Plutonium – the Most Deadly Substance Known to Man – I Heard That Someplace…

Pu238 powers spacecraft

Pu238 power source for Mars rover Curiosity

Long time readers know we once worked in the American Nuclear Weapons Complex and, specifically, at the Rocky Flats Plant. This blog began when the excellent, first-hand account An Insider’s View of Rocky Flats was published. Since then we’ve ranged far away from Rocky Flats.

Today I’d like to return to my transuranic roots, as it were. Plutonium-239 is an effective bomb because it’s relatively easy to handle in a military setting.

Don’t misunderstand me. It’s still a bomb, and a powerful and scary bomb at that. It must be guarded against misuse, whether accidental or intentional. But the plutonium inside is not terribly radioactive as it sits there (not compared to some medical isotopes) and, provided you keep it contained so no plutonium dusts are inhaled and it doesn’t catch fire, it doesn’t present a huge danger. Not even to Navy personnel who practically sit on nuclear warheads in submarines.

But that’s about radiation. What about toxicity?

Plutonium recently appeared on one of my favorite sites, Skeptoid. The researcher and host, Brian Dunning, periodically posts corrections to past podcasts, and posted this:

I mentioned plutonium as being the most toxic substance known… It’s one of those bits of pop culture knowledge that I uncritically parroted.

[A listener responded.]

The myth of extreme plutonium toxicity can be traced to unsubstantiated statements made by Ralph Nader and other anti-nuclear activists of the 1970s. He was challenged by renowned health physicist, Dr. Bernard Cohen of the University of Pittsburgh, who offered to ingest the amount of plutonium that Nader considered lethal.

I don’t know that I’d volunteer to swallow a dose of plutonium. The government would follow me to collect all my bodily effluvia for way too long to be convenient. But, yeah, as a healthy adult it would mostly pass through me, with little being dissolved or absorbed.

Dunning’s listener provided a link to “a list of substances…which are determined to pose the most significant potential threat to human health due to their known or suspected toxicity and potential for human exposure. Plutonium appears at number 120.” An American federal public health agency keeps the list here. The benzene used at Rocky Flats, once common in college and commercial labs, is more hazardous.

(In case you’re wondering, arsenic, lead, and mercury top the list, followed by vinyl chloride and polychlorinated biphenyls.)

The list was prepared for “substances that are most commonly found at facilities” at hazardous waste sites being cleaned up by the government. Plutonium was not commonly used at such sites. Fallout from old above-ground testing is everywhere, however, so if plutonium were the most hazardous substance known to man (a phrase I recall reading) it would be present at all sites, and should show up higher than #120.

This doesn’t mean the hazards of plutonium should be ignored or that clean-ups are unnecessary. It means that anyone, even a fine researcher, may repeat common claims without much consideration – inculcated, to use a favorite word, by repetition. That’s an error we’re all likely to fall into from time to time. We humans are more likely to believe something if we hear it over and over. I hope, when I’m corrected, I’m as gracious as Dunning.

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About Ponderer

Ponderer also writes science fiction and science-inspired rhyming poetry. Check her out at She worked at Rocky Flats for 22 years - you may know her as Kathy London.

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