When humans ingest opioids like oxycodone, they ultimately end up excreting traces of the drugs into the toilet. Those chemicals then end up in wastewater. And while many contaminants are filtered out of wastewater before it's released into the oceans, wastewater management systems can't entirely filter out drugs. Thus, opioids, antidepressants, the common chemotherapy drug Melphalan -- the mussels tested positive for all of them.
Source: https://www.cbsnews.com/news/mussels-test-positive-for-opioi...