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Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula lead(ethyl group)4. It was widely used as a fuel additive for much of the 20th century, first being mixed with gasoline beginning in the 1920s. This "leaded gasoline" had an increased octane rating that allowed engine compression to be raised substantially and in turn increased vehicle performance and fuel economy. TEL was first synthesized by German chemist Carl Jacob Löwig in 1853. American chemical engineer Thomas Midgley Jr., who was working for the U.S. corporation General Motors, was the first to discover its effectiveness as an Antiknock agent on December 9, 1921, after spending six years attempting to find an antiknock agent that was both highly effective and inexpensive.
Of the some 33,000 substances in total screened, lead was found to be the most effective antiknock agent, in that it necessitated the smallest concentrations necessary; a treatment of 1 part TEL to 1300 parts gasoline by weight is sufficient to suppress detonation. The four ethyl groups in the compound served to dissolve the active lead atom within the fuel. When injected into the combustion chamber, tetraethyllead decomposed upon heating into ethyl radicals, lead, and lead oxide. The lead oxide scavenges radicals and therefore inhibits a flame from developing until full compression has been achieved, allowing the optimal timing of Ignition timing, as well as the lowering of fuel consumption. Throughout the sixty year period from 1926 to 1985, an estimated 20 trillion liters of leaded gasoline at an average lead concentration of 0.4 g/L were produced and sold in the United States alone, or an equivalent of 8 million tons of inorganic lead, three quarters of which would have been emitted in the form of lead chloride and lead bromide. Estimating a similar amount of lead to have come from other countries' emissions, a total of more than 15 million tonnes of lead may have been released into the atmosphere.
In the mid-20th century, scientists discovered that TEL caused lead poisoning and was highly Neurotoxicity to the human brain, especially in children. Approximately 90% of the total lead in a human is present in the bones, deposited in the form of insoluble Lead(II) phosphate salt, with a half-life longer than twenty years. The United States and many other countries began phasing out the use of TEL in automotive fuel in the 1970s. With EPA guidance and oversight, the US achieved the total elimination of sales of leaded gasoline for on-road vehicles on January 1st, 1996.Newell R. G.; Rogers. K. The market-based lead-phasedown. Resources for the Future (Discussion paper) 2003, 3-37. By the early 2000s, most countries had banned the use of TEL in gasoline. In July 2021, the sale of leaded gasoline for cars was completely phased out worldwide following the termination of production by Algeria, prompting the United Nations Environment Program (UNEP) to declare an "official end" of its use in cars on August 30, 2021.
In 2011, researchers retroactively estimated the annual impact of tetraethyl lead worldwide to be the following: 1.1 million excess deaths, 322 million lost IQ points, 60+ million crimes, and 4% of worldwide GDP (around 2.4 trillion United States dollars per year).
The product is recovered by steam distillation, leaving a sludge of lead and sodium chloride. TEL is a Viscosity colorless liquid with a sweet odor.9788121934954, S. Chand Publishing. . ISBN 9788121934954 Because TEL is charge neutral and contains an exterior of alkyl groups, it is highly Lipophilicity and soluble in petrol (gasoline). This property, which allows it to dissolve so evenly and effectively in motor fuel, also allowed easy absorption by body fats and lipids and diffusion through the blood–brain barrier (BBB). The lead (II) ions (Pb2+) would accumulate within the limbic forebrain, frontal cortex, and hippocampus. (2025). 9780323033541 ISBN 9780323033541 Practically speaking, TEL is a "central nervous system toxin which produces an acute toxic psychosis."
There is no cure for direct poisoning by TEL. Inorganic lead compounds, such as those present in Exhaust gas, could be removed from the system through the administration of Chelation, which bind to the inorganic lead and flush them out of the body. However, highly lipid-soluble TEL cannot be removed this way, and treatments are of a supportive nature.
Despite decades of research, no reactions were found to improve upon this process; it is rather difficult, involves reactive metallic sodium, and converts only 25% of the lead to TEL. A related compound, tetramethyllead, was commercially produced by a different electrolytic reaction. However, tetramethyllead was even more difficult to make, and it did not find use beyond niche applications. A highly efficient pathway utilizing ethyl chloride with a slight excess of lithium was developed, with a TEL yield over lead of over 90%. However, by then the fuel additive had started to fall out of favor and into disrepute, and the process was never put into practice.
When TEL burns, it produces not only carbon dioxide and water, but also lead and lead(II) oxide:
Pb and PbO would quickly over-accumulate and foul an engine. For this reason, 1,2-dichloroethane and 1,2-dibromoethane were also added to gasoline as lead scavengers—these agents form volatile lead(II) chloride and lead(II) bromide, respectively, which flush the lead from the engine and into the air:
In 1935 a license to produce TEL was given to IG Farben, enabling the newly formed German Luftwaffe to use high-octane gasoline for high altitude flight. A company, Ethyl GmbH, was formed that produced TEL at two sites in Germany with a government contract from 10 June 1936.Rainer Karlsch, Raymond G. Stokes. "Faktor Öl". Die Mineralölwirtschaft in Deutschland 1859–1974. C. H. Beck, München, 2003, , p. 187.
In 1938 the United Kingdom Air Ministry contracted with ICI for the construction and operation of a TEL plant. A site was chosen at Holford Moss, near Plumley in Cheshire. Construction started in April 1939 and TEL was being produced by September 1940.
In the 1920s, before safety procedures were strengthened, 17 workers for the Ethyl Corporation, DuPont, and Standard Oil died from the effects of exposure to lead. The grim news was not well received by US legislators and a brief ban was put into place. However, it was lifted on recommendation of the United States Surgeon General and a panel of scientists in 1929, after extensive lobbying efforts by the aforementioned companies. It would be another half century until a similar effort was made to rein in the additive, spearheaded by the EPA in the 1980s. This time, concerns for health and the environment were aided by the increasing use of catalytic converters, which cannot tolerate TEL.
Ethyl Fluid's formulation consisted of:
It was found that dichloroethane and dibromoethane act in a synergistic manner, in that approximately equal quantities of both provide the best scavenging ability, thus preventing engines from fouling up due to deposits of inorganic lead within the pistons and exhausts.
The use of catalytic converters, mandated in the United States for 1975 and later model-year cars to meet tighter emissions regulations, started a gradual phase-out of leaded gasoline in the U.S. The need for TEL was lessened by several advances in automotive engineering and petroleum chemistry. Safer methods for making higher-octane blending stocks such as reformate and iso-octane reduced the need to rely on TEL, as did other antiknock additives of varying toxicity including metallic compounds such as methylcyclopentadienyl manganese tricarbonyl (MMT) as well as including methyl tert-butyl ether (MTBE), tert-amyl methyl ether (TAME), and ethyl tert-butyl ether (ETBE).
The first country to completely ban leaded gasoline was Japan in 1986.
Since January 1993, all gasoline powered cars sold in the European Union and the United Kingdom have been required to use unleaded fuel. This was to comply with the Euro 1 emission standards which mandated that all new cars to be fitted with a catalytic converter. Unleaded fuel was first introduced in the United Kingdom in June 1986.
Leaded gasoline was removed from the forecourts in the United Kingdom on January 1, 2000, and a Lead Replacement Petrol was introduced although this was largely withdrawn by 2003 due to dwindling sales. An exemption to the ban exists for owners of classic cars.
Vehicles designed and built to run on leaded fuel often require modification to run on unleaded gasoline. These modifications fall into two categories: those required for physical compatibility with unleaded fuel, and those performed to compensate for the relatively low octane of early unleaded fuels. Physical compatibility requires the installation of hardened exhaust valves and seats, or by use of additives. Compatibility with reduced octane was addressed by reducing compression, generally by installing thicker cylinder and/or rebuilding the engine with compression-reducing pistons (although modern high-octane unleaded gasoline has eliminated the need to decrease compression ratios ), and/or by retarding ignition timing.
Leaded gasoline remained legal as of late 2014 in parts of Algeria, Iraq, Yemen, Myanmar, North Korea, and Afghanistan. North Korea and Myanmar purchased their TEL from China, while Algeria, Iraq, and Yemen purchased it from the specialty chemical company Innospec, the world's sole remaining legal manufacturer of TEL. In 2011 several Innospec executives were charged and imprisoned for bribing various government state-owned oil companies to approve the sale of their TEL products.
NASCAR began experimentation in 1998 with an unleaded fuel, and in 2006 began switching the national series to unleaded fuel, completing the transition at the Fontana round in February 2007 when the premier class switched. This was influenced after blood tests of NASCAR teams revealed elevated blood lead levels.
High-percentage additives are that do not contain metals, but require much higher blending ratios, such as 20–30% for benzene and ethanol. It had been established by 1921 that ethanol was an effective antiknock agent, but TEL was introduced instead mainly for commercial reasons. such as TAME derived from natural gas, MTBE made from methanol, and ethanol-derived ETBE, have largely supplanted TEL. MTBE has environmental risks of its own and there are also bans on its use.
Improvements to gasoline itself decrease the need for antiknock additives. Synthetic iso-octane and alkylate are examples of such blending stocks. Benzene and other high-octane aromatics can be also blended to raise the octane number, but they are disfavored today because of toxicity and .
Early symptoms of acute exposure to tetraethyllead can manifest as irritation of the eyes and skin, sneezing, fever, vomiting, and a metallic taste in the mouth. Later symptoms of acute TEL poisoning include pulmonary edema, anemia, ataxia, convulsions, severe weight loss, delirium, irritability, hallucinations, nightmares, fever, muscle and joint pain, cerebral edema, coma, and damage to cardiovascular and renal organs.
Chronic exposure to TEL can cause long-term negative effects such as memory loss, delayed reflexes, neurological problems, insomnia, tremors, psychosis, loss of attention, and an overall decrease in IQ and cognitive function.
The carcinogenity of tetraethyllead is debatable. It is believed to harm the male reproductive system and cause birth defects.
Concerns over the lead poisoning eventually led to the ban on TEL in automobile gasoline in many countries. Some neurologists have speculated that the lead phaseout may have caused average IQ levels to rise by several points in the US (by reducing cumulative brain damage throughout the population, especially in the young). For the entire US population, during and after the TEL phaseout, the mean blood lead level dropped from 16 μg/dL in 1976 to only 3 μg/dL in 1991. The U.S. Centers of Disease control previously labelled children with 10 μg/dL or more as having a "blood lead level of concern". In 2021, the level was lowered in accordance with the average lead level in the U.S. decreasing to 3.5 μg/dL or more as having a "blood lead level of concern".
To settle the issue, the U.S. Public Health Service conducted a conference in 1925, and the sales of TEL were voluntarily suspended for one year to conduct a hazard assessment.Alan P. Loeb, "Paradigms Lost: A Case Study Analysis of Models of Corporate Responsibility for the Environment," Business and Economic History, Vol. 28, No. 2, Winter 1999, at 95. The conference was initially expected to last for several days, but reportedly the conference decided that evaluating presentations on alternative anti-knock agents was not "its province", so it lasted a single day. Kettering and Midgley stated that no alternatives for anti-knocking were available, although private memos showed discussion of such agents. One commonly discussed agent was ethanol. The Public Health Service created a committee that reviewed a government-sponsored study of workers and an Ethyl lab test, and concluded that while leaded gasoline should not be banned, it should continue to be investigated. The low concentrations present in gasoline and exhaust were not perceived as immediately dangerous. A U.S. Surgeon General committee issued a report in 1926 that concluded there was no real evidence that the sale of TEL was hazardous to human health but urged further study. In the years that followed, research was heavily funded by the lead industry; in 1943, Randolph Byers found children with lead poisoning had behavior problems, but the Lead Industries Association threatened him with a lawsuit and the research ended.
In the late 1920s, Robert A. Kehoe of the University of Cincinnati was the Ethyl Corporation's chief medical consultant and one of the lead industry's staunchest advocates, who would not be discredited until decades later by Dr. Clair Patterson's work on human lead burdens (see below) and other studies. In 1928, Dr. Kehoe expressed the opinion that there was no basis for concluding that leaded fuels posed any health threat. He convinced the Surgeon General that the dose–response relationship of lead had "no effect" below a certain threshold.Bryson, Christopher (2004). The Fluoride Deception, p. 41. Seven Stories Press. Citing historian Lynne Snyder. As the head of Kettering Laboratories for many years, Kehoe would become a chief promoter of the safety of TEL, an influence that did not begin to wane until about the early 1960s. But by the 1970s, the general opinion of the safety of TEL would change, and by 1976 the U.S. government would begin to require the phaseout of this product.
In the late 1940s and early 1950s, Clair Patterson accidentally discovered the pollution caused by TEL in the environment while determining the age of the Earth. As he attempted to measure lead content of very old rocks, and the time it took uranium to decay into lead, the readings were made inaccurate by lead in the environment that contaminated his samples. He was then forced to work in a cleanroom to keep his samples uncontaminated by environmental pollution of lead. After coming up with a fairly accurate estimate of the age of the Earth, he turned to investigating the lead contamination problem by examining ice cores from countries such as Greenland. He realized that the lead contamination in the environment dated from about the time that TEL became widely used as a fuel additive in gasoline. Being aware of the health dangers posed by lead and suspicious of the pollution caused by TEL, he became one of the earliest and most effective proponents of removing it from use. The Most Important Scientist You’ve Never Heard Of , BY Lucas Reilly, May 17, 2017, mentalfloss.com.
In the 1960s, the first clinical works were published proving the toxicity of this compound in humans, e.g. by Mirosław Jan Stasik.
In the U.S. in 1973, the United States Environmental Protection Agency issued regulations to reduce the lead content of leaded gasoline over a series of annual phases, which therefore came to be known as the "lead phasedown" program. EPA's rules were issued under section 211 of the Clean Air Act, as amended 1970. The Ethyl Corp challenged the EPA regulations in Federal court. Although the EPA's regulation was initially invalidated, the EPA won the case on appeal, so the TEL phasedown began to be implemented in 1976. Leaded gas was banned in vehicles with catalytic converters in 1975 due to damage of catalytic converters but it continued to be sold for vehicles without catalytic converters. Additional regulatory changes were made by EPA over the next decade (including adoption of a trading market in "lead credits" in 1982 that became the precursor of the Acid Rain Allowance Market, adopted in 1990 for SO2), but the decisive rule was issued in 1985. The EPA mandated that lead additive be reduced by 91 percent by the end of 1986. A 1994 study had indicated that the concentration of lead in the blood of the U.S. population had dropped 78% from 1976 to 1991. The U.S. phasedown regulations also were due in great part to studies conducted by Philip J. Landrigan.
In Europe, Professor Derek Bryce-Smith was among the first to highlight the potential dangers of TEL and became a leading campaigner for removal of lead additives from petrol.
From 1 January 1996, the U.S. Clean Air Act banned the sale of leaded fuel for use in on-road vehicles although that year the US EPA indicated that TEL could still be used in aircraft, racing cars, farm equipment, and marine engines. Thus, what had begun in the U.S. as a phase down ultimately ended in a phase-out for on-road vehicle TEL. Similar bans in other countries have resulted in lowering levels of lead in people's .
Taking cue from the domestic programs, the U.S. Agency for International Development undertook an initiative to reduce tetraethyl lead use in other countries, notably its efforts in Egypt begun in 1995. In 1996, with the cooperation of the U.S. AID, Egypt took almost all of the lead out of its gasoline. The success in Egypt provided a model for AID efforts worldwide.
By 2000, the TEL industry had moved the major portion of their sales to developing countries whose governments they lobbied against phasing out leaded gasoline. Leaded gasoline was withdrawn entirely from the European Union market on 1 January 2000, although it had been banned earlier in most member states. Other countries also phased out TEL. India banned leaded petrol in March 2000.
By 2011, the United Nations announced that it had been successful in phasing out leaded gasoline worldwide. "Ridding the world of leaded petrol, with the United Nations leading the effort in developing countries, has resulted in $2.4 trillion in annual benefits, 1.2 million fewer premature deaths, higher overall intelligence and 58 million fewer crimes", the United Nations Environmental Program said. The announcement was slightly premature, as a few countries still had leaded gasoline for sale as of 2017. On 30 August 2021 the United Nations Environment Program announced that leaded gasoline had been eliminated. The final stocks of the product were used up in Algeria, which had continued to produce leaded gasoline until July 2021.
In motor fuel
TEL was extensively used as a gasoline additive beginning in the 1920s, wherein it served as an effective antiknock agent and reduced exhaust Poppet valve and valve seat wear. Concerns were raised in reputable journals of likely health outcomes of fine particles of lead in the atmosphere as early as 1924.
Valve wear preventive
Tetraethyllead helps cool intake valves and is an excellent buffer against microwelds forming between exhaust valves and their Valve seat. Once these valves reopen, the microwelds pull apart and abrade the valves and seats, leading to valve recession. When TEL began to be phased out, the automotive industry began specifying hardened valve seats and upgraded materials which allow for high wear resistance without requiring lead.
Antiknock agent
A gasoline-fueled reciprocating engine requires fuel of sufficient octane rating to prevent uncontrolled combustion (pre-ignition and engine knock). Antiknock agents allow the use of higher compression ratios for greater fuel efficiency and peak power. Adding varying amounts of additives to gasoline allowed easy, inexpensive control of octane ratings. TEL offered the business advantage of being commercially profitable because its use for this purpose could be patented. Aviation fuels with TEL used in WWII reached octane ratings of 150 to enable turbocharged and supercharged engines such as the Rolls-Royce Merlin and Griffon to reach high horsepower ratings at altitude. In military aviation, TEL manipulation allowed a range of different fuels to be tailored for particular flight conditions.
"Ethyl Fluid"
For mixing with raw gasoline, TEL was most commonly supplied in the form of "Ethyl Fluid", consisting of TEL blended with 1,2-dichloroethane and 1,2-dibromoethane, which prevent lead from building up in the engine. Ethyl Fluid also contained a reddish dye to distinguish treated from untreated gasoline and discourage the use of leaded gasoline for other purposes such as cleaning.
Phaseout and ban
In most industrialized countries, a phaseout of TEL from road vehicle fuels was completed by the early 2000s because of concerns over air and soil lead levels and the Bioaccumulation neurotoxicity Lead poisoning. In the European Union, tetraethyllead has been classified as a Substance of Very High Concern and placed on the Candidate List for Authorization under Registration, Evaluation, Authorization and Restriction of Chemicals (REACH). Potential use of TEL would need to be authorized through the REACH authorization procedure. While not a complete ban, it introduces significant obligations such as a mandatory analysis of alternatives and socioeconomic analysis.
the UNEP-sponsored phase-out was nearly complete: only Algeria, Iraq, and Yemen continued widespread use of leaded gasoline, although not exclusively. In July 2021, Algeria had halted its sale.
Leaded-fuel bans
Leaded-fuel bans for road vehicles came into effect as follows:
Europe
North America
South America
Asia
法規類別： 行政 ＞ 勞動部 ＞ 職業安全衛生目
Oceania
Africa
(2025). 9780262048057, The MIT press. ISBN 9780262048057
In motor racing
Leaded fuel was commonly used in professional motor racing, until its phase out beginning in the 1990s. Since 1992, Formula One racing cars have been required to use fuel containing no more than 5 mg/L of lead.
Aviation gasoline
TEL remains an ingredient of 100 octane rating avgas for piston-engine aircraft. The current formulation of 100LL (low lead, blue) aviation gasoline contains of TEL, half the amount of the previous 100/130 (green) octane avgas (at 4.24 grams per gallon), and twice as much as the 1 gram per gallon permitted in regular automotive leaded gasoline prior to 1988 and substantially greater than the allowed 0.001 grams per gallon in automotive unleaded gasoline sold in the United States today. The United States Environmental Protection Agency, FAA, and others are working on economically feasible replacements for leaded avgas, which still releases 100 tons of lead every year.
Alternative antiknock agents
Antiknock agents are classed as high-percentage additives, such as alcohol, and low-percentage additives based on heavy elements. Since the main problem with TEL is its lead content, many alternative additives that contain less poisonous metals have been examined. A manganese-carrying additive, methylcyclopentadienyl manganese tricarbonyl (MMT or methylcymantrene), was used for a time as an antiknock agent, though its safety is controversial and it has been the subject of bans and lawsuits. Ferrocene, an organometallic compound of iron, is also used as an antiknock agent although with some significant drawbacks.
Toxicity
6 mL of tetraethyllead is enough to induce severe lead poisoning. The hazards of TEL content are heightened due to the compound's volatility and high lipophilicity, enabling it to easily cross the blood–brain barrier.
History
In 1853, German chemist Karl Jacob Löwig (1803–1890) first prepared what he claimed was Pb2(C2H5)3 from ethyl iodide and an alloy of lead and sodium.Löwig (1853) " Ueber Methplumbäthyl" (On meta-lead ethyl) Annalen der Chemie und Pharmacie, 88 : 318-322. In 1859, English chemist George Bowdler Buckton (1818–1905) reported what he claimed was Pb(C2H5)2 from zinc ethyl (Zn(C2H5)2) and lead(II) chloride.George Bowdler Buckton (1859) "Further remarks on the organo-metallic radicals, and observations more particularly directed to the isolation of mercuric, plumbic, and stannic ethyl," Proceedings of the Royal Society of London, 9 : 309–316. For Buckton's preparation of tetraethyl lead, see pages 312–314. Later authors credit both methods of preparation with producing tetraethyl lead.See, for example:
In fuel
TEL remained unimportant commercially until the 1920s.Kitman, J. (2 March 2000). "The Secret History of Lead." The Nation. Retrieved 17 August 2009. In 1921, at the direction of DuPont Corporation, which manufactured TEL, it was found to be an effective antiknock agent by Thomas Midgley, working under Charles Kettering at General Motors Corporation Research."Leaded Gasoline, Safe Refrigeration, and Thomas Midgley, Jr." Chapter 6 in S. Bertsch McGrayne. Prometheans in the Lab. McGraw-Hill: New York, 2002. General Motors the use of TEL as an antiknock agent and used the name "Ethyl" that had been proposed by Kettering in its marketing materials, thereby avoiding the negative connotation of the word "lead". Early research into "engine knocking" (also called "pinging" or "pinking") was also led by A.H. Gibson and Harry Ricardo in England and Thomas Boyd in the United States. The discovery that lead additives modified this behavior led to the widespread adoption of their use in the 1920s, and therefore more powerful, higher-compression engines. In 1924, Standard Oil of New Jersey (ESSO/EXXON) and General Motors created the Ethyl Gasoline Corporation to produce and market TEL. Deepwater, New Jersey, across the river from Wilmington, was the site for production of some of DuPont's most important chemicals, particularly TEL. After TEL production at the Bayway Refinery was shut down, Deepwater was the only plant in the Western hemisphere producing TEL up to 1948, when it accounted for the bulk of the Dupont/Deepwater's production.
Initial controversy
The toxicity of concentrated TEL was recognized early on, as lead had been recognized since the 19th century as a dangerous substance that could cause lead poisoning. In 1924, a public controversy arose over the "loony gas", after five workers died, and many others were severely injured, in Standard Oil refineries in New Jersey. There had also been a private controversy for two years prior to this controversy; several public health experts, including Alice Hamilton and Yandell Henderson, engaged Midgley and Kettering with letters warning of the dangers to public health. After the death of the workers, dozens of newspapers reported on the issue. The New York Times editorialized in 1924 that the deaths should not interfere with the production of more powerful fuel.
Modern findings
In the 1970s, Herbert Needleman found that higher lead levels in children were correlated with decreased school performance. Needleman was repeatedly accused of scientific misconduct by individuals within the lead industry, but he was eventually cleared by a scientific advisory council. Needleman also wrote the average US child's blood lead level was 13.7 μg/dL in 1976 and that Patterson believed that everyone was to some degree poisoned by TEL in gasoline.
Effect on crime rates
Reduction in the average blood lead level is believed to have been a major cause for falling violent crime rates in the United States. A statistically significant correlation has been found between the usage rate of leaded gasoline and violent crime: the violent crime curve virtually tracks the lead exposure curve with a 22-year time lag.Reyes, J. W. (2007). "The Impact of Childhood Lead Exposure on Crime". National Bureau of Economic Research. "a" ref citing Pirkle, Brody, et. al (1994). Retrieved 17 August 2009. After the ban on TEL, blood lead levels in U.S. children dramatically decreased. Researchers including Amherst College economist Jessica Wolpaw Reyes, Department of Housing and Urban Development consultant Rick Nevin, and Howard Mielke of Tulane University say that declining exposure to lead is responsible for an up to 56% decline in crime from 1992 to 2002. Taking into consideration other factors that are believed to have increased crime rates over that period, Reyes found that the reduced exposure to lead led to an actual decline of 34% over that period.
Lingering issues over time
Although leaded gasoline has long since ended its history of regular use in U.S. transportation, it has left high concentrations of lead in the soil adjacent to roads that were heavily used prior to its phaseout. These contaminated materials present health dangers even when merely touched or when components of it get Breathing. Children, especially those in poverty inside of the U.S., are particularly at risk.
See also
Further reading
(2025). 9783110434330, de Gruyter. ISBN 9783110434330
External links
Media articles
Official documents
Scientific papers and journal articles
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