Scientists are just beginning to learn what is inside thousands of mysterious ‘halo’ barrels submerged off the US coast.
The barrels were discovered in the deep waters of the San Pedro Basin, near Los Angeles, in 2021.
Scientists were initially worried that the barrels could contain DDT, a toxic pesticide that was banned in 1972 due to its serious environmental and health impact.
However, a new study now shows that the barrels contain an unknown caustic alkali waste, which is creating eerie halos as it leaches into the sea floor.
Using the remotely operated vehicle (ROV) SuBastian, the researchers carefully collected samples at a set distance from barrels with halos.
If the barrels contained DDT, the samples should have been acidic, however, the researchers found that the sediment around the barrels was actually extremely alkaline.
Lead author Dr Johanna Gutleben, researcher at UC San Diego’s Scripps Institution of Oceanography, says: ‘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?’
Scientists have finally solved the mystery of the ‘halo’ barrels which litter the ocean floor off the coast of Southern California
Scientists have found thousands of barrels of waste which were legally dumped at 14 deep-water sites off the coast of California between the 1930s and early 1970s
Between the 1930s and the 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, throughout those 40 years these sites were filled with ‘refinery wastes, filter cakes and oil drilling wastes, chemical wastes, refuse and garbage, military explosives and radioactive wastes.’
Sediments in the surrounding area are heavily contaminated with toxic chemicals, including the pesticide DDT.
DDT was previously manufactured in large quantities in Southern California by the Montrose Chemical Corporation in Torrance.
Between 1947 and 1982, the Montrose Chemical Company may have dumped up to 2,000 barrels a month of acidic sludge containing DDT into the ocean.
Haunting images of the so-called halo barrels surrounded by strange white rings sparked concerns that there could be even more DDT on the seabed than previously thought.
This would be a serious concern since the pesticide has been shown to increase the risk of cancer and persist for an extremely long time in the environment.
However, in a paper published in the journal PNAS Nexus, a group of researchers have finally solved this mystery.
While scientists feared that the barrels could contain the toxic pesticide DDT, a study of the surrounding sediment shows that they actually contained an unknown caustic alkaline substance
Although the area around the barrels was heavily contaminated with DDT, the concentration didn’t vary with distance from the barrels.
This suggests that the DDT pollution is unrelated to whatever might be leaking out from these strange containers.
Additionally, the researchers’ investigation revealed another strange feature: the sediment within the halo ring had turned as hard as concrete.
It was only when the ROV managed to chip away a piece of sediment and bring it back for analysis in the lab that the researchers began to understand what was happening.
When Dr Gutleben tested the pH of the samples, she found that the sediment was at pH 12, making it much more alkaline than a neutral pH of seven.
The hard crust was also revealed to be mostly made 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 keeps the pH in the surrounding sediment extremely high.
This alkaline substance has made it impossible for anything other than specialised bacteria, which normally live around hydrothermal vents, to survive
This alkaline sediment then reacts with seawater to form calcium carbonate, the main mineral in chalk, which creates the white, dusty halo around each barrel.
The researchers say this discovery could help improve efforts to map the scale of pollution in the historic dump sites.
Dr Gutleben says: ‘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 discovered that whatever was in the barrels has left a profound effect on the local ecosystem.
The barrels have transformed the sea floor in much the same way as a deep-sea hydrothermal vent.
Within the rings, the only bacteria that can survive are ‘extremophiles’ adapted to survive otherwise deadly alkaline environments.
Scientists analysing the substances say that it is ‘shocking’ that the pollutants are still effecting biodiversity on the sea floor over 50 years after the barrels were dumped
However, although a few species flourished in this harsh environment, the overall biodiversity was much lower than in the surrounding area.
What makes this so surprising is that the contents of the halo barrels are still affecting biodiversity decades after they were dumped.
Co-author Dr Paul Jensen, a marine microbiologist at UC San Diego’s Scripps Institution of Oceanography, says: ‘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.’
This article was originally published by a www.dailymail.co.uk . Read the Original article here. .