The everyday chemicals that humans ingest to relieve pain, fight depression and diabetes, or treat infection are winding up in the tissue of fish in Washington's Puget Sound.

A study in the journal Environmental Pollution detected unusually high levels of drugs like Advil, Benadryl, Prozac, and even birth control pills, in the tissue of salmon.

The culprit, according to the study, is human waste.

"About 45 of the 150 chemicals we examined were found in the fish," said James Meador, the lead author of the study and an aquatic toxicologist working with the National Oceanic and Atmospheric Administration. "Some of them were at high concentrations. That's the kind of information that raises eyebrows."

Over 4,000 pharmaceuticals are currently in use or in development in the United States. Many of them are finding their way into rivers, streams, and lakes, raising concerns about how exposure could impact wildlife, or even humans who consume fish.

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Meador's team focused on compounds that Americans pick up at their local pharmacy, or is frequently proscribed by doctors. Water samples from the sound, wastewater, and fish tissue were analyzed for the presence of 150 different types of chemicals.

One hundred and six wastewater treatment plants, discharging as much as 97,000 pounds of chemicals each year, are located around Puget Sound. Meador's team examined only two of them, but found ingredients from 81 drugs and personal-care products, at some of the highest concentrations in the country.

Hundreds of chemicals can be found in the waters of Puget Sound, but only a handful are regularly monitored by wastewater facilities, which require permits from Washington's Department of Ecology to operate. Chemical levels from pesticides, for example, must remain below a certain threshold before the water can be dumped into the sound. But pharmaceuticals, now ubiquitous in society, aren't monitored.

"There's a lot of chemicals that we already know cause problems for the salmon," said Amelia Apfel, who works with Puget Soundkeeper. "It's concerning to learn that they are more things in the water that we don't even know about."

While the presence of toxins sounds alarm bells for advocates like Apfel, more research is needed to understand the impact of chemicals on aquatic life, said Meador.

For example, metformin, a common diabetes medication, could hinder metabolic function, impacting a fish's growth. High exposure to antibiotics could result in antibiotic resistant bacteria, which could potentially lead to dangerous pathogens that could be passed along to people. Prozac or Zoloft, which might free a person from the grip of chronic depression, could very well negatively impact the behavior of fish.

"If that happens, the fish is toast." said Meador. "It doesn't last long. Predators hunt fish that stray from normal behavior."

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Chinook salmon migrate from the ocean to river headwaters in order to spawn. Meador and his team studied the fish because they spend several weeks each year swimming in areas of high chemical concentration. In previous studies, Meador found that the salmon that migrate through chemical-laden wastewater die at nearly twice the rate of fish in cleaner waters. Staghorn sculpin, which are abundant in Puget Sound, were also tested.

The researchers found that salmon had higher rates of toxicity than sculpin, which was surprising because sculpin are bottom-feeding fish that spend more time in the region.

"But young salmon eat a lot," said Meador. "They pass a lot of water over their gills, which allows the chemicals to be taken up into the gut of the fish."

It remains a challenge to figure out how to remove chemicals from waterways because the regulatory agencies aren't obligated to treat them like other pollutants. Meador hopes that by studying the impacts that everyday, household pharmaceuticals have on aquatic life, scientists will be better able to define a threshold for allowable levels of chemicals in the water.

"Several species of salmon are endangered," said Meador. "In the past we've looked at PCP and DDT. Pharmaceuticals are the next frontier."

Follow Elaisha Stokes on Twitter: @ElaishaStokes