Scientists from Portland State University and Washington State University collected and analyzed samples from 14 coastal locations identified as potentially polluted because they were near wastewater treatment plants, large population centers or rivers and streams that empty into the ocean, a WSU release reported Wednesday.
The researchers said they were surprised to find found high caffeine levels in two areas not near the potential pollution sources, while low levels of caffeine were recorded near large population centers.
High levels were also found following a late-season storm of wind and rain that triggered sewer overflows, they said.
The results suggest wastewater treatment plants are effective at removing caffeine but high rainfall and combined sewer overflows can flush the contaminants out to sea.
"Our study findings indicate that, contrary to our prediction, the waste water treatment plants are not a major source of caffeine to coastal waters," Portland State researcher Elise Granek said.
However, onsite waste disposal systems may be a big contributor of contaminants to Oregon's coastal ocean and need to be better studied to fully understand their contribution to pollution of ocean waters."
While levels of caffeine measured were well below a lethal dose for marine life, it could be affecting marine creatures in unknown ways, researchers said.
"We humans drink caffeinated beverages because caffeine has a biological effect on us -- so it isn't too surprising that caffeine affects other animals, too," Granek said.