It’s no secret that bad actors dump pollutants into our oceans, and this has been happening for decades. But when the LA Times reported several hotspots discovered as recently as 2020, it was originally surmised that the industrial waste barrels littered among them contained DDT, or a pesticide called Dichlorodiphenyltrichloroethane, that has long since been banned. Possibly up to 700 tons and 25,000 barrels of toxic DDT had been dumped. Dubbed the “halo” barrels because they feature nondescript white sediment halos underwater, scientists finally believe they know what’s actually contained within them. They’re leaking caustic alkaline waste into the surrounding area in concentrated amounts, keeping animal life away, and maybe even decimating it.
According to the U.S. Environmental Protection Agency, the graveyard, named the Southern California ocean disposal site #2, is spread across 14 deep-sea dump sites. These sites are purportedly filled with radioactive waste, refinery waste, chemical waste, oil-drilling waste, and military explosives, which were dumped between the 1930s and 1970s. Very little is known about what these dump sites contain, other than it’s likely harmful industrial waste of some kind. A 2021 report reveals it’s not DDT, however, following surveys conducted by teams at the Scripps Institute of Oceanography.
The timeline of the ‘halo’ barrel graveyard discovery
Backing up a little bit, when the LA Times reported on the barrel graveyard in 2020, discovered by scientific deep-sea robots, the prevailing theory was that they prominently stored DDT, the toxic pesticide, because they found it in heavy concentrations. At the time, it seemed to explain the whitish halos of sediment that had settled and appeared around many of the observed barrels.
Warranting further investigation, the Scripps Institute of Oceanography launched surveys in the area from 2021 to 2023 and discovered some pretty alarming details. They found over 27,000 shapes, likely barrels, with over 100,000 total debris objects littered across the seafloor. Despite identifying so many objects and such a concentrated area of waste, no one knew precisely what they contained — only theories.
While it has taken some time, sediment sample results are finally available from the earliest surveys. The team collected samples from five different barrels in 2021, using remotely operated deep-sea robots. The samples revealed that the levels of DDT contamination didn’t increase the closer they were to the barrels, so they contained something else. Hopefully, not more invisible plastics hiding away.
What do the barrels contain, then?
A 2025 study, published in PNAS Nexus by Johanna Gutleben and her team, reveals that three of the barrels actually contain caustic, toxic chemicals that are preventing animals and microbes from venturing close. They have an extremely high pH level, around 12 pH, which could well be damaging to organic matter. A pH level of 12.5 or above is considered hazardous. It should also be considered “a persistent pollutant” according to the study’s findings.
Not all of the barrels observed have the same white halos, however, so the researchers think the hazardous alkaline barrels could easily be identified going forward. That would allow for a more realistic assessment of the level of contamination and whether or not current estimates are accurate. Rough estimates put the number of halo barrels at around one-third of the total graveyard. No one has fully explored the site, however, so there could be much more. That’s going to be a lot of work to clean up. Maybe someone can engineer a toxic cleaning fungus, like the plastic-eating fungus that’s cleaning the ocean better than we are.
