Worrying levels of DDT found in deep-sea fish off Los Angeles

For several years now, one question has been the key to understanding how concerned we should be about the hundreds of tons of DDT that have been dumped off the coast of Los Angeles:

How, exactly, has this decades-old pesticide, a toxic chemical spread across the seafloor 3,000 feet underwater, continued to reenter the food web?

Now, in a long-awaited study, researchers have identified tiny zooplankton and mid- and deep-water fish as possible links between contaminated sediment and the ecosystem in general.

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

“This DDT contamination occurred several decades ago, there is no new source, it has been banned… but this old source is still contaminating deep ocean biota, which is really alarming,” said Eunha Hoh, whose lab at the San Diego State School of Public Health led the chemical analysis of the study. “We are not talking about the zooplankton collected in 1960, we are talking about the zooplankton collected nowin the deep ocean, which is still contaminated with DDT.”

Hoh's team had already found significant amounts of DDT-related chemicals in coastal feeding dolphins and condors (and a recent study by another team even linked an aggressive cancer in sea lions to DDT). But while it is clear that DDT has been accumulating at the top of the food chain, as The extent to which DDT reached these animals has been a mystery. Key questions remain about whether it comes from more shallow sources (such as the Palos Verdes Shelf Superfund site, where DDT had been discharged for years through the sewer system), or from deep-sea sediment itself.

“Really [hits home] “This concept is that nothing is left intact,” said Lihini Aluwihare, a chemical oceanographer whose lab at UC San Diego's Scripps Institution of Oceanography helped piece together the many multidisciplinary aspects of the study. “Establishing the current distribution of DDT contamination in deep-sea food webs lays the groundwork for thinking about whether these contaminants are also moving up through deep-ocean food webs to species that could be consumed by people.”

Margaret Stack, first author of a new study that found DDT in deep-sea organisms, is preparing for chemical analysis at the San Diego State School of Public Health.

(Austin Straub / For the Times)

The study, published Monday in Environmental Science & Technology Letters, is one of many research efforts sparked by a 2020 Los Angeles Times report detailing the little-known history of the ocean spill. coast of Southern California and how the country's largest DDT manufacturer had disposed of its waste at sea for years.

A team of scientists, in an attempt to map and scan the seafloor for DDT-related debris, instead discovered a multitude of discarded military explosives from the World War II era. Another team unearthed records showing that barrels of radioactive waste had also been dumped into the sea.

And during an urgent investigation into old and forgotten records, the U.S. Environmental Protection Agency discovered that from the 1930s to the early 1970s, 13 other areas off the coast of Southern California had also been approved for all type of discharges, including the disposal of various refinery wastes. byproducts and 3 million metric tons of oil waste.

As for DDT, which is short for 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 move and spread upon 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 chemist still It is likely to rise from the depths of the seafloor upon contact with zooplankton, which are eaten by deep-sea fish, which then swim up and are eaten by mid-water fish and marine mammals found increasingly higher up in the food chain.

Hoh joined forces 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 in Southern California to collect them.

In addition to zooplankton, which is a window to the base of the food chain, a particular type of fish, myctophids, turned out to be key.

To test myctophids for DDT and other related toxins, environmental chemists begin by extracting lipids through a multi-step process.

(Austin Straub / For the Times)

Also known as lanternfish, myctophids are small, unassuming fish that travel considerable distances from the depths of the ocean to the surface. (Myctophids, one of the most abundant and widespread fish in the world, account for approximately 65% ​​of all Earth's deep sea biomass.) The researchers methodically ground each fish sample and extracted the lipids (DDT tends to be stored in fat). and assessed contamination with an unprecedented level of scrutiny.

The findings have been sobering: everywhere they looked, they found DDT. Even the “control” samples they tried to collect (as a way to compare what a normal fish sample farther from the known dumping area would be like) ended up riddled with DDT.

“This is one of the missing pieces we were waiting to see,” said David Valentine, who has led the broader research community on this topic since his team at the University of California, Santa Barbara first shed light on the surprising quantities of DDT that still remain. spread across the seabed. “We know there's a lot of stuff down there… but seeing these compounds in deep-dwelling organisms really points to a link.”

Research into the history of ocean dumping in Southern California was 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, noticed a number of new and interesting clues.

One key to tracing DDT's legacy through the marine ecosystem is to identify and then compare the patterns of each chemical appearing in various animals, a technique called “untargeted analysis.” That can help identify where all the DDT comes from and how it moves and accumulates at different levels of the food chain.

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

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

Gold, who was not affiliated with the study but has spent more than 30 years pushing for DDT cleanups along the coast, said much more work needs to be done on all fronts to truly consider the chemical's legacy on the planet. southern California. In addition to DDT spread throughout the deep sea and the Palos Verdes Shelf, 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. Sen. Alex Padilla (D-Calif.) and Rep. Salud Carbajal (D-Santa Barbara), recently urged the Biden administration to dedicate long-term funds to both study and remedy the problem. . Meanwhile, EPA officials have been considering their next steps in collaboration with several 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 contamination and tracking its migration through the food web.

For environmental chemists Margaret Stack, first author of the latest study, and her colleague Raymmah Garcia, a doctoral candidate at Scripps, seeing once-popular pesticides like DDT continue to move so pervasively through the ecosystem makes them wonder about all the other chemicals. Without a doubt, they are still used today: chemicals that could also come back to haunt us many decades from now.

“I'm often 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 specialist at the San Diego State School of Public Health. “It doesn't seem like we're doing anything different.”

“How many more times,” he said, “are we going to go through the same story?”