In the 1940s and 1950s, the ocean off the coast of Los Angeles was a dumping ground for the country’s largest manufacturer of the pesticide DDT, a chemical now known to harm humans and wildlife. Due to the stubborn chemistry of DDT and its toxic degradation products, this pollution continues to impact Los Angeles coastal waters more than half a century later. While legal at the time, the details of this industrial-scale pollution of the marine environment at a landfill about 15 miles offshore near Catalina Island have deeply concerned scientists and the public since gaining greater recognition in 2020.
Now, new research by scientists at UC San Diego’s Scripps Institution of Oceanography and San Diego State University (SDSU) finds that deep-sea fish and sediment collected near the Catalina Island offshore landfill are contaminated with numerous chemicals related to DDT.
The study, published May 6 in the journal Environmental science and technology letters and funded by the National Oceanic and Atmospheric Administration, suggests that DDT-related chemicals dumped into the ocean decades ago may still be making their way into marine food webs.
Since the rediscovery of the offshore landfill near Catalina Island, scientists have been working to discern the scope and severity of the current problem. Of particular urgency are questions of whether the decades-old chemicals, now sitting on the seafloor thousands of feet underwater, remain in place or are circulating in marine ecosystems where the compounds could be harming wildlife or even posing risks to human health.
“These are deep-sea organisms that don’t spend much time at the surface and are contaminated with these DDT-related chemicals,” said Lihini Aluwihare, professor of ocean chemistry at Scripps and co-author 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.”
From 1948 until at least 1961, barges contracted by DDT producer Montrose Chemical Corporation sailed from the port of Los Angeles to Catalina and pumped manufacturing waste laden with sulfuric acid and up to 2% pure DDT directly into the Pacific Ocean. Legal until 1972, this offshore dumping largely escaped public scrutiny because it was overshadowed by another Montrose waste disposal practice: pumping a more dilute acid slurry that also contained DDT through Los Angeles County sewers and to the ocean off Palos Verdes. An estimated 100 tons of DDT ended up in the sediments of the Palos Verdes shelf, and the Environmental Protection Agency declared it an underwater Superfund Site in 1996. In 2000, a judge ordered the company to pay $140 million to remedy the damage. environmental. Since then, research has linked DDT contamination on the Palos Verdes Shelf to pollution and health problems for local wildlife, including sea lions, dolphins, bottom-feeding fish, and even California coastal condors ( probably from consuming dead marine mammals).
In 2011, UC Santa Barbara researcher David Valentine used an underwater robot to rediscover the Montrose landfill offshore near Catalina, at a location now known as Dumpsite 2. The findings leaped into the public consciousness. in 2020, when the Los Angeles Times published the first in a series of articles revealing the toxic legacy of the region’s offshore dumping.
Valentine and Scripps researchers have helped map the extent of the spill. To date, they have found DDT-related chemicals in an area of the seafloor larger than the city of San Francisco. What remains unknown is whether that pollution remains there or moves through the underwater environment in ways that pose dangers to marine life or humans.
Starting in 2021, Aluwihare, study co-author Eunha Hoh of SDSU, and other collaborators began a series of research efforts to work on two key questions: Are DDT-related chemicals lurking on the seafloor near the landfill 2? are being stirred up and ingested by marine life in the depths? And could they identify a kind of chemical fingerprint unique to pollution from Landfill 2 and other offshore landfills that could be used to distinguish them from pollutants emanating from the Palos Verdes shelf?
The team opportunistically collected sediment and deep-sea animal samples from the water column in the San Pedro Basin near Landfill 2 to analyze a wide range of DDT-related compounds. Research cruises to collect these samples were funded by the National Science Foundation and the Schmidt Ocean Institute.
Typically, DDT tests look for four to eight chemicals, but a 2016 paper co-authored by Hoh and Aluwihare identified 45 chemicals related to DDT in the blubber of dolphins off the coast of Southern California. The results showed that wildlife was exposed to a much larger set of DDT compounds in the real world. In the current study, the team tested this broader set of DDT-related chemicals, known as DDT+, in the hope that it could help develop a chemical fingerprint for Landfill 2 and the other offshore landfills used by Montrose. . Additionally, DDT+ testing will provide a more holistic picture of the extent of contamination in sediments and animals that might otherwise go undetected.
When the researchers analyzed the sediments for the presence of DDT+, they found no fewer than 15 chemicals, 14 of which had previously been detected in birds and marine mammals in Southern California.
The researchers collected 215 fish of three common species near Landfill 2. Chemical analysis revealed that the fish contained 10 DDT-related compounds, all of which were also present in the sediment samples.
Two of the fish species were collected between 546 meters (1,791 feet) and 784 meters (2,572 feet). Cyclone Acclinidens and Melanostigma hats — and the third, Leuroglossus stilbio, was collected between 546 meters (1,791 feet) and the surface. Species collected at shallower depths contained a lower concentration of contaminants and were missing a couple of DDT-related compounds that were Present in the deepest fish.
“None of these fish species are known to feed on seafloor sediment,” said Anela Choy, a biological oceanographer at Scripps and co-author of the study. “There must be another mechanism that exposes them to these contaminants. One possibility is that there are physical or biological processes that resuspend the sediments around Landfill 2 and allow these contaminants to enter deeper water food webs.”
The findings still cannot rule out the Palos Verdes Superfund site as a potential source of fish contamination, Aluwihare said. But several lines of evidence uncovered in the study—the lower overall concentrations and two missing DDT-related compounds in shallower-water fish species, as well as the overlap between contaminants found in the sediment and those found in mammals and seabirds) point to the alarming possibility that pollution is moving from the seafloor into the marine food web.
“Regardless of the source, this is evidence that DDT compounds are reaching the deep ocean food web,” said Margaret Stack, an SDSU environmental chemist and lead author of the study. “That’s a cause for concern because it’s not a big jump that ends up in marine mammals or even humans.”
Hoh said understanding the pathways by which DDT-related chemicals enter the food web is vital and “will help us determine what to do in terms of mitigation and what not to do in terms of offshore development that could make this problem worse.” by agitating these contaminants.”
Aluwihare said more work needs to be done to identify the source of the DDT contaminants they found in deep-sea fish and to establish whether the same contamination exists in larger open-ocean fish species that are consumed by people.
Numerous additional studies are being conducted to answer these pressing questions. Scripps and SDSU researchers are currently analyzing samples of target fish species from recreational anglers and commercial fisheries, including largemouth bass and sanddab, for DDT+. Comparing the chemicals and their concentrations found in these fish with sediment samples collected from the Palos Verdes Shelf and Landfill 2 may allow the team to determine the source of the toxins in these fish.
“We continue to see this DDT contamination in deep-sea organisms and ocean sediments more than 50 years after they were dumped there,” Hoh said. “I’m not sure if that company expected the consequences of its contamination to last this long, but it did.”
In addition to Aluwihare, Stack, Choy and Hoh, Raymmah Garcia, Tran Nguyen, Paul Jensen and Johanna Gutleben of Scripps, as well as William Richardot and Nathan Dodder of SDSU, were co-authors of the study.