Lead

Template:About Template:Redirect-distinguish Template:Featured article Template:Use dmy dates Template:Infobox lead Lead (Template:IPAc-en) is a chemical element; it has symbol Pb (from Latin Template:Lang) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is a shiny gray with a hint of blue. It tarnishes to a dull gray color when exposed to air. Lead has the highest atomic number of any stable element and three of its isotopes are endpoints of major nuclear decay chains of heavier elements.

Lead is a relatively unreactive post-transition metal. Its weak metallic character is illustrated by its amphoteric nature; lead and lead oxides react with acids and bases, and it tends to form covalent bonds. Compounds of lead are usually found in the +2 oxidation state rather than the +4 state common with lighter members of the carbon group. Exceptions are mostly limited to organolead compounds. Like the lighter members of the group, lead tends to bond with itself; it can form chains and polyhedral structures.

Since lead is easily extracted from its ores, prehistoric people in the Near East were aware of it. Galena is a principal ore of lead which often bears silver. Interest in silver helped initiate widespread extraction and use of lead in ancient Rome. Lead production declined after the fall of Rome and did not reach comparable levels until the Industrial Revolution. Lead played a crucial role in the development of the printing press, as movable type could be relatively easily cast from lead alloys.Template:Sfn In 2014, the annual global production of lead was about ten million tonnes, over half of which was from recycling. Lead's high density, low melting point, ductility and relative inertness to oxidation make it useful. These properties, combined with its relative abundance and low cost, resulted in its extensive use in construction, plumbing, batteries, bullets, shots, weights, solders, pewters, fusible alloys, lead paints, leaded gasoline, and radiation shielding.

Lead is a neurotoxin that accumulates in soft tissues and bones. It damages the nervous system and interferes with the function of biological enzymes, causing neurological disorders ranging from behavioral problems to brain damage, and also affects general health, cardiovascular, and renal systems. Lead's toxicity was first documented by ancient Greek and Roman writers, who noted some of the symptoms of lead poisoning, but became widely recognized in Europe in the late 19th century.

Physical properties

Atomic

A lead atom has 82 electrons, arranged in an electron configuration of [Xe]4f¹⁴5d¹⁰6s²6p². The sum of lead's first and second ionization energies—the total energy required to remove the two 6p electrons—is close to that of tin, lead's upper neighbor in the carbon group. This is unusual; ionization energies generally fall going down a group, as an element's outer electrons become more distant from the nucleus, and more shielded by smaller orbitals. The sum of the first four ionization energies of lead exceeds that of tin,Template:Sfn contrary to what periodic trends would predict. This is explained by relativistic effects, which become significant in heavier atoms,Template:Sfn which contract s and p orbitals such that lead's 6s electrons have larger binding energies than its 5s electrons.Template:Sfn A consequence is the so-called inert pair effect: the 6s electrons of lead become reluctant to participate in bonding, stabilising the +2 oxidation state and making the distance between nearest atoms in crystalline lead unusually long.Template:Sfn

Lead's lighter carbon group congeners form stable or metastable allotropes with the tetrahedrally coordinated and covalently bonded diamond cubic structure. The energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp³ orbitals. In lead, the inert pair effect increases the separation between its s- and p-orbitals, and the gap cannot be overcome by the energy that would be released by extra bonds following hybridization.Template:Sfn Rather than having a diamond cubic structure, lead forms metallic bonds in which only the p-electrons are delocalized and shared between the Pb²⁺ ions. Lead consequently has a face-centered cubic structureTemplate:Sfn like the similarly sizedTemplate:Sfn divalent metals calcium and strontium.Template:Sfn Template:Efn Template:Efn Template:Efn

Bulk

Pure lead has a bright, shiny gray appearance with a hint of blue.Template:Sfn It tarnishes on contact with moist air and takes on a dull appearance, the hue of which depends on the prevailing conditions. Characteristic properties of lead include high density, malleability, ductility, and high resistance to corrosion due to passivation.Template:Sfn

File:Angeln zubehoer grundblei 01.jpg

Lead fishing weights

Lead's close-packed face-centered cubic structure and high atomic weight result in a densityTemplate:Sfn of 11.34 g/cm³, which is greater than that of common metals such as iron (7.87 g/cm³), copper (8.93 g/cm³), and zinc (7.14 g/cm³).Template:Sfn This density is the origin of the idiom to go over like a lead balloon.Template:Sfn Template:Sfn Template:Efn Some rarer metals are denser: tungsten and gold are both at 19.3 g/cm³, and osmium—the densest metal known—has a density of 22.59 g/cm³, almost twice that of lead.Template:Sfn

Lead is a very soft metal with a Mohs hardness of 1.5; it can be scratched with a fingernail.Template:Sfn It is quite malleable and somewhat ductile.Template:Sfn Template:Efn The bulk modulus of lead—a measure of its ease of compressibility—is 45.8 GPa. In comparison, that of aluminium is 75.2 GPa; copper 137.8 GPa; and mild steel 160–169 GPa.Template:Sfn Lead's tensile strength, at 12–17 MPa, is low (that of aluminium is 6 times higher, copper 10 times, and mild steel 15 times higher); it can be strengthened by adding small amounts of copper or antimony.Template:Sfn

A disk of metal

A sample of lead solidified from the molten state

The melting point of lead—at 327.5 °C (621.5 °F)Template:Sfn—is very low compared to most metals.Template:Sfn Template:Efn Its boiling point of 1749 °C (3180 °F)Template:Sfn is the lowest among the carbon-group elements. The electrical resistivity of lead at 20 °C is 192 nanoohm-meters, almost an order of magnitude higher than those of other industrial metals (copper at Template:Val; gold Template:Val; and aluminium at Template:Val).Template:Sfn Lead is a superconductor at temperatures lower than 7.19 K;Template:Sfn this is the highest critical temperature of all type-I superconductors and the third highest of the elemental superconductors.Template:Sfn

Isotopes

Template:Main Natural lead consists of four stable isotopes with mass numbers of 204, 206, 207, and 208,Template:Sfn and traces of six short-lived radioisotopes with mass numbers 209–214 inclusive. The high number of isotopes is consistent with lead's atomic number being even.Template:Efn Lead has a magic number of protons (82), for which the nuclear shell model accurately predicts an especially stable nucleus.Template:Sfn Lead-208 has 126 neutrons, another magic number, which may explain why lead-208 is extraordinarily stable.Template:Sfn

With its high atomic number, lead is the heaviest element whose natural isotopes are regarded as stable; lead-208 is the heaviest stable nucleus. (This distinction formerly fell to bismuth, with an atomic number of 83, until its only primordial isotope, bismuth-209, was found in 2003 to decay very slowly.)Template:Efn The four stable isotopes of lead could theoretically undergo alpha decay to isotopes of mercury with a release of energy, but this has not been observed for any of them; their predicted half-lives range from 10³⁵ to 10¹⁸⁹ yearsTemplate:Sfn (at least 10²⁵ times the current age of the universe).

A piece of a gray meteorite on a pedestal

The Holsinger meteorite, the largest piece of the Canyon Diablo meteorite. Uranium–lead dating and lead–lead dating on this meteorite allowed refinement of the age of the Earth to 4.55 billion ± 70 million years.

Three of the stable isotopes are found in three of the four major decay chains: lead-206, lead-207, and lead-208 are the final decay products of uranium-238, uranium-235, and thorium-232, respectively.Template:Sfn These decay chains are called the uranium chain, the actinium chain, and the thorium chain.Template:Sfn Their isotopic concentrations in a natural rock sample depends greatly on the presence of these three parent uranium and thorium isotopes. For example, the relative abundance of lead-208 can range from 52% in normal samples to 90% in thorium ores;Template:Sfn for this reason, the standard atomic weight of lead is given to only one decimal place.Template:Sfn As time passes, the ratio of lead-206 and lead-207 to lead-204 increases, since the former two are supplemented by radioactive decay of heavier elements while the latter is not; this allows for lead–lead dating. As uranium decays into lead, their relative amounts change; this is the basis for uranium–lead dating.Template:Sfn Lead-207 exhibits nuclear magnetic resonance, a property that has been used to study its compounds in solution and solid state,Template:Sfn Template:Sfn including in the human body.Template:Sfn

Apart from the stable isotopes, which make up almost all lead that exists naturally, there are trace quantities of a few radioactive isotopes. One of them is lead-210; although it has a half-life of only 22.2 years,Template:Sfn small quantities occur in nature because lead-210 is produced by a long decay series that starts with uranium-238 (that has been present for billions of years on Earth). Lead-211, −212, and −214 are present in the decay chains of uranium-235, thorium-232, and uranium-238, respectively, so traces of all three of these lead isotopes are found naturally. Minute traces of lead-209 arise from the very rare cluster decay of radium-223, one of the daughter products of natural uranium-235, the rare beta-minus-neutron decay of thallium-210 (a decay product of uranium-238), and the decay chain of neptunium-237, traces of which are produced by neutron capture in uranium ores. Lead-213 also occurs in the decay chain of neptunium-237. Lead-210 is particularly useful for helping to identify the ages of samples by measuring its ratio to lead-206 (both isotopes are present in a single decay chain).Template:Sfn

In total, 43 lead isotopes have been synthesized, with mass numbers 178–220.Template:Sfn Lead-205 is the most stable radioisotope, with a half-life of around 1.70Template:E years.Template:NUBASE2020 Template:Efn The second-most stable is lead-202, which has a half-life of about 52,500 years, longer than any of the natural trace radioisotopes.Template:Sfn

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Chemistry

A flame with a small metal rod penetrating it; the flame near the rod is pale blue.

Flame test: lead colors flame pale blue

Bulk lead exposed to moist air forms a protective layer of varying composition. Lead(II) carbonate is a common constituent;Template:Sfn Template:Sfn Template:Sfn the sulfate or chloride may also be present in urban or maritime settings.Template:Sfn This layer makes bulk lead effectively chemically inert in the air.Template:Sfn Finely powdered lead, as with many metals, is pyrophoric,Template:Sfn and burns with a bluish-white flame.Template:Sfn

Fluorine reacts with lead at room temperature, forming lead(II) fluoride. The reaction with chlorine is similar but requires heating, as the resulting chloride layer diminishes the reactivity of the elements.Template:Sfn Molten lead reacts with the chalcogens to give lead(II) chalcogenides.Template:Sfn

Lead metal resists sulfuric and phosphoric acid but not hydrochloric or nitric acid; the outcome depends on insolubility and subsequent passivation of the product salt.Template:Sfn Organic acids, such as acetic acid, dissolve lead in the presence of oxygen.Template:Sfn Concentrated alkalis dissolve lead and form plumbites.Template:Sfn

Inorganic compounds

Template:See also

Lead shows two main oxidation states: +4 and +2. The tetravalent state is common for the carbon group. The divalent state is rare for carbon and silicon, minor for germanium, important (but not prevailing) for tin, and is the more important of the two oxidation states for lead.Template:Sfn This is attributable to relativistic effects, specifically the inert pair effect, which manifests itself when there is a large difference in electronegativity between lead and oxide, halide, or nitride anions, leading to a significant partial positive charge on lead. The result is a stronger contraction of the lead 6s orbital than is the case for the 6p orbital, making it rather inert in ionic compounds. The inert pair effect is less applicable to compounds in which lead forms covalent bonds with elements of similar electronegativity, such as carbon in organolead compounds. In these, the 6s and 6p orbitals remain similarly sized and sp³ hybridization is still energetically favorable. Lead, like carbon, is predominantly tetravalent in such compounds.Template:Sfn

There is a relatively large difference in the electronegativity of lead(II) at 1.87 and lead(IV) at 2.33. This difference marks the reversal in the trend of increasing stability of the +4 oxidation state going down the carbon group; tin, by comparison, has values of 1.80 in the +2 oxidation state and 1.96 in the +4 state.Template:Sfn

Lead(II)

Cream powder

Lead(II) oxide

Lead(II) compounds are characteristic of the inorganic chemistry of lead. Even strong oxidizing agents like fluorine and chlorine react with lead to give only PbF₂ and PbCl₂.Template:Sfn Lead(II) ions are usually colorless in solution,Template:Sfn and partially hydrolyze to form Pb(OH)⁺ and finally [Pb₄(OH)₄]⁴⁺ (in which the hydroxyl ions act as bridging ligands),Template:Sfn Template:Sfn but are not reducing agents as tin(II) ions are. Techniques for identifying the presence of the Pb²⁺ ion in water generally rely on the precipitation of lead(II) chloride using dilute hydrochloric acid. As the chloride salt is sparingly soluble in water, in very dilute solutions the precipitation of lead(II) sulfide is instead achieved by bubbling hydrogen sulfide through the solution.Template:Sfn

Lead monoxide exists in two polymorphs, litharge α-PbO (red) and massicot β-PbO (yellow), the latter being stable only above around 488 °C. Litharge is the most commonly used inorganic compound of lead.Template:Sfn There is no lead(II) hydroxide; increasing the pH of solutions of lead(II) salts leads to hydrolysis and condensation.Template:Sfn Lead commonly reacts with heavier chalcogens. Lead sulfide is a semiconductor, a photoconductor, and an extremely sensitive infrared radiation detector. The other two chalcogenides, lead selenide and lead telluride, are likewise photoconducting. They are unusual in that their color becomes lighter going down the group.Template:Sfn

Alternating dark gray and red balls connected by dark gray-red cylinders

Lead and oxygen in a tetragonal unit cell of lead(II,IV) oxide

Lead dihalides are well-characterized; this includes the diastatideTemplate:Sfn and mixed halides, such as PbFCl. The relative insolubility of the latter forms a useful basis for the gravimetric determination of fluorine. The difluoride was the first solid ionically conducting compound to be discovered (in 1834, by Michael Faraday).Template:Sfn The other dihalides decompose on exposure to ultraviolet or visible light, especially the diiodide.Template:Sfn Many lead(II) pseudohalides are known, such as the cyanide, cyanate, and thiocyanate.Template:Sfn Template:Sfn Lead(II) forms an extensive variety of halide coordination complexes, such as [PbCl₄]²⁻, [PbCl₆]⁴⁻, and the [Pb₂Cl₉]_n⁵ⁿ⁻ chain anion.Template:Sfn

Lead(II) sulfate is insoluble in water, like the sulfates of other heavy divalent cations. Lead(II) nitrate and lead(II) acetate are very soluble, and this is exploited in the synthesis of other lead compounds.Template:Sfn

Lead(IV)

Few inorganic lead(IV) compounds are known. They are only formed in highly oxidizing solutions and do not normally exist under standard conditions.Template:Sfn Lead(II) oxide gives a mixed oxide on further oxidation, Pb₃O₄. It is described as lead(II,IV) oxide, or structurally 2PbO·PbO₂, and is the best-known mixed valence lead compound. Lead dioxide is a strong oxidizing agent, capable of oxidizing hydrochloric acid to chlorine gas.Template:Sfn This is because the expected PbCl₄ that would be produced is unstable and spontaneously decomposes to PbCl₂ and Cl₂.Template:Sfn Analogously to lead monoxide, lead dioxide is capable of forming plumbate anions. Lead disulfide Template:Sfn and lead diselenideTemplate:Sfn are only stable at high pressures. Lead tetrafluoride, a yellow crystalline powder, is stable, but less so than the difluoride. Lead tetrachloride (a yellow oil) decomposes at room temperature, lead tetrabromide is less stable still, and the existence of lead tetraiodide is questionable.Template:Sfn

Other oxidation states

Template:See also

Nine dark gray spheres connected by cylinders of the same color forming a convex shape

The capped square antiprismatic anion [Pb₉]⁴⁻ from [K(18-crown-6)]₂K₂Pb₉·(en)_1.5Template:Sfn

Some lead compounds exist in formal oxidation states other than +4 or +2. Lead(III) may be obtained, as an intermediate between lead(II) and lead(IV), in larger organolead complexes; this oxidation state is not stable, as both the lead(III) ion and the larger complexes containing it are radicals.Template:Sfn Template:Sfn Template:Sfn The same applies for lead(I), which can be found in such radical species.Template:Sfn

Numerous mixed lead(II,IV) oxides are known. When PbO₂ is heated in air, it becomes Pb₁₂O₁₉ at 293 °C, Pb₁₂O₁₇ at 351 °C, Pb₃O₄ at 374 °C, and finally PbO at 605 °C. A further sesquioxide, Pb₂O₃, can be obtained at high pressure, along with several non-stoichiometric phases. Many of them show defective fluorite structures in which some oxygen atoms are replaced by vacancies: PbO can be considered as having such a structure, with every alternate layer of oxygen atoms absent.Template:Sfn

Negative oxidation states can occur as Zintl phases, as either free lead anions, as in Ba₂Pb, with lead formally being lead(−IV),Template:Sfn or in oxygen-sensitive ring-shaped or polyhedral cluster ions such as the trigonal bipyramidal Pb₅²⁻ ion, where two lead atoms are lead(−I) and three are lead(0).Template:Sfn In such anions, each atom is at a polyhedral vertex and contributes two electrons to each covalent bond along an edge from their sp³ hybrid orbitals, the other two being an external lone pair.Template:Sfn They may be made in liquid ammonia via the reduction of lead by sodium.Template:Sfn

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Organolead

Template:Main

A gray-green sphere linked to four black spheres, each, in turn, linked also to three white ones

Structure of a tetraethyllead molecule:
Template:Color box Carbon
Template:Color box Hydrogen
Template:Color box Lead

Lead can form multiply-bonded chains, a property it shares with its lighter homologs in the carbon group. Its capacity to do so is much less because the Pb–Pb bond energy is over three and a half times lower than that of the C–C bond.Template:Sfn With itself, lead can build metal–metal bonds of an order up to three.Template:Sfn With carbon, lead forms organolead compounds similar to, but generally less stable than, typical organic compoundsTemplate:Sfn (due to the Pb–C bond being rather weak).Template:Sfn This makes the organometallic chemistry of lead far less wide-ranging than that of tin.Template:Sfn Lead predominantly forms organolead(IV) compounds, even when starting with inorganic lead(II) reactants; very few organolead(II) compounds are known. The most well-characterized exceptions are Pb[CH(SiMe₃)₂]₂ and plumbocene.Template:Sfn

The lead analog of the simplest organic compound, methane, is plumbane. Plumbane may be obtained in a reaction between metallic lead and atomic hydrogen.Template:Sfn Two simple derivatives, tetramethyllead and tetraethyllead, are the best-known organolead compounds. These compounds are relatively stable: tetraethyllead only starts to decompose if heatedTemplate:Sfn or if exposed to sunlight or ultraviolet light.Template:Sfn Template:Efn With sodium metal, lead readily forms an equimolar alloy that reacts with alkyl halides to form organometallic compounds such as tetraethyllead.Template:Sfn The oxidizing nature of many organolead compounds is usefully exploited: lead tetraacetate is an important laboratory reagent for oxidation in organic synthesis.Template:Sfn Tetraethyllead, once added to automotive gasoline, was produced in larger quantities than any other organometallic compound,Template:Sfn and is still widely used in fuel for small aircraft.<ref>Template:Cite web</ref> Other organolead compounds are less chemically stable.Template:Sfn For many organic compounds, a lead analog does not exist.Template:Sfn

Origin and occurrence

Solar System abundancesTemplate:Sfn
Atomic number	Element	Relative amount
42	Molybdenum	0.798
46	Palladium	0.440
50	Tin	1.146
78	Platinum	0.417
80	Mercury	0.127
82	Lead	1
90	Thorium	0.011
92	Uranium	0.003

In space

Lead's per-particle abundance in the Solar System is 0.121 ppb (parts per billion).Template:Sfn Template:Efn This figure is two and a half times higher than that of platinum, eight times more than mercury, and seventeen times more than gold.Template:Sfn The amount of lead in the universe is slowly increasingTemplate:Sfn as most heavier atoms (all of which are unstable) gradually decay to lead.Template:Sfn The abundance of lead in the Solar System since its formation 4.5 billion years ago has increased by about 0.75%.Template:Sfn The Solar System abundances table shows that lead, despite its relatively high atomic number, is more prevalent than most other elements with atomic numbers greater than 40.Template:Sfn

Primordial lead—which comprises the isotopes lead-204, lead-206, lead-207, and lead-208—was mostly created as a result of repetitive neutron capture processes occurring in stars. The two main modes of capture are the s- and r-processes.Template:Sfn

In the s-process (s is for "slow"), captures are separated by years or decades, allowing less stable nuclei to undergo beta decay.Template:Sfn A stable thallium-203 nucleus can capture a neutron and become thallium-204; this undergoes beta decay to give stable lead-204; on capturing another neutron, it becomes lead-205, which has a half-life of around 17 million years. Further captures result in lead-206, lead-207, and lead-208. On capturing another neutron, lead-208 becomes lead-209, which quickly decays into bismuth-209. On capturing another neutron, bismuth-209 becomes bismuth-210, and this beta decays to polonium-210, which alpha decays to lead-206. The cycle hence ends at lead-206, lead-207, lead-208, and bismuth-209.Template:Sfn

Uppermost part of the nuclide chart, with only practically stable isotopes and lead-205 shown, and the path of the s-process overlaid on it as well that of the cycle on lead, bismuth, and polonium

Chart of the final part of the s-process, from mercury to polonium. Red lines and circles represent neutron captures; blue arrows represent beta decays; the green arrow represents an alpha decay; cyan arrows represent electron captures.

In the r-process (r is for "rapid"), captures happen faster than nuclei can decay.Template:Sfn This occurs in environments with a high neutron density, such as a supernova or the merger of two neutron stars. The neutron flux involved may be on the order of 10²² neutrons per square centimeter per second.Template:Sfn The r-process does not form as much lead as the s-process.Template:Sfn It tends to stop once neutron-rich nuclei reach 126 neutrons.Template:Sfn At this point, the neutrons are arranged in complete shells in the atomic nucleus, and it becomes harder to energetically accommodate more of them.Template:Sfn When the neutron flux subsides, these nuclei beta decay into stable isotopes of osmium, iridium, platinum.Template:Sfn

On Earth

File:Lingot de plomb de l'époque romaine. Mines de Cartagène Espagne.jpg

Lead ingot from Roman times, Cartagena, Spain

Lead is classified as a chalcophile under the Goldschmidt classification, meaning it is generally found combined with sulfur.Template:Sfn It rarely occurs in its native, metallic form.Template:Sfn Many lead minerals are relatively light and, over the course of the Earth's history, have remained in the crust instead of sinking deeper into the Earth's interior. This accounts for lead's relatively high crustal abundance of 14 ppm; it is the 36th most abundant element in the crust.Template:Sfn Template:Efn

The main lead-bearing mineral is galena (PbS), which is mostly found with zinc ores.Template:Sfn Most other lead minerals are related to galena in some way; boulangerite, Pb₅Sb₄S₁₁, is a mixed sulfide derived from galena; anglesite, PbSO₄, is a product of galena oxidation; and cerussite or white lead ore, PbCO₃, is a decomposition product of galena. Arsenic, tin, antimony, silver, gold, copper, bismuth are common impurities in lead minerals.Template:Sfn

A line chart generally declining towards its right

Lead is a fairly common element in the Earth's crust for its high atomic number (82). Most elements of atomic number greater than 40 are less abundant.

World lead resources exceed two billion tons. Significant deposits are located in Australia, China, Ireland, Mexico, Peru, Portugal, Russia, United States. Global reserves—resources that are economically feasible to extract—totaled 88 million tons in 2016, of which Australia had 35 million, China 17 million, Russia 6.4 million.Template:Sfn

Typical background concentrations of lead do not exceed 0.1 μg/m³ in the atmosphere; 100 mg/kg in soil; 4 mg/kg in vegetation, 5 μg/L in fresh water and seawater.Template:Sfn

Etymology

The modern English word lead is of Germanic origin; it comes from the Middle English Template:Lang and Old English Template:Lang (with the macron above the "e" signifying that the vowel sound of that letter is long).Template:Sfn The Old English word is derived from the hypothetical reconstructed Proto-Germanic Template:Lang ('lead').Template:Sfn According to linguistic theory, this word bore descendants in multiple Germanic languages of exactly the same meaning.Template:Sfn

There is no consensus on the origin of the Proto-Germanic Template:Lang. One hypothesis suggests it is derived from Proto-Indo-European Template:Lang ('lead'; capitalization of the vowel is equivalent to the macron).Template:Sfn Another hypothesis suggests it is borrowed from Proto-Celtic Template:Lang ('lead'). This word is related to the Latin Template:Lang, which gave the element its chemical symbol Pb. The word Template:Lang is thought to be the origin of Proto-Germanic Template:Lang (which also means 'lead'), from which stemmed the German Template:Lang.Template:Sfn

The name of the chemical element is not related to the verb of the same spelling, which is derived from Proto-Germanic Template:Lang ('to lead').Template:Sfn

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History

Prehistory and early history

A line chart generally growing to its right

World lead production peaking in the Roman period and the Industrial Revolution Template:Sfn

Metallic lead beads dating back to 7000–6500 BC have been found in Asia Minor and may represent the first example of metal smelting.Template:Sfn At that time, lead had few (if any) applications due to its softness and dull appearance.Template:Sfn The major reason for the spread of lead production was its association with silver, which may be obtained by burning galena (a common lead mineral).Template:Sfn The Ancient Egyptians were the first to use lead minerals in cosmetics, an application that spread to Ancient Greece and beyond;Template:Sfn the Egyptians had used lead for sinkers in fishing nets, glazes, glasses, enamels, ornaments.Template:Sfn Various civilizations of the Fertile Crescent used lead as a writing material, as coins,Template:Sfn and as a construction material.Template:Sfn Lead was used by the ancient Chinese as a stimulant,Template:Sfn as currency,Template:Sfn as contraceptive,Template:Sfn and in chopsticks.Template:Sfn The Indus Valley civilization and the Mesoamericans used it for making amulets;Template:Sfn and the eastern and southern Africans used lead in wire drawing.Template:Sfn

Classical era

Because silver was extensively used as a decorative material and an exchange medium, lead deposits came to be worked in Asia Minor from 3000 BC; later, lead deposits were developed in the Aegean and Laurion.Template:Sfn These three regions collectively dominated production of mined lead until Template:Circa.Template:Sfn Beginning c. 2000 BC, the Phoenicians worked deposits in the Iberian peninsula; by 1600 BC, lead mining existed in Cyprus, Greece, and Sardinia.Template:Sfn

File:Sling bullets BM GR1842.7-28.550 GR1851.5-7.11.jpg

Ancient Greek lead sling bullets with a winged thunderbolt molded on one side and the inscription Template:Lang ("take that") on the other sideTemplate:Sfn

Rome's territorial expansion in Europe and across the Mediterranean, and its development of mining, led to it becoming the greatest producer of lead during the classical era, with an estimated annual output peaking at 80,000 tonnes. Like their predecessors, the Romans obtained lead mostly as a by-product of silver smelting.Template:Sfn Template:Sfn Lead mining occurred in central Europe, Britain, Balkans, Greece, Anatolia, Hispania, the latter accounting for 40% of world production.Template:Sfn

A vaguely round plate illuminated from a side to increase the contrast. The characters curl around the contour.

The Lead Plaque of Magliano, Italy, bears an Etruscan inscription from mid-5th century BC.

Lead tablets were commonly used as a material for letters.Template:Sfn Lead coffins, cast in flat sand forms and with interchangeable motifs to suit the faith of the deceased, were used in ancient Judea.Template:Sfn Lead was used to make sling bullets from the 5th century BC. In Roman times, lead sling bullets were amply used, and were effective at a distance of between 100 and 150 meters. The Balearic slingers, used as mercenaries in Carthaginian and Roman armies, were famous for their shooting distance and accuracy.Template:Sfn

Ancient pipes in a museum case

Roman lead pipesTemplate:Efn

Lead was used for making water pipes in the Roman Empire; the Latin word for the metal, Template:Lang, is the origin of the English word "plumbing". Its ease of working, its low melting point enabling the easy fabrication of completely waterproof welded joints, and its resistance to corrosionTemplate:Sfn ensured its widespread use in other applications, including pharmaceuticals, roofing, currency, warfare.Template:Sfn Template:Sfn Template:Sfn Writers of the time, such as Cato the Elder, Columella, and Pliny the Elder, recommended lead (and lead-coated) vessels for the preparation of sweeteners and preservatives added to wine and food. The lead conferred an agreeable taste due to the formation of "sugar of lead" (lead(II) acetate), whereas copper vessels imparted a bitter flavor through verdigris formation.Template:Sfn

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The Roman author Vitruvius reported the health dangers of lead Template:Sfn<ref>Template:Cite book</ref> and modern writers have suggested that lead poisoning played a major role in the decline of the Roman Empire.Template:Sfn Template:Sfn Template:Efn Other researchers have criticized such claims, pointing out, for instance, that not all abdominal pain is caused by lead poisoning.Template:Sfn Template:Sfn According to archaeological research, Roman lead pipes increased lead levels in tap water but such an effect was "unlikely to have been truly harmful".Template:Sfn Template:Sfn When lead poisoning did occur, victims were called "saturnine", dark and cynical, after the ghoulish father of the gods, Saturn. By association, lead was considered the father of all metals.Template:Sfn Its status in Roman society was low as it was readily availableTemplate:Sfn and cheap.Template:Sfn

Confusion with tin and antimony

Since the Bronze Age, metallurgists and engineers have understood the difference between rare and valuable tin, essential for alloying with copper to produce tough and corrosion resistant bronze, and 'cheap and cheerful' lead. However, the nomenclature in some languages is similar. Romans called lead Template:Lang ("black lead"), and tin Template:Lang ("bright lead"). The association of lead and tin can be seen in other languages: the word Template:Lang in Czech translates to "lead", but in Russian, its cognate Template:Lang (Template:Lang) means "tin".Template:Sfn To add to the confusion, lead bore a close relation to antimony: both elements commonly occur as sulfides (galena and stibnite), often together. Pliny incorrectly wrote that stibnite would give lead on heating, instead of antimony.Template:Sfn In countries such as Turkey and India, the originally Persian name Template:Lang came to refer to either antimony sulfide or lead sulfide,Template:Sfn and in some languages, such as Russian, gave its name to antimony (Template:Lang).Template:Sfn

Middle Ages and the Renaissance

A white-faced woman in red clothes

Elizabeth I of England was commonly depicted with a whitened face. Lead in face whiteners is thought to have contributed to her death.Template:Sfn

Lead mining in Western Europe declined after the fall of the Western Roman Empire, with Arabian Iberia being the only region having a significant output.Template:Sfn Template:Sfn The largest production of lead occurred in South Asia and East Asia, especially China and India, where lead mining grew rapidly.Template:Sfn

In Europe, lead production began to increase in the 11th and 12th centuries, when it was again used for roofing and piping. Starting in the 13th century, lead was used to create stained glass.Template:Sfn In the European and Arabian traditions of alchemy, lead (symbol ♄ in the European tradition)Template:Sfn was considered an impure base metal which, by the separation, purification and balancing of its constituent essences, could be transformed to pure and incorruptible gold.Template:Sfn During the period, lead was used increasingly for adulterating wine. The use of such wine was forbidden for use in Christian rites by a papal bull in 1498, but it continued to be imbibed and resulted in mass poisonings up to the late 18th century.Template:Sfn Template:Sfn Lead was a key material in parts of the printing press, and lead dust was commonly inhaled by print workers, causing lead poisoning.Template:Sfn Lead also became the chief material for making bullets for firearms: it was cheap, less damaging to iron gun barrels, had a higher density (which allowed for better retention of velocity), and its lower melting point made the production of bullets easier as they could be made using a wood fire.Template:Sfn Lead, in the form of Venetian ceruse, was extensively used in cosmetics by Western European aristocracy as whitened faces were regarded as a sign of modesty.Template:Sfn Template:Sfn This practice later expanded to white wigs and eyeliners, and only faded out with the French Revolution in the late 18th century. A similar fashion appeared in Japan in the 18th century with the emergence of the geishas, a practice that continued long into the 20th century. The white faces of women "came to represent their feminine virtue as Japanese women",Template:Sfn with lead commonly used in the whitener.Template:Sfn

Outside Europe and Asia

In the New World, lead production was recorded soon after the arrival of European settlers. The earliest record dates to 1621 in the English Colony of Virginia, fourteen years after its foundation.Template:Sfn In Australia, the first mine opened by colonists on the continent was a lead mine, in 1841.Template:Sfn In Africa, lead mining and smelting were known in the Benue Trough Template:Sfn and the lower Congo Basin, where lead was used for trade with Europeans, and as a currency by the 17th century,Template:Sfn well before the scramble for Africa.

Industrial Revolution

A black-and-white drawing of men working in a mine

Lead mining in the upper Mississippi River region in the United States in 1865

In the second half of the 18th century, Britain, and later continental Europe and the United States, experienced the Industrial Revolution. This was the first time during which lead production rates exceeded those of Rome.Template:Sfn Britain was the leading producer, losing this status by the mid-19th century with the depletion of its mines and the development of lead mining in Germany, Spain, and the United States.Template:Sfn By 1900, the United States was the leader in global lead production, and other non-European nations—Canada, Mexico, and Australia—had begun significant production; production outside Europe exceeded that within.Template:Sfn A great share of the demand for lead came from plumbing and painting—lead paints were in regular use.Template:Sfn At this time, more (working class) people were exposed to the metal and lead poisoning cases escalated. This led to research into the effects of lead intake. Lead was proven to be more dangerous in its fume form than as a solid metal. Lead poisoning and gout were linked; British physician Alfred Baring Garrod noted a third of his gout patients were plumbers and painters. The effects of chronic ingestion of lead, including mental disorders, were also studied in the 19th century. The first laws aimed at decreasing lead poisoning in factories were enacted during the 1870s and 1880s in the United Kingdom.Template:Sfn

Modern era

A promotional poster for "COLLIER White Lead" (these words are highlighted) featuring a large image of a boy

Promotional poster for Dutch Boy lead paint, United States, 1912

Further evidence of the threat that lead posed to humans was discovered in the late 19th and early 20th centuries. Mechanisms of harm were better understood, lead blindness was documented, and the element was phased out of public use in the United States and Europe. The United Kingdom introduced mandatory factory inspections in 1878 and appointed the first Medical Inspector of Factories in 1898; as a result, a 25-fold decrease in lead poisoning incidents from 1900 to 1944 was reported.Template:Sfn Most European countries banned lead paint—commonly used because of its opacity and water resistanceTemplate:Sfn—for interiors by 1930.Template:Sfn

The last major human exposure to lead was the addition of tetraethyllead to gasoline as an antiknock agent, a practice that originated in the United States in 1921. It was phased out in the United States and the European Union by 2000.Template:Sfn

In the 1970s, the United States and Western European countries introduced legislation to reduce lead air pollution.Template:Sfn Template:Sfn The impact was significant: while a study conducted by the Centers for Disease Control and Prevention in the United States in 1976–1980 showed that 77.8% of the population had elevated blood lead levels, in 1991–1994, a study by the same institute showed the share of people with such high levels dropped to 2.2%.Template:Sfn The main product made of lead by the end of the 20th century was the lead–acid battery.Template:Sfn

From 1960 to 1990, lead output in the Western Bloc grew by about 31%.Template:Sfn The share of the world's lead production by the Eastern Bloc increased from 10% to 30%, from 1950 to 1990, with the Soviet Union being the world's largest producer during the mid-1970s and the 1980s, and China starting major lead production in the late 20th century.Template:Sfn Unlike the European communist countries, China was largely unindustrialized by the mid-20th century; in 2004, China surpassed Australia as the largest producer of lead.Template:Sfn As was the case during European industrialization, lead has had a negative effect on health in China.Template:Sfn

Production

A line chart of many lines, some longer than other, most generally growing towards its right

Primary production of lead since 1840

As of 2014, production of lead is increasing worldwide due to its use in lead–acid batteries.Template:Sfn There are two major categories of production: primary from mined ores, and secondary from scrap. In 2014, 4.58 million metric tons came from primary production and 5.64 million from secondary production. The top three producers of mined lead concentrate in that year were China, Australia, and United States.Template:Sfn The top three producers of refined lead were China, United States, and India.Template:Sfn According to the Metal Stocks in Society report of 2010, the total amount of lead in use, stockpiled, discarded, or dissipated into the environment, on a global basis, is 8 kg per capita. Much of this is in more developed countries (20–150 kg per capita) rather than less developed ones (1–4 kg per capita).Template:Sfn

The primary and secondary lead production processes are similar. Some primary production plants now supplement their operations with scrap lead, and this trend is likely to increase in the future. Given adequate techniques, lead obtained via secondary processes is indistinguishable from lead obtained via primary processes. Scrap lead from the building trade is usually fairly clean and is re-melted without the need for smelting, though refining is sometimes needed. Secondary lead production is therefore cheaper, in terms of energy requirements, than is primary production, often by 50% or more.Template:Sfn

Template:Clear

Primary

Most lead ores contain a low percentage of lead (rich ores have a typical content of 3–8%) which must be concentrated for extraction.Template:Sfn During initial processing, ores typically undergo crushing, dense-medium separation, grinding, froth flotation, drying. The resulting concentrate, which has a lead content of 30–80% by mass (regularly 50–60%),Template:Sfn is then turned into (impure) lead metal.

There are two main ways of doing this: a two-stage process involving roasting followed by blast furnace extraction, carried out in separate vessels; or a direct process in which the extraction of the concentrate occurs in a single vessel. The latter has become the most common route, though the former is still significant.Template:Sfn

**World's largest mining countries of lead, 2016**Template:Sfn
Country	Output (thousand tons)
Template:Flagu	2,400
Template:Flagu	500
Template:Flagu	335
Template:Flagu	310
Template:Flagu	250
Template:Flagu	225
Template:Flagu	135
Template:Flagu	80
Template:Flagu	76
Template:Flagu	75
Template:Flagu	41
Template:Flagu	41
Template:Flagu	40
Template:Flagu	40
Template:Flagu	35
Template:Flagu	33
Template:Flagu	33
Other countries	170

Two-stage process

First, the sulfide concentrate is roasted in air to oxidize the lead sulfide:Template:Sfn

2 PbS(s) + 3 O₂(g) → 2 PbO(s) + 2 SO₂(g)↑

As the original concentrate was not pure lead sulfide, roasting yields not only the desired lead(II) oxide, but a mixture of oxides, sulfates, and silicates of lead and of the other metals contained in the ore.Template:Sfn This impure lead oxide is reduced in a coke-fired blast furnace to the (again, impure) metal:Template:Sfn

2 PbO(s) + C(s) → 2 Pb(s) + CO₂(g)↑

Impurities are mostly arsenic, antimony, bismuth, zinc, copper, silver, and gold. Typically they are removed in a series of pyrometallurgical processes. The melt is treated in a reverberatory furnace with air, steam, sulfur, which oxidizes the impurities except for silver, gold, bismuth. Oxidized contaminants float to the top of the melt and are skimmed off.Template:Sfn Template:Sfn Metallic silver and gold are removed and recovered economically by means of the Parkes process, in which zinc is added to lead. Zinc, which is immiscible in lead, dissolves the silver and gold. The zinc solution can be separated from the lead, and the silver and gold retrieved.Template:Sfn Template:Sfn De-silvered lead is freed of bismuth by the Betterton–Kroll process, treating it with metallic calcium and magnesium. The resulting bismuth dross can be skimmed off.Template:Sfn

Alternatively to the pyrometallurgical processes, very pure lead can be obtained by processing smelted lead electrolytically using the Betts process. Anodes of impure lead and cathodes of pure lead are placed in an electrolyte of lead fluorosilicate (PbSiF₆). Once electrical potential is applied, impure lead at the anode dissolves and plates onto the cathode, leaving the majority of the impurities in solution.Template:Sfn Template:Sfn This is a high-cost process and thus mostly reserved for refining bullion containing high percentages of impurities.Template:Sfn

Direct process

In this process, lead bullion and slag is obtained directly from lead concentrates. The lead sulfide concentrate is melted in a furnace and oxidized, forming lead monoxide. Carbon (as coke or coal gas Template:Efn) is added to the molten charge along with fluxing agents. The lead monoxide is thereby reduced to metallic lead, in the midst of a slag rich in lead monoxide.Template:Sfn

If the input is rich in lead, as much as 80% of the original lead can be obtained as bullion; the remaining 20% forms a slag rich in lead monoxide. For a low-grade feed, all of the lead can be oxidized to a high-lead slag.Template:Sfn Metallic lead is further obtained from the high-lead (25–40%) slags via submerged fuel combustion or injection, reduction assisted by an electric furnace, or a combination of both.Template:Sfn

Alternatives

Research on a cleaner, less energy-intensive lead extraction process continues; a major drawback is that either too much lead is lost as waste, or the alternatives result in a high sulfur content in the resulting lead metal. Hydrometallurgical extraction, in which anodes of impure lead are immersed into an electrolyte and pure lead is deposited (electrowound) onto cathodes, is a technique that may have potential, but is not currently economical except in cases where electricity is very cheap.Template:Sfn

Secondary

Template:Further Smelting, which is an essential part of the primary production, is often skipped during secondary production. It is only performed when metallic lead has undergone significant oxidation.Template:Sfn The process is similar to that of primary production in either a blast furnace or a rotary furnace, with the essential difference being the greater variability of yields: blast furnaces produce hard lead (10% antimony) while reverberatory and rotary kiln furnaces produce semisoft lead (3–4% antimony).Template:Sfn

The ISASMELT process is a more recent smelting method that may act as an extension to primary production; battery paste from spent lead–acid batteries (containing lead sulfate and lead oxides) has its sulfate removed by treating it with alkali, and is then treated in a coal-fueled furnace in the presence of oxygen, which yields impure lead, with antimony the most common impurity.Template:Sfn Refining of secondary lead is similar to that of primary lead; some refining processes may be skipped depending on the material recycled and its potential contamination.Template:Sfn

Of the sources of lead for recycling, lead–acid batteries are the most important; lead pipe, sheet, and cable sheathing are also significant.Template:Sfn

Applications

A closed structure of black bricks

Bricks of lead (alloyed with 4% antimony) are used as radiation shielding.Template:Sfn

Contrary to popular belief, pencil leads in wooden pencils have never been made from lead. When the pencil originated as a wrapped graphite writing tool, the particular type of graphite used was named plumbago (literally, lead mockup).Template:Sfn

Elemental form

Lead metal has several useful mechanical properties, including high density, low melting point, ductility, and relative inertness. Many metals are superior to lead in some of these aspects but are generally less common and more difficult to extract from parent ores. Lead's toxicity has led to its phasing out for some uses.Template:Sfn

Lead has been used for bullets since their invention in the Middle Ages. It is inexpensive; its low melting point means small arms ammunition and shotgun pellets can be cast with minimal technical equipment; and it is denser than other common metals, which allows for better retention of velocity. It remains the main material for bullets, alloyed with other metals as hardeners.Template:Sfn Concerns have been raised that lead bullets used for hunting can damage the environment.Template:Efn Shotgun cartridges used for waterfowl hunting must today be lead-free in the United States,<ref>Template:Cite web</ref> Canada,<ref>Template:Cite web</ref> and in Europe.<ref>Template:Cite web</ref>

Lead's high density and resistance to corrosion have been exploited in a number of related applications. It is used as ballast in sailboat keels; its density allows it to take up a small volume and minimize water resistance, thus counterbalancing the heeling effect of wind on the sails.Template:Sfn It is used in scuba diving weight belts to counteract the diver's buoyancy.Template:Sfn In 1993, the base of the Leaning Tower of Pisa was stabilized with 600 tonnes of lead.Template:Sfn Because of its corrosion resistance, lead is used as a protective sheath for underwater cables.Template:Sfn

Yellow sculpture

A 17th-century gold-coated lead sculpture

Lead has many uses in the construction industry; lead sheets are used as architectural metals in roofing material, cladding, flashing, gutters and gutter joints, roof parapets.Template:Sfn Template:Sfn Lead is still used in statues and sculptures,Template:Efn including for armatures.Template:Sfn In the past it was often used to balance the wheels of cars; for environmental reasons this use is being phased out in favor of other materials.Template:Sfn

Lead is added to copper alloys, such as brass and bronze, to improve machinability and for its lubricating qualities. Being practically insoluble in copper, the lead forms solid globules in imperfections throughout the alloy, such as grain boundaries. In low concentrations, as well as acting as a lubricant, the globules hinder the formation of swarf as the alloy is worked, thereby improving machinability. Copper alloys with larger concentrations of lead are used in bearings. The lead provides lubrication, and the copper provides the load-bearing support.Template:Sfn

Lead's high density, atomic number, and formability form the basis for use of lead as a barrier that absorbs sound, vibration, and radiation.Template:Sfn Lead has no natural resonance frequencies;Template:Sfn as a result, sheet-lead is used as a sound deadening layer in the walls, floors, and ceilings of sound studios.Template:Sfn Organ pipes are often made from a lead alloy, mixed with various amounts of tin to control the tone of each pipe.Template:Sfn Template:Sfn Lead is an established shielding material from radiation in nuclear science and in X-ray roomsTemplate:Sfn due to its denseness and high attenuation coefficient.Template:Sfn Molten lead has been used as a coolant for lead-cooled fast reactors.Template:Sfn

Batteries

The largest use of lead in the early 21st century is in lead–acid batteries. The lead in batteries undergoes no direct contact with humans, so there are fewer toxicity concerns.Template:Efn People who work in lead battery production or recycling plants may be exposed to lead dust and inhale it.Template:Sfn The reactions in the battery between lead, lead dioxide, and sulfuric acid provide a reliable source of voltage.Template:Efn Supercapacitors incorporating lead–acid batteries have been installed in kilowatt and megawatt scale applications in Australia, Japan, and the United States in frequency regulation, solar smoothing and shifting, wind smoothing, and other applications.Template:Sfn These batteries have lower energy density and charge-discharge efficiency than lithium-ion batteries, but are significantly cheaper.Template:Sfn

Coating for cables

Lead is used in high voltage power cables as shell material to prevent water diffusion into insulation; this use is decreasing as lead is being phased out.Template:Sfn Its use in solder for electronics is also being phased out by some countries to reduce the amount of environmentally hazardous waste.Template:Sfn Lead is one of three metals used in the Oddy test for museum materials, helping detect organic acids, aldehydes, acidic gases.Template:Sfn Template:Sfn

Compounds

A crystal glass

Lead glass

File:PbCrO4 and PbCrO4•PbO.jpg

Lead yellow and lead red

In addition to being the main application for lead metal, lead–acid batteries are also the main consumer of lead compounds. The energy storage/release reaction used in these devices involves lead sulfate and lead dioxide:Template:Citation needed

Template:Chem(s) + Template:Chem(s) + 2Template:Chem(aq) → 2Template:Chem(s) + 2Template:Chem(l)

Other applications of lead compounds are very specialized and often fading. Lead-based coloring agents are used in ceramic glazes and glass, especially for red and yellow shades.Template:Sfn While lead paints are phased out in Europe and North America, they remain in use in less developed countries such as China,Template:Sfn India,Template:Sfn or Indonesia.Template:Sfn Lead tetraacetate and lead dioxide are used as oxidizing agents in organic chemistry. Lead is frequently used in the polyvinyl chloride coating of electrical cords.Template:Sfn Template:Sfn It can be used to treat candle wicks to ensure a longer, more even burn. Because of its toxicity, European and North American manufacturers use alternatives such as zinc.Template:Sfn Template:Sfn Lead glass is composed of 12–28% lead oxide, changing its optical characteristics and reducing the transmission of ionizing radiation,Template:Sfn a property used in old TVs and computer monitors with cathode-ray tubes. Lead-based semiconductors such as lead telluride and lead selenide are used in photovoltaic cells and infrared detectors.Template:Sfn

Biological effects

Template:Main Template:Chembox Lead has no confirmed biological role, and there is no confirmed safe level of lead exposure.Template:Sfn A 2009 Canadian–American study concluded that even at levels that are considered to pose little to no risk, lead may cause "adverse mental health outcomes".Template:Sfn Its prevalence in the human body—at an adult average of 120 mgTemplate:Efn—is nevertheless exceeded only by zinc (2500 mg) and iron (4000 mg) among the heavy metals.Template:Sfn Lead salts are very efficiently absorbed by the body.Template:Sfn A small amount of lead (1%) is stored in bones; the rest is excreted in urine and feces within a few weeks of exposure. Only about a third of lead is excreted by a child. Continual exposure may result in the bioaccumulation of lead.Template:Sfn

Toxicity

Lead is a highly poisonous metal (whether inhaled or swallowed), affecting almost every organ and system in the human body.Template:Sfn At airborne levels of 100 mg/m³, it is immediately dangerous to life and health.Template:Sfn Most ingested lead is absorbed into the bloodstream.Template:Sfn The primary cause of its toxicity is its predilection for interfering with the proper functioning of enzymes. It does so by binding to the sulfhydryl groups found on many enzymes,Template:Sfn or mimicking and displacing other metals which act as cofactors in many enzymatic reactions.Template:Sfn The essential metals that lead interacts with include calcium, iron, and zinc.Template:Sfn High levels of calcium and iron tend to provide some protection from lead poisoning; low levels cause increased susceptibility.Template:Sfn

Effects

Lead can cause severe damage to the brain and kidneys and, ultimately, death. By mimicking calcium, lead can cross the blood–brain barrier. It degrades the myelin sheaths of neurons, reduces their numbers, interferes with neurotransmission routes, and decreases neuronal growth.Template:Sfn 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 microcytic anemia.Template:Sfn

A chart of a human body with arrows pointing pieces of text to different parts of the body

Symptoms of lead poisoning

Symptoms of lead poisoning include nephropathy, colic-like abdominal pains, and possibly weakness in the fingers, wrists, or ankles. Small blood pressure increases, particularly in middle-aged and older people, may be apparent and can cause anemia.Template:Citation needed Several studies, mostly cross-sectional, found an association between increased lead exposure and decreased heart rate variability.Template:Sfn In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure has been shown to reduce fertility in males.Template:Sfn

In a child's developing brain, lead interferes with synapse formation in the cerebral cortex, neurochemical development (including that of neurotransmitters), and the organization of ion channels.Template:Sfn Early childhood exposure has been linked with an increased risk of sleep disturbances and excessive daytime drowsiness in later childhood.Template:Sfn High blood levels are associated with delayed puberty in girls.Template:Sfn The rise and fall in exposure to airborne lead from the combustion of tetraethyl lead in gasoline during the 20th century has been linked with historical increases and decreases in crime levels.Template:Citation needed

Exposure sources

Lead exposure is a global issue since lead mining and smelting, and battery manufacturing, disposal, and recycling, are common in many countries. Lead enters the body via inhalation, ingestion, or skin absorption. Almost all inhaled lead is absorbed into the body; for ingestion, the rate is 20–70%, with children absorbing a higher percentage than adults.Template:Sfn

Poisoning typically results from ingestion of food or water contaminated with lead, and less commonly after accidental ingestion of contaminated soil, dust, or lead-based paint.Template:Sfn Seawater products can contain lead if affected by nearby industrial waters.Template:Sfn Fruit and vegetables can be contaminated by high levels of lead in the soils they were grown in. Soil can be contaminated through particulate accumulation from lead in pipes, lead paint, residual emissions from leaded gasoline.Template:Sfn

The use of lead for water pipes is a problem in areas with soft or acidic water.Template:Sfn Hard water forms insoluble protective layers on the inner surface of the pipes, whereas soft and acidic water dissolves the lead pipes.Template:Sfn Dissolved carbon dioxide in the carried water may result in the formation of soluble lead bicarbonate; oxygenated water may similarly dissolve lead as lead(II) hydroxide. Drinking such water, over time, can cause health problems due to the toxicity of the dissolved lead. The harder the water the more calcium bicarbonate and sulfate it contains, and the more the inside of the pipes are coated with a protective layer of lead carbonate or lead sulfate.Template:Sfn

File:Kymographic recording of the effect of lead on frog heart..jpg

Kymographic recording of the effect of lead acetate on frog heart experimental set up

Ingestion of applied lead-based paint is the major source of exposure for children: a direct source is chewing on old painted window sills. Additionally, as lead paint on a surface deteriorates, it peels and is pulverized into dust. The dust then enters the body through hand-to-mouth contact or contaminated food or drink. Ingesting certain home remedies may result in exposure to lead or its compounds.Template:Sfn

Inhalation is the second major exposure pathway, affecting smokers and especially workers in lead-related occupations.Template:Sfn Cigarette smoke contains, among other toxic substances, radioactive lead-210.Template:Sfn "As a result of EPA's regulatory efforts, levels of lead in the air [in the United States] decreased by 86 percent between 2010 and 2020."<ref name="EPSLAP">Template:Cite web</ref> The concentration of lead in the air in the United States fell below the national standard of 0.15 μg/m³<ref name="EPAleadStandards">Template:Cite web</ref> in 2014.<ref name="EPALeadTrends">Template:Cite web</ref>

Skin exposure may be significant for people working with organic lead compounds. The rate of skin absorption is lower for inorganic lead.Template:Sfn

Lead in foods

Lead may be found in food when food is grown in soil that is high in lead, airborne lead contaminates the crops, animals eat lead in their diet, or lead enters the food either from what it was stored or cooked in.<ref>Template:Cite book</ref> Ingestion of lead paint and batteries is also a route of exposure for livestock, which can subsequently affect humans.<ref>Template:Cite journal</ref> Milk produced by contaminated cattle can be diluted to a lower lead concentration and sold for consumption.<ref>Template:Cite journal</ref>

In Bangladesh, lead compounds have been added to turmeric to make it more yellow.<ref name=Stan2019>Template:Cite news</ref> This is believed to have started in the 1980s and continues Template:As of.<ref name=Stan2019/> It is believed to be one of the main sources of high lead levels in the country.<ref>Template:Cite news</ref> In Hong Kong the maximum allowed lead level in food is 6 parts per million in solids and 1 part per million in liquids.<ref>Template:Cite web</ref>

Lead-containing dust can settle on drying cocoa beans when they are set outside near polluting industrial plants.<ref>Template:Cite web</ref> In December 2022, Consumer Reports tested 28 dark chocolate brands and found that 23 of them contained potentially harmful levels of lead, cadmium or both. They have urged the chocolate makers to reduce the level of lead which could be harmful, especially to a developing fetus.<ref>Template:Cite web</ref>

In March 2024, the US Food and Drug Administration recommended a voluntary recall on 6 brands of cinnamon due to contamination with lead,<ref>Template:Cite web</ref> after 500 reports of child lead poisoning.<ref>Template:Cite news</ref> The FDA determined that cinnamon was adulterated with lead chromate.<ref>Template:Cite web</ref>

Lead in plastic toys

According to the United States Center for Disease Control, the use of lead in plastics has not been banned as of 2024. Lead softens the plastic and makes it more flexible so that it can go back to its original shape. Habitual chewing on colored plastic insulation from stripped electrical wires was found to cause elevated lead levels in a 46-year-old man.<ref>Template:Cite web</ref> Lead may be used in plastic toys to stabilize molecules from heat. Lead dust can be formed when plastic is exposed to sunlight, air, and detergents that break down the chemical bond between the lead and plastics.<ref>Template:Cite web</ref>

Treatment

Template:See also Treatment for lead poisoning normally involves the administration of dimercaprol and succimer.Template:Sfn Acute cases may require the use of disodium calcium edetate, the calcium chelate, and the disodium salt of ethylenediaminetetraacetic acid (EDTA). It has a greater affinity for lead than calcium, with the result that lead chelate is formed by exchange and excreted in the urine, leaving behind harmless calcium.Template:Sfn

Environmental effects

A dusty dump

Battery collection site in Dakar, Senegal, where at least 18 children died of lead poisoning in 2008

The extraction, production, use, and disposal of lead and its products have caused significant contamination of the Earth's soils and waters. Atmospheric emissions of lead were at their peak during the Industrial Revolution, and the leaded gasoline period in the second half of the twentieth century.Template:Sfn

Lead releases originate from natural sources (i.e., concentration of the naturally occurring lead), industrial production, incineration and recycling, and mobilization of previously buried lead.Template:Sfn In particular, as lead has been phased out from other uses, in the Global South, lead recycling operations designed to extract cheap lead used for global manufacturing have become a well documented source of exposure.Template:Sfn Elevated concentrations of lead persist in soils and sediments in post-industrial and urban areas; industrial emissions, including those arising from coal burning,Template:Sfn continue in many parts of the world, particularly in the developing countries.Template:Sfn

Lead can accumulate in soils, especially those with a high organic content, where it remains for hundreds to thousands of years. Environmental lead can compete with other metals found in and on plant surfaces potentially inhibiting photosynthesis and at high enough concentrations, negatively affecting plant growth and survival. Contamination of soils and plants can allow lead to ascend the food chain affecting microorganisms and animals. In animals, lead exhibits toxicity in many organs, damaging the nervous, renal, reproductive, hematopoietic, and cardiovascular systems after ingestion, inhalation, or skin absorption.Template:Sfn Fish uptake lead from both water and sediment;Template:Sfn bioaccumulation in the food chain poses a hazard to fish, birds, and sea mammals.Template:Sfn

Anthropogenic lead includes lead from shot and sinkers. These are among the most potent sources of lead contamination along with lead production sites.Template:Sfn Lead was banned for shot and sinkers in the United States in 2017,Template:Sfn although that ban was only effective for a month,Template:Sfn and a similar ban is being considered in the European Union.Template:Sfn

Analytical methods for the determination of lead in the environment include spectrophotometry, X-ray fluorescence, atomic spectroscopy, and electrochemical methods. A specific ion-selective electrode has been developed based on the ionophore S,S'-methylenebis(N,N-diisobutyldithiocarbamate).Template:Sfn An important biomarker assay for lead poisoning is δ-aminolevulinic acid levels in plasma, serum, and urine.Template:Sfn

Restriction and remediation

An X-ray picture with numerous small pellets highlighted in white

Radiography of a swan found dead in Condé-sur-l'Escaut (northern France), highlighting lead shot. There are hundreds of lead pellets (a dozen is enough to kill an adult swan within a few days). Such bodies are sources of environmental contamination by lead.

By the mid-1980s, there was significant decline in the use of lead in industry.<ref>Template:Cite web</ref> In the United States, environmental regulations reduced or eliminated the use of lead in non-battery products, including gasoline, paints, solders, and water systems. Particulate control devices were installed in coal-fired power plants to capture lead emissions.Template:Sfn In 1992, U.S. Congress required the Environmental Protection Agency to reduce the blood lead levels of the country's children.Template:Sfn Lead use was further curtailed by the European Union's 2003 Restriction of Hazardous Substances Directive.Template:Sfn A large drop in lead deposition occurred in the Netherlands after the 1993 national ban on use of lead shot for hunting and sport shooting: from 230 tonnes in 1990 to 47.5 tonnes in 1995.Template:Sfn The usage of lead in Avgas 100LL for general aviation is allowed in the EU as of 2022.<ref name="q566">Template:Cite web</ref>

In the United States, the permissible exposure limit for lead in the workplace, comprising metallic lead, inorganic lead compounds, and lead soaps, was set at 50 μg/m³ over an 8-hour workday, and the blood lead level limit at 5 μg per 100 g of blood in 2012.Template:Sfn Lead may still be found in harmful quantities in stoneware,Template:Sfn vinyl Template:Sfn (such as that used for tubing and the insulation of electrical cords), and Chinese brass.Template:Efn Old houses may still contain lead paint.Template:Sfn White lead paint has been withdrawn from sale in industrialized countries, but specialized uses of other pigments such as yellow lead chromate remain,Template:Sfn especially in road pavement marking paint.<ref>Template:Cite web</ref> Stripping old paint by sanding produces dust which can be inhaled.Template:Sfn Lead abatement programs have been mandated by some authorities in properties where young children live.Template:Sfn The usage of lead in Avgas 100LL for general aviation is generally allowed in United States as of 2023.<ref>Template:Cite web</ref>

Lead waste, depending on the jurisdiction and the nature of the waste, may be treated as household waste (to facilitate lead abatement activities),Template:Sfn or potentially hazardous waste requiring specialized treatment or storage.Template:Sfn Lead is released into the environment in shooting places and a number of lead management practices have been developed to counter the lead contamination.Template:Sfn Lead migration can be enhanced in acidic soils; to counter that, it is advised soils be treated with lime to neutralize the soils and prevent leaching of lead.Template:Sfn

Research has been conducted on how to remove lead from biosystems by biological means: Fish bones are being researched for their ability to bioremediate lead in contaminated soil.Template:Sfn Template:Sfn The fungus Aspergillus versicolor is effective at absorbing lead ions from industrial waste before being released to water bodies.Template:Sfn Several bacteria have been researched for their ability to remove lead from the environment, including the sulfate-reducing bacteria Desulfovibrio and Desulfotomaculum, both of which are highly effective in aqueous solutions.Template:Sfn Millet grass Urochloa ramosa has the ability to accumulate significant amounts of metals such as lead and zinc in its shoot and root tissues making it an important plant for remediation of contaminated soils.<ref>Template:Cite journal</ref>

Notes

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References

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Bibliography

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External links

Template:AmCyc Poster Template:Wiktionary Template:Commons

Template:Portal bar Template:Periodic table (navbox) Template:Lead compounds Template:Authority control

Physical properties

Atomic

Bulk

Isotopes

Chemistry

Inorganic compounds

Lead(II)

Lead(IV)

Other oxidation states

Organolead

Origin and occurrence

In space

On Earth

Etymology

History

Prehistory and early history

Classical era

Confusion with tin and antimony

Middle Ages and the Renaissance

Outside Europe and Asia

Industrial Revolution

Modern era

Production

Primary

Two-stage process

Direct process

Alternatives

Secondary

Applications

Elemental form

Batteries

Coating for cables

Compounds

Biological effects

Toxicity

Effects

Exposure sources

Lead in foods

Lead in plastic toys

Treatment

Environmental effects

Restriction and remediation

See also

Notes

References

Bibliography

Further reading

External links