Evidence that fish are being contaminated by pharmaceuticals introduced into wastewater keeps building. That's clear as scientists look beyond drug levels in bodies of water and directly measure concentrations in the blood of fish that swim there, as one team undertook for a new study published July 26 in the journal Environmental Pollution. While experts say human health isn't at risk, unknowns remain, given the increases in pollution levels as the population grows.
For some drugs in the study, blood concentrations that would be high enough to treat a human were seen in comparable levels in fish – albeit in proportion to their much smaller body sizes and blood volumes – likely affecting them as well.
Metformin, a widely used and inexpensive medicine for treating diabetes, helps millions of Americans keep their blood sugar under control. However, metformin was one of the drugs found in significant levels in fish.
Antibiotics to fight infections, drugs to ease depression, statins to keep cholesterol in check and blood pressure medications to prevent heart attacks and strokes – while useful for people who need them – offer no benefits to the fish exposed to them.
For any drug, a measure is available indicating the concentration needed in the blood to have a therapeutic effect for humans. "We can measure that in fish," says lead study author James Meador, an environmental toxicologist at Northwest Fisheries Science Center in Seattle, part of the National Oceanographic and Atmospheric Administration, a federal agency. The overarching issue, Meador says, is that beneficial concentrations for humans are considered adverse for fish because those levels can change their normal physiology. In estuaries contaminated by discharge from wastewater plants and other toxic substances, he says, survival rates of young salmon are sometimes half of what's observed for young salmon in cleaner water.
On a more reassuring note, the total amount of medication in an 8-ounce piece of fish would be far too low to affect a person who ate it, Meador says.
In terms of human health, the public needn't be too worried, explains John Sumpter, a professor with Brunel University London, who has conducted research on the effects of pharmaceuticals on fish for more than two decades. "The only potential concern of significance is the possibility that antibiotics in the environment are leading to enhanced resistance in microorganisms and that this resistance transfers to human pathogens," he wrote in an email. Antibiotic resistance is a growing concern, since it could render our available drug treatments ineffective.
As for drug dosages, Sumpter says, "Contaminated fish contain truly minute amounts of pharmaceuticals compared to the amount in just one pill of any pharmaceutical."
For the new study, conducted on the West Coast, Meador's team focused on juvenile Chinook salmon and staghorn sculpin from estuaries affected by wastewater treatment plants in Puget Sound in Washington state. Along with antibiotics, antidepressants and statin drugs, the researchers also detected high levels of amphetamine in the fish. Chemicals like DEET, used to protect people from mosquitoes and ticks, also showed up in fish bodies.
The researchers also detected that fish were exposed to multiple drugs with similar actions. Potential for drug interactions in fish exists when drugs from the same antibiotic, antidepressant or blood-pressure medication class are combined.
While people can protect themselves from dangerous drug interactionsby reading package labels and checking with their pharmacists on land, "the fish don't have a choice," Meador points out. "They've got all these medicines coming at them at once. It's a very tricky problem to deal with but we are trying to get serious about mixtures and how they might affect fish and people who are sensitive to these things."
The prime culprit for fish contamination is medication that passes through the human body without being broken down, or metabolized, and then is released through the urine. "So it's basically going down the toilet," Meador says. "And it comes out into a wastewater treatment plant. Every city has one."
Water treatment for standard contaminants doesn't get rid of pharmaceuticals very well, Meador says. "They have a pipe that goes into a river, estuary or somewhere else. And it's just this continual stream of chemicals flowing out. There are millions of gallons per day coming out of these plants."
Fortunately, drug-tainted drinking waterdoesn't appear to be a human hazard. Although medications have been detected in rivers and groundwater in some parts of the U.S., Meador says, they've been in relatively low levels. "Toxicologists figure out how many gallons of water you need to drink per day to get a therapeutic dose," he says. "By and large, concentrations are well below levels of concern."
Other drugs and chemicals found in high levels in the fish studied included the asthma drug albuterol, testosterone, diphenhydramine (the active ingredient in Benadryl) and sertraline (the active ingredient in Zoloft). The authors noted that the drugs they tested for only make up a small percentage of the more than 4,000 pharmaceuticals on the market.
The findings build off a February 2016 study by Meador and colleagues that found unexpectedly high levels of medications like Prozac, caffeine, personal care products and insecticides in affected water, and in the bodies of young Puget Sound salmon.
One drug class alone stands out for its proven detrimental effect on wildlife, according to Sumpter. "Synthetic estrogens, first reported nearly 20 years ago, remain the only convincing example of a human-use pharmaceutical probably contributing to an effect on wild animals; in this case, fish," he says.
Compounds known as endocrine disruptors can change fish in subtle ways, Meador says. Suspected endocrine disruptors include certain pesticides, plastic additives, phtalates in personal care products and synthetic hormones. They likely account for the presence of "intersex" fish, which are male fish with female characteristics. Since 2005, smallmouth bass with intersex features have been identified in the Potomac River in the District of Columbia and tributaries in Maryland and West Virginia, including the Shenandoah River.
It makes sense to avoid contaminated food and water, if possible. "Know the fish you're eating, because sometimes fish are coming out of areas we know are polluted," Meador says. Most municipalities provide customers with water-quality reports for drinking water every year, and last week the nonprofit Environmental Working Group released its new national Tap Water Database.
Perspective is important for people evaluating their risk, Sumpter notes: "Use of illegal pharmaceuticals can and does kill people – think of the opioid problems in the U.S. presently – whereas any pharmaceuticals in food or drink have not and will not, as far as anyone can judge."
That said, consumers can do their part to reduce drug-related water contamination. Although flushing excess medication down the toilet only accounts for a small percentage of the total drug accumulation in wastewater, Meador says, it's worth avoiding. Instead, he advises taking advantage of drug take-back days in your community.
In addition to disposing of unused pharmaceuticals properly and avoiding unneeded prescriptions, Sumter says, consumers can speak up for the environment. "They could apply pressure to wastewater companies to improve wastewater treatment before they discharge effluent into rivers." In addition, Meador says, people could contact their representatives and encourage legislation to reduce these chemicals.