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Deep dive: Mercury’s promise of gold in South America

Kathleen Schuster
April 18, 2024

Mercury’s a known pollutant in fish, but did you know one of the biggest mercury emitters is actually small-scale gold mining? From sunken ships to shihuahuaco trees, we take a deep dive into the astounding history and science of mercury and the solutions that could break its toxic cycle.


In this episode of Living Planet, we delve into the fascinating history and science of mercury, and how it came to be a major pollutant in artisanal and small-scale gold mining.  

We speak with France Cabanillas, forestry engineer and project coordinator for the non-profit called Pure Earth in Madre de Dios, Peru; Ari Feinberg, postdoctoral fellow at the Blas Cabrera Institute of Physical Chemistry in Spain; Corey Malcom, lead historian for the Florida Keys History Center in Key West and Mario Rodas, the Environment and Energy Program Officer for the UN’s Development Program in Ecuador.

You can listen to this episode by clicking on the play button above. To hear more episodes of Living Planet, go to https://pod.link/livingplanet.

Got a question for us? Email livingplanet@dw.com. And, if you like the show, leave us a rating and review on whichever podcast platform you use – and tell a friend! 



Kathleen: Let’s look at those pictures that you sent me. Yeah, explain what I’m looking at here?

France Cabillinas: The next picture you can see is two pieces of clean gold […] both of them were produced by the miners, no?


Without mercury.


France: Without mercury.

Kathleen: This is Living Planet, I’m Kathleen Schuster. The man you just heard, France Cabanillas, works in Peru’s Amazon rainforest. A big part of his job is to minimize the impact of gold mining in the Amazon.

And that means reducing the use of mercury in gold production. You see, mercury, as it turns out, is a cheap and fast way to extract gold. Pretty much anyone can do it. Which is why it’s become such a big pollutant in the Amazon. And that’s what France Cabanillas would like to change.

Kathleen: Let’s look at the next picture.

France: Yes, you can see the shaking table. In the end it's the the gold powder that is in the very yellow color. Don’t know if you can see?

Kathleen: How long does this take compared to using the shaking table take compared to using mercury?

France: Ah, the shaking table for example it can takes one hour.


But with mercury, 30 minutes.


This practice of using mercury to extract gold is by no means unique to South America. On the contrary. It’s a widely practiced method used across the world.

But, the reason we’re going to look at South America in this episode is because there’s growing evidence that forests play an unparalleled role in cleaning up mercury pollution. And the Amazon rainforest is one of the most important “mercury sinks”.

So, on this episode of Living Planet, we’re doing a deep dive into mercury. The science and the history behind it. And the vicious cycle it’s created in South American gold mining that goes back hundreds of years.

A little good news upfront: there are solutions to this problem, and we are going to hear about them in this episode.

Stay with us.


Before we get into the complexity of mercury pollution and small-scale gold mining in the Amazon, it’s helpful to know how mercury works in the first place.

To get the ball rolling, I called up a Canadian researcher by the name of Ari Feinberg who’s been studying how mercury travels through our biosphere.

Ari Feinberg: Mercury is a tricky element. It’s highly volatile and it’s also a metal which is quite unique.

You probably know mercury as this silvery-looking liquid that was once commonly used in thermometers.

It’s also a pollutant that gets emitted naturally into the environment by volcanic eruptions and forest fires. But human activities have pushed the amount of mercury in the atmosphere to 500% above normal levels. And in the ocean, to 200% above normal levels. That’s according to figures from the European Environment Agency in 2018.

Ari Feinberg: So mercury is emitted by several different sources, the human sources and mercury include fossil fuel combustion, smelting, product use, artisanal gold mining.

Ari’s a postdoctoral fellow in Spain at the Blas Cabrera Institute of Physical Chemistry. Incidentally, Spain also plays an important part in this story of mercury and gold, but we’ll come back that a bit later.

Ari’s focused a lot of his research on how mercury acts once it’s in the atmosphere.

Ari Feinberg: And so once mercury is in the atmosphere, it can be transported globally and we find high levels of mercury in remote areas, even like the Arctic, for example.


and then once mercury deposits eventually into, into different ecosystems, because of its high volatility, it can be reemitted.


What he’s talking about here is something called the “mercury cycle.” Let’s say you have a coal-fired power plant. The pollution it pumps into the air contains many different toxins, including mercury. And it doesn’t just float around in one place.

Ari Feinberg: So, mercury has an atmospheric lifetime of around six months before it's removed from the atmosphere. And this means that it can really spread globally and travel thousands of kilometers in the atmosphere.

Eventually, it leaves the atmosphere and deposits in the soil or the water.

And water’s a big problem, because microbes in the water help turn mercury into an even more toxic substance called “methylmercury.”


Now, that methylmercury can do one of two things. It can stay in the water and build up in fish, for example – which is incidentally, where warnings about mercury in our seafood come from – or, if it’s closer to the surface, the mercury ultimately evaporates back into the air.

And since mercury doesn’t break down naturally in the environment, this happens over and over again.


Ari Feinberg: We call this the grasshopper effect that it can go from the atmosphere to the ocean, be readmitted and travel again and deposited and be readmitted.

And this is where forests come in. Ari says there’s growing research that trees help absorb mercury.

He recently headed a study at MIT, and according to their model, the Amazon rainforest makes up 30% of the world’s mercury sink. So, when the Amazon gets deforested,


the problem compounds: more mercury gets released into the air and the Amazon can’t help reabsorb it.

This study also puts forward a new idea: deforestation is also driving mercury pollution. And by their estimation, it’s probably responsible for about 10% of the 2,000 tons of mercury emitted by humans every year.

In the case of the South America, the story doesn’t quite end there…


Ari Feinberg: And so actually it takes hundreds of years for mercury to be really removed from the from the environment. And so we're still dealing today with pollution and mercury that's been occurring over history.


The historic emissions Ari mentioned just then are a big question mark for researchers. They know mercury sticks around for a long time, but it’s difficult to put an exact number on how much of the mercury still floating around is actually pollution from previous decades, or even centuries.


But what researchers do know is where mercury has been used heavily. And South America is one of those places…

… dating back to the Spanish conquistadors...

Time to dive into some Spanish colonial history…

Corey Malcom: The galleon that I had worked on and am most familiar with is a ship called the Nuestra Senora de Atocha that sank in 1622 very near Key West here

That’s Dr. Corey Malcom. He’s the lead historian for the Florida Keys History Center in Key West. He started his career as a maritime archaeologist.

The ship he’s talking about is the Nuestra Senora de Atocha.


One of the many ships that crossed the Atlantic to bring the riches of the Americas back to Spain. When it sank in a hurricane in the early 1600s, it took down a treasure trove of South American silver, gold and emeralds that would be worth over $1 billion today.

Corey Malcom: The Spanish system was really designed to exploit the riches of the Americas in those early days. And whether that was through … 

He says they discovered silver in what is now Mexico and then further south in Peru and Bolivia. In 1545, they came upon what would become one of the world’s most important silver mines in a place called Potosí, about 500 kilometers southeast of La Paz.


Corey Malcom: and for the first couple of decades, they would use sort of traditional smelting methods. You'd crush ore and heat it and try to you know get some of the silver to come out of there, but then in the mid-1560s, a new method of extracting silver from or became known, and that was mercury amalgamation.

What they did was turn the ore into something close to a powder. Then they added liquid mercury and some other chemical compounds. And the result was that the silver would bond with the mercury.


And then once they heated the amalgam up, the mercury would evaporate and leave behind pure silver.

He says this process revolutionized silver and gold mining for centuries.

Corey Malcom: That required, though, a huge amount of mercury, and so they would ship across the Atlantic Ocean from Spain to the New world; you know, what today we call quicksilver galleons, but they were they were just ships designed to carry large cargoes of mercury that very often wooden boxes, leather lined wooden boxes. They would fill with the liquid mercury. Put that down on the hold of the ship, load up other cargos and then sail across the ocean to near the mining districts.

It should be noted that Spain has the largest known mercury deposit on Earth in a place called Almadén. All in all, a third of the world’s mercury production over the past two millenia came from there.

In fact, if you’ve ever seen pictures of the bright red pigment the Romans used called vermilion, that also came from Almadén’s deposit of the ore called cinnabar. The same ore that mercury comes from. There’s also evidence the Romans developed an early technique using mercury to extract gold, too.  


Mercury has helped drive the centuries’ old dream of endless riches in the Americas. It’s also been part of a longer history of tragic side effects. From deadly longevity potions, to treatments for syphilis. And other examples, like the 19th century English hat makers who developed tremors and neurological symptoms after exposure to a mercury solution used on wool felt hats. That’s where the term mad as a hatter comes from. Today, though, there’s no denying its catastrophic impact on human health. Today, though, there’s no denying its catastrophic impact on human health.

Mario Rodas: The artisanal miners still have to burn their amalgam, and now they're doing it at their houses. You know, using tuna cans.

That’s Mario Rodas. He’s the Environment and Energy Program Officer for the UN’s Development Program in Ecuador, and one of the people trying to create incentives for miners to ditch mercury.

Mario Rodas: Even I've seen children performing the burning of the amalgam. And they are breathing the vapors coming out of the of the mercury. So this is this has been the, you know, not a good alternative. This has been this has been but much more or much worse than it was before.


The signs of mercury poisoning are very noticeable if you could study what happened in the Minamata Bay in Japan.

One of the reasons we know so much about the dangers of mercury now is because of a place called Minamata Bay. In the 1950s and 60s, residents in and around the Japanese city of Minamata experienced severe mercury poisoning from the local fish. The cause was the toxic runoff from a nearby chemical plant. At least 70,000 people were impacted, from birth defects to neurological impairment, and in some cases, death.

Years later, in 2013, a global treaty called Minamata Convention was introduced, and the result has been a global reduction in the use of mercury in batteries and electronic equipment, and also reduction in the burning of fossil fuels, too. Right now, 148 countries are in the process of phasing out mercury as per the treaty.

There’s been one sector that’s been really hard to eradicate mercury from, though, and that’s artisanal and small-scale gold mining.  


This is where about 20% of the world’s gold comes from. But it’s also the biggest single mercury polluter globally –emitting nearly 40% of this toxic pollutant, which is almost double the amount produced by coal combustion.


The thing is that mercury’s long journey through South American history has sped up with the help of the Interoceanic Highway. This highway runs from Peru’s Pacific Coast east through the Amazon and then back down to Brazil’s Atlantic coast.

It was built in the middle of a goldrush that’s saw gold production across the globe jump by 55% between 1995 and 2018.

And these two developments have spurred on, even more people to flock to gold rush towns. Especially to the epicenter of alluvial gold mining. A region called Madre de Dios in the Peruvian Amazon.

France Cabanillas: It was ready in 2012. Many, many people that before came here take, I don't know, three days, four days. Now they can go here in, I don't know, 8 hours, 10 hours by the highway, no? It's a very very easy way to come here, no?

That’s France Cabanillas, who we heard from at the beginning of the episode. He says the miners coming in droves to Madre de Dios are from impoverished communities.


For them, dealing with mercury is a risk many are willing to take to earn good money.

Peru is currently South America’s biggest gold producer. Its poverty rate hovers around 25%. Meaning, one in four doesn’t earn much more than the equivalent of 100 US dollars a month. So, the prospect of getting $60 for just one single gram of gold is good one.

One approach to put the breaks on this trend has been to ban mercury, but if anything that’s just made sellers and buyers turn to the black market. As Mario said, even burning amalgam in their homes using tuna cans.

Mario works with a global initiative called Planet Gold. One project they’ve slowly started to roll out works to show miners how much money they’re losing by using mercury.

Mario Rodas: What is happening right now is that an artisanal miner go to a plant with the mineral. The plant, perform an analysis and if they have 10 grams of gold per ton of mineral, the plant tells them that they have six.

Essentially, what’s happening is the miners are losing money left and right. There’s the processing fee. And then because mercury is fast, but not very thorough, there’s some gold left in the waste byproduct called the tailing that now belongs to the plant.

According to Mario, the miners end up losing 60% of their earnings.

So, the project Mario’s working is trying to create a better deal. They get miners to sell the ore to processing plants that are mercury free. In exchange, a lab analysis tells the miners exactly how much gold they have. And they get a bigger cut

Mario Rodas: We are telling them from the beginning you have 10 the plant will pay. The plant will pay them for seven, for example, because they need to process. But in that deal they are earning three more than they were used to, right? And they are not spending money and time in, you know, paying the plant and the mercury and process in the middle so that's the alternative we give.

He says they’ve started with two or three artisanal gold miners and their program is growing, and stands to become policy in Ecuador in the future.

Cutting down on mercury use is the only sure way to reduce these emissions. But what about the long-term impact from mercury exposure?


Studies on miners’ health have been limited because miners tend to be reluctant to come forward. A 2016 study by researchers from Duke University in the US took hair samples from hundreds of people living along the Interoceanic Highway, the Madre de Dios River and also from 2,000 people from a local indigenous reserve. They found that 40% of the residents had mercury levels above the maximum recommended by the World Health Organization.

One man who’s also been studying this is Stephan Böse-O-Reilly. He’s a pediatrician and professor for environmental and public health at the University Hospital Munich.

Stephan has been studying gold mining communities in South America, Africa and South East Asia. He says these countries often can’t afford a medical response to the mercury crisis.

Stephan Böse-O’Reilly: So the main diseases that these countries have to fight like AIDS or tuberculosis are of such importance that other diseases like for example mercury intoxication, there's not enough money, meaning there's not enough interest in the country as such. So, unfortunately, low and middle income countries don't have the financial means to really investigate into mercury intoxication in their countries, nor do they have the means to treat this kind of condition.

He says severe symptoms come from prolonged exposure over 10 to 20 years. The telltale signs are severe tremors or problems with coordination and cognitive decline. And there is no cure.


Children do stand a chance of making some recovery, though. More so than adults because other parts of their developing brains have an easier time compensating for a brain injury.

He says there are huge gaps in scientific knowledge, though. For example, a woman exposed to mercury for years can pass this on to a fetus. But researchers haven’t been able to study the long-term impacts over generations.

Stephan Böse-O’Reilly: There are a few studies that investigated into this relationship between mercury exposure, loss of cognitive function, and due to this loss of income due to reduced cognitive abilities. Meaning if a child is exposed in in the womb, it will not be as intelligent as it could be, so it will not earn as much money as it could during the rest of their life. These are theoretical studies which you cannot observe in field. So, the miners are as intelligent as other people as well, if you talk to them. But in general, a society is losing cognitive functions which make societies richer or poorer.

In today’s numbers, this means that up to 20 million people involved in this type of mining are exposed to high levels of mercury. He says that number is actually more like 100 million if you add the surrounding communities also at risk.

MUSIC In the South American context, the historic figures are mind boggling if you consider the countless men, women and children involved in exploitative mining over the past centuries. Many of them against their will…

Kathleen: Great…And the next picture is?

France: ok the first one, you can say a very very, how you say…

Going through France Cabanillas’ photos again, France Cabanillas is a forestry engineer and project coordinator for a non-profit called Pure Earth. One of the solutions they’ve been working on together is reforesting the Amazon.

It’s hard to look at his pictures and not notice the catastrophic impact of this vicious vector of deforestation, gold mining and mercury contamination on a fragile ecosystem like the Amazon.

France Cabanillas: It was a primary forest in the beginning, but now you can see a reforestation process that we did, that plantation with it in February 2023 In the second picture you can shihuahuaco tree. It’s like considered ...

The picture shows a worker standing on a large plot of saplings spaced about two meters apart. He’s holding on to a  fragile sapling with one hand and in the other hand a red canister.

These are shihuahuaco trees.


Shihuahuaco trees are the ancient giants of the Amazon. They can grow up to 60 meters tall, and the oldest ones are said to be more than 1,000 years old.

France Cabanillas: It’s like considered very, very important tree in the Amazon. It's like a very representative tree in the Amazon species in the Amazon, no? And you can see that it grow in that kind of land with different also ingredients that we put in the soil. It's not like the sand by themselves give that nutrients to them. shihuahuaco tree, no? In the third…

Kathleen: Yes, sorry.

France: Yeah?

Kathleen: No, sorry, just really quick. But yeah, looking at this, I mean it looks like it almost looks like you're, you're planting trees on a beach. That's what the soil looks like. It doesn't look anything like what I would associate with. There's. I know I just imagined, like really rich soil in the Amazon in this. Yeah, this looks like.

France: Exactly it is difficult, but, yes, we can do that. OK. It's possible, no? But...

Cutting the Amazon and then reforesting IT in a way that actually works means doing a lot of research first. That’s because, the soil found in rainforests is very low in nutrients.


The Amazon for example relies on fungi and bacteria to decompose organic matter like dead plants and animals – so once the forest is destroyed, all that’s left is sandy soil.

The good news he says is that reforestation can work, but in this case, requires at least three years of intensive care.

Which raises the question: why not just try to ban deforestation? He says this would create other problems.

France Cabanillas: If we think to ban for example the formal sector here in Madre de Dios, I am sure that you can have very, very strong socio-political conflict that may maybe never can solve, no? It's a very, very risk to think about that. And also because it's a legal activity. If we talk about the concessions, it's a legal activity. In the legal context, it's the same if we if I have mining concession or if I have a forestry concession of if I have eco-tourist concession is the same, it's the same category because all that activities are legal with authorization of the government.

Which is why part of the solution he’s been working on is to create two incentives for the miners. The first is that they help certify the miners to use non-mercury methods, like the shaking table. This method isolates the gold powder using water and a mechanized table that shakes. It takes about an hour, so twice as long as mercury, but it’s non-toxic, and the miners are more likely to get better yields.

The other is that they involve the miners in the reforestation process. He says these men and women often don’t come from the region and so once they are included in caring for the forest,


their connection to the Amazon begins to grow, too.

And another benefit, Cabanillas and other researchers from Pure Earth showed in a 2022 study that reforestation … did in fact …help prevent mercury … from reaching the watershed.

There’s one elephant in the room left to address, a golden elephant if you will. And that’s: where is the gold ending up? The answer is, unfortunately, not straightforward. Artisanal and small-scale gold mining is not illegal per se. There are many miners who work within the bounds of the law.

But it is a sector struggling to disentangle itself from organized crime, human exploitation, and international money laundering. Especially amid widespread poverty, corruption and gold prices that continue to rise.

We’ll be right back after this message from DW.


PROMO Cannabis Cowboys 

Today’s episode of Living Planet was produced by me, Kathleen Schuster and edited by Neil King.


Our sound engineer was Ziad Abou Sleiman.

To download this and past episodes of Living Planet, go to Apple podcasts, Spotify or wherever you get your podcasts. Don’t forget to hit the subscribe button.

We’re also available on DW’s website, www.dw.com.

You can also find this and other great podcasts on our YouTube channel DW podcasts.

Thanks for listening. Living Planet is produced by DW in Bonn, Germany.

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