DDT chemicals making way into deep-sea food web, alarming researchers

Marine life off the Los Angeles coast may still be impacted by the effects of a long-disused DDT dumping site, a report from UC San Diego's Scripps Institution of Oceanography and San Diego State University researchers found Monday.

In the 1940s and 1950s, the ocean off the coast of L.A. was a dumping ground for the nation's largest manufacturer of the pesticide DDT -- a chemical now known to harm humans and wildlife, according to researchers.

While legal at the time, details of this pollution some 15 miles offshore Catalina Island have deeply concerned scientists and the public since they gained wider recognition in 2020, the authors write.

According to their findings -- published Monday in the journal Environmental Science and Technology Letters -- deep-sea fish and sediments collected from near the dump site remain contaminated with numerous DDT-related chemicals.

"These are deep-sea organisms that don't spend much time at the surface and they are contaminated with these DDT-related chemicals," said Lihini Aluwihare, a 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 those contaminants are also moving up through deep-ocean food webs into species that might be consumed by people."

According to the authors, from 1948 until at least 1961, barges contracted by DDT-producer Montrose Chemical Corporation would motor from the Port of Los Angeles out toward Catalina and pump manufacturing waste laden with sulfuric acid and up to 2% pure DDT directly into the Pacific Ocean. This practice was legal until 1972 but largely overshadowed by Montrose's other waste disposal practice -- pumping a more dilute acidic slurry that also contained DDT through L.A. County sewers and into the ocean off Palos Verdes, researchers said.

That site is now an underwater Superfund site, and the researchers said they cannot yet rule it out as the cause of the deep-sea fish and sediment contamination.

Dumpsite 2, the Catalina site, was rediscovered in 2011 by UC Santa Barbara researcher David Valentine. The Los Angeles Times published a story exposing the dump site in 2020.

Since then, Aluwihare, study co-author Eunha Hoh of SDSU, and other collaborators began a series of research efforts. They seek to answer two main questions:

-- Are the chemicals at Dumpsite 2 being stirred up and ingested by marine life?; and

-- Is there a chemical fingerprint unique to what was dumped there in comparison to what was piped off Palos Verdes?

The researchers collected 215 deep-water fish spanning three common species near Dumpsite 2. Chemical analysis revealed that the fish contained 10 DDT-related compounds, all of which were also present in sediment samples taken at the same time, the authors write.

According to the researchers, species collected at shallower depths contained a lower concentration of contaminants and were missing a pair of DDT-related compounds that were present in the deepest fishes.

"None of these fish species are known to feed in the sediment of the seafloor," said Anela Choy, a biological oceanographer at Scripps and co-author of the study. "There must be another mechanism that is exposing them to these contaminants. One possibility is that there are physical or biological processes resuspending sediments around Dumpsite 2 and allowing these contaminants to enter deeper water food webs."

These findings lead the researchers to believe the concentrated chemicals on the sea floor are making their way into the wider food chain.

"Regardless of the source, this is evidence that DDT compounds are making their way into the deep ocean food web," said Margaret Stack, an environmental chemist at SDSU and the study's lead author. "That is cause for concern because it's not a big leap for it to end up in marine mammals or even humans."

Hoh said understanding the pathways by which DDT-related chemicals are entering the food web is vital.

"We are still seeing this DDT contamination in deep-sea organisms and ocean sediments more than 50 years after they were dumped there," she said. "I'm not sure if that company expected the consequences of their pollution to last this long, but they have."