Once suspected of containing the DDT of the pesticide, a new analysis shows that some barrels actually held caustic alkaline waste.
In 2020, striking photographs revealed rusty barrels dispersed in the seabed near Los Angeles, capturing generalized attention. At the beginning, corroded containers were suspected of containing pesticide DDT residues, especially since some were surrounded by pale halo -like rings in the sediments. However, the real content of barrels, as well as the cause of the strange halos, remained uncertain.
Research by the UC San Diego Institution of Oceanography Scripps has since specified that halo producer barrels contained caustic alkaline waste, which has infiltrated and modified the environment. Although the study could not determine the precise compounds inside, it noted that the production of DDT produced both alkaline and acid by-products. In addition, other large industries in the region, including refining oil, were known to free up large amounts of alkaline waste.
“One of the main flows of DDT production waste was[{” attribute=”” tabindex=”0″ role=”link”>acid, and they didn’t put that into barrels,” said Johanna Gutleben, a Scripps postdoctoral scholar and the study’s first author. “It makes you wonder: What was worse than DDT acid waste to deserve being put into barrels?”
Toxic transformations of the seafloor
The research showed that leaking alkaline waste reshaped parts of the seafloor into harsh habitats resembling natural hydrothermal vents — environments that host specialized microbes capable of surviving where most organisms cannot. According to the study’s authors, the scale and intensity of these impacts on marine ecosystems depend on both the number of barrels resting on the seafloor and the particular chemicals they released.
Even with these uncertainties, Paul Jensen, a Scripps emeritus marine microbiologist and the study’s senior author, explained that he had assumed such alkaline material would quickly dilute in seawater. Instead, it has remained intact for more than fifty years, leading him to conclude that this waste “can now join the ranks of DDT as a persistent pollutant with long-term environmental impacts.”
Released on September 9, 2025, in the Proceedings of the National Academy of Sciences Nexus and backed by NOAA along with the University of Southern California’s Sea Grant program, the study adds to Scripps’ longstanding efforts to investigate the toxic legacy of once-permitted dumping in Southern California’s offshore waters. The results also offer a visual method to distinguish barrels that once carried this alkaline waste.
“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,” said Gutleben. “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.”
https://www.youtube.com/watch?v=RKPUQ-IDML4
Video sequences of the exploration of Rov Subastian around the DDT Barrel 1 site in the border in southern California off the coast of Los Angeles. Credit: Schmidt Ocean Institute
Ocean dumping legacy in California
From the 1930s to the early 1970s, 14 basins with deep water off the coast of Southern California were used to eliminate “refinery waste, filter cakes and oil drilling waste, chemical waste, waste and garbage, military explosives and radioactive waste”, according to EPA. Investigations on the sea planks led by Scripps in 2021 and 2023 have documented thousands of throttles, including hundreds of military ammunition. The total number of barrels located on the bottom of the ocean is still unknown. The sediments of this region are strongly contaminated by the DDT, a pesticide prohibited in 1972 and now recognized as dangerous for humans and fauna. Sparse recordings of the period suggest that most DDT waste has been discharged directly into the sea.
Gutleben said that she and his co-authors had not initially undertaken to resolve the mystery of the Halo. In 2021, aboard the Schmidt Ocean Institute’s research ship FalkkorShe and other researchers have collected sediment samples to better understand contamination near Catalina. Use of remote vehicle operated (ROV) Auction, The team collected sediment samples at precise distances from five barrels, three of which had white halos.
The barrels featuring white halos presented an unexpected challenge: inside the white halos, the seabed suddenly became like concrete, preventing researchers from collecting samples with their carotage devices. Using the ROV robotic arm, the researchers collected a piece of the hardened sediments from one of Halo’s barrels.
DDT test and microbes
The team analyzed the sediment samples and the hard halo -hardened barrel crust for DDT concentrations, mineral content and microbial DNA. The sediment samples have shown that contamination of the DDT did not increase the barrels closer, deepening the mystery of what they contained.
During the analysis, Gutleben struggled to extract the microbial DNA from samples taken through the halos. After unsuccessful troubleshooting in the laboratory, Gutleben tested one of these pH samples. She was shocked to note that the pH of the sample was extremely high – about 12 years. All samples near barrels with halos have proven to be also alkaline. (An alkaline mixture is also known as a base, which means that it has a pH greater than 7 – as opposed to an acid which has a pH less than 7).
This explained the limited quantity of microbial DNA that she and her colleagues had been able to extract halo samples. The samples have proven to have a low bacterial diversity compared to other surrounding sediments and bacteria came from families suitable for alkaline environments, such as hydrothermal vents on the high seas and hot alkaline sources.
The hard crust analysis has shown that it was mainly composed of a mineral called Brucite. When alkaline waste fled barrels, it reacted with magnesium in sea water to create Brucite, which cemented sediments into a concrete crust. Brucite also dissolves slowly, which maintains the high pH in the sediments around barrels, and creates a place, only few extreme microbes can survive. Where this high pH meets the surrounding sea water, it forms calcium carbonate which is deposited in the form of white dust, creating the halos.
Sustainable ecological consequences
“This adds to our understanding the consequences of dumping these barrels,” said Jensen. “It is shocking that more than 50 years later, you always see these effects. We cannot quantify the environmental impact without knowing how many of these barrels with white halos are there, but it clearly has a localized impact on microbes.”
Previous research carried out by Lisa Levin, co-author of the study and emeritus biological oceanograph in Scripps, has shown that the biodiversity of small animals around barrels with halos was also reduced. Jensen said that approximately a third of barrels that have been observed visually had halos, but it is not clear if this ratio is true for the whole area and that it remains unknown to the number of barrels seated on the seabed.
Researchers suggest using white halos as indicators of alkaline waste could help quickly assess the extent of contamination of alkaline waste near Catalina. Then, Gutleben and Jensen declared that they were experimenting with the sediments contaminated by DDT collected on the emptying site to search for microbes capable of decomposing the DDT.
The slow microbial decomposition that researchers are now studying may be the only possible hope of eliminating the DDT decade ago. Jensen said that trying to physically withdraw the contaminated sediments would be, in addition to being a huge logistical challenge, would probably do more harm than good.
“The highest DDT concentrations are buried at around 4 or 5 centimeters below the surface – so it’s a bit contained,” said Jensen. “If you try to suck this, you would create a huge plume of sediment and stir this contamination in the water column.”
Reference: “The hot stories ends linked to the spill of industrial waste contained in a high seas basin” by Johanna Gutleben, Sheila Podell, Kira Mizell, Douglas Sweeney, Carlos Neira, Lisa A Levin and Paul R Jensen, September 9, 2025, Nexus pnas.
Doi: 10.1093 / PNASNEXUS / PGAF260
This research was funded by the National Oceanographic and Atmoshiric Administration Award NOS. NA23NMF4690462 and NA22OAR4690679 in Prj and LAL and at the Prix de la Mer Given of the University of South SCON-00003146 in LAL
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