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The end of August 2021 was the end of a sad century in the history of chemistry. Headlines proclaimed the world finally stopped using leaded gasoline. The UN announced Algeria used the last of its automotive leaded gasoline stockpile on August 30. 

Looking through today’s eyes, knowing the damage caused by leaded fuel, it seems impossible to consider putting lead into gasoline. Indeed, much of the reporting on leaded gasoline paints the inventor, Thomas Midgley, as a Shakespearean villain. Midgley is declared by some to be the person responsible for more environmental damage than anyone else in human history, the individual chemist responsible for impacting the most lives. The history is far more complex.  

My first encounters with the Midgley story conjured a picture of a rogue chemist operating on the fringes of the chemical enterprise. I was wrong. Midgley was awarded both the Perkin and Priestley medals, two of the highest honors in chemistry. He was elected to the National Academy. He was president of the ACS and a long-time board member. He was mainstream. He was lionized for his accomplishments, especially leaded gasoline. 

Attempts to get more horsepower out of internal combustion engines prompted a move to higher compression. Pushing to higher compression ratios dramatically increased engine performance, but uneven combustion caused engine knocking. In 1921, Midgley found tetraethyl lead (TEL) proved effective at very low concentrations to stop knocking. Added at 0.4 g/L, it doubles the horsepower of an engine. To reach the same horsepower, an engine could be half the size, burning half the fuel. TEL effectively doubled the constrained gasoline supply of the day. It was nothing short of revolutionary, except for the toxic part.  

The “dose makes the poison�� is well known, leading Midgley to ask whether the dose, the exposure, would be sufficiently low to be safe.  Testing showed animals survived exhaust vapors. Ways to distribute the lead were developed to limit potential for exposure in the supply chain.  Risks in handling were managed. Every time a concern was raised, steps were taken to mitigate the concern, or testing was done to demonstrate safety. Midgley investigated the hazard with the tools of the day and attempted to manage the risks.    

Running a thought experiment, suppose a potent organolead additive was discovered today that doubled gasoline mileage. It would be a sustainability boon, with the potential to halve atmospheric carbon emissions from autos. It would be a sustainability bust due to the hazards associated with lead. Is there an acceptable level of lead leaking into the environment in order to half transportation carbon emissions? Lead was present in gasoline at about a part per thousand by weight. Would a part per million be OK? A part per billion?

The answer that immediately comes to mind is there is no acceptable level. I wish it were that easy.

Electrification stands tall as one of the major ways the world will decarbonize. Many of the materials we’ll need for the photovoltaics, the wind turbines, the batteries, and the wires are metals. The extraction, smelting and purification will release lead from the ores. There aren’t zero lead options. We face Midgley’s dilemma, trading one environmental burden against another. 

Determining an acceptable level of lead emissions needed to reduce greenhouse gas emissions is, admittedly, a fool’s errand, fraught with peril and reliant upon many potentially flawed assumptions. I’ll use a false equivalency to set the limit, just for the sake of argument. I’ll take the lead pollution created in electric vehicle production, assume EV CO2 emissions are zero, and estimate how much lead is released for those reductions.  Many materials associated with lead are needed for EVs, but I’ll consider only copper. 

Copper production today releases nearly 13 thousand tons of lead. EVs will make up 7.5% of the operating fleet in 2030, increasing copper demand by 2.8 million tons. About 1800 tons of lead emissions will be associated with increased copper production needed just for EVs. I’ll assume 7.5% reduction in CO2. That reduction will release about 8 grams of lead per ton of avoided CO2 just for the copper associated with EVs.  

Applying this factor to the current global gasoline market of over 900 million tons, accounting for 3 billion tons of CO2 emissions, gives 13.5 ppm as the lead level in gasoline to halve the CO2 as proposed in the thought experiment. CO2 emissions are halved while emitting lead at the level EVs do per avoided CO2. That is about one-fortieth the level in leaded gasoline and much more than I expected. Peak leaded gas use in the U.S. occurred in 1970, placing 250 thousand tons of lead into the environment. For all the rhetoric about no safe lead levels, our best environmentally friendly technologies have an environmental lead footprint too close for comfort to leaded gasoline, a technology pariah. 

Midgely both knew and experienced the hazards of lead. Today, he is pilloried by many for concluding the benefits were worth the risk. Used in products or as a byproduct associated with other manufacturing, lead emissions continue. We continue to face Midgley’s dilemma. Just as he did, we trade benefits against lead’s risks. 

Editor’s Note: If you enjoyed this piece by Mark Jones, you may be interested in reading an expanded version of this article, which recently appeared in R&D World.