Hey Dr. Zoomie – every now and again I hear things about plutonium – that it’s the most toxic substance known, that it doesn’t occur in nature, that the Manhattan Project doctors would amputate an entire arm or leg if even just a little bit got into a wound, that some was released when Fukushima melted down…that sort of thing. Can you tell me how much of this is true and how much is BS?
Well…There’s a nice mix of misperception, reality, and BS in here. So let’s tackle these one at a time and see where each one falls out.
Is Plutonium the most toxic substance known?
|Substance (a few examples)||Fatal dose (micrograms per kg)|
|Crystalline botulinus toxin||0.000000005|
|Botulinus toxin A||0.000005|
Well…during the Manhattan Project there were 26 workers who accidentally ingested plutonium in quantities that are today considered to be fairly high – in excess of what, today, we would consider to be a lethal dose. Forty years later 22 of them were still alive – which would be surprising were plutonium really as toxic as many believe. Interestingly, a muckraking book about human experiments involving plutonium support this – the author listed case after case of terminally ill patients injected with plutonium who were unexpectedly still alive decades later – something we wouldn’t expect from “the most toxic substance known.” Don’t get me wrong – plutonium is toxic, along with lead, cadmium, selenium, and a number of other elements. And don’t even get me started on mushroom or shellfish toxins – those can make even toxicologists nervous (at least according to a toxicologist who used to work for me). So, sure, plutonium is toxic – it’s just not as extravagantly toxic as many believe, a lot of people have survived accidental and deliberate intake, and there are a number of naturally occurring toxins that are much more dangerous. The US Transuranium and Uranium Registry (https://ustur.wsu.edu/) maintains the most complete set of information in the world on plutonium intake and the resulting health effects. Rating: largely BS
Fatal doses of some toxins – and these don’t include shellfish, mushrooms, or ricin!
Is plutonium an entirely synthetic element?
Nope – I’ve got traces of plutonium in my home in some of the uranium minerals I collect – it’s formed when an atom of U-238 (which is 99.2% of the uranium atoms found in my uranium minerals) capture a neutron – the neutron can come from cosmic rays or from the spontaneous fission of U-238. The existence of natural plutonium was predicted in the 1940s and confirmed in 1951 by Glenn Seaborg and Charlies Levine. But wait – there’s more! It turns out that plutonium is also formed when stars explode – in this case, the heavier isotope Pu-244. In 1967 the geochemist P.K. Kuroda identified Pu-244 in meteorites that apparently intercepted some debris from a nearby supernova and more recently Pu-244 was found in deep-sea sediments (another supernova-formed radionuclide, Fe-60, has also been found in deep-sea sediments, showing that Earth has passed through the remnants of at least a few nearby supernova in the last few tens of millions of years. On Earth, natural plutonium exists as a handful of atoms here and there – supernovae make the stuff by the ton and distribute it over tens of lightyears. Rating: largely – but not entirely true, especially if we look beyond the Earth
Did the Manhattan Project doctors actually amputate an entire limb for just a little bit of plutonium?
Indeed they did – but they weren’t necessarily following what are now considered to be “best practices.” In their defense, plutonium had been discovered only a few years earlier and it existed in only microscopic quantities until 1944. The doctors knew that, in animals, it took only a few milligrams of plutonium per animal to be fatal while other experiments suggested that plutonium was more dangerous than radium due to the way that it distributed in bone. There wasn’t much time to do a full-blown toxicology study during wartime so the doctors had to go with their best (and safest) guess – amputating a limb would keep the plutonium from spreading through and poisoning the rest of the body. With time, more-involved medical studies helped to elucidate how plutonium distributed itself through the body and demonstrated that it was not as toxic as first thought – medical practices have changed over the last 80 years and now include administering “decorporation agents” to help remove plutonium from the body as well as just letting the plutonium pass out of the body naturally over time; the exact treatment depends on the amount of plutonium to which a person was exposed. Rating: correct, but based on a misunderstanding at the time
Was plutonium released from the reactor when Fukushima melted down?
Probably not. There was plutonium found in the soil near the Fukushima reactor plant, but it likely did not come from the reactor accident – there was a reasonable amount of plutonium released during the years of atmospheric nuclear weapons testing, as well as by the detonation of the plutonium-fueled “Fat Man” bomb during World War II. There are a number of isotopes of plutonium produced in nuclear reactors and by nuclear weapons (see how that happens in the next question) – some are relatively short-lived and others with much longer half-lives. If the plutonium around Fukushima was from the reactor then we’d expect to see both short-lived and long-lived nuclides…but that’s not what we saw. The only plutonium isotopes found were the longer-lived ones, strongly suggesting that they came from the nuclear weapons testing in the 1940s and 1950s, not from the much more-recent reactor accident. Rating: misguided
Bonus question! Why was there plutonium in the Fukushima reactors?
Nuclear reactor fuel is more than 90% U-238. Nuclear fission produces a lot of neutrons – more than a trillion neutrons pass through every cubic centimeter of the reactor in each second. It’s inevitable that some of those trillions of neutrons will be capture by some of those billions of uranium atoms, producing U-239 that decays to form Pu-239 over the next few weeks. But reactors will operate for over a year between refuelings, and individual fuel elements will remain in the reactor for several years before they’re finally removed. During this time there’s an appreciable amount of plutonium formed – not just Pu-239, but heavier isotopes as well. By the time the fuel rod is removed it will contain Pu-239, Pu-240, Pu-241, and still-heavier nuclides, as well as their decay products (e.g. Pu-241 decays to form Am-241, which decays to form Np-237). This happens in every uranium reactor in operation.
Addendum (Post updated on 7/18/2023)
Since posting the original piece I contacted the wonderful people at the US
Transuranium and Uranium Registries (https://ustur.wsu.edu/), asking about the long-
term effects of plutonium intake among some of the people they studied. They sent me
several papers and studies that were quite instructive. I won’t go into all the details here,
but there are a few things that are especially interesting.
From the standpoint of this posting, the most interesting information was found a table
published in a paper by scientists Baruch Gold and Ron Kathren (Causes of Death in a
Cohort of 260 Plutonium Workers) published in the journal Health Physics in 1998. The
USTUR, among other things, collects information and tracks the health of workers who
inhaled or ingested uranium, plutonium, americium, and other heavy, radioactive
elements. In this paper, Gold and Kathren point out that, as of that date, about a third of
the registrants had died and, of the survivors, the majority were over 70 years of age
with 7% over 80 years of age – in other words, of the entire population of about 700
registrants the average lifespan is likely going to exceed the expected lifespan for this
group of people. When accounting for what’s called the “healthy worker” effect (which
accounts for the fact that people with jobs tend to have better health care, a better diet,
more exercise, and so forth) it’s likely that the average lifespan of this group will be
comparable to we could expect of any similar group anywhere. Or, to be a little less
convoluted – it seems likely that their exposure to plutonium will not end up affecting the
lifespan of these workers, taken as a whole.
There’s also an interesting table in Gold and Kathren’s paper showing that, of the 260
workers who had died as of the date the paper was written, 87 (about 35%) had died of
cancer, and 66% of those had died of respiratory cancers; considering the rate of
smoking (about 40-50%) at the time these registrants were working, this is comparable
to similar groups in the US as a whole. In other words, plutonium exposure does not
seem to have caused these peoples’ illnesses nor their deaths.
The reason for mentioning this is to note that, contrary to what many think, we have a
fair amount of solid medical evidence that shows plutonium is not extraordinarily
dangerous – that people can (and have) been exposed to it, survived, and lived for
many years afterwards.
Photograph by Maksym Kozlenko