For decades, a graveyard of corroding barrels has littered the seafloor just off the coast of Los Angeles. It was out of sight, out of mind — a not-so-secret secret that haunted the marine environment until a team of researchers came across them with an advanced underwater camera.

Speculation abounded as to what these mysterious barrels might contain. Startling amounts of DDT near the barrels pointed to a little-known history of toxic pollution from what was once the largest DDT manufacturer in the nation, but federal regulators recently determined that the manufacturer had not bothered with barrels. (Its acid waste was poured straight into the ocean instead.)

Now, as part of an unprecedented reckoning with the legacy of ocean dumping in Southern California, scientists have concluded the barrels may actually contain low-level radioactive waste. Records show that from the 1940s through the 1960s, it was not uncommon for local hospitals, labs and other industrial operations to dispose barrels of tritium, carbon-14 and other similar waste at sea.

“This is a classic situation of bad versus worse. It’s bad we have potential low-level radioactive waste just sitting there on the seafloor. It’s worse that we have DDT compounds spread across a wide area of the seafloor at concerning concentrations,” said David Valentine, whose research team at UC Santa Barbara had first discovered the barrels and sparked concerns of what could be inside. “The question we grapple with now is how bad and how much worse.”

This latest revelation from Valentine’s team was published Wednesday in Environmental Science & Technology as part of a broader, highly anticipated study that lays the groundwork for understanding just how much DDT is spread across the seafloor — and how the contamination might still be moving 3,000 feet underwater.

Read more at The Los Angeles Times