Gasoline has always been harmful to human health, but it used to be even worse than it is today. For almost 70 years, refiners routinely added lead to it, turning it into an even more toxic mixture that might even have been linked to violent crime.

And sadly, although its dangers were known right from the beginning, what ultimately sparked the ban on leaded gas wasn’t so much that it hurt human health, but that it clogged catalytic converters.

Leaded gas was developed in 1923 by General Motors’ research corporation to solve the problem of pre-ignition, or “engine knock.” Normally, the spark plug ignites the gasoline when the piston is in its optimum position, but if the chamber is hot enough, the gas can spontaneously combust. This creates the pinging or knocking sound that gives the condition its name.

Higher-octane gas is less volatile, which reduces the risk of premature combustion. The researchers tried numerous additives to raise octane and finally settled on one that was simple, inexpensive, and could be patented: tetraethyl lead. GM and Standard Oil formed a partnership, the Ethyl Gasoline Corporation, to produce it.

The danger was evident from the start. The engineer who developed it became ill with lead poisoning, and two of his colleagues reportedly died of it. By 1924, as many as 15 workers had died and more than 40 became ill at the Standard Oil facility where the additive was manufactured. Shortly afterwards, the U.S. Surgeon General appointed a council to study the issue.

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The report was due in seven months. The council said that wasn’t long enough to properly analyze toxicology results, but even so, it eventually ruled that it had no grounds for prohibiting ethyl gasoline, “provided that its distribution and use are controlled by proper regulations.”

The car had won. Lead cured engine knock, protected internal components, was relatively cheap, and according to Ethyl Gasoline’s engineers, was the only additive that could be produced in large enough quantities to meet demand. It was dangerous, but it wasn’t going away anytime soon.

And it didn’t. Its importance actually increased, since engineers could now design more powerful, higher-compression engines that still remained knock-free. In 1927, the Surgeon General set a voluntary standard for oil refiners at 3 cubic centimetres per gallon (cc/g). But by 1958, the limit rose to 4 cc/g, following reports that while leaded gas had expanded over the previous decade, people were not showing increased lead levels in their bodies.

But blood lead levels had risen sharply since 1900, especially in children, where lead causes neurological development delays.

Ethyl gasoline wasn’t the only culprit, of course. Lead was also used in house paint, plumbing pipes, and cosmetics, along with food additives and packaging. But gasoline lead was everywhere: in the air and on the ground from tailpipe emissions, and in the water from run-off, spills, and leaking storage tanks. Studies showed that people living close to highways had far higher levels of lead in their bodies than those farther away from traffic.

Air pollution was becoming a political issue, and in 1963, the U.S. passed the Clean Air Act to deal with it. In 1970, the newly-formed Environmental Protection Agency (EPA) inherited that legislation, and in 1973, released a study confirming that airborne lead was threatening public health. It issued regulations that would take effect between 1975 and 1979, reducing gasoline lead from 2.0 grams per gallon—what most refiners were producing—to 0.5 grams. The oil companies immediately filed lawsuits, and the regulations stalled.

Ultimately, the solution came about another way. Smog was now a serious problem, and researchers determined it was caused by such auto emissions as nitrogen oxides, hydrocarbons, and carbon monoxide. The EPA insisted these pollutants be controlled, which left automakers scrambling to find solutions.

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Catalytic converter from 1974 – courtesy:GM

One that worked, and worked very well, was the catalytic converter, which started appearing on cars in 1975. But there was a drawback: lead ruined them. Ultimately, catalytic converter health accomplished what human health could not: on January 1, 1986, new EPA regulations reduced lead content by 90 per cent. By January 1, 1996, leaded gasoline was completely banned in the U.S. for on-road vehicles.

Canada phased out leaded gasoline in 1990, although an amendment allowed its use in race cars right up until 2010.

Ultimately, banning lead had an effect. In 1978, a U.S. government study found that approximately 13.5 million children under the age of five had elevated blood lead levels. By 2008, that had dropped to 250,000.

It has also been suggested that crime rates historically rose in conjunction with increased gasoline use, and sharply fell after leaded gasoline was phased out. The theory, simplistically presented, is that children born without exposure to it were less susceptible to lead-linked symptoms such as lower intelligence, higher aggression, and poor decision-making.

The theory is still controversial, with as many people arguing against it as for it, but it’s just one more twist to an additive that was developed with good intentions, but ultimately proved to be the devil in disguise.