Los Angeles, United States - September 09, 2025 New research from UC San Diego’s Scripps Institution of Oceanography reveals that decades-old barrels on the ocean floor off Los Angeles contain caustic alkaline waste, not just the pesticide DDT as once believed. Images of corroded barrels first captured public attention in 2020, with eerie white halos surrounding some barrels. The study shows these halos were created as the alkaline waste leaked from the barrels, cementing the surrounding sediment into a concrete-like crust. Johanna Gutleben, a Scripps postdoctoral scholar and lead author, said, “One of the main waste streams from DDT production was acid and they didn’t put that into barrels. It makes you wonder: What was worse than DDT acid waste to deserve being put into barrels?” The caustic waste has transformed portions of the seafloor into extreme environments, supporting specialized bacteria that survive in conditions similar to hydrothermal vents. Paul Jensen, senior author and emeritus marine microbiologist, noted that the alkaline waste has persisted for over 50 years, joining DDT as a long-term pollutant with ongoing environmental impacts. From the 1930s to the early 1970s, deep-water dump sites off Southern California received refinery and chemical wastes, military explosives, radioactive material, and garbage. Scripps-led surveys in 2021 and 2023 found thousands of objects, including hundreds of military munitions, but the total number of barrels remains unknown. Sediment analysis around the halos revealed extremely high pH levels, low bacterial diversity, and mineral brucite formation, explaining the concrete-like crust. These white halos provide a visual indicator for identifying alkaline waste, aiding future assessment of environmental contamination. “The highest concentrations of DDT are buried around 4 or 5 centimeters below the surface — so it’s kind of contained,” Jensen said, emphasizing that physical removal could worsen contamination. Researchers are now exploring microbial breakdown as a potential way to neutralize legacy pollutants.