A few years ago I attended an open house at the Stickney Water Reclamation Plant, southwest of Chicago. It was a lovely Saturday morning, and I was surprised by how many people had decided to spend it touring a sewage treatment operation. The crowd was so big that we had to be divided into groups. My group first watched a video, which explained that the plant’s effluent would be released into the Chicago Sanitary and Ship Canal, a thirty-mile-long waterway built in the late nineteenth century to rid the city of its ordure. After the video, we boarded a bus that shuttled us around the 413-acre complex. I was particularly struck by the aerated grit tanks, in which swirled a revolting brown liquid that resembled chocolate milk left out too long in the sun. At the tour’s conclusion, we all received goody bags containing a pair of plastic sunglasses and a postcard that cheerily proclaimed, “I followed the flush to the Stickney Water Reclamation Plant, the largest wastewater treatment plant in the world.”

I thought about my visit to Stickney several times while reading Lina Zeldovich’s The Other Dark Matter. Zeldovich, a journalist who now lives in New York, grew up in Russia, about five hundred miles east of Moscow. Her family had a small farm on the outskirts of the city of Kazan, and the farm had a small septic tank. Every fall her grandfather would don a hazmat suit and empty the contents of the tank into buckets. Then he would pour the glop around the tomato plants, under the apple trees, and into holes he dug in the strawberry patch. “My grandfather wouldn’t let all those riches go to waste,” she explains. In the spring, there would be more tomatoes, apples, and juicy red strawberries. The experience of watching her family’s filth transmogrified into food had a profound effect on Zeldovich, as she describes in a chapter titled “How I Learned to Love the Excrement.” Here was life coming full circle, from poop to produce and back again.

When Zeldovich immigrated to the US as an adolescent, she was dismayed to learn that most Americans were uninterested in sewage. She understood that New Yorkers didn’t have septic tanks or, for that matter, strawberry patches; still, it seemed to her there had to be a way to prevent all those “riches” from going to waste. Apparently the thought stayed with her, because when she grew up and became a journalist, she decided to specialize in what she calls “the science of poo.”

According to Zeldovich, the problem of how to deal with our “dark matter” has plagued humanity for millennia. As soon as people stopped moving around in pursuit of prey, the stuff began to pile up. Neolithic farmers may have had no idea of germ theory, but they were smart enough to know they didn’t want to live next to—or on top of—their own shit. They dug pits or ditches out in their fields to serve as open-air toilets. As the number of people living in close quarters grew, pits no longer sufficed. People turned to more sophisticated waste-disposal methods, usually involving water.

The first city known to have had a municipal sewage system was Knossos, on the island of Crete. At its height, around four thousand years ago, Knossos had some 100,000 inhabitants. Ceramic pipes directed its residents’ output to the sea, and the palace even had an early version of a flush toilet, with a bowl that could be emptied by pouring water from a pitcher.

Two thousand years later, Rome’s population was approaching a million, which meant it was producing ten times the excrement that Knossos had—roughly five hundred tons a day. The Romans built the Cloaca Maxima—the “greatest sewer”—to funnel waste into the Tiber. The tunnels of the Cloaca Maxima, “vaulted with close-fitting stones,” were so huge, the historian Strabo wrote, that there was “room enough even for wagons loaded with hay to pass through them.” The Romans also erected foricae, or public toilets, where dozens of people would sit, cheek by cheek, to do their business. (Primarily the lower classes used the foricae; the rich had private latrinae inside their homes.)

Even as sewage systems like Knossos’s and Rome’s solved one problem, they created new ones. Shit may not have been piling up on the streets, but now it was contaminating waterways. When cities like London and Paris became major commercial centers, in the Middle Ages, they too relied on rivers to rid them of their ordure. Ditto for New York and Chicago hundreds of years later. The dangers of this practice became acutely apparent when cholera, a waterborne disease, reached Europe and North America in the early 1830s.


Meanwhile, by flushing their waste out to sea, cities were forfeiting their collective “riches.” In 1843 Justus von Liebig, one of the pioneers of organic chemistry, lamented how much potentially valuable fertilizer was simply being washed away: “The quantity is immense which is carried down by the drains of London to the River Thames, serving no other purpose than to pollute its waters.” Inspired by Liebig, Edwin Chadwick, a prominent British lawyer and social reformer, advocated a system of “sewage farming,” by which London’s waste would be piped out to the countryside to be used as liquid manure. Some European cities—but not London—did indeed adopt sewage farming in the nineteenth century; Zeldovich reports that Berlin briefly ran a successful system. But the systems routinely ran into problems—too much of a good thing could cause land to become “sewage sick”—and eventually they were abandoned. The waste they had carried was once again directed out to sea.

At least in the Global North, much has changed since Chadwick’s day. Sewage treatment plants like Stickney manage, by and large, to keep raw sewage out of waterways, and this has mostly eliminated outbreaks of cholera as well as typhoid. But the practice of washing nutrients down the drain remains as big an issue as ever. “We are continuously taking nutrients from some parts of the planet and discharging them in others,” Zeldovich writes.

Of all the nutrients we’re redistributing, probably the most significant is nitrogen. It’s difficult for plants—and, by extension, plant eaters—to obtain nitrogen. In the air, it exists in a form—N2—that most living things can’t utilize. For hundreds of millions of years, plants have relied on specialized bacteria that “fix” nitrogen into a compound they can make use of. When people started farming, they figured out that legume crops, which harbor nitrogen-fixing bacteria in nodules on their roots, replenish soil. Manure and human waste, or “night soil,” also provide nitrogen for plants.

When synthetic fertilizer was invented, in the early twentieth century, the world was suddenly awash in nitrogen. This enabled people to grow a lot more food, which, in turn, enabled them to produce a lot more people, who produced a lot more shit. Via our wastewater treatment plants, we now introduce vast quantities of nitrogen into coastal environments, where it’s wreaking havoc. (Fertilizer runoff also contributes to the problem.)

Excess nitrogen in aquatic environments has many unfortunate consequences, one of the most visible being algae blooms. Depending on the algae, blooms can be toxic to fish and even humans. They can also produce aquatic dead zones, areas of low oxygen where few organisms can live. One of the world’s largest is in the Baltic Sea. Every summer, another large dead zone forms in the Gulf of Mexico, and officials in Washington State are concerned that dead zones could soon start forming in Puget Sound. “Fish and other marine life are struggling because most wastewater treatment plants currently do not have the technology in place to remove excess nutrients,” a recent press release from the state’s Department of Ecology explained.

As Zeldovich observes, our waste treatment methods have set up a vicious cycle. Since we don’t return our nitrogen output to our fields, as her grandfather did, our soils are getting depleted. They therefore require more synthetic fertilizer, which puts more nitrogen into the water. “Farm soils turn to dust while waterways suffocate from toxic algal blooms,” she writes.

It’s her contention, though, that “the sewage tide” is now turning. “Scientists and entrepreneurs all over the globe are finally looking at excrement in the same way as our thriftier ancestors did several centuries ago—as a resource, not as waste,” she writes. She spends much of The Other Dark Matter traveling to see the latest in toilet technology. In Israel she tests an apparatus that looks like a quilted tent. The unit, made by a company called HomeBiogas, converts poop into liquid fertilizer and also into methane, which can be used to power a stove. In Antananarivo, the capital of Madagascar, she visits a firm called Loowatt, which provides its customers with waterless latrines, then collects the contents and converts them—once again—into fertilizer and biogas. In the town of Elora, about fifty miles west of Toronto, she watches as fecal sludge is converted into a soil additive called LysteGro.

Zeldovich is an engaging writer. She loves puns and poop jokes. (Who doesn’t?) And her travels around the world are, in their own scatological way, inspiring. The projects she visits, though, are so small in scale that it’s hard to imagine them diverting more than a few buckets from the sewage tide. I don’t know how many units HomeBiogas would have to sell to treat as much waste as the Stickney plant, but probably the figure is in the millions. As Zeldovich herself notes, “In North America, most forms of sewage…are unwanted, so every municipality tries to get rid of them cheaply and quickly.” Will humanity ever get its shit together? Not in the foreseeable future, it seems.


Jo Handelsman, a plant pathologist who runs an interdisciplinary research center at the University of Wisconsin at Madison, is also interested in “dark matter.” Handelsman, however, uses the term to refer to soil. And the problem she’s concerned with is not that we have too much of the stuff, but too little. “The plight of the world’s soils is a silent crisis,” she writes in A World Without Soil.

According to the US Soil Taxonomy system, soil can be divided into twelve orders. These include gelisols, which are partially frozen and mainly found in the Arctic; oxisols, which are iron-rich and found mainly in the tropics; and mollisols, which are deep and dark and loaded with organic matter. The “silent crisis” Handelsman is concerned about encompasses all soil orders, but it’s the loss of mollisols that really worries her, since these feed the world. Ukraine, blessed with tens of thousands of square miles of mollisols, is known as “the breadbasket of Europe.” Every year, the country sheds more than 500 million tons of soil, and the losses are beginning to affect yields. Similar trends afflict the midwestern US. The mollisol-rich state of Iowa produces more corn and soybeans than most countries. The state has already “lost enough soil to see disturbing yield reductions, and the projections for the future are bleak,” Handelsman reports.

Agriculture requires rich soil, but most modern practices are, unfortunately, terrible for it. Prairie grasses are mostly perennials, with deep root systems. Plowing them up destroys the soil’s “architecture,” leaving it vulnerable to erosion. Trees have even deeper root systems; cutting down forests to carve out farmland leads to yet more erosion. The crops that replace trees and prairie grasses are usually annuals, with shallow root systems. These don’t hold soil well, and, in any event, get plowed up every year themselves. Corn, Handelsman writes, is a prime offender: “There is a saying among soil scientists that for every kilo of corn harvested, the field loses a kilo of soil.” A trillion kilos of corn, she notes, are harvested every year.

New soil is, of course, always being created as rocks break down and organic matter decomposes. But the process is far too slow to compensate for the damage that’s being done. The natural rate of soil production, according to Handelsman, is at best nine hundred pounds per acre per year. Around the globe, the annual loss from erosion now averages around six tons per acre per year. “That’s not sustainable!” she observes. And climate change is making matters worse. Increasingly, rain falls in intense bursts; the more force the water carries, the more soil it washes away. Fertilizer use can mask the effects of erosion, but only temporarily and at the expense of fish and other aquatic organisms. “As soil erosion intensifies worldwide, many countries may experience crop loss simultaneously, creating unprecedented food shortages,” Handelsman warns.

Like Zeldovich, Handelsman is concerned about feedback loops that turn big problems into insurmountable ones. Soils store tremendous amounts of carbon; according to Handelsman there’s three times as much carbon in the ground as in the atmosphere. When soils erode, carbon can be “mobilized” and released into the air, where it contributes to climate change. This leads to more erosion, and, well, you get the picture.

Handelsman extols traditional agriculture: “Long-lived agrarian societies tend their soils with care.” She points to the example of Papa Stour, one of Scotland’s Shetland Islands. For more than a thousand years, the inhabitants of Papa Stour practiced what’s known as plaggen agriculture, building up the island’s thin soils with copious quantities of manure, seaweed, and turf. She seems to suggest that today’s “silent crisis” could be solved, or at least ameliorated, by returning to traditional methods, but then admits this isn’t likely to happen. “These interventions may be too radical or difficult to scale up for widespread adoption,” she writes. And even if they were scalable, it isn’t really feasible to feed today’s world with medieval methods. It’s estimated that synthetic fertilizers support almost half of the 7.9 billion people now alive, and it’s tough to imagine how seaweed and manure and turf could make up for that (not to mention the fact that cutting turf is obviously damaging to the carved-up area). The addition of human waste might help, but Handelsman doesn’t go there.

Handelsman is a big advocate of no-till planting. “Conventional” planting on modern, industrialized farms involves turning over the top layer of soil before sowing. By contrast, no-till planting “preserves crop residue from the previous crop by drilling seeds directly into the soil through the stubble,” she explains. The practice preserves the soil’s architecture, significantly cuts down on carbon emissions, and improves water absorption. Compared with conventional planting, it reduces erosion by roughly three quarters. When the practice was first introduced, or rather reintroduced, in the 1970s, it was projected that by 2010 nearly 80 percent of the major crops grown in the US would be produced via no-till planting. In 2021 the figure was only 21 percent.

Farmers prefer tilling because it controls weeds. Those who “transition to no-till practices must adopt alternative weed-control measures,” Handelsman writes. These methods often involve herbicides, which cause problems of their own. One of the most widely used herbicides in the US is atrazine. The compound is suspected of being an endocrine disruptor and has been banned by the European Union. The US’s most popular herbicide is glyphosate, which is the active ingredient in Roundup. The World Health Organization’s International Agency for Research on Cancer has identified glyphosate as a probable human carcinogen. Handelsman is well aware of the hazards of herbicides but argues that these have to be weighed against other significant dangers, like climate change and “a world without soil.” “We aren’t even having the right conversation about risk,” she writes.

Handelsman is clearly frustrated by the world’s indifference to soil, without which, she points out, the surface of the planet would be barren and moonlike. She doesn’t seem to have much faith in her own ability to capture the public’s attention—she notes that only half the adults in the US read even a single nonfiction book per year—but instead wonders if a soil-themed video game might do the trick. Alternatively, perhaps Hollywood could produce “a scientifically accurate and spellbinding box office hit movie” that would finally raise awareness about soil. I had a hard time imagining the plot, but its title could be Let’s Get Dirty.