by For the past several years, one question has been critical to understanding how much we should be concerned about the hundreds of tons of DDT dumped off the coast of Los Angeles:
How, exactly, is this decades-old pesticide – a toxic chemical spread over the sea floor 3,000 feet underwater – re-entering the food web?
Now, in a much-anticipated study, researchers have identified tiny zooplankton and deep-water fish as potential links between the contaminated sediment and the larger 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 sea floor and animals higher up the food chain.
“This DDT pollution happened several years ago, there is no new source, it is banned … but this old source is yet polluting deep ocean biota, which is really scary,” said Eunha Hoh, whose lab at San Diego State School of Public Health led the chemical analysis of the study. “We’re not talking about zooplankton collected in 1960 — yes we are talking about collected zooplankton nowin the deep ocean, which is still contaminated with DDT.”
Hoh’s team had already found significant amounts of DDT-related chemicals in modern-day dolphins and coastal-feeding condors (and a recent study by another team even linked aggressive cancer in sea lions to DDT). But while DDT is clearly accumulating at the top of the food chain, how what DDT reached these animals is a mystery. Key questions remain as to whether it is coming from shallower sources (such as the Palos Verdes Shoal Superfund site, where DDT had been released for years through the sewage system), or from the deep-sea sediment itself.
“It really is [hits home] this concept that nothing has anything to do with it,” said Lihini Aluwihare, a chemical oceanographer whose lab at UC San Diego’s Scripps Institution of Oceanography helped bring together the many multidisciplinary aspects of the study. food webs lay the foundation for consider whether those contaminants are also moving up through the deep ocean food web to species that humans might eat.”
The study, published Monday in Environmental Science & Technology Letters, is one of several research efforts inspired by a 2020 Los Angeles Times report that detailed the little-known history of ocean dumping off the coast of Southern California — and how the the nation’s largest manufacturer of DDT. he had been disposing of his waste at sea for years.
One team of scientists, in an effort to map and scan the seabed for DDT-related waste, discovered dozens of discarded military explosives dating back to the Second World War. Another team showed records showing that barrels of radioactive waste had also been dumped at sea.
And during a frantic search of old and forgotten records, the U.S. Environmental Protection Agency discovered that 13 other areas off the coast of Southern California were also approved for all kinds of dumping from the 1930s to the early 1970s—including various refinery disposals. by-products and 3 million metric tons of petroleum waste.
Read more: History of DDT ocean dumping off LA coast is even worse than thought, EPA says
As for DDT, short for dichlorodiphenyltrichloroethane, scientists have so far confirmed that much of what is still sitting on the seabed is still in its most potent form buried barely 6 centimeters deep – raising concerns about how easily it can be remobilized and dispersed. by re-entering the food web.
In a world dominated by concerns about microplastics and “forever chemicals”, DDT remains an unresolved problem – long after the pesticide was banned in 1972 following Rachel Carson’s book “Silent Spring.”
Read more: Here’s what we know about the legacy of DDT dumping off the LA coast
With this latest study, the researchers tried to show how the chemical is likely to make its way up from the deep sea floor by contacting zooplankton, which eat deep-sea fish, then swim up and eat mid-water fish and mammals. sea higher and higher up the food chain.
Hoh joined Aluwihare’s lab at Scripps, where a microbiology team also provided sediment analysis and a deep-sea biologist helped decide which organisms to sample — and where across Southern California to collect them.
In addition to zooplankton, which is a window into the base of the food chain, a certain type of fish, myctophages, was crucial.
Also known as lantern fish, myctepids are tiny, unassuming fish that travel significant distances from the deep ocean all the way to the surface. (One of the most abundant and widespread fish in the world, mycopods make up about 65% of all the world’s deep-sea biomass.) The researchers methodically digest each fish sample, and the lipid extracted (which fat is usually stored in DDT) , and assessed the contamination with an unprecedented level of scrutiny.
The results were sobering: Wherever they looked, they found DDT. Even the “control” samples they tried to collect – as a way to compare what a typical fish sample would look like further away from the known dumping area – were full of DDT.
“This is one of the missing pieces that we are waiting to see,” said David Valentine, who leads the wider research community on this issue from his team at UC Santa Barbara who will lose the first light on the alarming amounts of DDT yet. spread across the seabed. “We know that there are a ton of things down there … but when you see the compounds in a deep organism-it really points to a connection.”
Valentine, who was not involved in the study, noted some interesting new clues.
One key to tracing the legacy of DDT through the marine ecosystem is to identify and then compare the patterns of each chemical seen in different animals—a technique known as “non-targeted analysis.” That can help fingerprint where all the DDT is coming from, and how it’s moving and accumulating at different levels of the food chain.
Monitoring programs typically use a targeted approach — searching for only four or eight specific DDT compounds. But by using non-targeted methods, the scientists in this new study were able to identify a whole series of chemicals related to DDT, including a highly dubious compound, TCPM, which poses unknown threats to the ecosystem. These currently unmonitored chemicals were also present in dolphin carcass clippings that washed ashore, as well as sediment collected near the known dumping area.
“This gives us a much more realistic view of what the potential ecological and human health impact can be,” said Mark Gold, an environmental scientist at the Natural Resources Defense Council. and monitoring a few DDT compounds “does not overestimate DDT concentrations in sediment and organisms”.
Gold, who was not affiliated with the study but has spent more than 30 years trying to clean up DDT along the coast, said there is much more work to be done on all sides to truly account for the chemical’s legacy in Southern California. . In addition to the spread of DDT across the deep sea and the Palos Verdes Shelf, the mouth of the Dominguez Channel has also been identified for years as a hot spot.
The road ahead is long. Twenty-four members of Congress, led by US Senator Alex Padilla (D-Calif.) and Representative Salud Carbajal (D-Santa Barbara), recently urged the Biden administration to commit long-term funding to study and improve issue. . In the meantime, officials at the EPA are 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, are also continuing to look for answers. Chief among them are determining the boundary of the dumping site, mapping the spread of pollution and tracking its migration across the food web.
For environmental chemists Margaret Stack, first author of the latest study, and co-author Raymmah Garcia, a doctoral candidate at Scripps, seeing popular pesticides such as DDT continue to move so pervasively through the ecosystem makes they wonder about all the other chemicals. are still in use today without question – chemicals that may have worried us many years ago.
“I often feel frustrated when I look at these data and then see that we are still using chemicals without testing them, without understanding their effects,” said Stack, a research specialist at the School of Health San Diego State Public. “It feels like we’re not doing anything different.”
“How many more times,” she said, “are we going to go through the same story?”
This story originally appeared in the Los Angeles Times.
