This is a transcript of the Gastropod episode, What Connects Bones, Bird Poop, and Toxic Green Slime? Hint: Without It, Half of Us Wouldn’t Be Alive Today, first released on April 25, 2023. It is provided as a courtesy and may contain errors.

BROADCASTER: New body cam footage showing a guy reportedly running from police and then jumping into a Cape Coral canal filled with toxic blue-green algae. Take a listen.

POLICE OFFICER: Just north of Beach Parkway. [BLEEP]

SUSPECT: Oh my God.

POLICE OFFICER 2: Come out of the water. You need to get out of that stuff, man. That is going to mess you up. [GAGGING]

POLICE OFFICER: Got himself in the middle of the algae and, uh, he’s not liking it very much.

POLICE OFFICER 2: Seriously, man, you need to, that is going to kill you. [BLEEP]

CYNTHIA GRABER: This sounds like just another day in Florida, but the cop was right, that algae can do some pretty serious damage. Just in case you were worried, the man was okay, although he was still arrested.

NICOLA TWILLEY: You might have heard of toxic algal blooms, they’re in the news almost every summer these days. You probably know that humans are to blame, we usually are. But this is a weirder, bigger, and much more problematic story than some nasty green slime.

GRABER: In this episode of Gastropod, we’re diving right into that slime-filled canal, luckily not literally, but we are getting into why the food for that algae has also been what’s caused us as a species to explode. In numbers, at least, just like the algae.

TWILLEY: Literally half of us that are alive today wouldn’t be if it wasn’t for this algae food. Which most of us know by the name fertilizer. Speaking of names, I’m Nicola Twilley, and yes, you’re listening to Gastropod, the podcast that looks at food through the lens of science and history.

GRABER: And I’m Cynthia Graber. In this episode, we’re telling the story of how our search for fertilizer has led us to dig up battlefields for bones and build the world’s longest conveyor belt in the middle of the desert. It’s the story of how a single element is essential to human life, but we’re running out of it. Some star characters include the beloved Dr. Seuss, and a guy who started this whole thing off by boiling his own urine.

TWILLEY: This episode was supported in part by the Alfred P. Sloan Foundation for the Public Understanding of Science, Technology and Economics. Gastropod is part of the Vox Media Podcast Network, in partnership with Eater.

[MUSIC]

GRABER: Back in the 1600s, people thought you could turn things like iron and copper into gold if you could first create something called a philosopher’s stone. Making this mythical philosopher’s stone, which was also an elixir for eternal life—it was the principal goal of alchemy and alchemists for centuries.

TWILLEY: The alchemist that matters for our story was called Hennig Brand. And, like many of his fellow alchemists, he was convinced you could make a philosopher’s stone out of human materials—hair, blood, all kinds of things.

DAN EGAN: Hennig Brand was a urine man. And, he was convinced that, you know, through urine he could fight his way to gold.

TWILLEY: And that was Dan Egan, he’s the author of a new book called the Devil’s Element.

EGAN: And it turned out that urine couldn’t really turn anything gold other than the snowbank.

TWILLEY: Hennig gathered barrels and barrels of urine and then he left it to fester until it grew worms—apparently two weeks’ steeping made it sufficiently putrid, no word on what wives number one or two, or his neighbors, thought about this. Then he boiled that putrid urine for days. And then he was left with black sludge, rather than a philosopher’s stone. So he moved on to step two, and cooked the sludge in an oven, and it did turn into pebbles!

EGAN: I think it was weeks of, of cooking and all sorts of hocus pocus. But in the end, out precipitated from some vapor, these little nuggets. Waxy kind of yellowish, whitish nuggets that cast this, this bewitching glow. This phosphorescent glow.

GRABER: The nuggets were literally glowing! Hennig must have thought he’d hit on something special, that maybe this was the philosopher’s stone, and it would turn things into gold!

TWILLEY: But no such luck.

EGAN: But it did glow in the dark and it was a real curiosity and I think that they were just, you know, bewitched by it. And so he named it phosphorus, which is Greek for bringer of light.

TWILLEY: Phosphorus didn’t turn anything into gold, but alchemists found a way to monetize it anyway. As always happens with new discoveries, phosphorus was hyped as a magical cure-all. It was a combination drug: an antidepressant, Viagra, and toothache relief all in one glowing nugget.

GRABER: One curious and kind of disturbing thing the alchemists noticed is that this medicine probably shouldn’t be used in the summer. Because it might set everything on fire.

EGAN: So these nuggets, if they warm a tick above room temperature, to like 80 degrees Fahrenheit, they combust and they will just burn through anything. So it’s pretty devilish. Hence, the devil’s element.

GRABER: Fortunately the folks making phosphorus medicine coated it with silver and gold which not only prevented it from catching fire but also turned something that is generally a toxic chemical into something basically harmless.

TWILLEY: The devil’s element is number 13 on the periodic table of elements, and Hennig the urine boiling alchemist was the first person to isolate it into its pure form.

GRABER: As the Earth was forming, phosphorus was one of the elements in the mantle. It’s not found in its pure flammable state normally, it’s bound up with oxygen to become stable and it’s called phosphate, but often people use phosphorus and phosphate interchangeably to refer to this really important mineral.

TWILLEY: Once the mantle cooled, phosphorus found its way onto Earth’s surface via volcanoes and lava. And over time, those volcanic rocks would get weathered away, and the phosphorus was slowly released.

EGAN: And every cell on earth needs phosphorus. So there was no life until this stuff started circulating into the environment.

GRABER: Phosphorus is a key player in photosynthesis, no phosphorus, no photosynthesis. That’s for plants, but it’s also key for animals too.

EGAN: You could say it’s in our DNA and you would be literal. Because it, sugar phosphates make up the backbone of the double helix of, of the DNA. But it’s also in our bones and teeth. It’s just a, it’s an essential component of, of many living systems within us.

TWILLEY: The availability of phosphorus regulated the expansion of life across the planet. Microbes, plants, animals, everything: there could only be as many as there was phosphorus to go around.

EGAN: Isaac Asimov called it life’s bottleneck. Like, you don’t have phosphorus, you don’t have life. So as this process of weathering rock occurred over billions of years, there slowly allowed more and more life to take hold. And once this phosphorus was freed from its rock hosts, it didn’t disappear. It was used by a cell. That cell would die. And something else would use it. And so that’s how life got started. And phosphorus was the great governor.

GRABER: We started this episode saying that we’re going to be talking about fertilizer, so obviously you probably already figured out that phosphorus is essential to helping make our crops grow. People in the past didn’t know that they needed phosphorus.

EGAN: We’ve been farming for 10,000 years and humans have intuited that you need to replenish land for things to grow. But they didn’t understand why.

TWILLEY: Over time, people probably eventually noticed that wherever they or their animals had taken a dump, or wherever people or animals were buried, plants would grow better.

EGAN: Humans knew that they needed to replenish the soil in some way, and they just started tinkering. And I think it was obvious early on that poop, human and otherwise, was pretty good fertilizer. So that was used. And, it just, the tinkering went on and on and nobody knew exactly why. But you know, they used everything. From bones to blood, to hair and and cloth.

GRABER: For thousands of years, people just relied on what they saw worked, and that was usually manure. But in England in the 17 and 1800s, they noticed that things grew really well where they had dumped shavings from knife factories, and the handles of these knives were made from animal bones.

EGAN: They had this miraculous property to make turnips and wheat grow. And they didn’t know why, but they did the job. We now know it’s because bones are lousy with phosphorus. But they didn’t know what it was, let alone have a name for it. They just knew that they wanted bones.

TWILLEY: At the time, England was in a bit of a bind. The Industrial Revolution, which started in England, had allowed the population to grow—but those people were moving to cities to work in factories and that meant their poo was not making back into the fields. And the land was getting depleted, which was bad timing because there were now more mouths to feed.

EGAN: So they had to be super efficient and so they were super aggressive in developing new, new fertilizer. And so once they seized on bones, they started the hunt for bones. And you know, by 1815, they were willing to go anywhere.

GRABER: Including digging up human bones, which until this point, frankly hadn’t been a big source of farm fertilizer.

EGAN: You know, the Battle of Waterloo in 1815, like 40,000 people fell in, like, 10 hours. It was just a slaughter. And a whole bunch of horses too. And so that’s a bunch of bones. And you would think that there would be some mass burial, some sacred site on that. And that battlefield, I went there. It didn’t seem a whole lot bigger than a few golf courses strung together. It was a pretty dense place for 40,000 people to die. But there hasn’t been a set of bones, with the exception of one, about five years ago, one, one skeleton was found. But it was news because there hasn’t been any bones pulled from that or found on that sacred land since the 1820s.

GRABER: The Brits had totally pulled every possible scrap of bone from that Belgian battlefield and shipped it back to England.

EGAN: And they actually built special mills to crush these bones into this magic powder that they spread on their crops.

TWILLEY: Just another moment in British history for me to be proud of. Unfortunately for my zombie ancestors there weren’t enough battlefields to plunder for bones to turn into bread. So the British started scavenging bones from everywhere, including Egyptian pyramids. And they ground up everything they found, from humans to mummified cats.

EGAN: And they pretty much, pretty soon ran out of bones. And, you know, the hell of this whole fertilizer business is, the more successful you are, the more people you get. And the more people you get, the more successful you have to be.

TWILLEY: More food means more babies live to adulthood and more adults make more babies, and then you need more food for all those new people.

GRABER: But luckily, before the British had entirely wiped the battlefields of Europe clean, and a few pyramids as well, something else had been going on. In early the 1800s, Alexander Humbolt, who was a famous scientist and explorer, he sailed along the western coast of South America and he ended up near what’s now Peru.

EGAN: And they came across these islands that had a horrible stench. And talking with the Indigenous residents were told that this stuff had this miraculous growing property. And so he decided to take a sample of it much to his crew’s chagrin, because it smelled really bad.

TWILLEY: The bird poo was there because the birds were eating the fish that were there, and the fish were there because they had followed this current, it’s now called the Humboldt current, which is full of nutrients and flows along the coast of South America.

EGAN: And the birds needed a place to nest and to poop, obviously. And they did so on these islands off of Peru where it really never rains.

GRABER: In a typical situation, the birds would poop and that would fertilize something else, and that would grow and then die and become food for something else. But not on these islands.

EGAN: Because it never rained. And so all this waste would accrete over many, many, many, many years to the point where there were mountains of it.

TWILLEY: The technical term for bird poo is guano, and these guano islands had been a source of fertilizer for Indigenous people for centuries, they were so valuable to the Inca that anyone who disturbed those birds got the death penalty.

GRABER: Europeans thought this fertilizer looked pretty great, but the Brits, who were looking to perhaps diversify their fertilizer portfolio, they saw real promise. In the early 1800s, a British governor of a remote volcanic island called St. Helena tested guano against other fertilizers like horse and pig manure, and guano was the clear winner.

TWILLEY: By the 1840s, with bones in short supply, the guano boom began.

EGAN: And so, soon the British, and much of Europe were shuttling shiploads of this stuff back to the continent and back to the mother island. And making fields bloom like they had never before. And at the time, these islands were so loaded with the stuff that there’s accounts where they were saying they couldn’t even calculate how long it would last. It’s basically going to last for… [LAUGHS] as far as we can see into the future.

GRABER: But of course, just like Europe’s bones, nothing lasts forever.

EGAN: As a matter of fact, those guano islands were pretty well played out by the end of the 1800S. So the hunt persisted from there.

TWILLEY: But back in the 1840s, when the guano first started arriving, something else happened—the first real breakthrough in phosphorus science since our friend Hennig and his boiled urine.

GRABER: There was another German phosphorus wrangler, he was a chemist named Justus von Liebig. He decided to try to figure out what specific elements plants needed to grow, what fertilizer was providing for them. Like most scientific advances, this research had been going on for a while, and there were other people who were looking into this too, but Liebig burned plants to figure out what they were made of, and he figured out that there were some nutrients that plants just couldn’t live without, including phosphorus.

TWILLEY: What Liebig became famous for is something called the idea of the limiting factor—basically, that if a plant didn’t get enough of any one of these nutrients, that would limit its growth. Whichever nutrient was in shortest supply was the limiting factor. He and other scientists gradually figured out that the key ones to add to soil for plants to grow were nitrogen, phosphorus, and potassium. NPK, to use their chemical names. And that’s the basis of fertilizer today.

GRABER: Scientists at the time figured out that bones were rich in phosphorus, and this was why they were so amazing as a fertilizer, so that knowledge sent Europeans into a phosphorus frenzy.

EGAN: So now they’re getting focused. And now they can, they don’t have to look for just certain materials. It’s not trial and error anymore. It’s, find phosphorous and watch things grow magnificently.

TWILLEY: Figuring out that the thing our crops needed was phosphorus and that phosphorus was in plants as well as bones—that opened up a whole new potential source to be exploited. Basically any fossilized creatures—animals *and* plants—that had floated down to the bottom of the ocean and broken down over time under a very particular set of conditions as they turned into sedimentary rocks—those rocks would contain phosphorus and so they were on the fertilizer menu too.

GRABER: So people started searching for these super special and kind of unusual sedimentary rocks to find new sources of phosphorus. A huge deposit was found in Florida in the 1880s. It was called Bone Valley, and it’s more than a million acres of land filled with the the fossilized remains of long-gone creatures like sabertooth tigers and giant manatees—and it was also filled with phosphorus-rich sedimentary rock.

EGAN: And so Bone Valley became just this kind of bonanza, you know. And, you know, there’s stories of the time, some may be apocryphal, but about, you know, people shooting each other over road bed gravel. Because they realized that these gravel or this pebble, these pebbles, wasn’t just inert rock. But it was also rich with phosphorus, with fertilizer, which is what the world was increasingly craving.

TWILLEY: Awesome. Unless you got shot. But based on Liebig’s whole limiting factor thing, phosphorus is not the only element that crops need. They need potassium too. Fortunately, there is a boatload of potassium available for the taking—these days, it’s typically mined from salt deposits and there are tons of them all over the world.

GRABER: The other main limiting nutrient for plants is nitrogen, like Liebig said. Manure has some nitrogen in it. Nitrogen also is everywhere around us, because it’s in the air, but plants can’t grab it straight from the air. So farmers have traditionally captured that air nitrogen by growing crops called legumes, like beans and lentils, because microbes on their roots fix nitrogen from the air, feed some to the legumes, and stick some in the soil.

TWILLEY: But that was a slow and steady kind of thing, not a miracle fix like sprinkling bone dust.

EGAN: And so we thought that we would be limited by these two things. And we were heavily dependent on like, animal manure for the nitrogen. And the phosphorus, we were finding, as we mentioned earlier, in, in other places, first in bones and then in bird poop, and then in these rock deposits.

TWILLEY: And then, in 1909, came a big nitrogen breakthrough.

EGAN: Well, fortunate for humanity, Fritz Haber, the German war criminal, and the winner of the Nobel Prize, came along and he basically figured out how to strip nitrogen from thin air.

GRABER: This was not a simple process, and in fact there have been entire books written about the story of figuring out how to get nitrogen from air and turn it into useful nitrogen fertilizer. The big challenge is that nitrogen in the air is bonded to other nitrogen atoms in a way that plants can’t use. The only thing in nature hot enough to break apart those bonds and get nitrogen into a plant-friendly format is a bolt of lightning.

TWILLEY: In the lab, Haber came up with a way to split them apart under super high pressure. And then another guy, Carl Bosch, figured out how to make Haber’s tiny, expensive lab sized reactor into a gigantic factory. And by 1913, the nitrogen limiting factor—it had become unlimited.

GRABER: Haber won the Nobel Prize for what has become known as making bread out of air. He then less happily went on to become a war criminal, he developed chlorine gas for the Germans, which they used during World War I, and then he developed poison gases for pesticides that were then used to kill people in concentration camps in World War II. So, kind of complicated legacy.

TWILLEY: Side note while we’re on the topic of war: the form of the nitrogen you arrive at at the end of the Haber Bosch process is an ingredient in fertilizer, yes, but it’s also a key ingredient in bombs, because it contains a concentrated source of oxygen and that is exactly what flammable materials need. That’s why Timothy McVeigh was able to blow up the Oklahoma City federal building in 1995 using a bomb made out of fertilizer

GRABER: Speaking of flammable materials, phosphorus, otherwise known as the devil’s element, it was and is super explosive. It’s been used for bombs since the late 1800s, it set Hamburg on fire in the second World War, it was used in grenades in the Vietnam War.

TWILLEY: Don’t try these things at home. Any of these things. But to get back to growing food, the Haber Bosch process really changed everything. Like Dan says, potassium is abundant, and now the nitrogen piece was essentially unlimited too. Which only left the devil’s element. Sure, you could find it in guano and sedimentary rocks, but we kept mining them out and needing to find new sources.

EGAN: There was no guarantee that the next generation was going to have enough. To the point that the President, President Roosevelt, President Franklin Roosevelt in the early thirties said essentially we need a national phosphorus policy. Because this has everything to do with our national security.

GRABER: The US even wrote this into a law that allowed any American citizen to seize an uninhabited island like those guano islands that might be a phosphorus reserve.

TWILLEY: Which helped kick off a global phosphorus grab, with wealthy nations just helping themselves to entire islands in the Pacific—even islands that often already had people living on them—and then mining all the phosphorus, making those islands uninhabitable and making Australia and New Zealand bloom. There are some really wild stories about this, we’ll be telling those in our special supporters newsletter, gastropod.com/support.

GRABER: We, that is we global humans, we have sources of phosphorus today that we can use to grow crops. There are some really big ones in Africa and in Asia and even here in the US. And mining all this phosphorus for farming has led to our population explosion. Without it, some scientists estimate that the Earth could only support about 4 billion people—today we’re at 8.

TWILLEY: But you all know what’s coming. We may get bread from air, but there is no such thing as a free lunch. The true cost of phosphorus—that’s coming up, after a word from our sponsors.

[BREAK]

EGAN: So, things changed dramatically for our water quality following World War II. And oddly enough, it’s because of our obsession with cleanliness.

GRABER: After World War II, we didn’t have to spend so much mental and physical energy making things like bombs and tanks, and so people developed things like washing machines instead. And the soap that we had used to clean our clothes before didn’t work as well in these newfangled machines.

EGAN: So they developed this synthetic soap detergent. And a big component of that detergent was phosphorous. And it was basically, it helped dispose of minerals that were in, in hard water. It was basically water softener.

TWILLEY: Phosphorous, it’s not just glow in the dark Viagra and a great fertilizer, it also cleans your clothes! And then that water runs out into the rivers and lakes and oceans.

EGAN: So, along that same time, people started noticing that the waters, you know, from the Great Lakes out to the Pacific coast, waters were turning soupy green. And we’ve been talking a lot about how phosphorus is a miraculous crop fertilizer. Well, unfortunately, it doesn’t stop fertilizing things when it washes off the landscape.

GRABER: It also fertilizes algae.

TWILLEY: There was phosphorous in fertilizer of course, and phosphorus in our poo and urine that wasn’t being fully removed during wastewater processing and now there was also phosphorous in these groovy new detergents and that all added up to a lot of phosphorous in lakes.

VOICEOVER: Lakes have one special problem. Fertilizers are made to grow crops. Washed into the lake, they grow weed. Household and industrial chemicals speed the growth. Lake shores become strands of slime. Only the weed thrives.

GRABER: This is a BBC documentary from the 1970s about environmental problems. One of the ones they focused on was Lake Erie, which is on the border of Canada and the US.

EGAN: So these water bodies, and I’ll focus specifically on Lake Erie, were just being overdosed with phosphorus by the 1950s and 60s. Primarily because of detergent, but also because of poor to non-existent wastewater treatment. And the consequence of this were huge and distressing. I mean, Lake Erie was suffering these algae blooms that are hard to imagine in scope. They were like 2000 square miles. So this wasn’t just a soupy goop that was an annoyance or unsightly and stinky. It was causing a dramatic decline in water quality because, so much algae was growing, it would eventually die, and its decomposition burned up so much oxygen that these dead zones were created. And this is why in the 1960s, the national media was referring to Lake Erie as America’s Dead Sea.

GRABER: KQED in San Francisco covered this major catastrophe in a documentary called Battling the Bloom.

VOICEOVER: In 1970, Lake Erie was in fact declared dead. Algal blooms generated by sewage and pollution from industrial waste had killed much of the lake’s aquatic life.

EGAN: I mean, it wasn’t really dead, but it was suffering from chronic phosphorous overdose, which was leading to chronic algae outbreaks. But at the time, they didn’t know exactly what was causing Lake Erie to get so foul, because we were dumping so much crap in there. It wasn’t just detergent, it was industrial excrements. It was, you know, our waters were basically dumping grounds.

TWILLEY: This is the same time the Cuyahoga River that drains into Lake Erie literally caught on fire. There was a lot of bad stuff being dumped into the lake and killing it and everything that lived in it. But phosphorous was the leading suspect in the case of the algae blooms

EGAN: Because of its obvious fertilizing properties. But the detergent industry really fought that idea because they weren’t interested in seeing their product disparaged or even removed from grocery shelves. So they fought the idea that it was phosphorous and they would argue that, oh, it’s, it’s carbon, or it’s nitrogen, or it’s something coming from, you know, all these heavy industries lining the Great Lakes and Western Lake Erie in particular.

GRABER: And that’s where this guy named David Schindler comes in. He was an American who got a job in Canada and he was really interested in studying lakes. And the Canadian government at the time had an idea to try to figure out what was polluting Lake Erie.

TWILLEY: Canada has a lot of lakes. Like really a lot. So many that they were willing to set aside 58 formerly unpolluted lakes on government land to use for pollution experiments, like oversized test tubes. This area is called the Experimental Lakes Area and it’s in western Ontario.

EGAN: They gave him permission to dose these lakes with various pollutants to see which would trigger an algae outbreak.

GRABER: One of the things the detergent industry was blaming was carbon from household sewage. So David took one entire lake and he said, I’m going to dose this whole lake with just phosphorus and nitrogen. If there’s an algae bloom, carbon is not a problem. And that’s just what happened. There was a bloom, carbon wasn’t the issue.

TWILLEY: So then David turned to another pristine lake, lake 226, and he split it into two.

EGAN: So it was the same lake, same body of water, same water chemistry. And they cut it in half with this giant polyurethane curtain.

GRABER: Because at this point the detergent industry was pointing its fingers at nitrogen. So the whole lake was dosed with nitrogen. But only half of the lake was also dosed with phosphorus.

EGAN: And a couple weeks later they flew up in a helicopter to see how things were going. And they looked down and one side of the lake was golf course green, neon green basically. And the other side of the lake was the deep Canadian blue water that you think about when you think about the Canadian wilderness. And it turned out the green side was the phosphorus side.

TWILLEY: It’s not that nitrogen doesn’t cause algae to grow, it does. But it’s back to the Liebig limiting factor idea: you need potassium, which is in water anyway, and nitrogen *and* phosphorus.

GRABER: In fact, you need a lot less phosphorus in comparison to nitrogen, you need a smaller dose of it for the same amount of growth. It’s just a lot more powerful as a growth element for algae in the lakes.

TWILLEY: This all is still a hot debate in the lake science community—they argue about how much phosphorus is contributing to the algal blooms versus nitrogen. And in the end, lakes are all a little bit different and they can all handle different amounts of different nutrients.

GRABER: But usually it is actually the phosphorus that’s contributing the most to algae blooms. Today, the EPA says phosphorus is generally considered the limiting factor in a freshwater ecosystem. Scientists say that the amount of phosphorus going into a lake is the best predictor of how bad the bloom is going to be.

TWILLEY: Back in the 1970s, David Schindler’s lake experiment seemed conclusive. It was really dramatic visual evidence: the phosphorus-dosed side was bright green. And that finally shut the detergent companies up.

EGAN: So these scientists had been making these arguments based on lab work and very, very detailed scientific reports that had lots of data points, and graphs that would make lawmakers eyes roll to the top of their head and make ’em go to sleep. Now, they had a picture. And, you know, it was, it was one of those, more than a thousand words. It was just all the difference in the world.

GRABER: After seeing these photos, lawmakers took a number of steps. Congress passed the Clean Water Act in 1972, it put in place regulations that forced factories and sewage treatment plans to clean up their waste, and it enforced those regulations too. As sewage plants increasingly improved their technology, they also took more and more of the phosphorus out of wastewater.

TWILLEY: Some states banned phosphorus from laundry detergent, especially those around the Great Lakes. There never was an official national ban, but there was a voluntary one from 1993. And then more recently, there have been some state level bans on phosphorus in dishwashing detergent. But Proctor and Gamble only eliminated it from Tide and their other detergents in 2014!

GRABER: Originally phosphorus may have been seen as a water softener, but it does actually contribute to cleaning clothes and dishes. It bonds with iron, which means it helps remove soil. Some consumers say the new phosphorus-free recipes aren’t as good and they actually add their own phosphates back in.

TWILLEY: Also don’t do that at home, dear listeners. Please.

GRABER: When this was all first coming out, in 1971, Dr. Seuss wrote what is still today a famous parable, a plea for us to protect the world around us, it’s called The Lorax.

MR. ONCELER: Now—who’d you say you were, little fella?

LORAX: Mister, I am the Lorax. I speak for the trees. I speak for the trees, for the trees have no tongues. And I am asking you, sir, at the top of my lungs. That, that thing, that horrible thing that I see! What’s that thing you made out of my truffula tree?

GRABER: In his book, Dr. Seuss specifically called out Lake Erie.

LORAX: You’re glumping the pond where the humming fish hum. No more can they hum for their gills are all gummed. So I’m sending them off. Oh, their future is dreary.

FISH: I hear things are just as bad up in Lake Erie.

EGAN: And and he was right. You know, it was a Lake Erie was a mess. And fish were looking to get out of that lake anyway possible. So in 1972, Dr. Seuss’s making fun of Lake Erie. In 1985, he pulls that line from the Lorax, after some researchers at Ohio State University wrote him and said, hey, you should come up and see Lake Erie today. It’s not the lake that you’re making fun of, or disparaging, 13 years ago.

TWILLEY: That’s how quickly cleaning up industrial and sewage pollution and reducing phosphorus in detergents—that’s how quickly it worked to clean up the lakes. Once again, KQED had the story.

RICK UNGER: I saw it as a beautiful lake as a little boy. Then in the sixties, I saw it turn into what was called the Dead Lake. And then I’ve seen it clean up to, just a pristine, beautiful lake.

VOICEOVER: Over the years, charter boat Captain Rick Unger, and those along Lake Erie’s shores have witnessed the evolution of the lake. Its comeback after the Clean Water Act was widely celebrated, and by the 1980s, the most productive fishery of the Great Lakes was once again attracting tourists and fishermen alike.

GRABER: So far, this all sounds surprisingly awesome. It’s not usually so easy to clean up a mess as huge as the one in Lake Erie. But maybe we shouldn’t break out the champagne.

VOICEOVER: By 2000, Lake Erie’s pollution problems were thought to be a thing of the past. But recently a new threat has emerged.

TWILLEY: It’s a new threat but it’s actually our old friend, the devil’s element, causing chaos again. So what is going so wrong this time—and what are we going to do about it? That story coming up, after the break.

[BREAK]

GRABER: Remember how Dr. Seuss changed the Lorax after Lake Erie got cleaned up?

EGAN: If he were alive today, he probably put that line back into the Lorax because Lake Erie is a mess again. And it’s because of phosphorus again. But this time it’s not detergents and industrial wastes. It’s runoff from agriculture fields. And the consequences of overdosing the landscape with relatively cheap phosphorus fertilizer for decades and decades.

GRABER: The phosphorus that’s a problem today is not the same phosphorus of yesterday. That was mostly coming into the lake from places that could be cleaned up, like a wastewater plant.

TWILLEY: And that’s exactly what the Clean Water Act did, it regulated something called point source pollution. Point source means you know the source of the pollution. It’s like a factory, a chimney stack, and you tell the owners to clean it up.

GRABER: Today, phosphorus is mostly coming from agriculture, and agriculture is by nature more spread out. It’s not a point source, and it was basically given a pass in 1972.

EGAN: Because it was just thought not to be that big of a problem. And also very difficult problem. You can plug a smoke stack or a pipe, but you can’t squeegee a farm field. So they thought that, this will get us far enough along, we don’t really need to worry about agriculture.

TWILLEY: La la la, everything’s great, oh wait, no it’s not. By the mid 90s, the algae was back and blooming again. And this time it was also super toxic!

EGAN: Today’s algae blooms are more likely to be toxic than the stuff, you know, plaguing Lake Erie in the 1960s. That was creating dead zones, but it wasn’t creating poisons.

GRABER: Dan says the reason Lake Erie is greener and meaner this time around is that there’s an additional problem, and that’s invasive mussels. They eat the nonpoisonous algae and leave the poisonous ones alone. The poisonous stuff is really poisonous, and not just to the mussels.

EGAN: And it’s, it’s also toxic to people. It’s a liver toxin. And there’s some emerging evidence that it may be associated with some neurological issues. And these are for people who don’t necessarily even live right next to the lake. These algae blooms can kick off aerosolized poisons.

GRABER: This is a problem in lots of different places in the country. Lots of different lakes and rivers are suffering, and sometimes that freshwater algae bloom gets so bad it even flows into the ocean.

BROADCASTER: There was nowhere to cool off along Mississipi’s coast today. A toxic algae bloom caused all of the state’s gulf coast beaches to close to swimmers. Going into the water there could cause rashes and nausea. People are also being told not to eat fish caught in the area.

EGAN: So then you got these freshwater algae blooms on the coast of Mississippi some 40 miles of beach in the summer of, I think it was 2019. Were closed from late June through the swimming season. I don’t know if you’ve been in Mississippi in July, but you want to swim that time of year. Because it is muggy and hot. And there were 20-some beaches that were closed because of the phosphorus pollution coming down the Mississippi. And just basically skunking up the Gulf Coast.

TWILLEY: Mississippi’s phosphorus-fuelled algal bloom meant no beach fun and swimming for humans, but it was also unpleasant for the creatures that live in the ocean. And when I say unpleasant, I mean disastrous. That 2019 bloom wiped out the state’s oyster beds, and it killed a whole bunch of fish and turtles and dolphins.

GRABER: Algae blooms in lakes have been known to poison drinking water. Lake Erie’s algae bloom led to half a million people in Toledo, Ohio not being able to drink their water or brush their teeth with it for three weeks. And over a couple of years, more than 300 people ended up in emergency rooms across the country after being exposed to this toxic algae-laden water.

TWILLEY: Algal blooms are super complicated. There are lots of things that can contribute to them and lots of reasons why they might be worse one season than another. This is an area of research that scientists are still working really hard to tease out. But phosphorus is often a big part of the problem.

GRABER: And when and why the blooms happen is also complicated. They tend to grow more when it’s warm out, which is the temperature that a lot of algae prefer, and also after it rains, which washes off algae food into the water.

TWILLEY: Algal blooms are not just a US problem, either. Lakes and rivers all over the world are covered in layers of this toxic green slime that’s blooming because of all the phosphorus we’ve dumped in the water, and scientists say that climate change is making matters worse because it leads to bigger storms with more rainfall and warmer water that the algae love.

GRABER: And there’s not much really we can do about these blooms once they happen, except wait until the algae die off. There are some tools, like adding clays to the water, or you could aerate it, basically bubble it, but that’s all super expensive and challenging to do at scale. So wouldn’t it be a better idea to stop the phosphorus pollution at its source?

TWILLEY: If only there was one source to look at. This is what makes today’s algal blooms harder to prevent than your grandad’s algal blooms, because the sources are mostly farming and they’re very hard to pin down.

GRABER: So in the past, farmers had easy access to fertilizer, it was cheap, it worked really well, they didn’t think there was any need to limit it.

EGAN: And so farmers were coached by soil experts to like, put a little more on. You know. As an insurance policy. In case things, the rainy season comes before the crops start, start growing. You want enough still on the land to be there for the crops.

TWILLEY: Farmers do apply less fertilizer these days, but we’re still dealing with the more generous applications they did in the past—the phosphorus has just built up in the soils, and when there are heavy rains, it washes into the water. This is called legacy phosphorus and it’s a big source of the phosphorus that’s fueling these blooms.

GRABER: Another thing that’s happened in agriculture over the recent decades is that as you regular listeners know, animal feedlots have gotten more and more concentrated. Today there are thousands of cattle smushed together in a small area, and they poop out a lot of nutrients.

EGAN: We have these massive sewage lagoons or manure lagoons now, as farms have gotten bigger and bigger. I mean, some in my home county up in Brown County, which is where Green Bay, Wisconsin is, there are dairies up there that have 10,000 head of cattle. And so they don’t just make milk every day. [LAUGHS] You know. They poop every day as well.

TWILLEY: And they do so with extreme abundance. Dan says each cow can produce something like 18 times as much poo as a human, so these new megafarms are actually producing the same amount of shit as a city of several million people.

GRABER: But these manure lagoons aren’t treated like human waste is. What happens instead is that the manure is applied to nearby farms as a fertilizer. This sounds like a good idea, manure has always been really valuable, but it’s not as important today because farms far away can just put on fertilizer. So manure is basically over-applied to nearby farms because it’s expensive to truck it. And so all that phosphorus and all that nitrogen too, it all just pretty much washes away.

EGAN: Too often fields that don’t need this nutrient boost, get it just because the manure’s got to go somewhere.

TWILLEY: Meanwhile, even though we humans are relatively modest in our poo production compared to cows, there are a lot of us. So is phosphorus in human waste part of the problem too?

EGAN: Human waste is not, to that extent, but it’s also more manageable because we’ve got it in pipes, in the form of, you know, sewers. It goes to wastewater treatment plants. And since the 1960s and 70s, we’ve gotten a lot better at pulling the phosphorus out of our urine and our feces.

GRABER: But so okay, we need all this phosphorus that is critical for feeding us, but it’s causing something that experts are calling phosphogeddon. It’s bad. But we’re not going to give up using phosphorus, so what are the solutions?

TWILLEY: Back in the 1970s, lake scientists came up with a prescription for Lake Erie—like a maximum dosage of phosphorus. And for a while, we kept below that threshold and everything was good.

EGAN: We’ve got a new prescription for it today, and it specifically calls for a 40% reduction in phosphorus, dissolved phosphorus, washing off the landscape into Lake Erie. If we can reduce it by 40 percent, we’ll solve the algae problem, the toxic algae problem.

GRABER: So in the 1970s we put laws in place to make that happen, how about today?

TWILLEY: So there are some positive initiatives going on—farmers are applying less fertilizer like we said, and some of them are being paid to create buffer zones and plant cover crops to help catch phosphorus before it runs off.

GRABER: But these are voluntary, they’re not laws, so there isn’t enough of this happening yet. When it comes to manure, that could be a really straightforward solution—we know where it is and we could in fact treat it.

EGAN: And perhaps we get to a point where some of these giant mega-farms are held accountable for the waste that ends up on the landscape that ends up in the water, that ends up growing all this algae.

TWILLEY: It is more expensive to do something other than spray cow shit all over nearby fields, but there’s also a cost associated with killing all our lakes. And that manure would have some real value for farms elsewhere.

EGAN: It’s been estimated that if we managed it for its fertilizer, if we basically treated it, processed it and repackaged it, and in like commercial grade chemical fertilizer, that could satisfy like half of our phosphorus needs.

TWILLEY: And there are some pilot projects that are doing exactly this—taking the manure from livestock farms and turning into fertilizer.

GRABER: Because this is the other part of our phosphorus problem. It’s not just that we’re polluting our waterways, it’s also that we desperately need it to produce our food, and like we said, each time we find a great new source of phosphorus, we do eventually use it up.

EGAN: The US, the main phosphate rock reserves that we have down in Florida, they’re set to play out in a matter of decades, like three or four decades. So at that point, we become dependent, or more dependent, on other countries for our nutritional security, which is a lot more dicey than being dependent on other countries for our energy security. Because there’s workarounds for oil. But as I mentioned earlier, there are no workarounds for phosphorus. It is required by every living thing.

TWILLEY: So those other countries Dan mentions, this is where the phosphorus situation gets even more high stakes.

EGAN: You don’t have to have a global scarcity to have global issues with phosphorus, because the deposits that are left, the reserves that are left, are not spread evenly across the globe. Seventy to 80% of them are in Western Sahara and Morocco. I think number two is China.

GRABER: Back in the 1970s, an area of northern Africa called Western Sahara was part of Spain. It’s also right next to Morocco. Spain found phosphorus in Western Sahara, and they invested hundreds of millions of dollars in it and even had a German firm design the world’s longest conveyor belt to get the phosphorus to the coast for shipping. You can see it from space.

EGAN: So just as, just as the mine was coming online in 1972, Spain was growing weary of, of being a colonial power. And they pulled out of Western Sahara. And neighboring Morocco, which viewed that territory all along as, as part of its native lands, occupied it. And set off what was basically what is basically a low grade war that started in the early seventies and is still simmering today.

TWILLEY: What that means is that Morocco currently controls those phosphorus reserves too, which makes it by far and away the top banana in terms of global phosphorus reserves. It also means that tens of thousands of Western Saharan people have been living as refugees in tent camps in Algeria since the 1970s.

EGAN: And, and, and a big reason is the contentiousness over the phosphorus that Morocco is harvesting from Western Sahara.

GRABER: Only about 14 percent of the phosphorus in use today comes from Western Sahara. It’s called blood phosphorus because of the war there. And according to Dan the only western country that still buys it is New Zealand. In general, these geopolitical issues around phosphorus—who has it, who controls it, who can get access to it—this could become a big deal in the future.

TWILLEY: So: on the one hand it’s killing our lakes, fouling our drinking water, wiping out aquatic life, and causing human death and disease too. And on the other hand, we rely on just a couple of places for our supply and we don’t really have a plan to make sure we aren’t going to get cut off.

GRABER: The thing is, unlike nitrogen, we can’t make it ourselves. There is no way to manufacture phosphorus in a factory. There’s just the stuff that was in the Earth’s mantle and now is in all plants and animals and some rocks.

TWILLEY: And we really need it. We are utterly dependent on phosphorus. It is the limiting factor.

EGAN: The fertilizer industry is quick to argue that we don’t have a phosphorus shortage coming anytime soon. Our reserves or our known deposits can keep us safe and fed for the next 300 to 400 years. Well, even if they’re right, that’s not a long period of time. Especially at a time when, you know, we’re on our way to adding another billion people on the planet and as developing nations developed tastes for meat, which is only natural, that’s very phosphorous intensive. So the, the stresses aren’t going to diminish if we keep on the path that we’re keeping on, they’re only going to increase. So whatever the number is, whether it’s a hundred years or 400 years, there’s a reckoning coming.

[MUSIC]

GRABER: It seems like we’ve ended this telling you all that this is an unsolvable problem. But there are some potential solutions. We’ll soon be jumping into a pile of poop—human poop—which is one of the potential ways out of this problem. We’ll be doing an episode on so-called humanure coming up soon.

TWILLEY: Thanks this episode to Dan Egan, he’s the author of The Devil’s Element: Phosphorus and a World Out of Balance. Thanks also to our awesome producer, Claudia Geib. And apologies for giving you all something else to worry about.

GRABER: We’ll be back in two weeks with something much tastier, ‘til then!