Lead is a chemical element; it has symbol Pb (from Latin plumbum) and atomic number 82. It is a heavy metals that is density 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 to a dull gray color when exposed to air. Lead has the highest atomic number of any stable nuclide and three of its are endpoints of major nuclear of heavier elements.
Lead is a relatively unreactive post-transition metal. Its weak metallic character is illustrated by its amphoteric nature; lead and react with and bases, and it tends to form . 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 catenation; it can form chains and polyhedral structures.
Since lead is easily extracted from its , 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. 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 and lead shot, weights, , , , lead paint, leaded gasoline, and lead shielding.
Lead is a neurotoxin that accumulates in soft tissues and bones. It damages the nervous system and interferes with the function of biological , causing neurological disorders ranging from behavioral problems to brain damage, and also affects general health, cardiovascular, and renal systems. lead poisoning 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.
The sum of the first four ionization energies of lead exceeds that of tin, contrary to what periodic trends would predict. This is explained by relativistic effects, which become significant in heavier atoms, which contract s and p orbitals such that lead's 6s electrons have larger binding energies than its 5s electrons. 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.
Lead's lighter carbon group congeners form stable or metastable with the tetrahedrally coordinated and covalent bond diamond cubic structure. The energy levels of their outer s-orbital and 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. Rather than having a diamond cubic structure, lead forms metallic bonding in which only the p-electrons are delocalized and shared between the Pb2+ ions. Lead consequently has a face-centered cubic structure like the similarly sized divalent metals calcium and strontium.
Lead's close-packed face-centered cubic structure and high atomic weight result in a density 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). This density is the origin of the idiom to go over like a lead balloon. 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.
Lead is a very soft metal with a Mohs hardness of 1.5; it can be scratched with a fingernail. It is quite malleable and somewhat ductile. 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. 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.
The melting point of lead—at 327.5 °C (621.5 °F)—is very low compared to most metals. Its boiling point of 1749 °C (3180 °F) is the lowest among the carbon-group elements. The electrical resistivity of lead at 20 °C is 192 ohm-meters, almost an order of magnitude higher than those of other industrial metals (copper at ; gold ; and aluminium at ). Lead is a superconductor at temperatures lower than 7.19 Kelvin; this is the highest critical temperature of all type-I superconductors and the third highest of the elemental superconductors.
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.) 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 years (at least 1025 times the current age of the universe).
Three of the stable isotopes are found in three of the four major : lead-206, lead-207, and lead-208 are the final decay products of uranium-238, uranium-235, and thorium-232, respectively. These decay chains are called the uranium chain, the actinium chain, and the thorium chain. 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; for this reason, the standard atomic weight of lead is given to only one decimal place. 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. Lead-207 exhibits nuclear magnetic resonance, a property that has been used to study its compounds in solution and solid state, including in the human body.
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, 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 of natural uranium-235, 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).
In total, 43 lead isotopes have been synthesized, with mass numbers 178–220. Lead-205 is the most stable radioisotope, with a half-life of around 1.70 years. 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.
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. Molten lead reacts with the to give lead(II) chalcogenides.
Lead metal resists sulfuric acid and phosphoric acid but not hydrochloric or nitric acid; the outcome depends on insolubility and subsequent passivation of the product salt. Organic acids, such as acetic acid, dissolve lead in the presence of oxygen. Concentrated will dissolve lead and form .
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.
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. There is no lead(II) hydroxide; increasing the pH of solutions of lead(II) salts leads to hydrolysis and condensation. 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.
Lead dihalides are well-characterized; this includes the diastatide 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). The other dihalides decompose on exposure to ultraviolet or visible light, especially the diiodide. Many lead(II) Pseudohalogen are known, such as the cyanide, cyanate, and thiocyanate. Lead(II) forms an extensive variety of halide coordination complexes, such as PbCl42−, PbCl64−, and the Pb2Cl9 n5 n− chain anion.
Lead(II) sulfate is insoluble in water, like the sulfates of other heavy divalent . Lead(II) nitrate and lead(II) acetate are very soluble, and this is exploited in the synthesis of other lead compounds.
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.
Negative oxidation states can occur as Zintl phases, as either free lead anions, as in Ba2Pb, with lead formally being lead(−IV), 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). 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. They may be made in liquid ammonia via the reduction of lead by sodium.
[[Carbon]]
[[Hydrogen]]
Lead|alt=A gray-green sphere linked to four black spheres, each, in turn, linked also to three white ones]]
Lead can form catenation, 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. With itself, lead can build metal–metal bonds of an order up to three. With carbon, lead forms organolead compounds similar to, but generally less stable than, typical organic compounds (due to the Pb–C bond being rather weak). This makes the organometallic chemistry of lead far less wide-ranging than that of tin. 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 PbCH(SiMe3)22 and Pb( η5-C5H5)2.
The lead analog of the simplest organic compound, methane, is plumbane. Plumbane may be obtained in a reaction between metallic lead and atomic hydrogen. Two simple derivatives, tetramethyllead and tetraethyllead, are the best-known organolead compounds. These compounds are relatively stable: tetraethyllead only starts to decompose if heated or if exposed to sunlight or ultraviolet light. With sodium metal, lead readily forms an equimolar alloy that reacts with to form organometallic compounds such as tetraethyllead. The oxidizing nature of many organolead compounds is usefully exploited: lead tetraacetate is an important laboratory reagent for oxidation in organic synthesis. Tetraethyllead, once added to automotive gasoline, was produced in larger quantities than any other organometallic compound, and is still widely used in avgas. Other organolead compounds are less chemically stable. For many organic compounds, a lead analog does not exist.
Solar System abundances ! style="text-align:center;" | Atomic number ! style="width:45%;" | Element ! style="padding-right: 5px; padding-left: 10px;" | 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 |
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-process and .
In the s-process (s is for "slow"), captures are separated by years or decades, allowing less stable nuclei to undergo beta decay. 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.
In the r-process (r is for "rapid"), captures happen faster than nuclei can decay. This occurs in environments with a high neutron density, such as a supernova or the merger of two . The neutron flux involved may be on the order of 1022 neutrons per square centimeter per second. The r-process does not form as much lead as the s-process. It tends to stop once neutron-rich nuclei reach 126 neutrons. At this point, the neutrons are arranged in complete shells in the atomic nucleus, and it becomes harder to energetically accommodate more of them. When the neutron flux subsides, these nuclei beta decay into stable isotopes of osmium, iridium, and platinum.
The main lead-bearing mineral is galena (PbS), which is mostly found with zinc ores. 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, and bismuth are common impurities in lead minerals.
World lead resources exceed two billion tons. Significant deposits are located in Australia, China, Ireland, Mexico, Peru, Portugal, Russia, and the 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, and Russia 6.4 million.
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 and 5 μg/L in freshwater and seawater.
There is no consensus on the origin of the Proto-Germanic *lauda-. One hypothesis suggests it is derived from Proto-Indo-European *lAudh- ('lead'; capitalization of the vowel is equivalent to the macron). Another hypothesis suggests it is borrowed from Proto-Celtic *ɸloud-io- ('lead'). This word is related to the Latin language plumbum, which gave the element its chemical symbol Pb. The word *ɸloud-io- is thought to be the origin of Proto-Germanic *bliwa- (which also means 'lead'), from which stemmed the German Blei.
The name of the chemical element is not related to the verb of the same spelling, which is derived from Proto-Germanic *laidijan- ('to lead').
Roman Republic 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. Roman metallurgy occurred in Central Europe, Roman Britain, the Balkans, Greece, Anatolia, and Hispania, the latter accounting for 40% of world production. Lead tablets were commonly used as a material for letters. , cast in flat sand forms and with interchangeable motifs to suit the faith of the deceased, were used in ancient Judea. 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.
Lead was used for making in the Roman Empire; the Latin word for the metal, plumbum, 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 corrosion ensured its widespread use in other applications, including pharmaceuticals, roofing, currency, and warfare. Writers of the time, such as Cato the Elder, Columella, and Pliny the Elder, recommended lead (or lead-coated) vessels for the preparation of Defrutum added to wine and food. The lead conferred an agreeable taste due to the formation of "sugar of lead" (lead(II) acetate), whereas copper or bronze vessels could impart a bitter flavor through verdigris formation.
The Roman author Vitruvius reported the health dangers of lead and modern writers have suggested that lead poisoning played a major role in the decline of the Roman Empire. Other researchers have criticized such claims, pointing out, for instance, that not all abdominal pain is caused by lead poisoning. According to archaeological research, Roman increased lead levels in tap water but such an effect was "unlikely to have been truly harmful". 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. Its status in Roman society was low as it was readily available and cheap.
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. In the European and Arabian traditions of alchemy, lead (symbol ♄ in the European tradition) 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. During the period, lead was used increasingly for adulteration 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. Lead was a key material in parts of the printing press, and lead dust was commonly inhaled by print workers, causing lead poisoning. 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. 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. 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 , a practice that continued long into the 20th century. The white faces of women "came to represent their feminine virtue as Japanese women", with lead commonly used in the whitener.
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.
In the 1970s, the United States and Western European countries introduced legislation to reduce lead air pollution. 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%. The main product made of lead by the end of the 20th century was the lead–acid battery.
From 1960 to 1990, lead output in the Western Bloc grew by about 31%. 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. 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. As was the case during European industrialization, lead has had a negative effect on health in China.
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.
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.
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. This impure lead oxide is reduced in a coke-fired blast furnace to the (again, impure) metal:
Impurities are mostly arsenic, antimony, bismuth, zinc, copper, silver, and gold. Typically they are removed in a series of Pyrometallurgy. The melt is treated in a reverberatory furnace with air, steam, and sulfur, which oxidizes the impurities except for silver, gold, and bismuth. Oxidized contaminants float to the dross and are skimmed off. 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. 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.
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. This is a high-cost process and thus mostly reserved for refining bullion containing high percentages of impurities.
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. 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.
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. 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.
Of the sources of lead for recycling, lead–acid batteries are the most important; lead pipe, sheet, and cable sheathing are also significant.
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. Concerns have been raised that lead bullets used for hunting can damage the environment.
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. It is used in scuba diving weight belts to counteract the diver's buoyancy. In 1993, the base of the Leaning Tower of Pisa was stabilized with 600 tonnes of lead. Because of its corrosion resistance, lead is used as a protective sheath for underwater cables.
Lead has many uses in the construction industry; lead sheets are used as architectural metals in roofing material, cladding, flashing, rain gutter and gutter joints, and on roof parapets. Lead is still used in statues and sculptures, including for armatures. In the past it was often used to tire balance; for environmental reasons this use is being phased out in favor of other materials.
Lead is added to copper alloys, such as brass and bronze, to improve machinability and for its lubricant 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.
Lead's high density, atomic number, and formability form the basis for use of lead as a barrier that absorbs sound, vibration, and radiation. Lead has no natural resonance frequencies; as a result, sheet-lead is used as a sound deadening layer in the walls, floors, and ceilings of sound studios. are often made from a lead alloy, mixed with various amounts of tin to control the tone of each pipe. Lead is an established lead shielding material from radiation in nuclear science and in X-ray rooms due to its denseness and high attenuation coefficient. Molten lead has been used as a coolant for lead-cooled fast reactors.
Other applications of lead compounds are very specialized and often fading. Lead-based coloring agents are used in and glass, especially for red and yellow shades. While lead paints are phased out in Europe and North America, they remain in use in less developed countries such as China, India, or Indonesia. 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. 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. Lead glass is composed of 12–28% lead oxide, changing its optical characteristics and reducing the transmission of ionizing radiation, a property used in old TVs and computer monitors with . Lead-based such as lead telluride and lead selenide are used in photovoltaic cells and infrared detectors.
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. Several studies, mostly cross-sectional, found an association between increased lead exposure and decreased heart rate variability. In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure has been shown to reduce fertility in males.
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 . Early childhood exposure has been linked with an increased risk of sleep disturbances and excessive daytime drowsiness in later childhood. High blood levels are associated with delayed puberty in girls. 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.
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. Seawater products can contain lead if affected by nearby industrial waters. 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, and residual emissions from leaded gasoline.
The use of lead for water pipes is plumbosolvency. Hard water forms insoluble protective layers on the inner surface of the pipes, whereas soft and acidic water dissolves the lead pipes. 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 hard water the more calcium bicarbonate and calcium sulfate it will contain, and the more the inside of the pipes will be coated with a protective layer of lead carbonate or lead sulfate.
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.
Inhalation is the second major exposure pathway, affecting smokers and especially workers in lead-related occupations. Cigarette smoke contains, among other toxic substances, radioactive lead-210. "As a result of EPA's regulatory efforts, levels of lead in the air in decreased by 86 percent between 2010 and 2020." The concentration of lead in the air in the United States fell below the national standard of 0.15 μg/m3 in 2014.
Skin exposure may be significant for people working with organic lead compounds. The rate of skin absorption is lower for inorganic lead.
In Bangladesh, lead compounds have been added to turmeric to make it more yellow. This is believed to have started in the 1980s and continues . It is believed to be one of the main sources of high lead levels in the country. In Hong Kong the maximum allowed lead level in food is 6 parts per million in solids and 1 part per million in liquids.
Lead-containing dust can settle on drying cocoa beans when they are set outside near polluting industrial plants. 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.
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. 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. Elevated concentrations of lead persist in soils and sediments in post-industrial and urban areas; industrial emissions, including those arising from coal burning, continue in many parts of the world, particularly in the developing countries.
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, kidney, reproductive, hematopoiesis, and cardiovascular systems after ingestion, inhalation, or skin absorption. Fish uptake lead from both water and sediment; bioaccumulation in the food chain poses a hazard to fish, birds, and sea mammals.
Anthropogenic lead includes lead from shot and Fishing sinker. These are among the most potent sources of lead contamination along with lead production sites. Lead was banned for shot and sinkers in the United States in 2017, although that ban was only effective for a month, and a similar ban is being considered in the European Union.
Analytical methods for the determination of lead in the environment include spectrophotometry, X-ray fluorescence, atomic spectroscopy and electrochemistry. A specific ion-selective electrode has been developed based on the ionophore S,S'-methylenebis (N,N-diisobutyldithiocarbamate). An important biomarker assay for lead poisoning is δ-aminolevulinic acid levels in plasma, serum, and urine.
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. Lead may still be found in harmful quantities in stoneware, Vinyl group (such as that used for tubing and the insulation of electrical cords), and Chinese brass. Old houses may still contain lead paint. White lead paint has been withdrawn from sale in industrialized countries, but specialized uses of other pigments such as yellow lead chromate remain, especially in road pavement marking paint.
Stripping old paint by sanding produces dust which can be inhaled. Lead abatement programs have been mandated by some authorities in properties where young children live.
Lead waste, depending on the jurisdiction and the nature of the waste, may be treated as household waste (to facilitate lead abatement activities), or potentially hazardous waste requiring specialized treatment or storage. Lead is released into the environment in shooting places and a number of lead management practices have been developed to counter the lead contamination. 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.
Research has been conducted on how to remove lead from biosystems by biological means: Fish bones are being researched for their ability to bioremediation lead in contaminated soil. The fungus Aspergillus versicolor is effective at absorbing lead ions from industrial waste before being released to water bodies. 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. 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 (Lakshmi et al., 2013).
Lead in plastic toys
Treatment
Environmental effects
Restriction and remediation
See also
Notes
Bibliography
Further reading
External links
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