Beneath the waves off Los Angeles, thousands of corroded metal barrels surrounded by ghostly white halos have puzzled scientists for years. Now, new research suggests these underwater mysteries hold a toxic secret—but not the one once assumed. The barrels, first noticed in 2011 and later found to number at least 25,000, have long been suspected of containing DDT, a now-banned pesticide. However, a study published in PNAS Nexus suggests the mystery barrels—particularly those surrounded by strange white halos on the seafloor—may actually hold caustic alkaline waste, Smithsonian reports.
The origins of the barrels are unclear, but historical records indicate that, from the 1930s through the early 1970s, companies were permitted to dispose of a wide range of industrial waste in Southern California waters. Items dumped included chemical byproducts, refinery and drilling waste, garbage, even explosives and radioactive material. The barrels remained largely unnoticed until a 2020 Los Angeles Times investigation drew renewed attention. For this study, researchers collected sediment samples near five barrels, including three with white halos, using remotely operated vehicles. While DDT was found throughout the seafloor, its concentration did not change based on proximity to the barrels.
Instead, samples near the white-haloed barrels had extremely high pH levels and minimal microbial life, implying the presence of alkaline waste, which DDT manufacturing produced, per a release. The halos themselves are likely the result of chemical reactions between the waste and seawater, forming minerals that leave visible rings, scientists say. Lead author Johanna Gutleben of Scripps Institution of Oceanography notes that alkaline waste was not previously considered, highlighting how little is known about the full range of dumped substances. Scientists cannot yet pinpoint the specific chemicals or estimate the total extent of contamination, but warn the effects could persist for thousands of years.
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