is being further curtailed by the European Union's RoHS directive. Lead may still be found in harmful quantities in stoneware, vinyl (such as that used for tubing and the insulation of electrical cords), and Chinese brass. Older houses may still contain substantial amounts of lead paint. White lead paint has been withdrawn from sale in industrialized countries, but the yellow lead chromate is still in use. Old paint should not be stripped by sanding, as this produces inhalable dust.

Lead salts used in pottery glazes have on occasion caused poisoning, when acidic drinks, such as fruit juices, have leached lead ions out of the glaze.[81] It has been suggested that what was known as "Devon colic" arose from the use of lead-lined presses to extract apple juice in the manufacture of cider. Lead is considered to be particularly harmful for women's ability to reproduce. Lead(II) acetate (also known as sugar of lead) was used by the Roman Empire as a sweetener for wine, and some consider this to be the cause of the dementia that affected many of the Roman Emperors and even be a partial reason for the Roman Empire's fall (see Decline of the Roman Empire#Lead poisoning).[82]

Biochemistry of poisoning

In the human body, lead inhibits porphobilinogen synthase and ferrochelatase, preventing both porphobilinogen formation and the incorporation of iron into protoporphyrin IX, the final step in heme synthesis. This causes ineffective heme synthesis and subsequent microcytic anemia.[83] At lower levels, it acts as a calcium analog, interfering with ion channels during nerve conduction. This is one of the mechanisms by which it interferes with cognition. Acute lead poisoning is treated using disodium calcium edetate: the calcium chelate of the disodium salt of ethylene-diamine-tetracetic acid (EDTA). This chelating agent has a greater affinity for lead than for calcium and so the lead chelate is formed by exchange. This is then excreted in the urine leaving behind harmless calcium.[84]

Exposure to lead and lead chemicals can occur through inhalation, ingestion and dermal contact. Most exposure occurs through ingestion or inhalation; in the U.S. the skin exposure is unlikely as leaded gasoline additives are no longer used. Lead exposure is a global issue as lead mining and lead smelting are common in many countries. Most countries have stopped using lead-containing gasoline by 2007.[85]

Lead exposure mostly occurs through ingestion. Lead paint is the major source of lead exposure for children. As lead paint deteriorates, it peels, is pulverized into dust and then enters the body through hand-to-mouth contact or through contaminated food, water or alcohol. Ingesting certain home remedy medicines may also expose people to lead or lead compounds.[85] Lead can be ingested through fruits and vegetables contaminated by high levels of lead in the soils they were grown in. Soil is contaminated through particulate accumulation from lead in pipes, lead paint and residual emissions from leaded gasoline that was used before the Environment Protection Agency issue the regulation around 1980.[86]

Inhalation is the second major pathway of exposure, especially for workers in lead-related occupations. Almost all inhaled lead is absorbed into the body, the rate is 20–70% for ingested lead; children absorb more than adults.[85]

Dermal exposure may be significant for a narrow category of people working with organic lead compounds, but is of little concern for general population. The rate of skin absorption is also low for inorganic lead.[85]

According to Agency for Toxic Substance and Disease Registry, a small amount of lead (1%) will store itself in bones and the rest will be excreted through urine and feces within a few weeks of exposure. Children have a harder time excreting lead. Only about 32% of lead will be excreted by a child.[87]

See also

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References

  1. ^ a b c d e f Polyanskiy 1986, p. 18.
  2. ^ Polyanskiy 1986, p. 14.
  3. ^ a b c Lide 2004, p. 12-220.
  4. ^ a b Lide 2004, p. 4-13.
  5. ^ Lide 2004, p. 12-219.
  6. ^ a b Lide 2004, p. 12-35.
  7. ^ Lide 2004, p. 12-37.
  8. ^ a b c Polyanskiy 1986, pp. 14–15.
  9. ^ a b c Polyanskiy 1986, p. 20.
  10. ^ Charles, J.; Kopf, P. W.; Toby, S. (1966). "The Reaction of Pyrophoric Lead with Oxygen". Journal of Physical Chemistry 70 (5): 1478. doi:10.1021/j100877a023. 
  11. ^ a b Polyanskiy 1986, p. 16.
  12. ^ a b c G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (2003). "The NUBASE evaluation of nuclear and decay properties". Nuclear Physics A 729: 3–128. Bibcode 2003NuPhA.729....3A. doi:10.1016/j.nuclphysa.2003.11.001. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf. 
  13. ^ a b Polyanskiy 1986, p. 19.
  14. ^ Polyanskiy 1986, p. 21.
  15. ^ a b c Polyanskiy 1986, p. 22.
  16. ^ a b Polyanskiy 1986, p. 28.
  17. ^ a b Pauling, Linus (1947). General Chemistry. W.H. Freeman. ISBN 0-486-65622-5. 
  18. ^ a b Polyanskiy 1986, p. 32.
  19. ^ Polyanskiy 1986, p. 33.
  20. ^ Polyanskiy 1986, p. 34.
  21. ^ Zuckerman, J. J.; Hagen, A. P. (1989). Inorganic Reactions and Methods, the Formation of Bonds to Halogens. John Wiley & Sons. p. 426. ISBN 978-0-471-18656-4. 
  22. ^ Brady, James E.; Holum, John R. (1996). Descriptive Chemistry of the Elements. John Wiley and Sons. ISBN 0-471-13557-7. 
  23. ^ a b Polyanskiy 1986, p. 43.
  24. ^ Windholz, Martha (1976). Merck Index of Chemicals and Drugs, 9th ed., monograph 8393. Merck. ISBN 0-911910-26-3. 
  25. ^ a b Polyanskiy 1986, p. 44.
  26. ^ a b c Hong, Sungmin; Candelone, Jean-Pierre; Patterson, Clair Cameron; Boutron, Claude F. (1994). "Greenland Ice Evidence of Hemispheric Lead Pollution Two Millennia Ago by Greek and Roman Civilizations". Science 265 (5180): 1841–1843. Bibcode 1994Sci...265.1841H. doi:10.1126/science.265.5180.1841. PMID 17797222. 
  27. ^ Heskel, Dennis L. (1983). "A Model for the Adoption of Metallurgy in the Ancient Middle East". Current Anthropology 24 (3): 362–366. doi:10.1086/203007. 
  28. ^ Callataÿ, François de (2005). "The Graeco-Roman Economy in the Super Long-Run: Lead, Copper, and Shipwrecks". Journal of Roman Archaeology 18: 361–372 (361–365). 
  29. ^ Settle, Dorothy M.; Patterson, Clair C. (1980). "Lead in Albacore: Guide to Lead Pollution in Americans". Science 207 (4436): 1167–1176. Bibcode 1980Sci...207.1167S. doi:10.1126/science.6986654. PMID 6986654.  see 1170f.
  30. ^ Squatriti, Paolo, ed. (2000). Working with water in medieval Europe : technology and resource use. Leiden: Brill. pp. 134 ff. ISBN 978-90-04-10680-2. 
  31. ^ Polyanskiy 1986, p. 8.
  32. ^ a b c d e f Samans, Carl H. (1949). Engineering Metals and their Alloys. MacMillan. 
  33. ^ "Primary Extraction of Lead Technical Notes". LDA International. Archived from the original on 22 March 2007. http://web.archive.org/web/20070322231927/http://www.ldaint.org/technotes1.htm. Retrieved 7 April 2007. 
  34. ^ a b c d "Primary Lead Refining Technical Notes". LDA International. Archived from the original on 22 March 2007. http://web.archive.org/web/20070322191856/http://www.ldaint.org/technotes2.htm. Retrieved 7 April 2007. 
  35. ^ "Global InfoMine – Lead Mining". GlobalInfoMine. http://www.infomine.com/commodities/lead.asp. Retrieved 17 April 2008. 
  36. ^ "Lead Information". LDA International. Archived from the original on 2007-08-27. http://web.archive.org/web/20070827030846/http://www.ldaint.org/information.htm. Retrieved 2007-09-05. 
  37. ^ "Mine Production: 4,117, 000 tonnes; Metal Production: 9,604,000 tonnes; Metal Usage: 9,569,000 tonnes" from "Lead and Zinc Statistics". International Lead and Zinc Study Group. http://www.ilzsg.org/static/statistics.aspx. Retrieved 2011-09-26.  (See also their definitions of terms.)
  38. ^ Reilly, Michael (May 26, 2007). "How Long Will it Last?". New Scientist 194 (2605): 38–39. Bibcode 2007NewSc.194...38R. doi:10.1016/S0262-4079(07)61508-5. ISSN 0262-4079. 
  39. ^ Brown, Lester (2006). Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble. New York: W.W. Norton. p. 109. ISBN 0-393-32831-7. 
  40. ^ Rooney, Corinne. "Contamination at Shooting Ranges" (PDF). The Lead Group, incorporated. http://www.lead.org.au/fs/shootingranges.pdf. Retrieved 7 April 2007. 
  41. ^ Ecology Center "Getting the Lead Out: Impacts of and Alternatives For Automotive Lead Uses"[1]
  42. ^ Crompton., T.R. (2000). Battery reference book. Oxford, England: Newnes. pp. 18/2–18/4. ISBN 978-0-7506-4625-3. http://books.google.com/?id=q58IX4BM7-0C&pg=PT210. 
  43. ^ Stellman, Jeanne Mager (1998). Encyclopaedia of Occupational Health and Safety. International Labour Organization. pp. 81.2–81.4. ISBN 978-92-2-109816-4. http://books.google.com/?id=nDhpLa1rl44C&pg=PT644. 
  44. ^ Structural shielding design for medical X-ray imaging facilities.. Bethesda, MD: National Council on Radiation Protection and Measurement. 2004. pp. 16–17. ISBN 978-0-929600-83-3. http://books.google.com/?id=DKu4YDjEluoC&pg=PA16. 
  45. ^ Tuček, Kamil; Carlsson, Johan; Wider, Hartmut (2006). "Comparison of sodium and lead-cooled fast reactors regarding reactor physics aspects, severe safety and economical issues". Nuclear Engineering and Design 236 (14–16): 1589. doi:10.1016/j.nucengdes.2006.04.019. http://www.ecolo.org/documents/documents_in_english/SFRvsLFR-05.pdf. 
  46. ^ Hong, Youlian and Bartlett, Roger, ed. (2008). Routledge Handbook of Biomechanics and Human Movement Science. London: Routledge. p. 250. ISBN 978-0-415-40881-3. http://books.google.com/?id=p7Ne5IjK5H0C&pg=PA250. 
  47. ^ Guruswamy, Sivaraman (2000). Engineering properties and applications of lead alloys. New York, NY: Marcel Dekker. p. 31. ISBN 978-0-8247-8247-4. http://books.google.com/?id=gDwOAAAAQAAJ&pg=PA31. 
  48. ^ Lansdown, Richard and Yule, William, ed. (1986). The Lead debate : the environment, toxicology, and child health. London: Croom Helm. p. 240. ISBN 978-0-7099-1653-6. http://books.google.com/?id=TtGmjOv9CUAC&pg=PA240. 
  49. ^ Audsley, George Ashdown (1988-04-01). The Art of Organ Building. 2. pp. 250–251. ISBN 978-0-486-21315-6. http://books.google.com/?id=I0h525OVoTgC&pg=PA503. 
  50. ^ Palmieri, Robert, ed. (2006). The Organ. New York u.a.: Garland. pp. 412–413. ISBN 978-0-415-94174-7. http://books.google.com/?id=cgDJaeFFUPoC&pg=PA412. 
  51. ^ Leonard, Alvin R.; Lynch, Glenn (1958). "Dishware as a Possible Source for Lead Poisoning". Calif. Med. 89 (6): 414–416. PMC 1512529. PMID 13608300. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1512529. 
  52. ^ Zweifel, Hans (2009). Plastics Additives Handbook. Hanser Verlag. p. 438. ISBN 978-3-446-40801-2. http://books.google.com/?id=WbBH5QFXOhoC&pg=PT475. 
  53. ^ Wilkes, C. E.; Summers, J. W.; Daniels, C. A.; Berard, M. T. (2005). PVC handbook. München: Hanser. p. 106. ISBN 978-1-56990-379-7. http://books.google.com/?id=YUkJNI9QYsUC&pg=PA106. 
  54. ^ Randerson, James (June 2002). "Candle pollution". NewScientist.com (2348). http://www.newscientist.com/article/mg17423481.900-candle-pollution.html. Retrieved 2007-04-07. 
  55. ^ Nriagu, J; Kim, MJ (2000). "Emissions of lead and zinc from candles with metal-core wicks". The Science of the Total Environment 250 (1–3): 37–41. doi:10.1016/S0048-9697(00)00359-4. PMID 10811249. 
  56. ^ Amstock, Joseph S. (1997). Handbook of glass in construction. McGraw-Hill Professional. pp. 116–119. ISBN 978-0-07-001619-4. http://books.google.com/?id=apWvKnKKrvsC&pg=PA116. 
  57. ^ "Applications for Lead". http://www.americanelements.com/pb.html. Retrieved 7 April 2007. 
  58. ^ Nakashima, T; Matsuno, K; Matsushita, T (2007). "Lifestyle-determined gender and hierarchical differences in the lead contamination of bones from a feudal town of the Edo period". Journal of occupational health 49 (2): 134–9. PMID 17429171. 
  59. ^ Nakashima, Tamiji; Hayashi, Haruki; Tashiro, Hiraku; Matsushita, Takayuki (1998). "Gender and Hierarchical Differences in Lead-Contaminated Japanese Bone from the Edo Period". Journal of Occupational Health 40: 55. doi:10.1539/joh.40.55. 
  60. ^ Ashikari, Mikiko (2003). "The memory of the women's white faces: Japaneseness and the ideal image of women". Japan Forum 15: 55. doi:10.1080/0955580032000077739. 
  61. ^ Hernberg, S (2000). "Lead poisoning in a historical perspective". American journal of industrial medicine 38 (3): 244–54. doi:10.1002/1097-0274(200009)38:3<244::AID-AJIM3>3.0.CO;2-F. PMID 10940962. 
  62. ^ "Lead replacement petrol phase-out – Information to motorists". Department for Transport (gov.uk). Archived from the original on 2009-05-20. http://web.archive.org/web/20090520014154/http://www.dft.gov.uk/pgr/roads/environment/lrp/leadreplacementpetrolphaseout. 
  63. ^ "National phase out of leaded petrol: Some questions and answers". Department of the Environment and Heritage, Australian Government. 2001. http://www.environment.gov.au/atmosphere/airquality/publications/qa.html. 
  64. ^ "Oregon Stations Phase Out Use of Leaded Gasoline.(Originated from The Register-Guard, Eugene, Ore.)". Knight Ridder/Tribune Business News. 4 October 1995. http://www.highbeam.com/doc/1G1-17539759.html. Retrieved 23 September 2008. 
  65. ^ Seyferth, Dietmar (2003). "The Rise and Fall of Tetraethyllead. 2". Organometallics 22 (25): 5154. doi:10.1021/om030621b. 
  66. ^ "Lood en zinkemissies door jacht" (in Dutch) (PDF). April 2010. http://www.emissieregistratie.nl/ERPUBLIEK/documenten/Water/Factsheets/Nederlands/Lood-%20en%20zinkemissies%20door%20jacht.pdf. 
  67. ^ Henkels, W. H.; Geppert, L. M.; Kadlec, J.; Epperlein, P. W.; Beha, H.; Chang, W. H.; Jaeckel, H. (September 1985). "Josephson 4 K-bit cache memory design for a prototype signal processor". Journal of Applied Physics (ISSN 0021-8979) (Harvard University) 58 (6): 2371. Bibcode 1985JAP....58.2371H. doi:10.1063/1.335960. 
  68. ^ "A history of pencils". www.pencils.com. http://www.pencils.com/pencil-history. Retrieved 7 April 2007. 
  69. ^ Golub, Mari S., ed. (2005). "Summary". Metals, fertility, and reproductive toxicity. Boca Raton, Fla.: Taylor and Francis. p. 153. ISBN 978-0-415-70040-5. http://books.google.com/?id=Qt8LEB7_HyQC&pg=PA153. 
  70. ^ "ToxFAQs: CABS/Chemical Agent Briefing Sheet: Lead". Agency for Toxic Substances and Disease Registry/Division of Toxicology and Environmental Medicine. 2006. Archived from the original on 2010-03-04. http://web.archive.org/web/20100304170300/http://www.atsdr.cdc.gov/cabs/lead/lead_cabs.pdf. 
  71. ^ Bergeson, Lynn L. (2008). "The proposed lead NAAQS: Is consideration of cost in the clean air act's future?". Environmental Quality Management 18: 79. doi:10.1002/tqem.20197. 
  72. ^ Heavy Metals Testing By Usp. Caspharma.com. Retrieved on 2012-01-23.
  73. ^ pharmaceutical – Britannica Online Encyclopedia. Britannica.com. Retrieved on 2012-01-23.
  74. ^ Jagadish Prasad, P. (2010). Conceptual Pharmacology. Universities Press. p. 648. ISBN 978817936799. 
  75. ^ Hu, Howard (1991). "Knowledge of diagnosis and reproductive history among survivors of childhood plumbism". American Journal of Public Health 81 (8): 1070–1072. doi:10.2105/AJPH.81.8.1070. PMC 1405695. PMID 1854006. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1405695. 
  76. ^ "NIOSH Adult Blood Lead Epidemiology and Surveillance". United States National Institute for Occupational Safety and Health. http://www.cdc.gov/niosh/topics/ABLES/ables-description.html. Retrieved 2007-10-04. 
  77. ^ Schoeters, Greet; Den Hond, Elly; Dhooge, Willem; Van Larebeke, Nik; Leijs, Marike (2008). "Endocrine Disruptors and Abnormalities of Pubertal Development". Basic & Clinical Pharmacology & Toxicology 102 (2): 168–175. doi:10.1111/j.1742-7843.2007.00180.x. PMID 18226071. 
  78. ^ Needleman, Herbert L.; Schell, Alan; Bellinger, David; Leviton, Alan; Allred, Elizabeth N. (1990). "The long-term effects of exposure to low doses of lead in childhood. An 11-year follow-up report". New England Journal of Medicine 322 (2): 83–88. doi:10.1056/NEJM199001113220203. PMID 2294437. 
  79. ^ "Download: Lead paint: Cautionary note". Queensland Government. http://www.derm.qld.gov.au/heritage/documents/tn_paint_lead.pdf. Retrieved 7 April 2007. 
  80. ^ "Lead Paint Information". Master Painters, Australia. Archived from the original on 2008-02-12. http://web.archive.org/web/20080212064750/http://www.qld.mpa.org.au/index.php/content/33/. Retrieved 7 April 2007. 
  81. ^ "CPG Sec. 545.450 Pottery (Ceramics); Import and Domestic – Lead Contamination". U.S. Food and Drug Administration. http://www.fda.gov/ICECI/ComplianceManuals/CompliancePolicyGuidanceManual/ucm074516.htm. Retrieved 2010-02-02. 
  82. ^ Angier, Natalie (August 21, 2007). "The Pernicious Allure of Lead". New York Times. http://www.nytimes.com/2007/08/21/science/21angi.html?_r=1&oref=slogin. Retrieved 7 May 2010. 
  83. ^ Cohen, Alan R.; Trotzky, Margret S.; Pincus, Diane (1981). "Reassessment of the Microcytic Anemia of Lead Poisoning". Pediatrics 67 (6): 904–906. PMID 7232054. http://pediatrics.aappublications.org/content/67/6/904.abstract. 
  84. ^ Laurence, D. R. (1966). Clinical Pharmacology(Third Edition). 
  85. ^ a b c d "Case Studies in Environmental Medicine Lead (Pb) Toxicity: How are People Exposed to Lead?". Agency for Toxic Substances and Disease Registry. Archived from the original on 2011-06-06. http://web.archive.org/web/20110606175014/http://www.atsdr.cdc.gov/csem/lead/pbroute_exposure2.html. 
  86. ^ "Information for the Community Lead Toxicity". Agency for Toxic Substances and Disease Registry. http://www.atsdr.cdc.gov/csem/lead/community/index.html. 
  87. ^ "Toxic Substances Portal – Lead". Agency for Toxic Substance and Disease Registry. http://www.atsdr.cdc.gov/PHS/PHS.asp?id=92&tid=22. 

Bibliography

  • Lide, D. R., ed. (2004). CRC Handbook of Chemistry and Physics (84th ed.). Boca Raton (FL): CRC Press. ISBN 978-0849304842. 
  • Polyanskiy, N. G. (1986). Fillipova, N. A. ed (in Russian). Аналитическая химия элементов: Свинец [Analytical Chemistry of the Elements: Lead]. Nauka. 

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