DDT Pollution Dumped off Los Angeles Coast Has Not Broken Down Decades Later, Scientists Find

In 2020, University of California (UC), Santa Barbara, scientist David Valentine used a deep-sea robot to confirm that the largest dichlorodiphenyltrichloroethane (DDT) maker in the U.S. had dumped tens of thousands of barrels of the toxic pesticide off the Los Angeles coast.

“Holy crap. This is real,” Valentine told the Los Angeles Times of his discovery. “This stuff really is down there. It has been sitting here this whole time, right off our shore.”

Now, after further investigation into the dumpings and their consequences, Valentine told more than 90 people gathered for a research update Thursday that the pollution is even worse than anticipated, as the Los Angeles Times reported further. 

“We still see original DDT on the seafloor from 50, 60, 70 years ago, which tells us that it’s not breaking down the way that [we] once thought it should,” he said. “And what we’re seeing now is that there is DDT that has ended up all over the place, not just within this tight little circle on a map that we referred to as Dumpsite Two.”

DDT is now recognized as a dangerous chemical linked to cancer in humans and mass animal fatalities, as The Guardian explained. It was the chemical that inspired Rachel Carson to write Silent Spring after a friend living in Massachusetts told her about bird die-offs in Cape Cod following sprayings, according to the Natural Resources Defense Council. However, it was once immensely popular, and its production was centered in Southern California, according to The Guardian. The company Montrose Chemical Corp. of California opened a plant near Torrance in 1947 and operated it until 1982, the Los Angeles Times reported in 2020. Shipping logs reveal that it dumped as many as 2,000 barrels of DDT sludge per month for as much as 767 tons of the chemical between 1947 and 1961. Beyond Montrose, the U.S. Environmental Protection Agency (EPA) says that several other companies dumped industrial waste in the zone between Los Angeles and Catalina Island referred to as Disposal Site #2.

The Los Angeles Times story on Valentine’s find prompted renewed calls for investigation into the impacts of the dumping, with Sen. Dianne Feinstein (D-Calif.) securing $5.6-million in Congressional money for research, according to the Los Angeles Times. In 2021, UC San Diego’s Scripps Institution of Oceanography led a mapping effort of more than 36,000 acres of seafloor and discovered 27,000 likely DDT barrels as well as more than 100,000 other human objects, as the institute reported at the time. 

“Unfortunately, the basin offshore Los Angeles had been a dumping ground for industrial waste for several decades, beginning in the 1930s. We found an extensive debris field in the wide area survey,” chief scientist of the expedition and director of the Marine Physical Laboratory at Scripps Institution of Oceanography Eric Terrill said in the press release. “Now that we’ve mapped this area at very high resolution, we are hopeful the data will inform the development of strategies to address potential impacts from the dumping.”

Valentine, meanwhile, has continued to investigate the problem, mapping and sampling the seafloor between Catalina Island and Los Angeles in recent months, according to the Los Angeles Times. 

Beyond the persistence and reach of the chemical pollution — it covers a seafloor area greater than San Francisco – another concern is that it is concentrated only around six centimeters (approximately two inches) below the top of the seafloor sediment. 

“Trawls, cable lays could reintroduce this stuff back up to the surface,” Valentine told the Los Angeles Times thursday. “And animals feeding — if a whale goes down and burrows on the seafloor, that could kick stuff up.”

Also announced at Thursday’s update were new mapping plans from Scripps, this time using sonar and photographs. 

In response to the article, Feinstein touted the importance of Congressional funding and quick action.

“The federal funding we secured will be significant for advancing research to understand the scope and scale of DDT pollution off the coast of Southern California. We must act quickly to clean this up,” she tweeted.