80. Mercury: Fatally Toxic And Probably In Your Mouth

Even if you hate tuna, have flawless teeth, and only use digital thermometers, humans have historically not been shy about getting a mouthful of mercury.

Featured above: In Jean Cocteau’s 1950 film Orphée, the title character enters the underworld by walking through a magic mirror. The effect was achieved with one enormous vat of mercury.

Show Notes

Mercury reacts with aluminum to form an amalgam in much the same way it reacts with gold, silver, and several other metals. Since modern airplanes are made almost entirely of aluminum… well, it would be very bad if that reaction took place 30,000 feet above the ground.

The following video starts with a demonstration of mercury forming an amalgam with gold, then shows the even wilder reaction mercury has with aluminum:

Being such a visually striking element, there are lots of videos online of people doing strange things with mercury. For instance, here’s CodysLab doing the floating anvil trick:

Oh man, I didn’t even get to go into the ridiculous world of intrigue that is the tuna industry. It’s pretty wild, Slate has more.

References are forthcoming, as well as more show notes, if I have time. In the meanwhile, one last tidbit: The Matrix is a movie that’s rife with allusions and homages to famous films and philosophical texts. There’s good reason to believe the scene pictured below is a reference to the Cocteau film featured at the top of this post. (The Wachowskis used computers rather than mercury, though. The Matrix is a movie that holds up surprisingly well, but in this case, I think the older effect aged much better.)

Episode Script

Only three elements share their names with both {planets in our solar system} and {gods in the Roman pantheon}. Four, if you count tellurium. Mercury has held that distinction far longer than any of the others, and it’s also the most thematically consistent.

The god came first, of course, sometime around the fourth century BCE. Mercury was the patron of merchandise, as well as trickery, travel, and communication. Being quick on one’s feet can be helpful in all those endeavors, and he was, in the most literal sense, fleet of foot. That’s the reason why his name was lent to the other two things. The planet, being the closest object to our sun, appears to travel across the night sky faster than anything else, so the association between the two was a no-brainer.1

The element, meanwhile, is a surprisingly slippery liquid that can also move pretty swiftly. For this reason, the Greeks called it hydrargyrum, loosely meaning “silver water” or “quicksilver,” and the origin of its symbol, Hg.2 Additionally, the alchemists thought mercury just needed a little push in the right direction to turn into gold, the metal that was closely linked with the sun. Coincidentally, on the periodic table, mobile mercury is directly adjacent to solar gold, just like the planet.

You might not find any of this particularly surprising, but there’s another connection you could draw between the deity and the atom. Along with his other roles, the Roman god was what’s known in mythology circles as a psychopomp — a figure who helps usher the recently deceased into the afterlife. The Valkyries did this in Norse mythology, and the Grim Reaper can be seen as a modern-day psychopomp.3

This framing works for the element as well, because for all of its many incredible traits, one you should surely keep in mind is that mercury could lead you to your death.

You’re listening to The Episodic Table Of Elements, and I’m T. R. Appleton. Each episode, we take a look at the fascinating true stories behind one element on the periodic table.

Today, we’re going mad over mercury.

A quick glance is all it takes to appreciate the unique allure that quicksilver has held through the ages: It’s liquid metal! When James Cameron needed to invent a cybernetic assassin more terrifying than Arnold Schwarzenegger, he gave it the power to turn into silvery goo.

But that’s not the whole picture. As we learned in episode 31, gallium liquefies just above room temperature. If you’ve seen what that looks like, then you know that gallium makes a lackluster substitute for mercury. Something just seems off about it.

A big part of it comes down to either material’s ability to wet a surface; that is, to adhere to a surface it touches. Mercury is very “dry.” When spilled on clothing, mercury doesn’t get soaked up. It just keeps rolling. Similarly, skin and wood and glass are all nonstick surfaces for element 80. That’s actually what made mercury such a useful liquid for thermometers and barometers. It would expand and contract without sticking to the glass tube, allowing for clean, accurate readings of temperature and pressure.

Gallium, on the other hand, is very wet. When held with bare hands, it will actually stain the skin a dark graphite color.

Mercury also has a very high coefficient of surface tension. In other words, it holds itself together really tightly. Small amounts of mercury can bead up into globules that are almost perfectly spherical. Combined with its inability to stick to most surfaces, a mercury spill has a tendency to scatter as minuscule droplets, spread far and wide, and worm its way into the tiniest nooks and crannies. It’s a huge pain in the tuchus to clean up spilled mercury.

In comparison, spilled gallium acts more like milk, and unless it’s a hot summer day, eventually it’ll re-solidify, making cleanup relatively easy.

A final notable difference between the two is their density. A kilogram of mercury takes up less than half the space a kilogram of gallium does — and gallium isn’t exactly light. Nearly anything will float in a big enough pool of mercury, including bullets, cinder blocks, and even anvils.

The toxicity is kind of a big deal, though, so for as mesmerizing as mercury is, it’s been replaced by gallium and other materials except when strictly necessary.

Using the periodic table as our map, mercury’s toxicity is to be expected. Cadmium is directly overhead in group 12, and the rest of this period includes thallium, lead, polonium, astatine, and radon. We find ourselves once again in Poisoner’s Row.

One of the biggest problems with mercury isn’t just that it’s poisonous, but once it gets into an ecosystem, it stays there basically forever. This famously became a known public health issue in the 1970s when a chemistry professor decided to test mercury levels in canned tuna. The alarmingly high levels within prompted greater testing, and ultimately, the FDA issued a recall of more than a million cans of tuna.4

Scientists thought that the mercury might have resulted from wanton industrial pollution that had been on the rise over the previous decades. Eventually, though, someone who worked at a museum realized they had a can of tuna that was manufactured in the 19th century and never opened. They tested the meat in that can, and it exhibited mercury levels just as high as contemporary tuna. This is not a new problem.

Tuna accumulates high amounts of mercury through a process called biomagnification. Plankton absorb toxins from their environment, and some of those toxins can’t be excreted. So the plankton acts to concentrate toxin levels within its own body. Other animals come along and eat the plankton, concentrating the toxins further, and so on. An apex predator in such an ecosystem subsists off animals that have already been consolidating mercury for generations before further intensifying mercury levels in its own body. That’s why fish like sharks and tuna display the highest amounts of mercury.

Coincidentally, tuna often has a lot of selenium, too, and selenium happens to counteract the toxic effects of mercury. That’s why it went unnoticed for so long, and why there’s debate today over just how dangerous it is to eat tuna.5 As we’ll see later, the mere presence of mercury isn’t necessarily a good indicator of danger.

In other contexts, though, the hazards presented by element 80 are more certain.

The old saying “mad as a hatter” is based on historical truth, as mercury-induced psychosis was an occupational hazard for hat makers as recently as the early 20th century. Hatters would use mercury nitrate to separate fur from an animal’s pelt and then matt that fur into felt. Work with the substance long enough, and a hatter would probably come down with a case of erethism mercurialis.6 7 8

It’s a neurological disorder that can cause full-body tremors and behavioral changes like depression, shyness, and irritability. Particularly far-gone cases could cause irreparable damage to the kidneys, brain, and other organs.

The debilitating effects of mercury have been suspected for thousands of years, but that didn’t stop physicians from prescribing it as medicament for just as long. It was just such a weird material that it had to have some curative ability. It was prescribed for influenza, parasites, melancholy, and just about anything else. It actually did help soothe the sores of syphilitic patients, although it did nothing to actually cure that affliction.9

You might wonder why anyone would use mercury as medicine when they knew it could kill. In this case, it’s for much the same reason as antimony: mercury is a potent laxative. Sometimes that is the effect a patient desires, but even when it’s not, people believed that this might purge an ailment from a sick person’s body.

In the late 18th century, Dr. Benjamin Rush was one of the most enlightened minds in America. He was a physician, a professor, the Surgeon General of the Continental Army, and one of the 56 men to sign the Declaration of Independence.10 11 He advocated for a number of causes that would have been quite progressive in his time, such as free public education, opposition to slavery, a humane approach to the treatment of mental disorders, and the importance of personal hygiene.

In 1803, after purchasing the Louisiana Territory from France, Thomas Jefferson sought to establish a foothold in the western half of North America before any European powers could stake a claim. (The preexisting civilizations were not given the same consideration, for… some reason.) So Jefferson commissioned Meriwether Lewis and William Clark to lead a team of 45 pioneers, scientists, interpreters, and navigators to blaze a trail to the continent’s edge. They also brought a dog.12 13 14 15 16

Preparations for an expedition as dangerous as this had to be thorough, so Jefferson introduced the party to the highly esteemed Dr. Rush. He taught Lewis all about frontier medicine, including the right way to practice bloodletting. He also provided medicinal wine, fine Turkish opium, and 600 “Bilious Pills,” mercury-based laxatives that were also known as “thunderclappers.” For all the nice things there are to say about Dr. Rush, it would seem that the Lewis and Clark expedition succeeded in spite of his help, rather than because of it.

That success was truly remarkable, for it was an incredibly perilous journey. The explorers were beset with exotic diseases, hostile wildlife, rugged terrain, and at least one occasion of terrible judgement. On August 11, 1806, Pierre Cruzatte mistook Lewis for an elk and shot him in the derriere.

Lewis was bothered by this development — he later wrote, “I called out to him damn you you have shot me … but received no answer.” — but after a few weeks, he fully recovered.17 Amazingly, only one member of the team died over the three-year journey: Sergeant Charles Floyd, who perished after contracting appendicitis. It’s not exactly a glamorous way to leave this world, but at least his friend didn’t shoot him in the butt.18

Everyone else who embarked on the journey, including the dog, survived to tell the tale. They returned to St. Louis on September 25, 1806, with maps, illustrations, specimens, and artifacts providing a rich and priceless picture of the continent’s western half.

It’s especially strange, then, that the Lewis and Clark expedition was seemingly wiped from public consciousness almost immediately. The journals written by the explorers, which were extensive and comprehensive, were never once published in the century that followed. Nineteenth-century historian Henry Adams wrote nine volumes about the Jefferson and Madison administrations, and the expedition warranted nothing more than a single, rather dismissive sentence. Truly a footnote in the history books.

The expedition was sort of rediscovered in 1906 after one publisher realized how valuable these materials were. Archaeologists and historians, newly interested in the party, wanted to reconstruct the excursion by following in the footsteps of Lewis and Clark. Tracking a trail that’s been cold for generations might seem like an impossible task, yet historiographers have managed to accomplish precisely that — and it’s thanks to Dr. Benjamin Rush.

Life on the trail meant eating what was available, rather than what might be ideal, and most of the time that amounted to meat. Bison, beaver tail, elk (obviously), and even the meat of dogs who were much less fortunate than the one who accompanied them. (Clark was the only one who couldn’t bear the thought.) Sometimes the pioneers ate as much as nine pounds of meat per day.

You gotta do what you gotta do, but that can wreak havoc on a person’s intestinal tract. In other words, these guys had plenty of reason to break out Dr. Rush’s thunderclappers. And once ahem released into an environment, mercury sticks around — even if it’s not getting eaten by algae. I don’t know who had the job of digging up bygone latrines, but it worked. Historians were able to reconstruct the expedition’s trail by connecting the dots they left littering the landscape.

So how come hatters suffered a slow descent into lunacy as a result of their work with mercury, but these guys could pop mercury pills like Tic Tacs while walking across the country and back?

It has to do with the form in which the mercury is encountered. Liquid mercury is actually not its most toxic form. That’s why you can find countless videos online of people touching liquid mercury, or even standing in tubs full of the stuff, with little fear of harm. Don’t get me wrong, it’s not a good idea to play with liquid mercury, but it’s not the most foolish thing you can find on YouTube.

The biggest problem with liquid mercury is that it readily turns into its more toxic form. A puddle of liquid mercury will slowly but steadily evaporate, filling the surrounding air with invisible vapor. Unlike the liquid form, which can pass through the digestive system mostly intact, mercury vapor is easily absorbed by the lungs, where it’s quickly ferried everywhere else in the body.

Inhaling small amounts over a long period of time can cause chronic poisoning, but a big enough whiff can also kill with startling speed. The sailors aboard the HMS Triumph learned this lesson in the most unfortunate way one stormy night in 1810.

A Spanish ship off the coast of Cadiz found itself in need of assistance amidst the rain and rocking waves, and the Triumph was glad to provide assistance. They were also glad to help themselves to the cargo aboard the Spanish ship, which mostly consisted of leather bags full of mercury. On the Spanish ship, these bags had been kept isolated, but the sailors on the Triumph kept their haul in their own living quarters. It wasn’t long before people started exhibiting classic signs of acute mercury poisoning, like swollen gums and excessive salivating. Many of the sailors fell gravely ill, and a few died, but the livestock fared far worse: Mercury vapor killed every last animal on board the Triumph, right down to the cockroaches.19

So keep safety in mind while you look for the perfect sample of mercury to display in your element collection. And try not to panic when I say there’s a good chance you already have a little mercury firmly planted in your skull. It’s okay! I do, too.

For centuries, mercury has been used in dental fillings — as far back as the seventh century CE in China. In many ways, mercury is the perfect material for such an application, because it demonstrates some unique and remarkable properties.

When alloyed with certain other metals, like gold, silver, and tin, mercury absorbs and liquefies the other metal to form what’s called an amalgam. It’s truly bizarre to witness — it happens quickly, and the liquid will actually pull more material toward itself like some kind of hungry blob. This all happens at room temperature, by the way, so be careful with any jewelry you might be wearing while working with mercury. The resulting paste remains pliable for a while, but as it dries, it expands. This means when it’s placed within a cavity, it will grow to fill in every little crevice in the tooth — important for preventing further infection.

When locked up in amalgam form, the mercury within is generally regarded as inert and safe.20 21 Nonetheless, some people see it as a risk not worth taking, especially when newer alternatives are completely free of hazardous chemicals — and also blend in more easily than shiny metal.

Transitioning away from amalgam fillings will make the world safer in at least one regard: Dental fillings are the most common way that crematoria introduce mercury to the atmosphere. Regulations are starting to make this less of an issue, but it serves as a rather morbid reminder that the things we put into our bodies don’t just affect ourselves.

Aside from some real corner cases, like electrical switches that recognize when they’re being tilted, mercury is a lot less accessible than it used to be. It says a lot when the most reliable source of an element is a corpse. Personally, I would not recommend pursuing such an avenue of acquisition unless you happen to be a medical student with a very loose interpretation of what it means to donate one’s body to science.

Thanks for listening to The Episodic Table of Elements. Music is by Kai Engel. To learn why you can’t bring mercury on an airplane, visit episodic table dot com slash H g.

Next time, we’ll talk less about gallium and more about thallium.

Until then, this is T. R. Appleton, reminding you to keep your sample of mercury in an airtight and shatter-resistant container, the same way you might already be keeping any osmium tetroxide.


  1. Mythology Source, Mercury: The Roman God Of Trade. Mike Greenberg, October 26, 2020.
  2. Elementymology And Elements Multidict, Mercury. Peter van der Krogt.
  3. Listverse, Top 10 Psychopomps Of Ancient And Modern Mythology. Michael van Duisen, June 15, 2013.
  4. The New York Times, Mercury In Tuna Leads To Recall. Richard D. Lyons, December 16, 1970.
  5. Ecotoxicology And Environmental Safety, Biomagnification Of Mercury And Its Antagonistic Relationship With Selenium In Yellowfin Tuna Thunnus albacares In The Trophic Web Of Baja California Sur, Mexico. Alfredo Ordiano-Flores, Rene Rosíles-Martínez, and Felipe Galván-Magaña, December 1, 2012.
  6. UniSci, ‘Mad Hatters’ Long Gone, But The Mercury Lingers On. Johan Varekamp, June 25, 2002.
  7. History.com, Where Did The Phrase “Mad As A Hatter” Come From? Elizabeth Nix, last updated August 22, 2018.
  8. Amusing Planet, The Mad World Of Hate Making. Kaushik Patowary, February 19, 2021.
  9. The Toronto Star, Mercury Was Considered A Cure — Until It Killed You. Lydia Kang, edited excerpt from Quackery, Nate Pedersen. October 22, 2017.
  10. NPR, ‘Rush’: The Other Founding Father From Philadelphia Named Benjamin. Melissa Block, September 2, 2018.
  11. Reference.com, How Many Men Signed The Declaration Of Independence? Last updated April 9, 2020.
  12. National Geographic, Sex, Dog Meat, And The Lash: Odd Facts About Lewis And Clark. Anthony Brandt, December 8, 2003.
  13. Encyclopedia Britannica, Lewis And Clark Expedition. Jay H. Buckley, last updated October 22, 2020.
  14. History.com, Lewis And Clark Expedition. Last updated March 16, 2021.
  15. Discovering Lewis & Clark, Lewis’s Dog Seaman.
  16. The National Park Service, Seaman.
  17. Discovering Lewis & Clark, Hunting Accident: Lewis’s Closest Call.
  18. Sioux City History, Floyd, Sergeant Charles.
  19. Gizmodo, This Shipwreck Gave Doctors The First Clue Mercury Might Not Be Good For You. Esther Inglis-Arkell, December 7, 2015.
  20. AZ Central, When Did They Stop Using Mercury In Fillings? Diane Craig, last updated September 30, 2017.
  21. WebMD, Is Mercury In Fillings Really A Problem? Reviewed by Jacqueline Brooks, May 29, 2001.

9 Replies to “80. Mercury: Fatally Toxic And Probably In Your Mouth”

    1. I’ll answer these in order!
      1. Nothing, really. The way I’m using them, they are synonymous and interchangeable.
      2/3. Hm, what’s the connection between mercury and bismuth or zinc? I know zinc shares a group with mercury, but that’s about it.
      4. Copernicium, one of the extremely short-lived elements we’ve only ever seen in a lab.

    1. When it comes to materials science, there’s a focus on those materials’ physical properties. I suppose someone felt that “material” was the most suitable word in that case.
      And yep, bismuth is non toxic!

  1. HGTV – Hahaha. Great work, one of your best. I always listen out for the little punch line at the end. Tried telling my son how funny it was but he just didn’t get it.

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