Scrutinizing city sewage to study our health

Sewage offers a few advantages as a pool of information. For one thing, it’s anonymous. And yet it captures a little something from everyone. “You can pretty much guarantee that most people are going to be using the sewer system,” says Dan Burgard, an environmental analytical chemist at the University of Puget Sound in Tacoma, Washington.

And it’s fast. To find out about health and drug use, researchers typically rely on surveys and data collected by hospitals or during arrests. “There’s often a substantial lag time, as many as two or three years sometimes, before that data become available,” says Kevin Bisceglia, an environmental chemist at Hofstra University in Hempstead, New York. Besides, “If you ask someone about their illegal behavior they’re not necessarily going to tell you accurately.”

Sewage offers a more immediate—and honest—snapshot of what the city is up to. “Sometimes a million people or more are represented in a single 24-hour sample,” Halden says.

He and his colleagues have examined how chemicals in our waste can seep into the environment. In 2002, they found that triclocarban, an ingredient in antibacterial soaps, was not broken down during wastewater treatment. It showed up in sewage sludge, the solid muck left after treatment that is sometimes used to fertilize crops. “That opens a pathway for chemicals…potentially being taken up by plants and making it right back to our dinner plates,” Halden says.

A chemical that won’t break down during treatment and likes to collect in solids is worrying, he adds. “It’s actually the same chemistry that will persist in our bodies when we get exposed and will become sequestered…in body fat.”

Halden and his colleagues found that triclocarban and a similar chemical, triclosan, were persisting in sewage sludge at treatment plants across the nation and pollutingMinnesota’s freshwater lakes. There’s some evidence that these chemicals may disrupt the body’s hormonal activity. Plus they don’t seem to be more effective at preventing sickness than washing with regular soap and water.

Halden and his colleagues reported their concerns to multiple federal agencies and at a congressional briefing panel. In 2016, the U.S. Food and Drug Administration banned the chemicals from over-the-counter antibacterial washes and soaps.

“We used a million pounds per year of the chemical in the United States but there was no information about what happens to that million pounds once we wash our hands,” Halden says. “This is unfortunately not an isolated case; there are still a lot of chemicals where we need to understand better what happens to them.”

Sewage can also reveal what germs are brewing in a city. “When someone gets sick they shed a huge amount of bacteria or viruses,” Halden says. “Even a few sick individuals create a signal in the sewage, and we can measure that.” Those pathogens can serve as an early warning that an outbreak is at hand. Israel has been using its sewers to monitor polio virus for decades

With climate change and warming temperatures, different pathogens are expected to migrate away from the tropics. “We can actually follow the invasion of Zika virus and other viruses by looking at wastewater,” Halden says. Scientists could also track germs over time to watch for developing antibiotic resistance.

Waste may give a rough sense of a community’s overall health. “When you go to the doctors office you would never think twice about handing your specimen over,” Halden says. Sewage surveillance is a bit like taking a urine or stool sample from an entire city. Scientists could examine how often certain medicines are prescribed, or look for hormones and other chemicals our bodies make that can indicate stress or certain illnesses. Bisceglia and his team have measured cotinine, a breakdown product of nicotine, in Boston wastewater to calculate how many cigarettes the city’s smokers consume per day.

Illegal drugs also leave their mark in sewage. These traces can reveal patterns of use, the emergence of new drugs, or whether law enforcement strategies are working. “If they have a major drug seizure in a particular community, do they actually see that drop in use?” Bisceglia says.

For years, Europe has monitored drugs like cocaine and ecstasy in sewage. A continent-wide network has sampled urine and poop from more than 60 cities and towns. It has started to detect regional patterns—like how cocaine is more popular in southern and western Europe, and ecstasy and cocaine tend to be urban drugs.

Researchers are considering whether sewage might shed some light on the opioid epidemic. Unfortunately, this will be difficult. Heroin is quickly converted into morphine, and morphine in wastewater will be flowing from legal sources like hospitals too. “I can give you exactly how much morphine is in our samples, but telling you where it comes from is difficult,” Burgard says.

Then there’s fentanyl, a synthetic opioid that is 50 to 100 times more potent than morphine. That means people need to use less to get high, and it’s harder to find because the concentration is low. And other opioids can be difficult to pick out too.