First it was the eerie images of barrels leaking on the seafloor not far from Catalina Island. Then the shocking realization that the nation’s largest manufacturer of DDT had once used the ocean as a huge dumping ground — and that as many as half a million barrels of its acid waste had been poured straight into the water.

Now, scientists have discovered that much of the DDT — which had been dumped largely in the 1940s and ’50s — never broke down. The chemical remains in its most potent form in startlingly high concentrations, spread across a wide swath of seafloor larger than the city of San Francisco.

“We still see original DDT on the seafloor from 50, 60, 70 years ago, which tells us that it’s not breaking down the way that (we) once thought it should,” said UC Santa Barbara scientist David Valentine, who shared these preliminary findings Thursday during a research update with more than 90 people working on the issue. “And what we’re seeing now is that there is DDT that has ended up all over the place, not just within this tight little circle on a map that we referred to as Dumpsite Two.”

These revelations confirm some of the science community’s deepest concerns — and further complicate efforts to understand DDT’s toxic and insidious legacy in California. Public calls for action have intensified since The Times reported in 2020 that dichlorodiphenyltrichloroethane, banned in 1972, is still haunting the marine environment today. Significant amounts of DDT-related compounds continue to accumulate in California condors and local dolphin populations, and a recent study linked the presence of this once-popular pesticide to an aggressive cancer in sea lions. (...)

treaty to protect the world's oceans