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Lead () is a chemical element with the Chemical symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal density than most common materials. Lead is Mohs scale, Ductility, and has a relatively low melting point. When freshly cut, it appears shiny gray with a bluish tint, but it to dull gray on exposure 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 shown by its Amphoterism behavior: lead and react with both and bases, and it tends to form . Lead compounds usually occur in the +2 oxidation state rather than the +4 state common in lighter members of the carbon group, with exceptions mostly limited to organolead compounds. Like the lighter members of the group, lead can catenation, forming chains and polyhedral structures.
Easily extracted from its , lead was known to prehistoric peoples in the Near East. Galena is its principal ore and often contains silver, encouraging its widespread extraction and use in ancient Rome. Production declined after the fall of Rome and did not reach similar levels until the Industrial Revolution. Lead played a role in developing the printing press, as movable type could be readily cast from lead alloys. In 2014, annual global production was about ten million tonnes, over half from recycling. Lead's high density, low melting point, ductility, and resistance to Redox, together with its abundance and low cost, supported its extensive use in construction, plumbing, batteries, bullet, mass, , pewter, , , Tetraethyllead, and lead shielding.
Lead is a neurotoxin that accumulates in soft tissues and bones. It damages the nervous system, interferes with biological , and can cause neurological disorders ranging from behavioral problems to brain damage. It also affects cardiovascular and renal systems. Lead's toxicity was noted by ancient Greek and Roman writers, but became widely recognized in Europe in the late 19th century.
Lighter carbon-group congeners of lead form stable or metastable Allotropy with the tetrahedrally coordinated, covalent bond diamond cubic structure. In these elements, the Atomic orbital and Atomic orbital energy levels are close enough to allow mixing into four hybrid sp3 orbitals. In lead, however, the inert pair effect increases the separation between s- and p-orbitals so much that the energy gain from hybridization is insufficient to overcome this gap. Instead of a diamond cubic arrangement, lead forms metallic bonding in which only the p-electrons are delocalized and shared among Pb2+ ions. Consequently, lead adopts a face-centered cubic structure, similar to the divalent metals calcium and strontium.
Its close-packed face-centered cubic structure and high atomic mass give lead a density of 11.34 g/cm3, 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 high density is the origin of the idiom to go over like a lead balloon. Some rarer metals are denser: tungsten and gold are both 19.3 g/cm3, while osmium—the densest known metal—has a density of 22.59 g/cm3, nearly twice that of lead.
Lead is soft, with a Mohs scale of 1.5, and can be scratched with a fingernail. It is very malleable and moderately ductile. Its bulk modulus—a measure of resistance to compression—is 45.8 GPa, compared with 75.2 GPa for aluminium, 137.8 GPa for copper, and 160–169 GPa for Carbon steel. Lead's tensile strength is low, at 12–17 MPa (around six times lower than aluminium, ten times lower than copper, and fifteen times lower than mild steel). Strength can be increased by alloying with small amounts of copper or antimony.
Lead melts at 327.5 °C (621.5 °F), a relatively low melting point compared to most metals, and has a boiling point of 1749 °C (3180 °F), the lowest among the carbon-group elements. Its electrical resistivity at 20 °C is 192 ohm-meters, almost an order of magnitude higher than that of good conductors (copper: ; gold: ; aluminium: ). Lead becomes a superconductor below 7.19 Kelvin, which is the highest critical temperature among type-I superconductors and the third highest among the elemental superconductors.
With its high atomic number, lead is the heaviest element whose natural isotopes are considered stable; lead-208 is the heaviest stable nucleus known. This distinction previously belonged to bismuth (atomic number 83) until its sole primordial isotope, bismuth-209, was found in 2003 to decay extremely slowly. Although the four stable isotopes of lead could theoretically undergo alpha decay to mercury isotopes with an energy release, no such decay has been observed; their predicted half-lives range from 1035 to 10189 years, at least 1025 times the current age of the universe.
Three of lead's stable isotopes—lead-206, lead-207, and lead-208—are the end products of the three major natural : the uranium chain (from uranium-238), the actinium chain (from uranium-235), and the thorium chain (from thorium-232), respectively. The isotopic composition of a rock sample depends on the presence of these parent isotopes; for example, lead-208 abundance can vary from about 52% in ordinary samples to as much as 90% in thorium ores. For this reason, the standard atomic weight of lead is reported to only one decimal place. Over time, the ratios of these isotopes to lead-204 increase as they are produced by radioactive decay. These variations allow for lead–lead and uranium–lead dating. Lead-207 exhibits nuclear magnetic resonance, a property used to study its compounds in both solution and solid states, including in biological systems such as the human body.
Lead reacts with fluorine at room temperature to form lead(II) fluoride. Its reaction with chlorine is similar but requires heating, as the resulting chloride layer reduces further reactivity. Molten lead combines with the to produce lead(II) chalcogenides.
The metal resists attack by sulfuric acid and phosphoric acid but not by hydrochloric or ; the difference arises from the insolubility and subsequent passivation of certain lead salts. Organic acids, such as acetic acid, dissolve lead in the presence of oxygen. Concentrated can also dissolve lead, producing .
The electronegativity values further reflect this behavior: lead(II) has a value of 1.87, and lead(IV) has 2.33. This represents a reversal in the general trend of increasing stability of the +4 oxidation state down the carbon group; by comparison, tin has electronegativities of 1.80 (+2 state) and 1.96 (+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 Ion. 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 phase, 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 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 plumbocene.
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 Haloalkane 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, 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, 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, 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.
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.
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 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. Lead mining occurred in central Europe, Roman Britain, Balkans, Greece, Anatolia, Hispania, the latter accounting for 40% of world production. Lead tablets were commonly used as a material for letters. Lead coffins, 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 slinger, used as mercenaries in Carthaginian and Roman armies, were famous for their shooting distance and accuracy.
Lead was used for making water pipes 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, warfare. Writers of the time, such as Cato the Elder, Columella, and Pliny the Elder, recommended lead (and lead-coated) vessels for the preparation of Grape syrup 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.
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 lead pipes 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 Adulterant 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, sulfur, which oxidizes the impurities except for silver, gold, 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. Shotgun cartridges used for waterfowl hunting must today be lead-free in the United States, Canada, and in Europe.
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, 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 lubricating qualities. Being practically insoluble in copper, the lead forms solid globules in imperfections throughout the alloy, such as Grain boundary. 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 Photovoltaics cells and infrared detectors.
Symptoms of lead poisoning include Kidney disease, 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, 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 contains, and the more the inside of the pipes are 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. Tobacco 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.
In March 2024, the US Food and Drug Administration recommended a voluntary recall on 6 brands of cinnamon due to contamination with lead, after 500 reports of child lead poisoning. The FDA determined that cinnamon was adulterated with lead chromate.
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, Haematopoiesis, 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. The usage of lead in Avgas 100LL for general aviation is generally allowed in United States as of 2023.
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.
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. 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.
Treatment
Treatment for lead poisoning normally involves the administration of dimercaprol and succimer. Acute cases may require the use of disodium calcium edetate, the calcium Chelation, 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.
Environmental effects
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.
Restriction and remediation
By the mid-1980s, there was significant decline in the use of lead in industry. In the United States, environmental regulations reduced or eliminated the use of lead in non-battery products, including gasoline, paints, solders, and water systems. Scrubber were installed in coal-fired power plants to capture lead emissions. In 1992, U.S. Congress required the Environmental Protection Agency to reduce the blood lead levels of the country's children. Lead use was further curtailed by the European Union's 2003 Restriction of Hazardous Substances Directive. 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. The usage of lead in Avgas 100LL for general aviation is allowed in the EU as of 2022.
See also
Notes
Bibliography
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Further reading
(2025). 9783110441079, De Gruyter. ISBN 9783110441079 Table of contents
External links
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