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HomeUSScientists uncover startling concentrations of pure DDT along seafloor off L.A. coast

Scientists uncover startling concentrations of pure DDT along seafloor off L.A. coast


First there were the eerie images of barrels leaking on the seabed not far from Catalina Island. Then the shocking realization that the country’s largest DDT maker once used the ocean as a huge dumping ground, with up to half a million barrels of its acidic waste having been dumped directly into the water.

Now, scientists have discovered that much of the DDT, which had been largely discarded in the 1940s and 1950s, never broke down. The chemical remains in its most potent form in surprisingly high concentrations, spread across a wide swath of seafloor larger than the city of San Francisco.

“We still see original DDT on the seafloor from 50, 60, 70 years ago, which tells us it’s not breaking down the way (we) once thought it should,” said the UC Santa Barbara scientist, David Valentine, who shared this preliminary data. findings Thursday during a research update with more than 90 people working on the issue. “And what we’re seeing now is that there’s DDT ended up everywhere, not just within this tight little circle on a map we’re referring to as Dumpsite Two.”

These revelations confirm some of the deepest concerns of the scientific community and further complicate efforts to understand the insidious and toxic legacy of DDT in California. Public calls for action have intensified since The Times reported in 2020 that dichlorodiphenyltrichloroethane, banned in 1972, still plagues the marine environment today. Significant amounts of DDT-related compounds continue to accumulate in California condors and local dolphin populationsand a recent study linked the presence of this once-popular pesticide to aggressive cancer in sea lions.

With a $5.6 million research push from Congress, at the urging of Sen. Dianne Feinstein (D-Calif.), numerous federal, state, and local agencies have since joined with scientists and environmental nonprofits to determine the scope of contamination lurking 3,000 feet underwater. (Another $5.2 million, supervised by California Sea Grantwill be distributed this summer to kick off another 18 months of research).

The findings so far have been a surprising development. after another. A preliminary sonar mapping effort led by the Scripps Institution of Oceanography identified at least 70,000 debris-like objects on the seafloor.

The United States Environmental Protection Agency, after combing thousands of pages of old records, found that other companies had also dumped other toxic chemicals, as well as millions of tons of oil drilling waste, decades ago in more than a dozen areas off the coast of southern California.

“When the DDT was removed, it is highly likely that other materials, either from the tanks on the barges or from barrels that were pushed over the side of the barges, would have been removed at the same time,” said Acting Deputy John Lyons. . director of EPA’s Region 9 Superfund Division. He noted that the new science being shared this week is critical in answering one of the agency’s burning questions: “Is the pollution moving? And is it moving in a way that threatens the marine environment or human health?

In recent months, Valentine, whose research team first brought this decades-old problem back to public consciousness, has been mapping and collecting samples of the seafloor between the Los Angeles and Catalina coasts.

Sediment analysis so far shows that the most concentrated layer of DDT is only about 6 centimeters deep, raising questions about how easily these still potent chemicals could be remobilized.

“Trawls, cable runs could reintroduce these things back to the surface,” Valentine said. “And the feeding of the animals: if a whale sinks and buries itself at the bottom of the sea, that could lift things up.”

Postdoc Sebastian Krause, left, works with David Valentine, a principal investigator at the University of California, Santa Barbara, to recover a tube of sediment collected from the seafloor where DDT waste was dumped into the ocean decades ago.

(Austin Straub / For The Times)

On a cold winter morning between two storms, Valentine and a team of students boarded the RV/Yellowfin and set out to collect more seafloor samples along key points on a hotspot map they had been putting together.

As his students cut and cataloged each layer of mud, they gaped at the tiny worms, snails, and starfish that lived in the depths of the sea. They squinted at each tube sticking out of the water and laughed apprehensively when asked about all the chemicals they could possibly get their hands on.

“The goal is to collect as much mud as possible so we don’t have to go back out every time we have a question,” Valentine explained as the boat’s mechanical pulley churned for the eighth time that day. “We’re starting to build a really unique data set… that will help us understand the temporal history of how things were transported, how they were transformed, and what their ultimate destination is.”

Samples from the seafloor are arranged in various jars in David Valentine's lab.

Sediment samples, collected from the seabed where DDT was spewed decades ago off the Catalina coast, are arranged in jars at a UC Santa Barbara lab.

(Austin Straub / For The Times)

Other scientists have also been figuring out the many pieces of this deep-ocean puzzle.

Thursday’s research updates included plans for Scripps’ next mapping expedition, which will scan the seafloor with advanced sonar technology and also take hundreds of thousands of photos. Microbiologists shared their latest studies on whether deep-sea microbes could help biodegrade some of the pollution, and chemical oceanographers discussed the many ways they have been trying to identify “fingerprints” that could help determine where the pollution is coming from. DDT and how. and if it moves

Biological oceanographers, marine ecologists, and fisheries scientists also began to connect some dots about the various organisms they found living in the contaminated sediment, as well as midwater species that could potentially move deeper-water chemicals closer to home. the surface.

They all noted that there were uncomfortably high concentrations of DDT and DDT-related compounds in the samples they studied. Even the “control” samples they tried to collect, as a way of comparing what a normal sediment or fish sample would look like further away from the dump area, ended up riddled with DDT.

“This suggests to us, very preliminary, that there is some potential connection — there is connectivity in these deep food webs across basins and throughout the system,” said Lihini Aluwihare, a marine chemist at Scripps.

In addition to all this research, EPA has been developing its own sampling plan, in collaboration with a number of state and federal agencies, to understand the many other chemicals that had also been dumped into the ocean. The hope, the officials said, is that the groundbreaking science currently being conducted on the dumping of DDT in the deep ocean will ultimately inform how future investigations of other offshore dumping sites could be conducted, either along the coast of southern California or in other parts of the country.

Mark Gold, an environmental scientist with the Natural Resources Defense Council who has worked on the DDT problem since the 1990s, he said that as he listened to the latest research findings, he couldn’t help but think that “the landfills in our nation’s oceans have horrible pollution problems. And yet they are not supervised.”

There are also shallower areas. off the coast of Palos Verdes and in the mouth of the Canal Domínguez which have been known DDT hot spots for decades. Figuring out how to clean up those contaminated areas in an underwater environment has been his own complicated saga.

For Katherine Pease of Heal the Bay, an environmental group that has ensured that the public remains involved in this issue in a substantial way, these latest revelations have been eye-opening.

This is, after all, what it really means to live with a chemical forever. After all these decades, scientists are still uncovering disturbing new surprises about the full extent of the contamination.

“We are still dealing with this legacy of treating the ocean as a dumping ground,” said Pease, Heal the Bay’s director of science and policy. “And the public, whether it’s people who like to fish … or people who like to swim and visit the ocean, we all need to understand the history that happened, as well as the impacts. And partly that’s to learn — to make sure that we’re able to protect our public health, but also to think about how we’re treating the ocean. nowas well as in the future.”

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