https://www.inverse.com/article/4523...-opioid-crisis

Every two years, Washington Department of Fish and Wildlife scientists take mussels out of a pristine aquaculture source on Whidbey Island and place them in the more urbanized regions of the Puget Sound. Because mussels are filter feeders, their tissues are a good way to measure pollution of all kinds, including contaminants like cocaine or pharmaceutical drugs. On Thursday, local news reported that a new substance has been found in the mussels: opioids.
The contaminants got into the Puget Sound through discharge from wastewater treatment plants, which filter water from local toilets. When humans ingest opioids, they excrete traces of the drugs in their urine, and even wastewater treatment isn’t enough to get rid of all of it. The trace chemicals are being categorized as “contaminants of emerging concern.”