Mussels containing oxycodone was thousands of times lower than the therapeutic dose in treating humans.
The mussels came from very urban areas and are reportedly not near any commercial shellfish beds where mussels are harvested for food.
"It's telling me there's a lot of people taking oxycodone in the Puget Sound area".
Surfactants, in particular, are "known to have estrogenic effect on organisms, so they affect the hormone system of some animals in an estrogenic way, such as feminizing male fish and making female fish reproductive before they're ready", Lanksbury explained. This marks the first time the opioid has ever been found in marine life in Washington. When humans ingest opioids, traces of the drug end up in the toilet, CBS News said.
But the potential presence of oxycodone in fish would be concerning, however, as they do metabolize opioids.
Scientist Andy James at the Puget Sound Institute assisted with the study.
The Department uses mussels to get a reading on pollution in waterways because they're "filter feeders", meaning they absorb contaminants from their surroundings into their tissues.
CNN reports that a number of other pharmaceuticals were found in the mussels' tissue including seven types of antibiotics, five antidepressants, more than one antidiabetic drug, and a chemotherapy agent.
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Scientists have not studied whether mussels are harmed by oxycodone.
Scientists who track pollution have discovered traces of the pain reliever oxycodone in some Puget Sound mussels. This is how the opioids get into the Puget Sound. The drug was found at "levels where we might want to look at biological impacts", according to James.
"We sent 18 samples (of mussels) to a laboratory up in Canada and asked for a suite of pharmaceutical and personal care products", Lanksbury said.
Lanksbury said the research couldn't have been done without an army of citizen science volunteers who put the mussels out in low tide during the winter, and retrieved them three months later.
Almost two decades ago, the U.S. Geological Survey conducted a study and found "measurable amounts" of medications in a whopping 80 percent of water samples that were collected from 139 steams across 30 states.
Two were near Bremerton's shipyard and one was in Elliot Bay near Harbor Island in Seattle.
Of 18 areas researchers utilized, three indicated hints of oxycodone.
Every other year, the department specifically monitors herring, English sole, Chinook salmon and mussels for contaminants.