Concerning levels of DDT found in deep-sea fish off the coast of Los Angeles

For several years, one question has been essential to understand how concerned we should be about the hundreds of tons of DDT dumped off the coast of Los Angeles:

How, exactly, did this decades-old pesticide – a toxic chemical spread on the seafloor 3,000 feet underwater – continue to re-enter the food web?

Now, in a much-anticipated study, researchers have identified tiny zooplankton and mid- to deep-water fish as potential links between the contaminated sediments. and the largest ecosystem.

For the first time, chemical analyzes have confirmed that these deep-sea organisms are contaminated with many DDT-related compounds that match similar chemical patterns found on the seafloor and in animals higher up the food chain.

“This DDT pollution happened decades ago, there is no new source, it has been banned… but this old source is always polluting deep ocean biota, which is really alarming,” said Eunha Hoh, whose San Diego State School of Public Health lab led the study’s chemical analysis. “We are not talking about the zooplankton collected in 1960, we are talking about the zooplankton collected NOWin the depths of the ocean, which are still polluted with DDT.

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Hoh’s team had already discovered significant amounts of DDT-related chemicals in dolphins and condors that feed on the coasts today (and a recent study by another team even linked cancer aggressive in sea lions and DDT). But even though DDT clearly accumulates at the top of the food chain, how It remains a mystery whether DDT reached these animals. Key questions remain about whether DDT comes from more shallow sources (such as the Palos Verdes Plateau Superfund site, where DDT had been released for years via the sewer system) or from deep-sea sediments. sailors themselves.

“This concept that nothing is intact is really striking,” said Lihini Aluwihare, a chemical oceanographer whose lab at UC San Diego’s Scripps Institution of Oceanography helped piece together the study’s many multidisciplinary aspects. “Establishing the current distribution of DDT contamination in deep-sea food webs lays the foundation for consideration of whether these contaminants also move up through deep-sea food webs to species likely to be consumed by humans. »

Margaret Stack, first author of a new study revealing the presence of DDT in deep-sea organisms, prepares for a chemical analysis at the San Diego State School of Public Health.

(Austin Straub / For Time)

The study, published Monday in Environmental Science & Technology Letters, is one of several research efforts sparked by a 2020 Los Angeles Times report that detailed the little-known history of offshore ocean spills. Southern California coast – and how the country’s largest manufacturer of DDT has been dumping its waste into the sea for years.

A team of scientists, in an attempt to map and analyze the seafloor for DDT-related waste, have discovered a host of abandoned military explosives dating back to World War II. Another team discovered documents showing barrels of radioactive waste had also been dumped at sea.

And during an urgent investigation into old and forgotten records, the U.S. Environmental Protection Agency discovered that between the 1930s and early 1970s, 13 other areas off the southern coast of the California had also been approved for all kinds of spills, including the disposal of various refinery wastes. by-products and 3 million tonnes of petroleum waste.

As for DDT, which is the abbreviation of dichlorodiphenyltrichloroethane, scientists have so far confirmed that much of what is still on the seafloor remains in its most potent form and is buried just 6 centimeters deep, raising concerns about the ease with which it could remobilize and spread by re-entering the food web.

In a world dominated by concerns about microplastics and “forever chemicals,” DDT persists as an unsolved problem — long after the pesticide was banned in 1972 following Rachel Carson’s book “Silent Spring.”

With this latest study, the researchers sought to demonstrate how the chemical is still It is likely that it rises from the deep sea floor coming into contact with zooplankton, which are eaten by deep-sea fish, which then swim up and are eaten by pelagic fish and marine mammals higher and higher in the sea. food chain.

Hoh partnered with Aluwihare’s lab at Scripps, where a microbiology team also provided sediment analysis and a deep-sea biologist helped determine which organisms to sample and where to collect them in Southern California.

In addition to zooplankton, which provide a window into the base of the food chain, a particular type of fish, myctophids, has been shown to be essential.

To analyze myctophids for DDT and other associated toxins, environmental chemists begin by extracting the lipids in a multi-step process.

(Austin Straub / For Time)

Also known as lanternfish, myctophids are tiny, unassuming fish that travel remarkable distances from the depths of the ocean to the surface. (One of the most abundant and widespread fish in the world, myctophids make up about 65 percent of all Earth’s deep-sea biomass.) The researchers methodically ground each fish sample and extracted the lipid (DDT tends to to be stored in fat). , and assessed the contamination with an unprecedented level of scrutiny.

The results were sobering: everywhere they looked, they found DDT. Even the “control” samples they attempted to collect – to compare what a normal fish sample might look like further away from the known spill area – ended up being riddled with DDT.

“This is one of the missing pieces that we’ve been waiting to see,” said David Valentine, who has led the broader research community on this question since his team at UC Santa Barbara shed light for the first time on the surprising quantities of DDT still present. spread on the seabed. “We know there’s a ton of stuff out there… but the presence of these compounds in deep-dwelling organisms really indicates a connection.”

Research into the history of offshore spills in Southern California has been spurred by the discovery of mysterious, corroded barrels dumped off the coast of Los Angeles.

(David Valentine / ROV Jason)

Valentine, who was not involved in the study, noted a number of interesting new clues.

One of the keys to tracking the legacy of DDT in the marine ecosystem is to identify and then compare the patterns of each chemical appearing in various animals – a technique called “untargeted analysis.” This can help determine where all the DDT comes from and how it moves and accumulates at different levels of the food chain.

Monitoring programs generally use a targeted approach – looking for only four to eight specific DDTs. compounds. But using non-targeted methods, scientists in this new study were able to identify a range of DDT-related chemicals, including one particularly suspect compound, TCPM, which poses an unknown threat to the ecosystem. These currently unmonitored chemicals were also present in the blubber of dolphin carcasses washed ashore, as well as in sediment collected near the known spill area.

“It gives us a much more realistic view of what the potential impacts on the environment and human health may be,” said Mark Gold, an environmental scientist at the Natural Resources Defense Council. The study, he says, lays bare how the traditional approach of testing and monitoring only a few DDT compounds “vastly underestimates DDT concentrations in sediments and in organisms.”

Gold, who was not affiliated with the study but has spent more than 30 years promoting DDT cleanup along the coast, said more needs to be done on all fronts to truly address accounts for the legacy of this chemical in Southern California. In addition to DDT prevalent in the deep sea and on the Palos Verdes Plateau, the mouth of the Dominguez Channel has also been identified for decades as a hot spot.

The road ahead is long. Twenty-four members of Congress, led by U.S. Senator Alex Padilla (D-Calif.) and Representative Salud Carbajal (D-Santa Barbara), recently urged the Biden administration to dedicate long-term funding to the study and to solving the problem. . EPA officials, meanwhile, are considering next steps in collaboration with a number of state and federal agencies.

Academic research groups, including those in San Diego and the one led by Valentine at UC Santa Barbara, also continue to search for answers. The main ones are determining the boundaries of the landfill, mapping the spread of pollution and monitoring its migration through the food web.

For environmental chemists Margaret Stack, first author of the latest study, and Raymmah Garcia, a doctoral student at Scripps, seeing once-popular pesticides such as DDT continue to move so ubiquitously throughout the ecosystem brings them to s Ask about all other chemicals. undoubtedly still in use today – chemicals that could also come back to haunt us decades from now.

“I often feel frustrated when I look at this data and then see that we’re still using chemicals without testing them, without understanding their impacts,” said Stack, a research scientist at the state’s School of Public Health from San Diego. “It’s like we’re not doing anything differently.”

“How many more times,” she said, “are we going to relive the same story?