Leaded Gasoline

Tetra-ethyl lead, abbreviated TEL, is an organometallic compound with the formula (CH3CH2)4Pb. Once a common antiknock additive in gasoline (petrol), TEL usage was largely discontinued because of the toxicity of lead and its deleterious effect on catalytic converters. It is still used as an additive in aviation fuel for piston engine powered aircraft.

Tetraethyl lead was once used extensively as an additive in gasoline (petrol) for its ability to increase the fuel's octane rating. A high enough octane rating is required to prevent detonation ("knock" or "ping").  Antiknock agents allow the use of higher compression ratios for greater efficiency and peak power. The use of TEL in gasoline was started in the US while in Europe alcohol was initially used. The advantages of leaded gasoline from its higher energy content and storage quality eventually led to a universal switch to leaded fuel. One of the greatest advantages of TEL over other antiknock agents or the use of high octane blend stocks is the very low concentrations needed. Typical formulations called for 1 part of ethyl fluid (prepared TEL) to 1260 parts untreated gasoline. Competing antiknock agents must be used in higher amounts and/or give a lower energy content than TEL.

TEL was found to be an effective antiknock agent by Thomas Midgley in 1921, working under Charles Kettering at General Motors Research.  Due to its extreme toxicity, many early TEL researchers, including Midgley, developed lead poisoning and dozens died.   In 1924, Standard Oil of New Jersey (ESSO/EXXON) and General Motors created the Ethyl Gasoline Corporation to produce and market TEL.  In 1972, the EPA launched an initiative to phase out leaded gasoline.  The Ethyl Corp. sued the EPA and the EPA won, so the phaseout began in 1976 and was completed by 1986. A 1994 study indicated that the concentration of lead in blood dropped 78% from 1978 to 1991.

In the early 1950s, Clair Cameron 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 forced to work in a clean room 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 tetra-ethyl lead 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 tetra-ethyl lead, he was one of the earliest opponents of its use. Since the lead industry was powerful and used its influence to protect its practices, Patterson often found research funding withdrawn, and the trustees of his university were pressured to fire him or keep him quiet. He was even excluded from the 1971 US National Research Council panel that was investigating lead poisoning, despite the fact that he was the leading expert on atmospheric lead.

Leaded gasoline was withdrawn entirely from the European Union market on the 1 January 2000, although it had been banned much earlier in most member states. It was only recently phased out in China (around 2001). In the United Kingdom a small amount of leaded gasoline ("four star petrol") is still permitted to be manufactured and sold, albeit with a higher rate of fuel tax.