Tetraethyllead
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Tetraethyllead (commonly styled tetraethyl lead), abbreviated TEL, is an organolead compound with the formula Pb( C2H5)4. It is a
fuel A fuel is any material that can be made to react with other substances so that it releases energy as thermal energy or to be used for work. The concept was originally applied solely to those materials capable of releasing chemical energy but ...
additive, first being mixed with
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
beginning Beginning may refer to: * ''Beginning'' (album), by Pakho Chau * ''Beginning'' (play), a 2017 play by David Eldridge * ''Beginning'' (film), a Georgian-French drama film *"Beginning", a song by heavy metal band Kotipelto *"Beginning", a 2018 trac ...
in the 1920s as a patented
octane rating An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonating ...
booster that allowed engine compression to be raised substantially. This in turn increased vehicle performance and fuel economy. TEL was first synthesised by German chemist
Carl Jacob Löwig Carl Jacob Löwig (17 March 1803 – 27 March 1890) was a German chemist and discovered bromine independently of Antoine Jérôme Balard. He received his PhD at the University of Heidelberg for his work with Leopold Gmelin. During his research o ...
in 1853. American
chemical engineer In the field of engineering, a chemical engineer is a professional, equipped with the knowledge of chemical engineering, who works principally in the chemical industry to convert basic raw materials into a variety of products and deals with the ...
Thomas Midgley Jr. Thomas Midgley Jr. (May 18, 1889 – November 2, 1944) was an American mechanical and chemical engineer. He played a major role in developing leaded gasoline (tetraethyl lead) and some of the first chlorofluorocarbons (CFCs), better known i ...
, who was working for
General Motors The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
, was the first to discover its effectiveness as an antiknock agent in 1921, after spending several years attempting to find an
additive Additive may refer to: Mathematics * Additive function, a function in number theory * Additive map, a function that preserves the addition operation * Additive set-functionn see Sigma additivity * Additive category, a preadditive category with f ...
that was both highly effective and inexpensive. Concerns were later raised over the toxic effects of
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
, especially on children. On cars not designed to operate on leaded gasoline, lead and lead oxides coat the catalyst in
catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...
s, rendering them ineffective, and can sometimes foul spark plugs. Starting in the 1970s, many countries began phasing out TEL in automotive fuel. In 2011 a study, backed by the United Nations, estimated that the removal of TEL had resulted in $2.4 trillion in annual benefits, and 1.2 million fewer premature deaths. TEL is still used as an additive in some grades of
aviation fuel Aviation fuels are petroleum-based fuels, or petroleum and synthetic fuel blends, used to power aircraft. They have more stringent requirements than fuels used for ground use, such as heating and road transport, and contain additives to enhanc ...
.
Innospec Innospec Inc., formerly known as Octel Corporation and Associated Octel Company, Ltd., is a specialty chemical company. It comprises three business units: Fuel Specialties, responsible for the development and supply of additives for fuels and wh ...
has claimed to be the last firm legally making TEL but, , TEL was being produced illegally by several companies in China. In July 2021, the sale of leaded gasoline for cars was completely phased out worldwide, prompting the
United Nations Environment Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on th ...
(UNEP) to declare an "official end" of its use in cars on August 30, 2021.


Synthesis and properties

TEL is produced by reacting chloroethane with a
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...
. The product is recovered by steam distillation, leaving a sludge of lead and sodium chloride. TEL is a
viscous The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the inter ...
colorless
liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, a ...
with a sweet odor. Because TEL is charge neutral and contains an exterior of alkyl groups, it is highly
lipophilic Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lipo ...
and soluble in petrol (gasoline). This property, which allows it to dissolve so evenly and effectively in motor fuel also allows it to diffuse through the blood–brain barrier, and accumulate within the limbic forebrain, frontal cortex, and hippocampus. Despite decades of research, no reactions were found to improve upon this process that is rather difficult, involves metallic sodium, and converts only 25% of the lead to TEL. A related compound,
tetramethyllead Tetramethyllead, also called tetra methyllead and lead tetramethyl, is a chemical compound used as an antiknock additive for gasoline. Its use is being phased out for environmental considerations. The National Institute for Occupational Safety a ...
, was commercially produced by a different electrolytic reaction. A process with
lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid el ...
was developed but never put into practice.


Reactions

A noteworthy feature of TEL is the weakness of its four C–Pb bonds. At the temperatures found in
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
s, TEL decomposes completely into lead as well as combustible, short-lived ethyl radicals. Lead and lead oxide scavenge radical intermediates in
combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
reactions. Engine knock is caused by a
cool flame A cool flame or invisible flame is a flame having a maximal temperature below about . It is usually produced in a chemical reaction of a certain fuel-air mixture. In contrast to an ordinary flame, the reaction is not vigorous and releases little hea ...
, an oscillating low-temperature combustion reaction that occurs before the proper, hot ignition. Lead quenches the pyrolysed radicals and thus kills the radical chain reaction that would sustain a cool flame, preventing it from disturbing the smooth ignition of the hot flame front. Lead itself is the reactive antiknock agent, and the ethyl groups serve as a gasoline-soluble carrier. 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 Lead(II) chloride (PbCl2) is an inorganic compound which is a white solid under ambient conditions. It is poorly soluble in water. Lead(II) chloride is one of the most important lead-based reagents. It also occurs naturally in the form of the mi ...
and
lead(II) bromide Lead(II) bromide is the inorganic compound with the formula PbBr2. It is a white powder. It is produced in the burning of typical leaded gasolines.Michael J. Dagani, Henry J. Barda, Theodore J. Benya, David C. Sanders "Bromine Compounds" in Ullma ...
, respectively, which flush the lead from the engine and into the air: : :


In motor fuel

TEL was extensively used as a gasoline additive beginning in the 1920s, wherein it served as an effective
antiknock agent An antiknock agent is a gasoline additive used to reduce engine knocking and increase the fuel's octane rating by raising the temperature and pressure at which auto-ignition occurs. The mixture known as gasoline or petrol, when used in high comp ...
and reduced exhaust
valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...
and
valve seat The valve seat in an internal combustion gasoline or diesel engine is the surface against which an intake or an exhaust valve rests during the portion of the engine operating cycle when that valve is closed. The valve seat is a critical compon ...
wear. Concerns were raised in reputable journals of likely health outcomes of fine particles of lead in the atmosphere.


Valve wear preventive

Tetraethyllead helped cool intake valves and was an excellent buffer against microwelds forming between exhaust valves and their
seats A seat is a place to sit. The term may encompass additional features, such as back, armrest, head restraint but also headquarters in a wider sense. Types of seat The following are examples of different kinds of seat: * Armchair, a chair eq ...
. 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-fuelled reciprocating engine requires fuel of sufficient
octane rating An octane rating, or octane number, is a standard measure of a fuel's ability to withstand compression in an internal combustion engine without detonating. The higher the octane number, the more compression the fuel can withstand before detonating ...
to prevent uncontrolled combustion (preignition and
detonation Detonation () is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it. Detonations propagate supersonically through shock waves with ...
). Antiknock agents allow the use of higher compression ratios for greater efficiency and peak
power Power most often refers to: * Power (physics), meaning "rate of doing work" ** Engine power, the power put out by an engine ** Electric power * Power (social and political), the ability to influence people or events ** Abusive power Power may a ...
. 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 The Rolls-Royce Merlin is a British liquid-cooled V-12 piston aero engine of 27-litres (1,650  cu in) capacity. Rolls-Royce designed the engine and first ran it in 1933 as a private venture. Initially known as the PV-12, it was late ...
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. In 1935 a licence to produce TEL was given to
IG Farben Interessengemeinschaft Farbenindustrie AG (), commonly known as IG Farben (German for 'IG Dyestuffs'), was a German chemical and pharmaceutical conglomerate (company), conglomerate. Formed in 1925 from a merger of six chemical companies—BASF, ...
, enabling the newly formed German to use high-octane gasoline. A company, Ethyl GmbH, was formed that produced TEL at two sites in Germany with a government contract from 10 June 1936. In 1938 the United Kingdom
Air Ministry The Air Ministry was a department of the Government of the United Kingdom with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964. It was under the political authority of the Secretary of State ...
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.


"Ethyl Fluid"

For mixing with raw gasoline, TEL was most commonly supplied in the form of "Ethyl Fluid", which consisted of TEL blended with 1,2-dichloroethane and 1,2-dibromoethane. 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. In the 1920s before safety procedures were strengthened, 17 workers for the
Ethyl Corporation Ethyl Corporation is a fuel additive company headquartered in Richmond, Virginia, in the United States. The company is a distributor of fuel additives. Among other products, Ethyl Corporation distributes tetraethyl lead, an additive used to make ...
,
DuPont DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...
, and
Standard Oil Standard Oil Company, Inc., was an American oil production, transportation, refining, and marketing company that operated from 1870 to 1911. At its height, Standard Oil was the largest petroleum company in the world, and its success made its co-f ...
died from the effects of exposure to lead. Ethyl Fluid's formulation consisted of: * 61.45% Tetraethyllead * 18.80% 1,2-Dichloroethane * 17.85% 1,2-Dibromoethane * 1.90% Inerts and dyes Dichloroethane and dibromoethane act in a synergistic manner, where equal or approximately equal quantities of both provide the best scavenging ability.


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 accumulative neurotoxicity of lead. In the European Union, tetraethyllead has been classified as a
Substance of Very High Concern A substance of very high concern (SVHC) is a chemical substance (or part of a group of chemical substances) concerning which it has been proposed that use within the European Union be subject to authorisation under the REACH Regulation. Indeed, l ...
and placed on the Candidate List for Authorisation under
Registration, Evaluation, Authorisation and Restriction of Chemicals Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) is a European Union regulation dating from 18 December 2006. REACH addresses the production and use of chemical substances, and their potential impacts on both human he ...
(REACH). Potential use of TEL would need to be authorised through the REACH authorisation procedure. While not a complete ban, it introduces significant obligations such as a mandatory analysis of alternatives and socioeconomic analysis. The use of
catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...
s, 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 Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium blending stocks for high-o ...
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 Methylcyclopentadienyl manganese tricarbonyl (MMT or MCMT) is an organomanganese compound with the formula (C5H4CH3)Mn(CO)3. Initially marketed as a supplement for use in leaded gasoline, MMT was later used in unleaded gasoline to increase the o ...
(MMT) as well as
oxygenate Oxygenated chemical compounds contain oxygen as a part of their chemical structure. The term usually refers to oxygenated chemical compounds added to fuels. Oxygenates are usually employed as gasoline additives to reduce carbon monoxide and soot ...
s including methyl tertiary-butyl ether (MTBE), ''tert''-amyl methyl ether (TAME), and ethyl ''tert''-butyl ether (ETBE). Lead-replacement additives were scientifically tested, and some were approved by the Federation of British Historic Vehicle Clubs at the UK's
Motor Industry Research Association An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
in 1999. In Europe, Professor
Derek Bryce-Smith Derek Bryce-Smith (1926–2011) was a chemist and professor of Organic Chemistry at the University of Reading from 1956 until his retirement in 1991. His work included organometallic chemistry, radical chemistry, photochemistry, environmental scie ...
was among the first to highlight the potential dangers of TEL and became a leading campaigner for removal of lead additives from petrol. However, leaded motor fuel re-entered the UK market in small quantities from 2000 in response to lobbying from classic-car organisations who contended their vehicles would be rendered useless without leaded fuel. Bayford & Co was the only wholesale supplier. 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. Compatibility with reduced octane was addressed by reducing compression, generally by installing thicker cylinder
head gasket In an internal combustion engine, a head gasket provides the seal between the engine block and cylinder head(s). Its purpose is to seal the combustion gases within the cylinders and to avoid coolant or engine oil leaking into the cylinders. Leak ...
s and/or rebuilding the engine with compression-reducing pistons, although modern high-octane unleaded gasoline has eliminated the need to decrease compression ratios. Leaded gasoline remained legal as of late 2014 in parts of
Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...
,
Iraq Iraq,; ku, عێراق, translit=Êraq officially the Republic of Iraq, '; ku, کۆماری عێراق, translit=Komarî Êraq is a country in Western Asia. It is bordered by Turkey to Iraq–Turkey border, the north, Iran to Iran–Iraq ...
,
Yemen Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the Saudi Arabia–Yemen border, north and ...
,
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
,
North Korea North Korea, officially the Democratic People's Republic of Korea (DPRK), is a country in East Asia. It constitutes the northern half of the Korea, Korean Peninsula and shares borders with China and Russia to the north, at the Yalu River, Y ...
, and
Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan,; prs, امارت اسلامی افغانستان is a landlocked country located at the crossroads of Central Asia and South Asia. Referred to as the Heart of Asia, it is bordere ...
. North Korea and Myanmar purchased their TEL from China, while Algeria, Iraq, and Yemen purchased it from the specialty chemical company
Innospec Innospec Inc., formerly known as Octel Corporation and Associated Octel Company, Ltd., is a specialty chemical company. It comprises three business units: Fuel Specialties, responsible for the development and supply of additives for fuels and wh ...
, 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. the
UNEP The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on ...
-sponsored phase-out was nearly complete: only Algeria, Iraq, and Yemen continued widespread use of leaded gasoline, although not exclusively. In July 2021, Algeria—the last country to sell leaded gasoline—had halted its sale.


Leaded-fuel bans

Leaded-fuel bans for road vehicles came into effect as follows:


= Europe

= *Austria: 1989 *Bosnia and Herzegovina: 2009 *Croatia: 2006 *Czech Republic: 2001 *Denmark: 1994 *
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...
: 1 January 2000 *Finland: 1994 *France: 2000 *Germany: 1996 *Gibraltar: 2001 *Greece: 2002 *Hungary: 1999 *Ireland: 1 January 2000 *Italy: 1 January 2002 *Monaco: 2000 *Netherlands: 1998 *Norway: 1997 *Poland: December 2000 *Slovenia: 2001 *Spain: 1 August 2001 *Portugal: 1999 *Romania: 2005 *Russia: 2003 *Serbia: 2010 *Sweden: 1995 *Switzerland: 2000 *Ukraine: 2003 *United Kingdom: 1 January 2000


= North America

= *Antigua and Barbuda: 1991 *Canada: December 1990 *United States (including Puerto Rico): 1 January 1996 **California: 1992 *Bahamas: 1996 *Belize: 1997 *Bermuda: 1990 *Costa Rica: 1996 *Dominican Republic: 1999 *El Salvador: 1992 *Guatemala: 1991 *Haiti: 1998 *Honduras: 1996 *Mexico: 1998 *Nicaragua: 1995 *Panama: 2002 *Trinidad and Tobago: 2000


= South America

= *Argentina: 1998 *Bolivia: 1995 *Brazil: 1989 or 1991 *Chile: 2001 or 2005 *Colombia: 1991 *Guyana: 2000 *Peru: 2004 *Suriname: 2001 *Uruguay: 2004 *Venezuela: 2005


= Asia

= *Afghanistan: 2016 *Bangladesh: 1999 *China: 2000 *Hong Kong: 1999 *India: March 2000 *Saudi Arabia: 2001 *Indonesia: 2006 *Iran: 2003 *Iraq: 2018https://wedocs.unep.org/bitstream/handle/20.500.11822/25422/MapWorldLead_March2018.pdf?sequence=1&isAllowed=y https://wedocs.unep.org/bitstream/handle/20.500.11822/25756/MapWorldLead_July2018.pdf?sequence=1&isAllowed=y *Japan: 1986 *Malaysia: 2000 *Myanmar: 2016 *Nepal: 2000 *North Korea: 2016 *Pakistan: 2001 *Philippines: 2000 *Singapore: 1998 *South Korea: 1993 *Sri Lanka: 1999 *Taiwan: 2000 *Thailand: 1996 *Turkey: 2006 *United Arab Emirates: 2003 *Vietnam: 2001 *Yemen: 2018


= Oceania

= *Australia: 2002 *New Zealand: 1996 *Guam: 1 January 1996 (USA)


= Africa

= *Egypt: 1999 *South Africa: 2006 *Leaded petrol was supposed to be completely phased out continent-wide on 1 January 2006, following a ban initiated from the 2002 Earth Summit. However, in Algeria refineries needed to be altered; as a result, leaded fuel remained available in parts of
Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...
, with phaseout scheduled for 2016. After the Algerian Government outlawed the sale of leaded petrol throughout all of Algeria, leaded petrol has now been effectively phased out.


In motor racing

Leaded fuel was commonly used in professional
motor racing Motorsport, motorsports or motor sport is a global term used to encompass the group of competitive sporting events which primarily involve the use of motorized vehicles. The terminology can also be used to describe forms of competition of two ...
, until its phase out beginning in the 1990s. Since 1993,
Formula One Formula One (also known as Formula 1 or F1) is the highest class of international racing for open-wheel single-seater formula racing cars sanctioned by the Fédération Internationale de l'Automobile (FIA). The World Drivers' Championship, ...
racing cars have been required to use fuel containing no more than 5 mg/L of lead.
NASCAR The National Association for Stock Car Auto Racing, LLC (NASCAR) is an American auto racing sanctioning and operating company that is best known for stock car racing. The privately owned company was founded by Bill France Sr. in 1948, and hi ...
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.


Aviation gasoline

TEL remains an ingredient of 100
octane Octane is a hydrocarbon and an alkane with the chemical formula , and the condensed structural formula . Octane has many structural isomers that differ by the amount and location of branching in the carbon chain. One of these isomers, 2,2,4-Tri ...
avgas Avgas (aviation gasoline, also known as aviation spirit in the UK) is an aviation fuel used in aircraft with spark-ignited internal combustion engines. ''Avgas'' is distinguished from conventional gasoline (petrol) used in motor vehicles, w ...
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 The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
, and others are working on economically feasible replacements for leaded avgas, which still releases 100 tons of lead every year. Children living near airports servicing small (piston-engine) aircraft have measurably higher concentrations of lead in their blood.


Alternative antiknock agents

Antiknock agents are classed as ''high-percentage'' additives, such as alcohol, and ''low-percentage'' additives based on
heavy elements upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...
. 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 Methylcyclopentadienyl manganese tricarbonyl (MMT or MCMT) is an organomanganese compound with the formula (C5H4CH3)Mn(CO)3. Initially marketed as a supplement for use in leaded gasoline, MMT was later used in unleaded gasoline to increase the o ...
(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 Ferrocene is an organometallic compound with the formula . The molecule is a complex consisting of two cyclopentadienyl rings bound to a central iron atom. It is an orange solid with a camphor-like odor, that sublimes above room temperature, a ...
, an
organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
compound of
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
, is also used as an antiknock agent although with some significant drawbacks. High-percentage additives are
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...
s that do not contain metals, but require much higher blending ratios, such as 20–30% for
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...
and
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an Alcohol (chemistry), alcohol with the chemical formula . Its formula can be also written as or (an ethyl ...
. It had been established by 1921 that ethanol was an effective antiknock agent, but TEL was introduced instead mainly for commercial reasons.
Oxygenate Oxygenated chemical compounds contain oxygen as a part of their chemical structure. The term usually refers to oxygenated chemical compounds added to fuels. Oxygenates are usually employed as gasoline additives to reduce carbon monoxide and soot ...
s such as
TAME Tame may refer to: *Taming, the act of training wild animals *River Tame, Greater Manchester *River Tame, West Midlands and the Tame Valley * Tame, Arauca, a Colombian town and municipality * "Tame" (song), a song by the Pixies from their 1989 al ...
derived from natural gas,
MTBE Methyl ''tertiary''-butyl ether (MTBE), also known as methyl tert-butyl ether and ''tert''-butyl methyl ether, is an organic compound with a structural formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly sol ...
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 An alkylation unit (alky) is one of the conversion processes used in petroleum refineries. It is used to convert isobutane and low-molecular-weight alkenes (primarily a mixture of propene and butene) into alkylate, a high octane gasoline componen ...
are examples of such blending stocks. Benzene and other high-octane
aromatics Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
can be also blended to raise the octane number, but they are disfavored today because of
toxicity Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
and
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...
icity.


Toxicity

Tetraethyllead is highly toxic, with as little as 6 mL being enough to induce severe lead poisoning. The hazards of TEL's lead content are heightened due to the compound's volatility and high
lipophilicity Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. Such non-polar solvents are themselves lip ...
, enabling it to easily cross the blood–brain barrier and accumulate in the
limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''Ps ...
, frontal cortex, and
hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
, making
chelation therapy Chelation therapy is a medical procedure that involves the administration of chelating agents to remove heavy metals from the body. Chelation therapy has a long history of use in clinical toxicology and remains in use for some very specific me ...
ineffective. 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 Pulmonary edema, also known as pulmonary congestion, is excessive liquid accumulation in the tissue and air spaces (usually alveoli) of the lungs. It leads to impaired gas exchange and may cause hypoxemia and respiratory failure. It is due t ...
,
anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...
, ataxia, convulsions, severe weight loss, delirium, irritability, hallucinations, nightmares, fever, muscle and joint pain, swelling of the brain, coma, and damage to cardiovascular and renal organs. Chronic exposure to TEL can cause long-term negative effects such as
memory loss Amnesia is a deficit in memory caused by brain damage or disease,Gazzaniga, M., Ivry, R., & Mangun, G. (2009) Cognitive Neuroscience: The biology of the mind. New York: W.W. Norton & Company. but it can also be caused temporarily by the use o ...
, delayed reflexes, neurological problems, insomnia, tremors, psychosis, loss of attention, and an overall decrease in IQ and cognitive function. The
carcinogenity A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...
of tetraethyllead is debatable. It is believed to harm the male reproductive system and cause birth defects. Concerns over the toxicity of lead 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."


History

In 1853, German chemist Karl Jacob Löwig (1803–1890) first prepared what he claimed was Pb2(C2H5)3 from
ethyl iodide Ethyl iodide (also iodoethane) is a colorless flammable chemical compound. It has the chemical formula C2H5I and is prepared by heating ethanol with iodine and phosphorus.''Merck Index of Chemicals and Drugs'', 9th ed., monograph 3753 On contact ...
and an alloy of lead and sodium. In 1859, English chemist George Bowdler Buckton (1818–1905) reported what he claimed was Pb(C2H5)2 from
zinc ethyl Diethylzinc (C2H5)2Zn, or DEZ, is a highly pyrophoric and reactive organozinc compound consisting of a zinc center bound to two ethyl groups. This colourless liquid is an important reagent in organic chemistry. It is available commercially as a sol ...
(Zn(C2H5)2) and
lead(II) chloride Lead(II) chloride (PbCl2) is an inorganic compound which is a white solid under ambient conditions. It is poorly soluble in water. Lead(II) chloride is one of the most important lead-based reagents. It also occurs naturally in the form of the mi ...
. Later authors credit both methods of preparation with producing tetraethyl lead.


In fuel

Regardless of the details of the chemical discoveries, tetraethyl lead remained unimportant commercially until the 1920s.Kitman, J. (2 March 2000)
"The Secret History of Lead."
''
The Nation ''The Nation'' is an American liberal biweekly magazine that covers political and cultural news, opinion, and analysis. It was founded on July 6, 1865, as a successor to William Lloyd Garrison's '' The Liberator'', an abolitionist newspaper tha ...
''. Retrieved 17 August 2009.
In 1921, at the direction of DuPont Corporation, which manufactured TEL, it was found to be an effective
antiknock agent An antiknock agent is a gasoline additive used to reduce engine knocking and increase the fuel's octane rating by raising the temperature and pressure at which auto-ignition occurs. The mixture known as gasoline or petrol, when used in high comp ...
by Thomas Midgley, working under
Charles Kettering Charles Franklin Kettering (August 29, 1876 – November 25, 1958) sometimes known as Charles Fredrick Kettering was an American inventor, engineer, businessman, and the holder of 186 patents. For the list of patents issued to Kettering, see, Le ...
at
General Motors Corporation The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
Research. General Motors
patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...
ed 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 Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
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 ExxonMobil, an American multinational oil and gas corporation presently based out of Texas, has had one of the longest histories of any company in its industry. A direct descendant of John D. Rockefeller's Standard Oil, the company traces its roo ...
(ESSO/EXXON) and General Motors created the
Ethyl Gasoline Corporation Ethyl Corporation is a fuel additive company headquartered in Richmond, Virginia, in the United States. The company is a distributor of fuel additives. Among other products, Ethyl Corporation distributes tetraethyl lead, an additive used to make ...
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 Alice Hamilton (February 27, 1869Corn, JHamilton, Alice''American National Biography'' – September 22, 1970) was an American physician, research scientist, and author. She was a leading expert in the field of occupational health and a pioneer ...
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. To settle the issue, the
U.S. Public Health Service The United States Public Health Service (USPHS or PHS) is a collection of agencies of the Department of Health and Human Services concerned with public health, containing nine out of the department's twelve operating divisions. The Assistant ...
conducted a conference in 1925, and the sales of TEL were voluntarily suspended for one year to conduct a hazard assessment. 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 The surgeon general of the United States is the operational head of the United States Public Health Service Commissioned Corps (PHSCC) and thus the leading spokesperson on matters of public health in the federal government of the United States. Th ...
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 The Lead Industries Association (LIA) was a trade organization that in 1925 made it possible for Tetraethyllead to be an additive of commercial gasoline and later incorporated in 1928 to promote the interests of the lead industry. The National Lead ...
threatened him with a lawsuit and the research ended. In the late 1920s, Robert A. Kehoe of the
University of Cincinnati The University of Cincinnati (UC or Cincinnati) is a public research university in Cincinnati, Ohio. Founded in 1819 as Cincinnati College, it is the oldest institution of higher education in Cincinnati and has an annual enrollment of over 44,00 ...
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 Clair Cameron Patterson (June 2, 1922 – December 5, 1995) was an American geochemist. Born in Mitchellville, Iowa, Patterson graduated from Grinnell College. He later received his Ph.D. from the University of Chicago and spent his entire prof ...
'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 The dose–response relationship, or exposure–response relationship, describes the magnitude of the response of an organism, as a function of exposure (or doses) to a stimulus or stressor (usually a chemical) after a certain exposure tim ...
of lead had "no effect" below a certain threshold. 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 Cameron Patterson Clair Cameron Patterson (June 2, 1922 – December 5, 1995) was an American geochemist. Born in Mitchellville, Iowa, Patterson graduated from Grinnell College. He later received his Ph.D. from the University of Chicago and spent his entire profe ...
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 A cleanroom or clean room is an engineered space, which maintains a very low concentration of airborne particulates. It is well isolated, well-controlled from contamination, and actively cleansed. Such rooms are commonly needed for scientif ...
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 Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...
. 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. In the 1960s, the first clinical works were published proving the toxicity of this compound in humans, e.g. by
Mirosław Jan Stasik Mirosław Jan Stasik (born 27 January 1929 r. in Łódź) is a Polish people, Polish Physician, medical doctor and Toxicology, research toxicologist. Education and early career Stasik graduated from Łódź School of Medicine (now Medical Univ ...
.


Modern findings

In the 1970s,
Herbert Needleman Herbert Leroy Needleman (December 13, 1927 – July 18, 2017) researched the neurodevelopmental damage caused by lead poisoning. He was a pediatrician, child psychiatrist, researcher and professor at the University of Pittsburgh, an elected ...
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. In the U.S. in 1973, the
United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
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. 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. Then 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. 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 phasedown 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
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
streams. 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 much earlier in most member states. Other countries also phased out TEL.
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
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 Programme said. The announcement was slightly premature, as a few countries still have leaded gasoline for sale as of 2017. On 30 August 2021 the
United Nations Environment Programme The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on th ...
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.


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 Amherst College ( ) is a private liberal arts college in Amherst, Massachusetts. Founded in 1821 as an attempt to relocate Williams College by its then-president Zephaniah Swift Moore, Amherst is the third oldest institution of higher educatio ...
economist Jessica Wolpaw Reyes, Department of Housing and Urban Development consultant Rick Nevin, and Howard Mielke of
Tulane University Tulane University, officially the Tulane University of Louisiana, is a private university, private research university in New Orleans, Louisiana. Founded as the Medical College of Louisiana in 1834 by seven young medical doctors, it turned into ...
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. Although leaded gasoline is largely gone in North America, it has left high concentrations of lead in the soil adjacent to roads that were heavily used prior to its phaseout. Children are particularly at risk if they consume this.


See also

*
Elmer Keiser Bolton Elmer Keiser Bolton (June 23, 1886 – July 30, 1968) was an American chemist and research director for DuPont, notable for his role in developing neoprene and directing the research that led to the discovery of nylon. Personal life Bolton wa ...
*
Lead abatement Lead abatement includes lead-based paint abatement activities, such as inspections, risk assessments, as well as removal. Lead abatement must be performed by educated, certified professionals with proper safety protocols to limit lead exposure. T ...
*
List of petrol additives Petrol additives increase petrol's octane rating or act as corrosion inhibitors or lubricants, thus allowing the use of higher compression ratios for greater efficiency and power. Types of additives include metal deactivators, corrosion inhibito ...


References


Further reading

*


External links


Media articles


The Man Who Warned the World About Lead
(PBS / NOVA)
The Most Important Scientist You’ve Never Heard Of
BY Lucas Reilly, May 17, 2017, mentalfloss.com
The World Has Finally Stopped Using Leaded Gasoline. Algeria Used The Last Stockpile
August 30, 2021, Heard on All Things Considered, Camila Domonoske, NPR.


Official documents

*U.S. Gov't, National Institute for Occupational Safety and Health


Scientific papers and journal articles

*Kovarik, Bill (1999)

* ttps://www.aopa.org/advocacy/advocacy-briefs/regulatory-brief-avgas-100ll-alternatives True unleaded alternative for 100LL needed for general aviation*Jamie Lincoln Kitman:
The Secret History of Lead
'. In: The Nation, 2 March 2000. {{Authority control Organolead compounds Antiknock agents