SAN DIEGO — Marine scientists say they have found what they believe to be as many as 25,000 barrels that possibly contain DDT dumped off the Southern California coast near Catalina Island, where a massive underwater toxic waste site dating back to World War II has long been suspected.
The sightings of 27,345 “barrel-like” images were captured by researchers at the University of California San Diego’s Scripps Institution of Oceanography. They mapped more than 36,000 acres of seafloor between Santa Catalina Island and the Los Angeles coast in a region previously found to contain high levels of the toxic chemical in sediments and in the ecosystem.
Historical shipping logs show that industrial companies in Southern California used the basin as a dumping ground until 1972, when the Marine Protection, Research and Sanctuaries Act, also known as the Ocean Dumping Act, was enacted, Scripps said.
The exact location and extent of the dumping was not known until now.
The territory covered was “staggering,” said Eric Terrill, chief scientist of the expedition and director of the Marine Physical Laboratory at Scripps Institution of Oceanography.
“It really was a surprise to everybody who’s worked with the data and who sailed at sea,” he told reporters Monday.
The study provides “a wide-area map” of the barrels, though it will be up to others to confirm through sediment sampling that the containers hold DDT, Terrill said..
The long-term impact on marine life and humans is still unknown, said Scripps chemical oceanographer and professor of geosciences Lihini Aluwihare, who in 2015 co-authored a study that found high amounts of DDT and other man-made chemicals in the blubber of Bottlenose Dolphins that died of natural causes.
“These results also raise questions about the continued exposure and potential impacts on marine mammal health, especially in light of how DDT has been shown to have multi-generational impacts in humans,” said Aluwhihare, who was not part of the survey expedition. “How this vast quantity of DDT in sediments has been transformed by seafloor communities over time and the pathways by which DDT and its degraded products enter the water column food web are questions that remain to be explored.”
Scientists conducted the survey from March 10-24 following a Los Angeles Times report last year about evidence that DDT was dumped into the ocean near Catalina.
“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,” Terrill said.
Scientists used an underwater drone to map the seafloor. University of California Santa Barbara professor David Valentine discovered concentrated accumulations of DDT in the sediments in the same region and spotted 60 barrels on the seafloor in 2011 and 2013. Researchers used those barrels as a starting point.
High levels of DDT have been detected in the region’s other marine mammals, and the chemical has been linked to cancer in sea lions.
The Los Angeles Times reviewed shipping logs from a disposal company supporting Montrose Chemical Corp. of California, a DDT-producing company. The logs showed 2,000 barrels of DDT-laced sludge were dumped in the deep ocean each month from 1947 to 1961 off Catalina, and other companies also dumped there until 1972.
Scripps researchers say they hope their survey will support clean-up efforts.
Barrels and 25,000 other objects highly suspected to be barrels were spotted in nearly all areas of the 36,000 acres surveyed and extended beyond the dumpsite limits, which is roughly 12 miles (20 kilometers) offshore Los Angeles, and 8 miles (12 kilometers) from Catalina Island, according to Scripps.
The map also shows patterns that indicate how the barrels were dumped.
The expedition on the Sally Ride research vessel included a team of 31 scientists, engineers, and crew conducting 24-hour operations and two autonomous underwater vehicles.
The search entailed work at depths up to 3,000 feet (900 meters), along a steep seafloor between Catalina and Los Angeles. The robots flew 65 feet (20 meters) above the seafloor.
Sonar technology would send signals that would reflect the seafloor and create images of what was resting on it. That helped researchers get a high-resolution map that so they could identify the barrels. The sonar settings enabled them to detect objects as small as a coffee cup, Scripps said.
Associated Press writer Elliot Spagat in San Diego contributed to this report.