Lead: Difference between revisions

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Lead [[mining]] and [[smelting]] began in the [[New World]] almost as soon as the first colonists were settled. By [[1621]] the metal was being mined and forged in [[Virginia]]. The low melting temperature of lead made it highly malleable, even at the most primitive forges. Furthermore, lead's resistance to [[corrosion]] greatly enhanced its strength and durability. Technological progress in the [[American colonies]] and the American republic was to owe a great deal to this useful and abundant metal.
Lead [[mining]] and [[smelting]] began in the [[New World]] almost as soon as the first colonists were settled. By [[1621]] the metal was being mined and forged in [[Virginia]]. The low melting temperature of lead made it highly malleable, even at the most primitive forges. Furthermore, lead's resistance to [[corrosion]] greatly enhanced its strength and durability. Technological progress in the [[American colonies]] and the American republic was to owe a great deal to this useful and abundant metal.
===Lead in Modern Times===
===Lead in Modern Times===
By the [[twentieth century]], the U.S. had emerged as the world's leading producer and consumer of refined lead. According to the [[National Academy of Science]]'s report on Lead in the Human Environment, the [[United States]] was by 1980 consuming about 1.3 million tons of lead per year. This quantity, which represents roughly 40 percent of the world's supply, translates into a usage rate of 5,221 grams of lead per American per annum: a rate of dependence on lead and lead-containing products nearly ten times greater than that of the ancient Romans! According to Jerome O. Nriagu, the world's leading authority on lead poisoning in antiquity, the comparable Roman rate of lead usage was approximately 550 grams per person per year.
By the [[twentieth century]], the U.S. had emerged as the world's leading producer and consumer of refined lead. According to the [[National Academy of Science]]'s report on Lead in the Human Environment, the [[United States]] was by 1980 consuming about 1.3 million tons of lead per year. This quantity, which represents roughly 40 percent of the world's supply, translates into a usage rate of 5,221 grams of lead per American per annum: a rate of dependence on lead and lead-containing products nearly ten times greater than that of the ancient Romans! According to Jerome O. Nriagu, the world's leading authority on lead poisoning in antiquity, the comparable Roman rate of lead usage was approximately 550 grams per person per year.


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===Forms===
===Forms===
Natural lead is a mixture of four stable isotopes: <sup>204</sup>Pb (1.48%), <sup>206</sup>Pb (23.6%), <sup>207</sup>Pb (22.6%), and <sup>208</sup>Pb (52.3%). Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements: <sup>206</sup>Pb for the uranium series, <sup>207</sup>Pb for the actinium series, and <sup>208</sup>Pb for the thorium series. Twenty seven other isotopes of lead, all of which are radioactive, are recognized.
Natural lead is a mixture of four stable isotopes: <sup>204</sup>Pb (1.48%), <sup>206</sup>Pb (23.6%), <sup>207</sup>Pb (22.6%), and <sup>208</sup>Pb (52.3%). Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements: <sup>206</sup>Pb for the uranium series, <sup>207</sup>Pb for the actinium series, and <sup>208</sup>Pb for the thorium series. Twenty seven other isotopes of lead, all of which are radioactive, are recognized.
==Uses==
==Uses==
Its alloys include solder, type metal, and various antifriction metals. Great quantities of lead, both as the metal and as the dioxide, are used in storage batteries. Much metal also goes into cable covering, plumbing, ammunition, and in the manufacture of tetraethyl lead, (CH<sub>3</sub>CH<sub>2</sub>)<sub>4</sub>Pb.
Its alloys include solder, type metal, and various antifriction metals. Great quantities of lead, both as the metal and as the dioxide, are used in storage batteries. Much metal also goes into cable covering, plumbing, ammunition, and in the manufacture of tetraethyl lead, (CH<sub>3</sub>CH<sub>2</sub>)<sub>4</sub>Pb.
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Lead oxide is used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. The nitrate and the acetate are soluble salts. Lead salts such as lead arsenate have been used as insecticides, but their use in recent years has been practically eliminated in favor of less harmful organic compounds.  
Lead oxide is used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. The nitrate and the acetate are soluble salts. Lead salts such as lead arsenate have been used as insecticides, but their use in recent years has been practically eliminated in favor of less harmful organic compounds.  


====Lead Paint====
===Lead Paint===
In more recent years lead was widely used to extend the protective properties of [[paints]], helped automobiles attain better fuel efficiency, protected occupation ally exposed workers from harmful [[radiation]] and provided a suitably dense material for [[ammunition]] and [[fishing]] weights. Even though it is no longer used in many of these applications, millions of homes remain painted with lead paint. It's been estimated that (as of 2008) a large percentage of the residential housing in San Francisco which was built prior to 1978 probably has lead-based paint. Lead-based paint chips, as well as soil and household dust contaminated with lead are the primary sources of childhood lead poisoning.
In more recent years lead was widely used to extend the protective properties of [[paints]], helped automobiles attain better fuel efficiency, protected occupation ally exposed workers from harmful [[radiation]] and provided a suitably dense material for [[ammunition]] and [[fishing]] weights. Even though it is no longer used in many of these applications, millions of homes remain painted with lead paint. It's been estimated that (as of 2008) a large percentage of the residential housing in San Francisco which was built prior to 1978 probably has lead-based paint. Lead-based paint chips, as well as soil and household dust contaminated with lead are the primary sources of childhood lead poisoning.
====Lead as a fuel additive====
Not the least significant of those U.S. lead uses, although the one subject to the sharpest decline in the past decades, has been in the automotive industry. Since 1923 -- with a brief interruption in [[1925]] -- the U.S. has made extensive use of [[tetraethyl lead]] as an anti-knock, octane-boosting gasoline additive
Considerable ballyhoo surrounded the introduction of tetraethyl lead in the early [[1920s]]. Iodine, aniline, selenium, and other substances had all fallen by the wayside in the frantic search for a fuel additive that would improve engine performance and reduce engine knock.
Then in December [[1921]], three [[General Motors]] engineers -- [[Charles Kettering]], [[Thomas Midgeley]], and [[Thomas Boyd]] -- reported tremendous success with their first test of tetraethyl lead. Through the [[Ethyl corporation]], then a GM subsidiary, GM quickly began touting this lead compound as the virtual savior of the American [[automobile industry]].
The discovery was indeed extremely important. It paved the way for the development of the high-power, high-compression [[internal combustion engine]]s that were to win [[World War II]] and dominate the U.S. automotive industry until the early [[1970s]].
Unfortunately, the use of tetraethyl lead created almost as many problems as it solved. The first danger sign was the mysterious illness that forced Thomas Midgeley to spend weeks convalescing in the winter of [[1923]]. Midgeley had been experimenting rather recklessly with the various methods of manufacturing tetraethyl lead, and he did not at first realize just how dangerous the substance was in its concentrated liquid state.
The deadliness of tetraethyl lead was sadly confirmed in the summer of [[1924]]. Workers engaged in producing the additive fell sick and died at several refineries in New Jersey and Ohio. Banner headlines greeted each new fatality until a total of 15 workers had lost their lives -- and their minds.
Terrifying rumors circulated about the madness that had put some of the doomed into straitjackets before it put them six feet under. It was not long before journalists were calling leaded fuel "loony gas." Ironically, the gas in question was routinely dyed "a wine color" that made it reminiscent in more ways than one of something served at a Roman orgy.
In May 1925, the [[Surgeon General]] temporarily suspended the production and sale of leaded gasoline. He appointed a panel of experts to investigate the recent fatalities that had "occurred in the manufacture and mixing of the concentrated tetraethyl lead." The panel was also asked to weigh "the possible danger" that might arise "from...wide distribution of a lead compound" through its sale as a gasoline additive.
Industry dominated the Surgeon General's investigatory committee, which included only one genuine environmental visionary, [[Dr. Alice Hamilton]] of [[Harvard University]]. The [[Coolidge Administration]] gave the panel just seven months to design, run, and analyze its tests.
The committee's final report, published in June [[1926]], complained of the time constraints under which it had been forced to operate. Seven months was "not sufficient," argued the panel, "to produce detectable symptoms of lead poisoning" in experimental subjects because of the very slow gestation of that toxicological syndrome.
Nevertheless, the Surgeon General's panel ruled that there were "no good grounds for prohibiting the use of ethyl gasoline...as a motor fuel, provided that its distribution and use are controlled by proper regulations." The coming decades of [[Depression]], total war, and post-war boom were hardly conducive to the implementation of "proper regulations" for leaded gasoline. Indeed, no compulsory standards were set for the industry until the early 1970s when [[EPA]] began its long, hard struggle to phase down lead levels in U.S. gasoline.
One saturnine prophecy marred the otherwise sanguine 1926 report to the Surgeon General. By [[1985]] these words were to reverberate with particular resonance down the corridors of time:
<blockquote>
"It remains possible that, if the use of leaded gasolines becomes widespread, conditions may arise very different from those studied by us which would render its use more of a hazard than would appear to be the case from this investigation. Longer experience may show that even such slight storage of lead as was observed [among human guinea pigs] in these [1925] studies may lead eventually to recognizable lead poisoning or to chronic degenerative diseases of a less obvious character. In view of such possibilities the committee feels that the investigation begun under their direction must not be allowed to lapse.... With the experience obtained and the exact methods now available, it should be possible to follow closely the outcome of a more extended use of this fuel and to determine whether or not it may constitute a menace to the health of the general public after prolonged use or under conditions not now foreseen.... The vast increase in the number of automobiles throughout the country makes the study of all such questions a matter of real importance from the standpoint of [[public health]]."
</blockquote>
Needless to say, this advice fell on deaf ears during the gin-soaked, jazz-crazed [[Roaring Twenties]].
=====Voluntary restriction=====
In [[1927]] the Surgeon General set a voluntary standard for the oil industry to follow in mixing tetraethyl lead with gasoline. This standard -- 3 cubic centimeters per gallon (cc/g) -- corresponded to the maximum then in use among refiners, and thus imposed no real restraint. Even without prodding, however, the industry did take giant strides toward instituting safer working conditions in oil refineries, thereby protecting individual laborers in the microcosm of the workplace.
Three decades later, the Surgeon General actually raised the lead standard to 4 cc/g (equivalent of 4.23 grams per gallon). This voluntary standard once again represented the outside range of industry practice. Nevertheless, the Surgeon General concluded in 1958 that a loosening of the voluntary standard posed no threat to the health of the average American: "During the past 11 years, during which the greatest expansion of tetraethyl lead has occurred, there has been no sign that the average individual in the U.S. has sustained any measurable increase in the [[Blood lead levels|concentration of lead in his blood]] or in the daily output of lead in his [[urinalysis|urine]]."


The actual industry average during the 1950s and the 1960s hovered in the vicinity of 2.4 grams per total gallon. The [[Department of Health, Education and Welfare]] (HEW), which was home to the [[Surgeon General]] starting with the [[Kennedy Administration]], had authority over lead emissions under the [[Clean Air Act of 1963]]. The criteria mandated by this statute were still in the draft stage when the Act was reauthorized in [[1970]] and a new agency called [[EPA]] came into existence.
===Tetra-ethyl lead as a gasoline additive===


By then, the adverse effects of America's decades-old addiction to fossil fuel in general and leaded fuel in particular were becoming obvious to all. In January [[1971]], EPA's first Administrator, William D. Ruckelshaus, declared that "an extensive body of information exists which indicates that the addition of alkyl lead to gasoline...results in lead particles that pose a threat to public health."
{{main|Gasoline|Tetra-ethyl lead}}
Tetra-ethyl lead, commonly referred to as TEL, is a viscous liquid with the chemical formula (CH<sub>3</sub>CH<sub>2</sub>)<sub>4</sub>Pb.  Once widely used (circa 1925 to 1990) to increase the [[octane rating]] of [[gasoline]] ([[petrol]]), TEL usage in gasoline has been largely phased out by most nations primarily because of the toxicity of the lead [[emission]]s from [[internal combustion engine]]s burning gasoline containing TEL. Another reason for discontinuing TEL usage was that it degraded the efficiency of the [[catalytic converter]]s installed in automotive vehicles to reduce their emissions of [[Air pollution|air pollutants]].


It should be emphasized, however, that scientific evidence capable of documenting this conclusion did not exist in previous decades. Only very recently have scientists been able to prove that low-level lead exposure resulting from automobile emissions is harmful to human health in general, but especially to the health of children and pregnant women.
===Ammunition===


EPA took an emphatic stand on the issue in its final health document on the subject, "EPA's Position on the Health Implications of Airborne Lead," which was released on November 28, [[1973]]. This study confirmed what preliminary studies had already suggested: namely, that lead from automobile exhaust was posing a direct threat to public health. Under the Clean Air Amendments of 1970, that conclusion left EPA with no option but to control the use of lead as a fuel additive known to "endanger the public health or welfare."
The very next month, in December 1973, EPA issued regulations calling for a gradual reduction in the lead content of the total gasoline pool, which includes all grades of gasoline. The restrictions were scheduled to be implemented starting on January 1, 1975, and to extend over a five-year period. The average lead content of the total gasoline pool of each refinery was to be reduced from the level of approximately 2.0 grams per total gallon that prevailed in 1973 to a maximum of 0.5 grams per total gallon after January 1, 1979. Litigation was to postpone implementation of this phasedown for two years.
=====A viable alternative for fuel=====
Starting with the 1975 model year, U.S. automakers responded to EPA's lead phasedown timetable by equipping new cars with pollution-reducing catalytic converters designed to run only on unleaded fuel. Fittingly, a key component of these catalysts that were to be the undoing of lead was that noblest of [[noble metals]], [[platinum]].
EPA estimates that ambient lead levels dropped 64 percent between [[1975]] and [[1982]].
In 1982, with the introduction of unleaded gasoline well underway, EPA developed a new standard intended to apply strictly to leaded gasoline. In October of that year the agency promulgated a standard of 1.1 grams per leaded gasoline (gplg). This was roughly equivalent to the standard of 0.5 per total gallon that had become effective in 1980. But by focusing on leaded gallons only, EPA's new standard narrowed the range of lead content deviation and set the stage for significant reductions still to come.
On the basis of all that is known about the history of lead and its adverse effects on human health, it is impossible not to appreciate the EPA's decision to ban lead altogether from U.S. gasoline.
====Ammunition====
Lead, due to its density, has long been used as a military projectile, including as a sling bullet prior to the invention of firearms. While there are some reports of lead poisoning from bullets not removed from a living body, the kinetic effects of being shot usually far outweigh any chemical toxicity.<blockquote>Lead poisoning from a retained bullet or missile is rare and is usually  
Lead, due to its density, has long been used as a military projectile, including as a sling bullet prior to the invention of firearms. While there are some reports of lead poisoning from bullets not removed from a living body, the kinetic effects of being shot usually far outweigh any chemical toxicity.<blockquote>Lead poisoning from a retained bullet or missile is rare and is usually  
dependent on the location of the missile in a bone or immediately adjacent  
dependent on the location of the missile in a bone or immediately adjacent  
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==Health effects==
==Health effects==
Lead can be an acute and chronic poison. Lead compounds are more toxic than the metal, but the metal needs to be handled with care; respiratory protection is needed when aerosols of lead may be produced. <ref name=PbMSDS>{{citation
Lead can be an acute and chronic poison. Lead compounds are more toxic than the metal, but the metal needs to be handled with care; respiratory protection is needed when aerosols of lead may be produced. <ref name=PbMSDS>{{citation
  | url = http://www.jtbaker.com/msds/englishhtml/l2347.htm
  | url = http://www.jtbaker.com/msds/englishhtml/l2347.htm
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Transcutaneous absorption of inorganic lead is minimal. However, organic lead, such as tetraethyl lead found in leaded gasoline, may enter through the skin. Tetraethyl lead, the main organic compound in leaded gasoline, is converted in the body to triethyl lead and inorganic lead.
Transcutaneous absorption of inorganic lead is minimal. However, organic lead, such as tetraethyl lead found in leaded gasoline, may enter through the skin. Tetraethyl lead, the main organic compound in leaded gasoline, is converted in the body to triethyl lead and inorganic lead.
===Diagnosis and treatment of childhood lead poisoning===
===Diagnosis and treatment of childhood lead poisoning===
From a public health standpoint, the most serious concern is chronic lead poisoning in children. <ref name=Badawy2006 /> There are a number of suggestive physical symptoms, most notably a "lead line" along the gums. A thorough history is extremely important, to identify factors such as exposure to lead paint. Blood lead levels are the definitive test.
From a public health standpoint, the most serious concern is chronic lead poisoning in children. <ref name=Badawy2006 /> There are a number of suggestive physical symptoms, most notably a "lead line" along the gums. A thorough history is extremely important, to identify factors such as exposure to lead paint. Blood lead levels are the definitive test.


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===Behavioural effects===
===Behavioural effects===
[[Antisocial behaviour]]s and serious, violent criminal activities were shown to be correlated to male sex, [[poverty]], [[tobacco]] smoke exposure ''in utero'', and being reared by antisocial parents. A 2008 [[prospective study]] suggested that lead exposure in the womb and in early life was another important determinant of later life violence and antisocial behaviour.<ref name="pmid18507497">{{cite journal |author=Wright JP, Dietrich KN, Ris MD, ''et al'' |title=Association of prenatal and childhood blood lead concentrations with criminal arrests in early adulthood |journal=[[PLoS Med.]] |volume=5 |issue=5 |pages=e101 |year=2008 |month=May |pmid=18507497 |doi=10.1371/journal.pmed.0050101 |url=http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050101}}</ref>
[[Antisocial behaviour]]s and serious, violent criminal activities were shown to be correlated to male sex, [[poverty]], [[tobacco]] smoke exposure ''in utero'', and being reared by antisocial parents. A 2008 [[prospective study]] suggested that lead exposure in the womb and in early life was another important determinant of later life violence and antisocial behaviour.<ref name="pmid18507497">{{cite journal |author=Wright JP, Dietrich KN, Ris MD, ''et al'' |title=Association of prenatal and childhood blood lead concentrations with criminal arrests in early adulthood |journal=[[PLoS Med.]] |volume=5 |issue=5 |pages=e101 |year=2008 |month=May |pmid=18507497 |doi=10.1371/journal.pmed.0050101 |url=http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050101}}</ref>


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==References and notes==
==References and notes==
This article outline was originally sourced from http://periodic.lanl.gov/elements/82.html (Los Alamos National Labs)
and the history section from http://www.epa.gov/history/topics/perspect/lead.htm (Jack Lewis EPA Journal - May 1985) accessed on 3/22/08


{{Reflist|2}}
{{Reflist|2}}

Revision as of 12:10, 23 April 2009

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Lead
207.2(1) +2
+4
  Pb
82
[Xe]6s24f145d106p2 14,6,p
[ ? ] Post-Transition Metal:
Properties:
corrosion-resistant, dense, ductile, and malleable blue-gray transition metal
Hazard:
toxic


Lead is a chemical element, of the class of heavy metals, and is abundant in nature. Lead has the symbol Pb (from the Latin Plumbum). Its atomic number is 82. Lead is a very corrosion-resistant, dense, ductile, and malleable blue-gray metal that has been used for at least 5,000 years.[1] Template:TOC-left Early uses of lead included building materials, pigments for glazing ceramics, and pipes for transporting water. Prior to the early 1900s, uses of lead were primarily for ammunition, brass, burial vault liners, ceramic glazes, leaded glass and crystal, paints or other protective coatings, pewter, and water lines and pipes. The advent of the electrical age and communications, which were accelerated by technological developments in World War I, resulted in the addition of bearing metals, cable covering, caulking lead, solders, and type metal to the list of lead uses. With the growth in production of public and private motorized vehicles and the associated use of starting-lighting-ignition (SLI) lead-acid storage batteries and terne metal for gas tanks after World War I, demand for lead increased. Later, radiation shielding in medical analysis and video display equipment and as an additive in gasoline also increased usage.

History

Long known, mentioned in Exodus. The ancients regarded lead as the father of all metals, but the deity they associated with the substance was Saturn, the ghoulish titan who devoured his own young. The very word "saturnine," in its most specific meaning, applies to an individual whose temperament has become uniformly gloomy, cynical, and taciturn as the results of lead intoxication.

In the rigidly hierarchical world of the ancients, lead was the plebeian metal deemed suitable for a vast variety of everyday uses. . Lead products were, to a certain degree, accessible even to the poorest proletarian. But only the chosen few were at the top of the social totem pole were able to regularly indulge their insatiable craving for lead-containing products.

Lead was a key component in face powders, rouges, and mascaras; the pigment in many paints ("crazy as a painter" was an ancient catch phrase rooted in the demented behavior of lead-poisoned painters); a nifty spermicide for informal birth control; the ideal "cold" metal for use in the manufacture of chastity belts; a sweet and sour condiment popular for seasoning and adulterating food; a wine preservative perfect for stopping fermentation or disguising inferior vintages; the malleable and inexpensive ingredient in pewter cups, plates, pitchers, pots and pans, and other household artifacts; the basic component of lead coins; and a partial ingredient in debased bronze or brass coins as well as counterfeit silver and gold coins.

Most important of all was lead's suitability as inexpensive and reliable piping for the vast network plumbing that kept Rome and the provincial cities of the Roman Empire supplied with water. Indeed, the very word "plumbing" comes from the Latin word for lead, plumbum. The lead pipes that were the vital arteries of ancient Rome were forged by smithies whose patron saint, Vulcan, exhibited several of the symptoms of advanced lead poisoning: lameness, pallor, and wizened expression.

Addicted to Lead

The Romans were aware that lead could cause serious health problems, even madness and death. However, they were so fond of its diverse uses that they minimized the hazards it posed. Romans of yesteryear, like Americans of today, equated limited exposure to lead with limited risk. What they did not realize was that their everyday low-level exposure to the metal rendered them vulnerable to chronic lead poisoning, even while it spared them the full horrors of acute lead poisoning.

The symptoms of acute lead intoxication appeared most vividly among miners who were thrown into unhealthy intimacy with the metal on a daily basis. Romans reserved such debilitating and backbreaking labor for slaves. Some of these unfortunates were forced to spend all of their brief and blighted lives underground, out of sight and out of mind. The unpleasantness of lead mining was further neutralized late in the Empire when the practice was prohibited in Italy and consigned completely to the provinces.

Lead smelting, which had once been commonplace in every Roman city and town, eventually followed mining operations to the provinces. Italy, the heart of imperial Rome, grew tired of the noxious fumes emanating from lead smelting forges. The obvious damage to the health of smithies and their families was a matter of little or no concern.

Roman aristocrats, who regarded labor of any sort as beneath their dignity, lived oblivious to the human wreckage on which their ruinous diet of lead depended. They would never dream of drinking wine except from a golden cup, but they thought nothing of washing down platters of lead-seasoned food with gallons of lead-adulterated wine.

The result, according to many modern scholars, was the death by slow poisoning of the greatest empire the world has ever known. Symptoms of "plumbism" or lead poisoning were already apparent as early as the first century B.C. Julius Caesar for all his sexual ramblings was unable to beget more than one known offspring. Caesar Augustus, his successor, displayed not only total sterility but also a cold indifference to sex.

The first century A.D. was a time of unbridled gluttony and drunkenness among the ruling oligarchs of Rome. The lead concealed in the food and wine they devoured undoubtedly had a great deal to do with the outbreak of unprecedented epidemics of saturnine gout and sterility among aristocratic males and the alarming rate of infertility and stillbirths among aristocratic women.

Still more alarming was the conspicuous pattern of mental incompetence that came to be synonymous with the Roman elite. This creeping cretinism manifested itself most frighteningly in such clearly degenerate emperors as Caligula, Nero, and Commodus. It is said that Nero wore a breastplate of lead, ostensibly to strengthen his voice, as he fiddled and sang while Rome burned. Domitian, the last of the Flavian emperors, actually had a fountain installed in his palace from which he could drink a never-ending stream of leaded wine.

Medieval and Renaissance Lead

During the Middle Ages, lead was widely used by alchemists as a key component in procedures thought to be capable of generating gold from baser metals. Lead served an even more lofty function when leaded type launched Gutenberg's galaxy late in the fifteenth century. Mass printing was crucial to the eradication of ignorance that led to the upheavals of the Reformation and the Enlightenment. Lead could even be found in considerable quantities in decorative fixtures, roofs, pipes, and windows in the castles and cathedrals of Europe

Kinkier and more destructive uses of lead never lagged far behind. The advantages of the metal as an invisible and slow-acting poison were not lost on the Lucrezia Borgias and Catherine de Medicis of Renaissance Europe. Lead was known to be extremely convenient for eliminating inconvenient relatives. In fact, the world-weary French jokingly referred to the metal as poudre de la succession -- or succession powder. Another sinister latter-day use of lead was, of course, in the mass production of pistols, rifles, and cannons and the ammunition designed to blaze a bloody trail from their barrels.

Lead mining and smelting began in the New World almost as soon as the first colonists were settled. By 1621 the metal was being mined and forged in Virginia. The low melting temperature of lead made it highly malleable, even at the most primitive forges. Furthermore, lead's resistance to corrosion greatly enhanced its strength and durability. Technological progress in the American colonies and the American republic was to owe a great deal to this useful and abundant metal.

Lead in Modern Times

By the twentieth century, the U.S. had emerged as the world's leading producer and consumer of refined lead. According to the National Academy of Science's report on Lead in the Human Environment, the United States was by 1980 consuming about 1.3 million tons of lead per year. This quantity, which represents roughly 40 percent of the world's supply, translates into a usage rate of 5,221 grams of lead per American per annum: a rate of dependence on lead and lead-containing products nearly ten times greater than that of the ancient Romans! According to Jerome O. Nriagu, the world's leading authority on lead poisoning in antiquity, the comparable Roman rate of lead usage was approximately 550 grams per person per year.

Sources and properties

Lead is obtained chiefly from an ore called galena, which is primarily lead sulfide (PbS), by a roasting process. Anglesite, cerussite, and minim are other common lead minerals.

Properties

Lead is a bluish-white metal of bright luster. It is very soft, highly malleable, ductile, and a poor conductor of electricity. It is very resistant to corrosion; lead pipes bearing the insignia of Roman emperors, used as drains from the baths, are still in service. It is used in containers for corrosive liquids (such as sulfuric acid) and may be toughened by the addition of a small percentage of antimony or other metals.

Forms

Natural lead is a mixture of four stable isotopes: 204Pb (1.48%), 206Pb (23.6%), 207Pb (22.6%), and 208Pb (52.3%). Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements: 206Pb for the uranium series, 207Pb for the actinium series, and 208Pb for the thorium series. Twenty seven other isotopes of lead, all of which are radioactive, are recognized.

Uses

Its alloys include solder, type metal, and various antifriction metals. Great quantities of lead, both as the metal and as the dioxide, are used in storage batteries. Much metal also goes into cable covering, plumbing, ammunition, and in the manufacture of tetraethyl lead, (CH3CH2)4Pb.

The metal is very effective as a sound absorber, is used as a radiation shield around X-ray equipment and nuclear reactors, and is used to absorb vibration. White lead, the basic carbonate, sublimed white lead, chrome yellow, and other lead compounds are used extensively in paints, although in recent years the use of lead in paints has been drastically curtailed to eliminate or reduce health hazards.

Lead oxide is used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. The nitrate and the acetate are soluble salts. Lead salts such as lead arsenate have been used as insecticides, but their use in recent years has been practically eliminated in favor of less harmful organic compounds.

Lead Paint

In more recent years lead was widely used to extend the protective properties of paints, helped automobiles attain better fuel efficiency, protected occupation ally exposed workers from harmful radiation and provided a suitably dense material for ammunition and fishing weights. Even though it is no longer used in many of these applications, millions of homes remain painted with lead paint. It's been estimated that (as of 2008) a large percentage of the residential housing in San Francisco which was built prior to 1978 probably has lead-based paint. Lead-based paint chips, as well as soil and household dust contaminated with lead are the primary sources of childhood lead poisoning.

Tetra-ethyl lead as a gasoline additive

For more information, see: Gasoline and Tetra-ethyl lead.

Tetra-ethyl lead, commonly referred to as TEL, is a viscous liquid with the chemical formula (CH3CH2)4Pb. Once widely used (circa 1925 to 1990) to increase the octane rating of gasoline (petrol), TEL usage in gasoline has been largely phased out by most nations primarily because of the toxicity of the lead emissions from internal combustion engines burning gasoline containing TEL. Another reason for discontinuing TEL usage was that it degraded the efficiency of the catalytic converters installed in automotive vehicles to reduce their emissions of air pollutants.

Ammunition

Lead, due to its density, has long been used as a military projectile, including as a sling bullet prior to the invention of firearms. While there are some reports of lead poisoning from bullets not removed from a living body, the kinetic effects of being shot usually far outweigh any chemical toxicity.

Lead poisoning from a retained bullet or missile is rare and is usually

dependent on the location of the missile in a bone or immediately adjacent to a joint. A review of the literature revealed only 14 cases in which there was adequate laboratory documentation of plumbism caused by a retained bullet or missile. Only one of these previously reported cases resulted in death. We report a second death due to lead poisoning from a retained bullet

with elevated blood lead levels documented by toxicologic analysis.[2]

There is, however, concern about the environmental effects of large quantities of bullets and shotgun pellets in nature, and there have been efforts to remove lead from military firing ranges, where they may leach into groundwater. A number of programs, generically called "green bullets", have tried to replace lead with a less toxic metal, usually tungsten with nonmetalic material.[3] Questions have been raised, however, about the safety of tungsten. [4]

Health effects

Lead can be an acute and chronic poison. Lead compounds are more toxic than the metal, but the metal needs to be handled with care; respiratory protection is needed when aerosols of lead may be produced. [5]

With the reduction in lead tetraethyl, most lead poisoning is from inorganic compounds. In children, oral ingestion from contaminated hands or chewing lead-painted objects is most common, but it can be inhaled or absorbed through the skin.

Factors influencing absorption are coupled to the absorption of essential metal nutrients such as iron and calcium.[6] The amount absorbed is affected by factors including:

  • Amount of absorbable solution; acid media have greater absorption
  • Particle size. Smaller particles are more likely to be absorbed.
  • In the presence of deficiencies of iron, calcium, zinc, copper, and protein, lead absorption will increase.
  • High intake of fats and oils increase absorption, but leafy green vegetables and other nutrients decrease absorption.

Transcutaneous absorption of inorganic lead is minimal. However, organic lead, such as tetraethyl lead found in leaded gasoline, may enter through the skin. Tetraethyl lead, the main organic compound in leaded gasoline, is converted in the body to triethyl lead and inorganic lead.

Diagnosis and treatment of childhood lead poisoning

From a public health standpoint, the most serious concern is chronic lead poisoning in children. [6] There are a number of suggestive physical symptoms, most notably a "lead line" along the gums. A thorough history is extremely important, to identify factors such as exposure to lead paint. Blood lead levels are the definitive test.

With low to moderate levels, prevention, decontamination, and supportive measures usually suffice. At significant levels, after confirmatory retesting, chelation therapy is warranted, starting with oral succimer (an analog of dimercaprol), with parenteral edetate calcium disodium, then a combination of this agent and dimercaprol. These are not benign drugs and careful risk-benefit analysis is needed.

Behavioural effects

Antisocial behaviours and serious, violent criminal activities were shown to be correlated to male sex, poverty, tobacco smoke exposure in utero, and being reared by antisocial parents. A 2008 prospective study suggested that lead exposure in the womb and in early life was another important determinant of later life violence and antisocial behaviour.[7]

In the United States, low-level lead exposure in infancy is a major factor of attention deficit hyperactivity disorder (ADHD), coming slightly before prenatal tobacco exposure.[8] Lead exposure, as opposed to tobacco exposure through maternal smoking, is not a clear-cut issue. Subclinical hyperactivity and consecutive intellectual deficits may well be attributed to background levels of lead to which the whole population is exposed. In a sample of 97 children and teens diagnosed with ADHD, blood lead levels were correlated to hyperactivity-impulsiveness (but not inattention-disorganization), and this behavioural derangement was demonstrated to be causative of IQ deficits. It was concluded that lead impaired cognitive control and, neurophysiologically, the circuits connecting the striatum to the frontal cortex.[9]

References and notes

  1. ↑ Intro sourced from http://minerals.usgs.gov/minerals/pubs/commodity/lead/ accessed 4/03/2008
  2. ↑ DiMaio VJ, DiMaio SM, Garriott JC, Simpson P. (1983), "A fatal case of lead poisoning due to a retained bullet.", Am J Forensic Med Pathol 4 (2): 165-169;4(2):165-9. Links
  3. ↑ Pizza, Arthur R., "Green Bullet Program", U.S. Army
  4. ↑ Deputy Assistant Secretary of Defense for Force Health Protection and Readiness Policy and Programs (August 28, 2008), Tungsten/Nickel/Cobalt Alloy Study
  5. ↑ Mallinckrodt/Baker Chemicals, Materials Data Safety Sheet: Lead Metal
  6. ↑ 6.0 6.1 Badawy, Mohamed K (Apr 20, 2006), "Toxicity, Lead", eMedicine
  7. ↑ Wright JP, Dietrich KN, Ris MD, et al (May 2008). "Association of prenatal and childhood blood lead concentrations with criminal arrests in early adulthood". PLoS Med. 5 (5): e101. DOI:10.1371/journal.pmed.0050101. PMID 18507497. Research Blogging.
  8. ↑ Braun JM, Kahn RS, Froehlich T, Auinger P, Lanphear BP (December 2006). "Exposures to environmental toxicants and attention deficit hyperactivity disorder in U.S. children". Environ. Health Perspect. 114 (12): 1904–9. PMID 17185283. PMC 1764142. [e]
  9. ↑ Nigg JT, Knottnerus GM, Martel MM, et al (February 2008). "Low blood lead levels associated with clinically diagnosed attention-deficit/hyperactivity disorder and mediated by weak cognitive control". Biol. Psychiatry 63 (3): 325–31. DOI:10.1016/j.biopsych.2007.07.013. PMID 17868654. Research Blogging.
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