Understanding the extent of an environmental wasteland.
Eric Terrill ’93, PhD ’98, knew barrels of toxic chemicals had been dumped in the ocean waters between Los Angeles and Catalina Island, but the scale of the dump site was unknown. A previous study had even indicated that dichlorodiphenyltrichloroethane, or DDT, may be in some of the barrels. Then, while conducting a survey of the seafloor in the area, the sonar data began to be overwhelming, becoming impossible to count while at sea.
“It was like trying to count stars in the Milky Way,” says Terrill, a researcher at Scripps Institution of Oceanography. “We soon realized that manually counting these targets just wouldn’t work.”
Spurred by investigative reporting by the Los Angeles Times, Terrill led the March 2021 expedition aboard research vessel Sally Ride using advanced underwater robotics and side-scan sonar to locate the barrels dumped on the seafloor decades ago. They ended up needing to use machine learning to develop an algorithm to count objects for them, yielding more than 27,000 targets with high confidence to be classified as a barrel and an excess of 100,000 total debris objects on the seafloor—and this was just at one of two known dumpsites.
Historical records show that between 1947 and 1961, an estimated half a million barrels of DDT-laced sludge and other chemical waste may have been dumped offshore. While unfathomable now, no regulations had been put in place to ban such dumping until 1972, when the Marine Protection, Research and Sanctuaries Act, also known as the Ocean Dumping Act, was created.
UC Santa Barbara geochemist, David Valentine ’95, MS ’96, had also heard tales of historic dumping and, in 2011 and 2013, used a combination of submersible vehicles to find scores of barrels—including some which appeared to be leaking. His 2019 research publication on these findings also heightened awareness.
“The fact that there could be half a million barrels down there… We owe it to ourselves to figure out what happened, what’s actually down there and how much it’s all spreading,” Valentine told the Los Angeles Times.
As the extent of this dumpsite becomes clearer, scientists are on a quest to understand the fingerprint of the DDT in the marine ecosystem and determine how to best mitigate the problem. For instance, the discovery of these barrels may help provide context to recent findings of DDT in marine mammals. In 2015, a study from Scripps chemical oceanographer Lihini Aluwihare and her then-PhD student, Nellie Shaul, co-authored a study that showed extremely elevated levels of DDT in dolphin blubber. And in 2020, the Marine Mammal Center reported cancer affecting nearly 1 in 4 adult sea lions along the California coast.
“The extent of the dumping ground being uncovered helps explain the high body burden of DDT we’ve seen in top predators in Southern California waters,” says Aluwihare. “It appears to be entering the water column food web from the seafloor, but how this is happening remains to be explored. Given the multi-generational impacts of DDT, we need to study this to understand the health of the ecosystem and seafood we consume.”
Last summer, Aluwihare visited the dumpsite that Terrill had surveyed earlier to collect organisms that live at depths greater than 650 feet. Along with Scripps biological oceanographer Anela Choy, the team will investigate which organisms may be transferring DDT from the seafloor up through the marine food web. Scientists also hope to look at Scripps’ decades-old archive of marine specimens to see when DDT concentrations began appearing.
In a separate summer research expedition, Scripps scientists Lisa Levin, PhD ’82, Paul Jensen, PhD ’06, and Greg Rouse collected marine specimens and sediment samples near six barrels. Sponges and other invertebrates living on barrels were slurped up by a deep sea robot, as were samples of microbial halos, bearing eerie resemblance to fried eggs. They hope to evaluate these specimens to determine what role microbes might play in potentially bioremediating, or consuming, the chemicals coming out of the barrels.
“Understanding the scope of the problem is the first step to determining a solution,” says Terrill. “The mapping of one of the dumpsite is just a start, but we still have a lot to science to do.”
Learn more and support UC San Diego’s efforts to understand the impacts of the dumpsite at tritonmag.com.ddt