The Cleanroom Trail

The Contaminated Clock

Mara: Chicago, 1948. Kent Hall, one of the oldest buildings on campus, and a very dusty lab inside it. A young chemist, Clair Patterson, has been handed a problem his advisor called, as Caltech's magazine tells it, 'duck soup': a simple calculation that would make a young scientist famous. The calculation is the age of the Earth.

Eli: And that's where the listener's question begins: why did a scientist trying to work out the age of the Earth end up fighting the industry behind leaded petrol? Today's angle is the cleanroom trail.

Mara: It didn't stay a calculation. The environment in that dusty room was extremely unfavorable for lead work, and the processing blank—about 0.1 microgram—held roughly as much lead as a typical isotope-analysis sample contained.

Eli: Duck soup is a big promise for a whole planet.

Mara: The method was uranium-lead dating. Uranium decays into lead at a known, steady rate, and different kinds of uranium make different kinds of lead. Measure the ratios of those leads in tiny zircon crystals, and the rock gives up its age.

Eli: So the lead is sand in an hourglass. Weigh what's fallen, read the time.

Mara: As long as nothing else drops sand in. Something did. Samples of known age kept coming back impossibly old, with more lead than decay could ever account for. So he went looking, and found lead everywhere: in glassware, tap water, paint, dust, on his clothes, in his hair, on his skin. He said later it took him 'years and years to work out where the lead was coming from and how to get the lead out of these things.'

Eli: Plenty of scientists would have called that an annoyance, fixed it and forgotten it.

Mara: Not him. To Patterson it wasn't a nuisance but a clear sign of lead contamination from human activities, something that needed investigating. For now, that was his reading.

Eli: First he needed a room without it. At Caltech, by 1953, inside an older building, he built one of the first ultra-clean laboratories, stripping lead out of the whole process so what he measured came from the sample, not the room.

Mara: He said it plainly: 'No one else had a clean lab. It didn't exist.'

Eli: Then the meteorites. His Chicago supervisor had worked out that iron meteorites carry the lead the solar system started with, unchanged, because there's no uranium in them to add more. Patterson compared lead ratios in Earth materials against that starting point.

Mara: And with five samples instead of one, he got 4.55 billion years. That's when the Earth reached its present mass.

Eli: So the clean room was the real instrument. Clean enough to date a planet meant clean enough to see how much lead was everywhere else.

Mara: And he didn't let it go. With the age settled, his quest to date the solar system turned into a hunt for the lead itself. He was convinced people had put it there. Proving that was another matter.

The Inverted Ocean

Eli: Proving it meant finding what natural looked like. Patterson was blunt about it: 'I wanted to know what this natural level of lead is. I didn't care two hoots about verifying what the contamination was. I was forced to measure the contamination in order to arrive at the natural level.' So he went to the sea. With a fellow geochemist he studied ocean sediments, and their 1962 results showed dissolved lead reaching the open ocean at seven times the rate of a million years before.

Mara: Same hunt as in his lab, just with an ocean for a sample.

Eli: Then the water column, measuring the ocean from the surface down to the depths. In 1963 he and another colleague reported that deep ocean water had three to ten times less lead than the surface. That's backwards. For most elements, barium for one, it runs the other way.

Mara: So the lead was coming in from above, not up from below.

Eli: That's where he went. Patterson said that extrapolating his ocean profiles worldwide produced an amount of lead equal to what gasoline was producing. In his words, 'It could easily be accounted for by the amount of lead that was put into gasoline and burned and put in the atmosphere.' They named the likely culprit: tetraethyl lead, the petrol additive burned in car engines and blown out of the tailpipe.

Mara: That suspicion had a history. On May 20th, 1925, a conference on tetraethyl lead met in Washington, every major party represented. Production and sale of leaded gasoline were suspended for a time while the health questions were looked into.

Eli: For a time. Now Patterson had the sea and the tailpipe lining up, Mara, but lining up isn't proof, and the people who'd owned the lead question since 1925 told it very differently.

The Kehoe Paradigm

Mara: Their story centres on one man. After 1925, the further studies recommended were never carried out. For the next four decades, every study of tetraethyl lead came from labs and scientists funded by Ethyl and General Motors. At the centre was a pathologist, Robert Kehoe, the industry's go-to scientist, and Ethyl's chief medical adviser from 1925 until he retired.

Eli: So for forty years, leaded petrol's only safety checkers were paid by its makers.

Mara: Kehoe said so himself at a 1966 hearing: his lab 'was the only source of new information.'

Eli: His case had two parts. Everyone has lead in their blood, he said, and below 80 micrograms per deciliter it has no effect on the body whatsoever. He promoted the view that it was normal for lead to be in all human beings, and that the body had ways of eliminating it. That's the reading he held, alongside industry figures like Felix Wormser and P. N. Gammelgard: a natural, harmless baseline people had adapted to.

Mara: Which recasts that dusty lab in Chicago. By Kehoe's account, lead in all human beings was just what a normal world looks like.

Eli: The other reading, Mara, is Patterson's: the ocean said this lead was arriving from the air, in amounts matching gasoline, and far above anything natural.

Mara: What neither side had yet was the air from before leaded petrol.

Eli: Patterson, meanwhile, had visitors. Three days after his 1963 paper appeared, four lead and petroleum industry representatives, Ethyl officials among them, were waiting in his Caltech office. He thought they'd come to discuss his findings. By his account, they tried to 'buy me out through research support that would yield results favourable to their cause.' He refused.

Mara: Turning down the money didn't settle the science, though.

Eli: It didn't. Kehoe's baseline and Patterson's suspicion were both still claims about the past. Settling it meant finding somewhere the old air had been kept.

The Polar Archive

Mara: He found it in Greenland, where snow builds up in layers, each holding a dated record of what was in the air when it fell, a diary of the atmosphere. In the summer of 1964 a snowstorm swallowed the sun. He tried to navigate by sun compass and couldn't, so he marked the group's tracks by stopping to plant a flag every couple of feet. He drilled the yearly layers there, and later in Antarctica, and took the samples back to a clean room, with its own clean-air supply and every surface scrubbed, floors included.

Eli: Some of those layers were laid down thousands of years before any car.

Mara: And the older, deeper ice was comparatively clean. Recent ice was not. So the stray lead in Kent Hall, dust swamping samples that held about as little lead as the processing itself added, wasn't simply the Earth's background. It was new.

Eli: His team's numbers: in Greenland, lead rose about two hundredfold over three thousand years, the clean ice all at the bottom. They put more than 99 percent of today's excess down to human activity. An anthropogenic surge, in other words: made by people, not volcanoes or sea spray.

Mara: Which leaves Kehoe's threshold, a line below which lead supposedly does nothing, resting on a baseline that turns out to be modern. Forty years of a research monopoly, the only funder also the only checker, had built on it.

Eli: And it reached past Greenland. In 1965 Patterson wrote that the Northern Hemisphere's air held a thousand times the natural amount of lead, and that people were under 'severe chronic lead insult.' The ocean's layers fit too: the surface catches what falls from the sky, so it carries more than the deep. And tetraethyl lead leaves the tailpipe as very fine lead particles.

Mara: Even the meteorite lead, the solar system's untouched starting ratios, could only be read in a room that clean. Now the same room had measured the sky. How the industry would answer a thousandfold number, Eli, was about to become the rest of his career.

The Retaliation

Eli: By June 1966, that number had Patterson at a Senate hearing in Washington.

Mara: His point there came down to two words. Officials, he said, confused natural lead in the body with normal lead. Normal was just the modern average. Natural meant what existed before human contamination, and he wanted normal replaced with typical. And he had bones. Bone holds on to lead, so a skeleton is a record of the exposure behind it. His research found modern humans carried a thousand times the lead of their prehistoric ancestors. On campus he became 'the lead man.'

Eli: Natural against normal. Kehoe's whole case lived in the gap between those words.

Mara: And the cost to Patterson had started three years before.

Eli: It came through money and boards, not papers: pressure aimed at funders and trustees. Patterson recalled the Public Health Service refusing to renew his research contract, and the American Petroleum Institute dropping a substantial contract that had backed him for years. 'They not only stopped funding me,' he said, 'they tried to get the Atomic Energy Commission to stop giving me anything.' And oil-industry members of Caltech's board of visitors pressed his dean to let him go.

Mara: He answered with a lecture predicting future scientists would show Ethyl was poisoning people and the environment, and its operations would be shut down.

Eli: Then, in 1970, a National Academies panel on airborne lead, and Patterson wasn't asked. Six industrial toxicologists were on it. He was passed over for fear he was too extreme and unwilling to compromise. Kehoe maintained that grants and panels went by scientific merit and consensus, not deliberate suppression.

Mara: Patterson's reading is that it was deliberate retaliation. And where the pressure landed points somewhere: his environmental and public health grants were the target, while his meteorite isotope work was largely left alone. It cost him funding and very nearly his job, and the fight took the rest of his career, thirty-three years of hearings, lawsuits and media battles. Whether government would act on his numbers or the industry's was the open question.

The Clear Sky

Eli: The first lever was the 1970 Clean Air Act. It didn't ban lead. It gave a new federal body, the Environmental Protection Agency, power to regulate fuel additives found harmful. The EPA proposed cuts in 1972 and announced a phasedown in 1973. Cars from the 1975 model year had to run unleaded, because they carried catalytic converters, exhaust cleaners that needed unleaded fuel.

Mara: And the industry fought it in court.

Eli: A court first set the rules aside as arbitrary and capricious. On appeal they were upheld, with the court saying regulation under the act 'should precede, and hopefully prevent, the perceived harm.'

Mara: By 1986 the limit was a tenth of a gram per gallon. On January 1st, 1996, leaded gasoline for road vehicles was fully banned. Patterson put his part simply: 'My work was used to get the lead out of gasoline.' The EPA later showed the act cut lead emissions by 96 percent in its first twenty years. And the bodies he'd measured changed with the air: blood lead in Americans fell by more than 80 percent after the phaseout. By 1995, the EPA's administrator was calling it 'one of the great environmental achievements of all time.'

Eli: That drop was more than 80 percent, a steep fall.

Mara: Patterson fought the leaded-petrol industry because the lead ruining his Earth-dating samples wouldn't go away, and getting it out meant finding where it came from. The trail ran from his laboratory to the sea to the Greenland ice, and it ended at car exhaust spread over the planet.

Eli: Back in Kent Hall, it was supposed to be duck soup. Those impossibly old samples were the first reading of the air, not the rocks.

Mara: Some of it is still open. Unredacted National Research Council letters could show whether industry lobbyists asked for Patterson's exclusion from the airborne-lead panel, or organizers acted alone. Grant records could show who besides the National Science Foundation paid for the polar trips. And Caltech board records could show whether Ethyl formally offered to endow a chair in exchange for his dismissal, or it stayed an unrecorded verbal proposal.

Eli: For listeners reading further, look into Clair Patterson.

Mara: Follow science with us for more stories as researchers challenge entrenched consensus.

Eli: That's it for today. I'm Eli.

Mara: And I'm Mara. Thanks for listening, and until next time on Angle.