Scientists have found the answer to thousands of ‘halo’ barrels that have been submerged off the US coast.
Initially, the barrels were discovered in the waters of the San Pedro Basin, near Los Angeles, four years ago in 2021.
They believed there was a danger of them containing DDT, which is a pesticide that is toxic, and therefore banned in 1972 as it has a dangerous impact on the environment as well as health.
But a new study found there is an unknown caustic alkali waste inside of the barrels.
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This waste has a very big impact on the reason behind the halos.
To find out more, the researchers used a remotely operated vehicle, SuBastian, collecting samples at specific distances from the barrels and the halos.
Had the barrels in fact contained DDT, the samples tested would have been acidic in nature, however, they were alkaline.
Lead author Dr Johanna Gutleben, researcher at UC San Diego's Scripps Institution of Oceanography, said of the findings: “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?”
As it turns out, it was the caustic waste, which also created the mysterious halos after leaching into the sea floor.
This occurred in the early 1930s and the early 1970s; where thousands of items were dumped at 14 sites off the coast of Southern California.
According to the Environmental Protection Agency, this included ‘refinery wastes, filter cakes and oil drilling wastes, chemical wastes, refuse and garbage, military explosives and radioactive wastes.'
It also included DDT.
But while there, the rings were caused by the alkaline.
The paper, which was published in the journal PNAS Nexus, found that although the barrels were heavily contaminated with DDT, the DDT pollution is unrelated to the halos.
The leaching of the alkaline was also hard as cement, so they knew it couldn’t have been related to DDT.
When the ROV chipped a piece of sediment for analysis, researchers realised it was alkaline, not acidic.
Dr Gutleben said: “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 the sediment changed the ecosystem surrounding the barrels, and within the rings, only ‘extremophiles’ bacteria could survive.
Co-author Dr Paul Jensen said: “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 localised impact on microbes.”
So, at least now the mystery has been solved.
Probably shouldn’t do diving in that area, though. Caustic waste is not something you want to be exposed to.
Britt Jones