Credit: La-Citta-Vita/Flickr

Those hardest hit by the opioid epidemic are the people who become addicted—and the family members and friends who deal with the fallout. In 2017, opioids contributed to about 47,600 deaths by overdose in the US, according to the Centers for Disease Control and Prevention (CDC). And that year, 23 states saw significant increases in opioid-related deaths over the previous year.

But some researchers worry that another, lesser casualty of this epidemic could be the environment. As opioid use continues to proliferate, the drugs enter more people’s bodies, where they break down into metabolites—often other opioids—that end up in wastewater. Scientists have detected opioids downstream of wastewater treatment plants and are concerned about the potent drugs’ possible effects on organisms who live in those waters.

But until recently, these researchers didn’t know much about the extent of the problem. Wastewater treatment plants are not required to monitor or report opioids in their discharge. So several labs across the US have taken matters into their own hands. They have begun measuring how much of these drugs is present in rivers and streams as a first step toward understanding what effect the compounds might have on the environment.

What’s prompted scientists’ concern about opioids in the environment is that humans aren’t the only animals who respond to the drugs. A 2017 study by Randall T. Peterson and Gabriel D. Bossé at the University of Utah found that, when presented with options, zebrafish will willingly dose themselves with an opioid and that the fish undergo withdrawal symptoms when the drug is removed (Behav. Brain Res. 2017, DOI: 10.1016/j.bbr.2017.08.001).

The researchers were studying addiction rather than environmental exposure during this experiment. So they released a concentrated plume of 6 mg/L hydrocodone solution into the fish’s tank—a level that would definitely show a behavioral effect if one existed but not kill or sedate the fish. The zebrafish in this study would swim over an underwater platform that triggered the release of the drug, regardless of where the platform was placed. When the opioid was withheld from the tank, the fish showed “a lot of the physiological responses that you would see with any kind of withdrawal,” Peterson says.

Peterson and Bossé observed that once the fish had been conditioned to self-administer the drug, they would undergo risky behaviors—such as swimming into shallow water—to dose themselves. “Changes in behavior have consequences,” Peterson says. In the wild, this behavior could put the fish at greater risk for predation.

Of course, the concentrations that the University of Utah team studies are not what would be found in the environment—typically in the range of nanograms per liter to micrograms per liter. But lower concentrations could still have some effect, Peterson says. It’s also possible that if multiple opioids lurked in the water at low concentrations, they could have an additive impact, but studies have yet to confirm this effect in fish. In particular, researchers worry about the potential environmental effects of the synthetic opioid fentanyl, which the National Institute on Drug Abuse estimates is 50–100 times as potent as morphine and which caused the sharpest increase in human deaths from opioid use in 2017.

Studying changes to fish behavior at low environmental concentrations, though, is difficult. So far, some studies find evidence for altered behavior, while others do not. A 2019 study found that ecotoxicologists interpreting the same data can arrive at very different conclusions (Sci. Total Environ., DOI: 10.1016/j.scitotenv.2019.02.090). It’s also difficult to properly simulate the conditions fish would experience in the wild. In moving water, opioids and their metabolites are likely not evenly dispersed, so pinpointing their precise levels is problematic. But a handful of labs scattered across the US are up for that challenge.

Examining effluent

Cookeville is a city of about 33,000 located in one of the top 15 states for opioid deaths as of 2017: Tennessee. Water from the Cookeville Wastewater Treatment Plant (CWTP) runs out to Pigeon Roost Creek, goes through Falling Water River, and eventually joins Center Hill Lake, which is where the city draws its drinking water. “Anything that we ingest eventually gets released into the wastewater system,” says Tammy Hatfield Boles, an environmental scientist at Tennessee Tech University. The treated water is then heavily diluted before making it back to the city’s taps.

Boles, who studied incoming and outgoing water at CWTP for 2 years, presented her results during a Division of Environmental Chemistry symposium at the American Chemical Society Spring 2019 National Meeting in Orlando, Florida, on April 2. Her group worked closely with CWTP. “We love it when we don’t have to go into the influent and effluent and bail water,” Boles says. The plant provided Boles with samples, which her group then tested in its lab.

She and her team used solid-phase extraction (SPE) and liquid chromatography–tandem mass spectrometry (LC-MS/MS) to analyze samples of influent and effluent. From four sampling events ranging from July 21, 2015, to March 22, 2016, Boles’s lab detected an average of 5.58 ng/L of hydrocodone and 4.74 ng/L of oxycodone in the city’s discharge. Morphine, hydromorphone, and oxymorphone showed up from time to time but were usually below the detection limit of the team’s instruments. Boles says large creatures like people have no reason to worry about drinking water with contaminants at these ultralow levels.

Furthermore, from October 2016 to December 2017, the levels of all the prescription opioids that Boles’s lab was tracking dropped below detectable levels. John Buford, assistant plant superintendent, says CWTP optimized its biological disinfection process in April 2015, switching from a purely oxidizing process to an oxidizing and reducing process. In November 2016, the plant replaced its old ultraviolet disinfection machine with a new one. Tennessee’s opioid prescribing rate had been declining since 2010, another factor that may have contributed to the drop in their readings.

Cookeville is a small city, but Boles says areas that are more densely populated are associated with higher discharge of pharmaceuticals and personal care products (PPCPs) in their wastewater. “I think what I’ve found is a very small part of a larger overall picture,” Boles adds.

And studies in this field are just beginning. Boles is working to further improve the team’s process and would like to start sampling for fentanyl. Fentanyl use may increase as states crack down on prescription opioids. Boles says fentanyl could pose more environmental risk because it’s so potent; it’s also more dangerous to handle and can be difficult for labs to obtain for testing.

Probing the Potomac

Credit: Courtesy of Arion Leahigh

The Potomac River flows from West Virginia’s Potomac Highlands to the Chesapeake Bay. Along the way, it passes Washington, DC, which in 2017 ranked fourth among US states in opioid deaths per 100,000 people, according to the CDC. Arion Leahigh, a fifth-year PhD student in Gregory Foster’s lab at George Mason University, has set her sights on tracking opioids in the Potomac. She visits sampling locations in the DC metro area by boat or by foot, using a portable, battery-operated pump to collect water and a grab sampler to obtain sediment. Leahigh comes from a small town in Pennsylvania that’s been hurt by the availability of illicit drugs. She’s helping optimize her lab’s processes for detecting opioids and other PPCPs.

Like Boles, Leahigh uses a combination of SPE and LC-MS/MS to assess the concentrations of opioids in the water. She also reported her findings during the recent ACS meeting in Orlando. She found maximum values ranging from 5.18 to 83.36 ng/L of the opioid tramadol at different locations along the Potomac. In addition to opioids, her team has turned up caffeine and nicotine in almost every sample, plus blood pressure medication, antidepressants, anti-inflammatories, and antihistamines.

Credit: Tammy Hatfield Boles

Leahigh’s group is working to obtain effluent samples from local wastewater treatment plants so they can understand where the drugs they’re finding are coming from. Currently, they don’t know which ones are coming out in which effluent. If they don’t find a drug downstream, it could be because their method can’t detect it, the drug has broken down, or it’s not evenly dispersed. “Are they in the water? Are they settling down to the sediment? Are they breaking down and becoming harmless?” Leahigh asks. Once they know what the plants are putting out, they can start to understand the differences in concentrations.

Leahigh’s lab is at the Potomac Science Center, which is located directly on the Potomac. The team plans to put out an autosampler to measure fluctuations throughout an entire tidal cycle. Right now, the researchers are beholden to the tides because they’re using a boat to access sampling sites, which requires a certain depth of water. She hopes this new strategy will help them determine whether concentrations fluctuate with the tide or at certain times of day.

Studying the sound

In the Pacific Northwest, some researchers are forgoing water samples altogether for monitoring opioids. Jennifer Lanksbury runs the Washington Department of Fish and Wildlife’s Puget Sound Mussel Monitoring program, one of several long-term programs that monitors local wildlife under the Toxics-Focused Biological Observing System.

The system tracks contaminants in various food webs throughout the Puget Sound using indicator species such as English sole, Pacific herring, and Chinook salmon. Native mussels are the system’s nearshore indicator. By looking at the tissues of these animals, the scientists can determine the relative amounts of drugs in the surrounding water.

Credit: David Toth

Mussels are filter feeders, so “you’re much more likely to find a contaminant in mussel tissues than you are to pick it up in water or even sediment,” Lanksbury explains. “We call them our little aquatic vacuum cleaners.” Unlike fish, mussels don’t have a liver with which to metabolize contaminants, “so the contaminants in their tissues reflect pretty well what’s in their local environment.”

The mussels grow at an aquaculture farm off the shore of Whidbey Island, about 90 km northwest of Seattle. Volunteers bag the mussels in nets suspended in antipredator cages and transplant them to up to 100 sites throughout the sound every other October. The mussels remain in the water for about 3 months before they’re removed and sent back to the lab, where about half the mussels from each cage are blended into a slurry and sent off to various analytical facilities for testing.

The program typically looks at ongoing contaminants, such as polycyclic aromatic hydrocarbons, and legacy contaminants, such as polychlorinated biphenyls and the insecticide dichlorodiphenyltrichloroethane. But in 2017, Lanksbury teamed up with Andy James, a senior research scientist at the University of Washington Tacoma, to screen some of the mussels for PPCPs. Of the 18 samples they screened, 3 tested positive for oxycodone—the first indication of opioid contamination in the Puget Sound. The samples came from three of the most urban sites: two in Seattle and one in Bremerton; at its highest, oxycodone was present at 1.5 ng/g of the sample’s wet weight, which Lanksbury and James consider a low concentration. While most legacy contaminants enter the sound from stormwater runoff, Lanksbury suspects PPCPs are entering the water mostly via wastewater effluent. “The message is that there are multiple sources of contamination in nearshore Puget Sound,” she says. “Depending on which chemical you’re interested in, it could be more one source than the other.”

Lanksbury and James are more concerned about some of the other PPCPs their screen turned up, including antibiotics, selective serotonin reuptake inhibitors from antidepressants, alkylphenol ethoxylates from detergents, and the chemotherapy drug melphalan, a possible carcinogen that was present at half the mussel sites at surprising levels. “We don’t want to see chemotherapy drugs in the environment,” Lanksbury says.

Like Boles, Lanksbury and James stress that their findings are not cause for concern for human health. For one thing, these mussels were planted in urbanized areas. Lanksbury says the mussels grown for food at Puget Sound’s aquaculture farms, located in more rural areas, are really clean. For another, James points out that a person would need to eat more than 100 lb (45.4 kg) of the contaminated mussels to reach a therapeutic dose of oxycodone—and that eating that many mussels would surely lead to other ailments.


Wastewater plants in the US are regulated nationally by the Environmental Protection Agency’s National Pollutant Discharge Elimination System, which does not require them to test for opioids or other pharmaceuticals in their discharge. For the contaminants they are required to remove, such as ammonia, the plants are highly effective, Boles and Leahigh say. Lanksbury would like to pinpoint how much of each PPCP is coming from each plant, but those data aren’t available yet because many of these efforts have only just begun.