SAN DIEGO — Back in the 1940s, chemical companies started using the ocean off the Los Angeles coast as a convenient dumping ground for toxic manufacturing waste. Researchers in California say one of the biggest culprits was Montrose Chemical Corporation, which discharged massive amounts of the now-banned pesticide DDT directly into the Pacific near Catalina Island. Unfortunately, a new study finds that ocean life is still paying the price for this — over 50 years after DDT’s banning.
Although the dumping stopped in 1961, a team at UC San Diego says DDT and its poisonous byproducts are incredibly resistant to breaking down. They have lingered in a toxic form that continues contaminating marine ecosystems. In fact, their new findings reveal that fish in the Los Angeles coastal area are still testing positive for DDT in 2024. DDT was officially banned in 1972, but the discovery of deep-sea fish carrying the pesticide is sparking new fears that local seafood eaters may also be at risk.
“These are deep-sea organisms that don’t spend much time at the surface and they are contaminated with these DDT-related chemicals,” says Lihini Aluwihare, a professor of ocean chemistry at UC San Diego’s Scripps Institution of Oceanography, in a university release. “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.”
From 1948 to at least 1961, Montrose contracted shipping barges to regularly travel from the Port of Los Angeles out toward Catalina Island, where they would pump acid waste laced with up to two percent pure DDT directly overboard into the ocean. While overshadowed at the time by Montrose’s other dumping practices into the LA County sewer system, this offshore pollution has gained increased scrutiny and concern in recent years.
In 2011, a robotic submarine rediscovered the offshore dumpsite, now called “Dumpsite 2,” which turned out to be contaminating a sprawling area of seafloor larger than San Francisco. Mapping by scientists has since revealed the staggering scale of the dumping, but many lingering questions remain about its spread through the region’s marine environment.
During this latest study, published in the journal Environmental Science and Technology Letters, the researchers tested for over 45 different DDT-related compounds across a wide range of samples – a more comprehensive analysis than typical testing, which only looks for four to eight of these chemicals. Not only did they find at least 15 different toxic DDT byproducts present in the seafloor sediments, but the team detected 10 different compounds inside the bodies of three species of deep-sea fish collected near Dumpsite 2.
“None of these fish species are known to feed in the sediment of the seafloor,” says Anela Choy, a biological oceanographer at Scripps. “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.”
The most unnerving concern emerging from the study is that if the pollution is circulating from the seafloor into smaller creatures and fish, it could eventually build up in larger marine animals that humans consume.
“Regardless of the source, this is evidence that DDT compounds are making their way into the deep ocean food web,” says 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.”
“We are still seeing this DDT contamination in deep-sea organisms and ocean sediments more than 50 years after they were dumped there,” adds Eunha Hoh, another study co-author from SDSU. “I’m not sure if that company expected the consequences of their pollution to last this long, but they have.”
While the new findings can’t definitively say whether the contamination originated at Dumpsite 2 or the infamous Palos Verdes Shelf Superfund site where Montrose also discharged waste, the unique pattern of pollutants provides clues that point to the offshore dumping as the likely source.
The researchers note that many additional studies are now underway to solve the remaining mysteries and determine whether any potential human health risks exist from seafood contamination linked to the legacy of offshore dumping. However, the findings underscore how pollution decisions made decades ago can continue to come back to haunt us — and potentially poison our food.
