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Jeffrey Hawkins Writer likes to say that the average drop of water entering the Mississippi River headwaters north of Minnesota will be used 11 times before it reaches the Gulf of Mexico. That drop might irrigate crops, flow through wastewater treatment plants, pour out of residential taps, move through digestive systems, arc into toilet bowls, swirl down into sewers, and then do it over again. Whatever its fate along its 2,300-mile journey South, this water will mix with all kind of chemicals, human metabolites, and unnatural compounds. Writer can attest to that. When he floated down the big river in the early 1990s on a government research boat measuring contaminants, he detected everything from heavy metals to pesticides to caffeine.

But the waters of Colorado, Writer’s current base of employment, should be an entirely different matter. On a late September morning, Writer and I are driving along the outskirts of Boulder. The road is lined with picturesque stands of cottonwoods and willows; sheep graze lazily in sun-dappled fields. The seasoned environmental engineer points to craggy, snow-capped mountain peaks looming over the hills above us, a source of virgin water feeding into the Boulder Reservoir, the town’s primary source of drinking water, and eventually its main tributary, Boulder Creek.

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We are on our way to the heart of town, where Writer, a hydrologist at the United States Geological Survey (USGS), wants to show me a favorite local haunt near the University of Colorado, Boulder. It’s a bucolic spot on Boulder Creek where families swim, dogs frolic, and children go tubing in the summer. Upstream of Boulder’s central wastewater facilities, the crystal clear water is fed mainly by the runoff from the Arapaho Glacier and scores of streams like it, migrating down from the Rockies through waterways notched into the hills.

So when we pull up and step out of the car, it comes as somewhat of a surprise when Writer tells me what’s in the water. Recently, he picked up significant traces of a drug called lamotrigine, a compound prescribed to treat epilepsy and manic depression. The metabolites, he speculated, came from the one source of treated wastewater upstream of the reservoir, located in a tiny 1,445-person mountain town called Nederland.

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“Even here in this pristine stream, there’s no running away from it,” Writer says. “What we’re seeing is how medicated our society is. These compounds are extremely persistent and show up wherever you look for them.”

In recent years, watershed studies across the United States have turned up eye-opening levels of antidepressants, butalbital (a barbiturate), sulfamethoxazole (an anti-bacterial), carbamazepine (an anti-seizure medication often used to treat bipolar disorder), as well as metabolites of caffeine, cigarettes, steroids, and lipid regulators. According to the USGS, pharmaceutical traces can be found in 80 percent of United States streams. 

Despite the ominous findings, the impact of all these metabolites on human health is not yet fully understood. A 2011 U.S. Government Accountability Office report “confirmed the presence of pharmaceuticals in drinking water throughout the nation,” though added “the human health effects of exposure to these pharmaceuticals is largely unknown.”

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The drug traces in the nation’s water supply cast into sharp focus an issue seldom discussed in environmental science, but bound to become prominent in the future: the increasingly outmoded state of wastewater treatment plants.

For many years, wastewater treatment was a relatively simple proposition. Back in the old days, biologists assumed most pollution was tied up in solids or contained in bacteria and pathogens. So most wastewater treatment plants removed debris, separated solids from liquids, usually by using gravity or other physical means, and then disinfected the liquid that remained, before releasing it back into the watershed. Many plants exposed the water to chlorine gas, a cheap, highly reactive element that quickly oxidizes and kills microorganisms and bacteria carrying scourges like cholera, pneumonia, or typhus.

Now, however, with improvements in the ability to detect tiny yet potent trace elements in the water, along with an explosion of highly medicated urban populations, biologists are finding plenty of things to worry about. (A 2005 to 2008 survey revealed that 1 in every 10 Americans over age 12 is taking antidepressants, a 400 percent increase over the previous survey, conducted between 1988 and 1994.)

U.S. waterways are a pharmaceutical soup, and that soup is becoming more difficult to identify and filter everyday.

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One fear is “nutrient pollution,” a phenomenon caused by the release of too much nitrogen and phosphorous by wastewater plants and agricultural runoff back into the environment. Phosphorous is a common ingredient in most synthetic dish and hand soaps, laundry detergents, and disinfectants, while nitrogen is a key component of the metabolic byproducts produced by humans and livestock. Aquatic vegetation has reacted to the surge in nutrient-rich wastewater like a weightlifter on steroids, blooming into gargantuan oxygen-sucking fields of pond scum that blot out sunlight. Today, algae blooms are threatening a wide array of iconic watersheds, including the Gulf of Mexico and the Chesapeake Bay.

More dramatic are hermaphrodite fish. In the past decade, numerous studies have shown that “endocrine disruptors,” or hormonal metabolites like birth control pills, tamoxifen, and steroids, are creating intersex fish. In studies done all over the world, normally male fish downstream of wastewater plants appear to be growing ovary tissue in their testes, while female fish have been found with sperm-producing nests in their ovaries instead of eggs. The chemicals also affect sexual differentiation in the womb, tilting the balance of male to female fish dramatically. In one study conducted downstream of Boulder’s wastewater treatment plant, researchers found a 10 to 90 ratio of male to female fish.

Biologists are alarmed to learn that feel-good drugs like Prozac are making little fish recklessly apathetic to the dangers of the bigger fish who like to eat them. Blissing out on Prozac, after all, is a quality of life boon if you’re a neurotic New Yorker dealing with the stress of preschool tuition payments, angry cabbies, and demanding bosses. But it can prove fatal in the ruthless arena of nature, where hesitation can mean you’re someone else’s lunch. “If you want to draw the parallel to humans, it is like an impaired driver who is slow to pick up a threat and respond to it,” says Heiko Schoenfuss, a professor of Toxicology at Minnesota’s St. Cloud State University, who exposed larval fathead minnows to Prozac at different doses. 

Vance Trudeau, a biologist at the University of Ottawa, who has found evidence of “sexual side effects” in goldfish exposed to traces of Prozac in his lab, says “Prozac is the tip of the iceberg.” He adds that U.S. waterways are becoming a “pharmaceutical soup,” and he, along with Writer and other biologists, say that soup is becoming more difficult to identify and filter everyday. “Most sewage treatment plants have not been built with the removal of pharmaceuticals in mind because it wasn’t something people were thinking about,” Trudeau says. “To upgrade is prohibitively expensive. So pretty much anything we take ends up in the water.”

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Many pharmaceuticals are explicitly designed to break down slowly in the human body. But that has a downside. The active ingredients in delayed-release drugs are often tied up in a matrix of insoluble compounds that are expelled before they have released their load.

In Colorado, it takes about two hours for raw sewage to travel from the toilet bowls of central Boulder to the North 75th Street Wastewater Treatment Facility on the outskirts of town. The sprawling plant sits on rolling green pastures, fronted by rows of solar panels, a half a football field up from the banks of the surging waters of Boulder Creek.

On a clear morning, I follow Leigh Rickert, an affable, grey-haired maintenance manager into a boxy, concrete building on the edge of the compound. Rickert informs me that we have entered the gateway for the 13 million gallons of raw sewage expected to arrive that day. Already the stench is worse than a row of Porta-Potties at the end of a weeklong rock festival.

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Rickert motions to two oversized metal grates that rise up from depths of the bubbling mess flooding out of two massive intake pipes. The grates are the first step in the crude sorting process that transforms the refuse-choked, chocolate-brown incoming waters into treated outflow, as clear as a mountain spring.

Stepping past an impressive array of detritus trapped by the grates, we head outside and into a complex of humungous basins. We walk over a vast web of metal catwalks and gaze down on three sets of massive, brackish, bubbling, stinky vats of water known as “aeration pools.” The pools, Rickert explains, are filled with billions of microorganisms that love nothing better than to feast on the nitrogen and carbon compounds in human waste.

“That is called a floating mixer,” Rickert says, pointing to the top of an oversized, rotating metal disc poking out of the muck like an iceberg. “Basically it keeps the food coming to the bugs. The bugs eat shit and die, and when they die, their body is a more stable entity than what they ate.”

We walk over a vast web of metal catwalks and gaze down on three sets of massive, brackish, bubbling, stinky vats of water.

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Five years ago, Boulder became one of a growing number of towns to install an “activated sludge” process, a cutting edge, $28.5 million upgrade, that takes nitrogen-rich human waste, feeds it to microorganisms, and transforms what would otherwise escape in water runoff to feed biosolids that can be carted away and used as fertilizer or released as a harmless nitrogen gas—the kind that constitutes 78 percent of the Earth’s atmosphere.

Every day, plant operators feed hundreds of thousands of gallons of human waste into the three basins. The water resides in the basins for 24 hours, during which the microorganisms cleanse it of from 50 to 55 percent of its nitrogen, at which point it is allowed to migrate to the next stage in the process. Although the microorganisms prefer to snack on the simple nitrogen and carbon compounds excreted in human waste, once they are done, they will move on to more complex compounds.

“Most of the microorganisms are common soil bacteria and are pretty good at adapting to whatever food is there,” explains Chris Douville, the plant’s wastewater treatment manager. “They’re like kids at the cafeteria. They’re going to hit the donuts and Pringles first, then move on to burgers and rice, and maybe have a salad at the end.”

Douville says the process is removing some of the estrogens and other hormones present in the water, chemicals that for years were allowed to pass back into the Boulder watershed. Even so, many of the neurotropic substances are so exotic that the snacking microorganisms ignore them. Other substances take so long to break down in the vats that while microbes are munching on other compounds, they are flushed out of the system.

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“Antidepressants are atypical of most organic compounds that organisms typically encounter, and organisms may not have the requisite biochemical tools or enzymes to metabolize these compounds,” Writer had told me. “More research is needed to evaluate why, but many of the antidepressants seem to be quite environmentally persistent.”

Cleansing those lingering drug compounds from the wastewater is an arduous and expensive process. “The only other options we know of at this time use advanced techniques, such as chemical techniques to oxidize and destroy them, or filtering out completely pure H20,” Douville says. “But at this scale that would cost several hundreds of millions of dollars.”

Nearly all the scientists I interviewed lamented the multiplication of drug compounds. “As soon as we find a compound in the water, pharmaceutical companies are saying we found a better one,” says Mike Thurman, a UC Boulder chemist who has been analyzing water samples for psychoactive pharmaceutics since 2008.  “It’s hard to keep up; they’re already changing compounds.”

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The detection of pharmaceuticals in treated wastewater has led some researchers to take the next logical step—they have begun to search for evidence of illegal drugs in the water. And they have not been disappointed. In the U.S., about 22.5 million Americans aged 12 and older—or 8.7 percent of the population—used illegal drugs in 2011, according to a survey conducted by the Substance Abuse and Mental Health Survey Administration. That effectively means that while 11 percent of the population is flooding sewer systems with antidepressants and their metabolites, almost 10 percent are excreting metabolites from drugs such as marijuana, cocaine, heroin, or methamphetamine into the nation’s water supplies.

“Residues of illicit drugs can reach sewage treatment plants in substantial amounts, escaping degradation, and be released into surface waters,” wrote Ettore Zuccato and Sara Castiglioni, of the Department of Environmental Health Sciences, Mario Negri Institute for Pharmacological Research, in a 2009 survey. The Italian researchers identified drug traces in waterways in Italy, England, and Switzerland. “Environmental concentrations are low, but risks for human health and the environment cannot be excluded,” they wrote. “Morphine, cocaine, methamphetamine, and ecstasy all have potent pharmacological activities, and their presence as complex mixtures in surface waters may be toxic to aquatic organisms.”

“Society has to ask the question—why are we finding such a variety of antidepressants at these levels?”

In 2007, a team led by Oregon State Chemist Jennifer Field garnered nationwide headlines announcing they had tested the sewage of 10 major cities for drugs and discovering, among other things, that concentrations of methamphetamine in Las Vegas were 500 percent those in Omaha, and twice that of Oklahoma City.

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Some of these substances almost certainly make it in the drinking water. In 2009, a team led by Maria Huerta-Fontela of the Spanish company AGBAR-Aigües de Barcelona, examined the drinking water from a Spanish drinking water treatment plant. Most amphetamine-type stimulants and nicotine were completely removed by the processes. But 10 percent of caffeine and about 26 percent of Benzoylecgonine, the main metabolite of cocaine, survived and was still present in the filtered water.

A number of experts agree that, for now, there is little evidence that trace elements of either legal or illegal drugs in the water are dangerous to human health.

Daniel R. Dietrich, head of the Environmental Toxicology Research Group at the University of Konstanz, Germany, who has studied drug compounds in waterways, likes to tell a joke about aspirin—which routinely makes it way into sewage discharge—to drive the point home. Dietrich notes that he lives and works in a community on the border of Lake Konstanz, where Swabians are famed for being cheap. Some researchers have found small amounts of a popular nonsteroidal anti-inflammatory known as diclofenac in the water. “We always make the joke that in order for one Swabian with a headache to avoid paying for a single pill, he would have to drink a million liters of water a day,” Dietrich says. “There’s no data that would suggest people could have adverse effects at those concentrations.” Similarly, Oregon State’s Field told one reporter in 2008 that you’d have to drink 1,000 liters of raw sewage to get a typical dose of cocaine.

Some researchers remain wary of dangers. Thurman, the UC Boulder chemist, notes that comparable concentrations of pesticides are considered contamination and usually prompt government intervention. “We’re seeing these things in the water in parts per billion. When we get parts per billion on pesticides it’s a big deal. Society has to ask the question—why are we finding such a variety of antidepressants at these levels? We’re using pesticides, at least we know why we are using then.”

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It’s an issue that will only grow more pronounced, notes Bryan W. Brooks, Ph.D., director of the Baylor University Environmental Health Science Program, and one of the first scientists to identify Prozac in the water. While in the past great cities were built on great waterways, that is no longer the case for megacities emerging in the 21st century. Increasingly, populations are expanding into areas veined with seasonal water streams and rivers. In Texas, the population is expected to double in the next 40 to 50 years.

With more people comes more wastewater, and that, Brooks says, is turning natural stream-flow patterns, often intermittent trickles, into steady flowing waterways deluged with millions of gallons of treated human wastewater. More people also means that wastewater, with its pharmaceutical traces, is being channeled into uses across society. “We depend on what was once wastewater for potable, for industry, for agriculture, and also to base flows to maintain coastal fisheries,” Brooks says.

As the sun goes down in the Rockies, Writer and I stand on the banks of the Boulder Creek, watching a flood of wastewater gush out of a huge pipe from the treatment plant, merging with the alpine waters surging by. The water is headed to the St. Vrain River, where it will join a flow carrying wastewater from the town of Lyons. Just down from that confluence, the city of Longmont will siphon off the water for drinking, only to be expelled by a resident into a toilet bowl, sending it toward another sewage treatment plant, and then dumped back into the river again. There it will join the Big Thompson River, carrying pure streams and discharges from Rocky Mountain National Park, continue south, and merge into the mighty Mississippi.

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Writer draws my attention to our beautiful surroundings. The nearby cottonwoods are home to several bald eagles nests. “The eagles nest in the cottonwoods and prey on the fish,” Writer says. He points to several humongous carp in the foaming creek below us. “See those carps there? They’re swimming in 100 percent effluent.” I have to wonder if the carp seem so docile because they found the conditions so pleasant. Or because their apathetic daze is induced by imbibing too much Prozac.

Adam Piore, a contributing editor at Discover, is a freelance writer based in New York.

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