Scientists Unlock Secrets of Mysterious 'Halo' Barrels Off U.S. Coast

Unraveling the Mystery of Mysterious 'Halo' Barrels

Scientists are making significant progress in understanding what lies inside thousands of enigmatic "halo" barrels submerged off the coast of the United States. These barrels were first discovered in the deep waters of the San Pedro Basin, near Los Angeles, in 2021. Initially, researchers feared that these containers might hold DDT, a toxic pesticide banned in 1972 due to its severe environmental and health impacts. However, recent findings have revealed a different story.

A new study has shown that the barrels contain an unknown caustic alkali waste, which is creating eerie halos as it seeps into the seabed. Using a remote-operated vehicle named SuBastian, scientists collected samples at specific distances from the barrels with halos. If the barrels contained DDT, the surrounding sediment would likely be acidic. Instead, the research team found that the sediment was extremely alkaline.

Dr. Johanna Gutleben, the lead author of the study and a researcher at UC San Diego's Scripps Institution of Oceanography, explained: "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?"

Between the 1930s and early 1970s, thousands of items were legally dumped at 14 deep-water sites off the coast of Southern California. According to the Environmental Protection Agency, these sites were filled with various types of waste, including refinery wastes, filter cakes, oil drilling wastes, chemical wastes, refuse, garbage, military explosives, and radioactive materials. Sediments in the surrounding area are heavily contaminated with toxic chemicals, including DDT.

The Montrose Chemical Corporation in Torrance was responsible for manufacturing DDT in large quantities in Southern California. Between 1947 and 1982, the company may have dumped up to 2,000 barrels a month of acidic sludge containing DDT into the ocean. The haunting images of the so-called halo barrels surrounded by strange white rings initially raised concerns that there could be even more DDT on the seabed than previously thought. This would be a serious issue since DDT has been linked to increased cancer risk and can persist in the environment for an extended period.

However, a paper published in the journal PNAS Nexus has finally shed light on this mystery. While the area around the barrels is heavily contaminated with DDT, the concentration does not vary with distance from the barrels. This suggests that the DDT pollution is unrelated to whatever might be leaking from these containers.

Another strange feature observed by the researchers was the sediment within the halo ring, which had turned as hard as concrete. When the ROV managed to chip away a piece of sediment and bring it back for analysis, the researchers began to understand the situation better. Dr. Gutleben tested the pH of the samples and found that the sediment had a pH of 12, making it much more alkaline than neutral pH 7. The hard crust was also identified as primarily composed of a mineral called brucite.

When the alkaline waste leaked out of the barrel, it reacted with magnesium in the water to form brucite, which cemented the sediment into a concrete-like crust. As the brucite slowly dissolves into the water, it maintains an extremely high pH in the surrounding sediment. This alkaline sediment then reacts with seawater to form calcium carbonate, the main mineral in chalk, creating the white, dusty halo around each barrel.

This discovery could help improve efforts to map the scale of pollution in historic dump sites. Dr. Gutleben emphasized: "DDT was not the only thing that was dumped in this part of the ocean, and we have only a very fragmented idea of what else was dumped there. We only find what we are looking for, and up to this point, we have mostly been looking for DDT. Nobody was thinking about alkaline waste before this, and we may have to start looking for other things as well."

The researchers also found that the contents of the barrels have significantly impacted the local ecosystem. The barrels have transformed the sea floor similarly to deep-sea hydrothermal vents. Within the rings, only bacteria adapted to survive in deadly alkaline environments, known as extremophiles, can thrive. Although some species flourished in this harsh environment, overall biodiversity was much lower than in the surrounding area.

What makes this finding surprising is that the effects of the halo barrels are still influencing biodiversity decades after they were dumped. Co-author Dr. Paul Jensen, a marine microbiologist at UC San Diego's Scripps Institution of Oceanography, stated: "It’s shocking that 50-plus years later, you’re still seeing these effects. We can’t quantify the environmental impact without knowing how many of these barrels with white halos are out there, but it’s clearly having a localized impact on microbes."