JOHANNA MAYER: After the Second World War, Japan was in a bad state. The people were demoralized, American troops had occupied the country, and the economy was just devastated. Entire cities were leveled to the ground.

But amidst the devastation emerged a little beacon of hope, a coastal city called, Minamata, just a day's drive from where the atomic bombs dropped. Minamata had grown into an industrial powerhouse, churning out chemicals used to make everything from plastics to perfume. Employment was up, smokestacks chugged away. The place was thriving.

Until one day, in 1953, an unusual affliction took hold. This affliction would be Minamata's canary in the coal mine. But instead of canaries, the victims were cats.

KAITLYN SCHWALJE: The cats had begun to dance, or that's the best way people could describe it.

JOHANNA MAYER: Meet writer and filmmaker Kaitlyn Schwalje.

KAITLYN SCHWALJE: The reality was much more sinister than it sounds. What looked like cats dancing was really convulsions, uncontrollable and uncoordinated body twitches and spasms. They drooled, spun in circles, and flung themselves into the sea in what the residents of Minamata described as cat suicide.

The cause of this dancing cat fever wasn't demonic possession or a sudden love for dancing. It was a case of environmental poisoning. And the poison was mercury.

JOHANNA MAYER: From Science Friday, this is Science Diction. I'm Johanna Mayer.

KAITLYN SCHWALJE: And I'm Kaitlyn Schwalje. Today, we're talking about the word mercury.

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JOHANNA MAYER: The once town, now city, of Minamata had a serious problem on its hands. This mysterious illness was slithering its way in, first affecting cats, and then every living creature in the city. Pigs got sick. Birds fell dead out of the sky.

And over a few years the symptoms took a turn from unusual to terrifying when in the mid-1950s the first human case appeared. It was a little girl. All the records say about her is that she was five years old.

And in the spring of 1956, she was rushed to the hospital for examination. She struggled to speak and to walk, and like the cats, she had convulsions. Two days after she got sick her two-year-old sister started showing symptoms, then a neighbor.

Soon, eight similar cases were identified. By May, a local doctor reported what he called, an epidemic of an unknown disease of the central nervous system. Because the cases seem clustered, people believe the illness was contagious. Homes were disinfected, and afflicted individuals were isolated and even shunned by other Minamata residents.

KAITLYN SCHWALJE: The strange symptoms became known simply as the strange disease, and eventually Minamata disease. Soon, a formal investigation was underway to find the cause of this mysterious epidemic. Researchers from the nearby Kumamoto University were enlisted in the search.

They interviewed more than 100 households, examining patients, noting where they lived, what they drank, what they ate, and came to the conclusion that whatever it was it probably wasn't contagious. It seemed it had something to do with eating local fish. All eyes quickly shifted to Minamata Bay.

If it had been contaminated, there were plenty of suspects to choose from. But eventually, the investigation narrowed in on one company-- Chisso, the same company responsible for turning the humble village into an industrial city. At 1.1 in every 10 Minamata residents worked for Chisso. But, and here's a big but, while it was busy boosting the local economy, Chisso was also poisoning the local water with mercury.

JOHANNA MAYER: Mercury, element number 80 on the periodic table. Maybe you've seen silvery globs of it spring from the glass shards of a broken thermometer. The only metal liquid at room temperature, mercury moves like water, but beads and gathers.

Aristotle called it quicksilver. And in a respectful nod, mercury, the element, was named after the Roman messenger God Mercury, speedy and tricky.

KAITLYN SCHWALJE: And before we knew it could kill us, humanity had a steamy love affair with the stuff. Alchemists believed mercury was a raw material from which you could create any metal, including gold. Neolithic cultures painted blood red mercury sulfide onto skulls and bones in burial rituals. And mercury and it's compounds have been promoted as a cure all for centuries.

Used to treat everything from Abraham Lincoln's melancholia, to Louisa May Alcott typhoid fever, the first emperor of a unified China, Qin Shi Huangdi, even drank mercury in a tonic, believing it could grant immortality. And we loved it, until it started messing with our heads. One of the early glimpses of mercury's Jekyll and Hyde quality came in the late 19th century.

For 200 years, hat makers had been using mercury salts to soften and prepare fur pelts. But by the 1800s, milliner's discovered the unfortunate side effect of losing one's mind. Hatmakers soon became known for their tremors and slurred speech and erratic behavior. This is where some people think we get the phrase "mad as a hatter."

And eventually, it became common knowledge. Mercury is not the elixir of life. It's more like the opposite.

JOHANNA MAYER: Still, we do encounter small amounts of mercury in our day to day lives. It's in some teeth fillings. And a compound of mercury is used in some vaccines as a preservative, about the same amount as you get from eating a can of tuna. To be clear, there is no evidence that this small amount harms us.

KAITLYN SCHWALJE: But in larger quantities, or chronic exposure, different story. By the 1950s, at least we knew better than to drink it. But mercury was a hard habit to kick. It was the lifeblood of global manufacturing, a vital component in making batteries, light bulbs, paints, pesticides, the list goes on. And back in Minamata, the Chisso factory is dumping it out to sea.

Methylmercury, and of all the types of mercury, including all known compounds, methylmercury is the one you most want to stay away from. Its absorption rate is nearly 100%, meaning that when you swallow it, almost all of it makes its way into your blood and spreads to every part of your body and accumulates in high concentrations in the brain. On an MRI scan, you can actually see its effects. The poison brain looks deflated.

JOHANNA MAYER: So yeah. Methylmercury is bad. But surely, what Chisso was doing was different. Surely, a tiny bit of mercury mixed with all that water would dilute it enough to render it harmless. The argument for all pollution ever.

Mercury was the wonder ingredient the world over. And the Chisso factory did not want to let it go. Chisso needed mercury to produce a chemical called, acetaldehyde, which was used in the production of polyvinyl chloride, or PVC, a.k.a. plastic. It was big business, and its byproduct, was mercury.

So despite what seemed like a very obvious link between the factory's operations and the recent poisoning cases, production in Minamata was not going to stop without conclusive proof. Chisso was like, yes, we are dumping waste and byproducts, including mercury, into the water. But look, these researchers don't know what they're talking about. They're peddling all sorts of environmental toxin theories.

First it was manganese, and selenium, and thallium. They can't make up their minds. Why would this mercury theory be any more accurate?

KAITLYN SCHWALJE: But with each year, more and more people got sick, dozens of cases with new and equally terrifying symptoms-- numbness, muscle weakness, narrowing fields of vision, insomnia, and death. And whatever was happening, it was also reshaping the next generation of Minamata residents. Babies were born with higher rates of what looked like cerebral palsy, fewer boys were born, and as news of the strange Minamata illness spread, it decimated the local fishing industry. No one wanted to buy their fish.

But Chisso wasn't listening. The government wasn't listening. And fishermen, stripped of their livelihoods, were furious.

In 1959, six years into the crisis with nowhere to turn, they rioted. Over 1,000 fishermen converged on company grounds to demand compensation. After Chisso refused to negotiate, hundreds rushed the building and trashed the place, throwing typewriters out of the windows.

When police showed up, fishermen smashed the windshield of one of their jeeps. Fighting continued for hours, leaving dozens injured on both sides. Still, Chisso didn't budge. And for the next decade, the press seemed sympathetic to the company, challenging the victims, and covering the story in a way that even suggested they were insane.

JOHANNA MAYER: Chisso did try to appease the locals at one point. They started making some annuity payments to families, but insisted that the payments weren't compensation, they were simply a quote "token of the company's sympathy." And in 1959, they made a big show of installing a fancy water filtration system. They called it, the Cyclotor. Chisso president, Kiichi Yoshioka, even drank a glass of water, filtered by the system, as a proof of confidence.

What Chisso didn't tell people, is that the glass of water the president drank wasn't actually wastewater. They also didn't tell anyone about a recent experiment by one of their employees, Dr. Hajim Hosokawa. Hosokawa was the director of the company's factory hospital, and he'd been tracking the disease from the start. He was actually the one who first reported the outbreak to the local health department.

And when suspicion zeroed in on industrial wastewater, Hosokawa decided to run a simple experiment. He took a little bit of wastewater from the plant, sprinkled it on some cat food, fed it to a cat a little bit each day. And sure enough, after a few months, the cat began to dance. Clearly, there was something bad in the water.

KAITLYN SCHWALJE: But this was industrial wastewater, concentrated stuff. Of course this was going to make cats sick. That's why the company was dumping it out to sea, so that it would get diluted into harmless concentrations. Except there was a little problem with Chisso's dilution solution for pollution-- biology.

Methylmercury dumped into the sea might start off as relatively dilute, but fish absorb it from the water through their gills, and they get it in their food. The mercury toxin works its way up the food chain from plankton, to little fish, to bigger fish, and even bigger fish, getting more and more concentrated along the way. So that by the time it lands on a human plate, it's a serious dose of poison.

JOHANNA MAYER: Chisso hushed up Dr. Hosokawa's research. They ordered him to stop his experiments, and eventually agreed to let him continue only if he kept them a secret. But Hosokawa didn't let up.

A couple of years later, when he retired, he took all his secret specimen's with him, sent them to another researcher at a nearby university, and finally they had all the pieces-- mystery solved. In 1968, 12 years after that little five-year-old girl first presented with convulsions and trouble walking, the local government officially confirmed the cause of Minamata disease-- methylmercury, and Chisso was the culprit.

KAITLYN SCHWALJE: By the time the official verdict came, Chisso had stopped dumping mercury, not because the government forced them to stop, but because the company switched to a new technology for developing plastics, a technology that didn't require mercury as a catalyst. But the damage was done, and Chisso had to pay out big time for its crime, about $2 billion. To date, more than 65,000 people have applied for victim compensation.

JOHANNA MAYER: Minamata turned a corner after the poisoning. The mercury-laced sediment was dredged up and buried. Newly installed nets contain the contaminated fish within Minamata Bay, away from fishermen and the hungry mouths of Minamata residents. And regular testing of the water, fish, and air quality tracked levels of environmental pollutants.

Minamata became a real Cinderella story. Once an industrial polluter whose name roused fear in neighboring Japanese communities, became something of an environmental utopia. The waist, low carbon, hellbent on renewable energy and safe forestry, and fishing practices. At the height of its transformation, it even won Japan's top eco-city contest.

KAITLYN SCHWALJE: The world was not better off for the Minamata disaster, but it learned a necessary lesson. Outside of Japan, scientists and industry giants took notice of both the havoc little mercury could inflict when unrestrained, but also of the good that came in containing it. In 2013, an international treaty was adopted. It was named the Minamata Convention on Mercury.

Over 120 countries signed on, making a pact to ban new mercury mines and control releases and to never repeat the Minamata tragedy. Using mercury refashioned tools and processes to improve the world, we made preservatives, telescopes, thermometers, and neon signs. But in the process, we also poisoned ourselves and the environment. In order to get the good without the bad, we had to learn its ways because mercury, enchanting in its silvery liquid form, the stuff of immortality potions and dancing cats, was a force to be reckoned with.

JOHANNA MAYER: This episode of Science Diction was written by Kaitlin Schwalje and produced by Elah Feder and me, Johanna Mayer. Elah is our editor and senior producer. Daniel Peterschmidt sound designed this episode and composed all the music, except the tembo march which is by Tim Garland from the Audio Network. We had fact checking help from Danya Abdelhameid and Robin Palmer.

Nadja Oertelt is our chief content officer, and she recently pitched us a story for the show. She says, few people realize that the expression "to squirrel away" originally referred to the once popular hobby of squirrel watching, as in, I'm going to squirrel away in Sri Lanka next month. I hope I see a grizzled giant squirrel.

There were squirreling societies, squirreling magazine's. Most respectable homes had a squirrel dropping display case at the entrance. From 1962 through 1967, the mayor of Cleveland was a squirrel.

Unfortunately, squirrel watching was so deeply engrossing that our mortal enemies, the birds, soon realized they could exploit our squirrel watching stupor to viciously peck the backs of our heads. And so for survival purposes, we switched to watching birds. And that's where we get the phrase, "to squirrel away" from squirrel watching.

KAITLYN SCHWALJE: And before we knew it could kill us, humanity had a steamy love affair with the stuff.

JOHANNA MAYER: Yeah, Nadja. Everyone knows about squirreling. Not a story. See you next week.

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