The ocean floor off Los Angeles is littered with secrets from the past -- and some of them are still leaking. More than half a century after industrial companies dumped thousands of barrels into the Pacific, scientists are uncovering disturbing evidence that what's seeping out may be more than just the infamous pesticide DDT.
New research from the Scripps Institution of Oceanography at UC San Diego shows that many of the corroded barrels, some encircled by ghostly white halos on the seabed, contain highly caustic alkaline waste. Far from dissipating, this chemical brew has persisted for decades, turning patches of the seafloor into extreme environments where only specialized microbes can survive.
A toxic mystery solved
When remotely operated vehicles first captured images of the barrels in 2020, the eerie white halos puzzled researchers. The assumption was that DDT waste was at play, given the region's history of pesticide dumping. But sediment samples told a different story. The halos, it turns out, were created by leaks of alkaline material -- a byproduct not just of DDT manufacturing but also of oil refining and other mid-20th-century industries along the California coast.
The waste reacted with seawater minerals, creating hardened crusts and concrete-like patches on the seafloor. Instead of dissolving quickly, the alkaline waste has proven surprisingly resilient, forming ecosystems hostile to most marine life yet oddly hospitable to extremophiles, microbes more commonly associated with hydrothermal vents.
"Worse than acid waste?"
The discovery has scientists asking tough questions. "One of the main waste streams from DDT production was acid, and they didn't put that into barrels," said Johanna Gutleben, lead author of the study. "It makes you wonder: what was considered worse than DDT acid waste to deserve being sealed in barrels?"
Her team's findings suggest that alkaline waste may now be joining DDT as a "persistent pollutant," capable of shaping ecosystems for generations.
Uncharted scale of dumping
The scale of the problem remains murky. From the 1930s to the early 1970s, at least 14 official dump sites off Southern California received not only chemical waste but also oil byproducts, military explosives, and even radioactive material. Recent surveys by Scripps scientists revealed thousands of objects scattered across the seafloor, from discarded munitions to uncounted barrels. Exactly how many of those contain alkaline waste -- and how many still leak -- remains unknown.
Prior studies have already confirmed that the broader seafloor is heavily contaminated with DDT. Now the realization that alkaline waste is also present deepens the mystery of what else lies hidden in the sediment.
The living impact
The halos are more than visual markers; they are signs of an ecological shift. Bacterial diversity in these zones plummets, and small animal biodiversity is reduced as well. Where white dust settles on the seabed, the ecosystem takes on the characteristics of a chemical wasteland.
"The shocking part," said Paul Jensen, a senior researcher on the project, "is that more than 50 years later, these effects are still visible. This isn't just history -- it's ongoing."
Looking forward
For now, scientists are using the halos as diagnostic tools to identify contaminated sites quickly. Some are experimenting with DDT-laden sediments in search of microbes capable of breaking down the pesticide. But large-scale cleanup appears unlikely: disturbing the contaminated layers could spread toxins further into the water column.
Instead, the Pacific may be left to carry the scars of a time when dumping industrial waste at sea was legal and largely unquestioned.
Gutleben and her colleagues stress that what has been uncovered so far is likely only a fraction of the picture. "We only find what we're looking for," she said. "Until now, we weren't even looking for alkaline waste. Who knows what else is out there?"