In the 1940s and 1950s, a large pesticide manufacturer dumped DDT into the ocean off the coast of Los Angeles. We now know that DDT is harmful to humans and wildlife. Even though it was legal at the time, the pollution from the DDT continues to affect L.A.’s coastal waters more than 50 years later. The stubborn chemistry of DDT and its toxic breakdown products are still causing problems.Research conducted by scientists at UC San Diego’s Scripps Institution of Oceanography and San Diego State University (SDSU) has shed light on the concerning pollution of the marine environment near Catalina Island. This pollution has been a cause for alarm since it gained widespread attention in 2020. The study, which was published in the journal Environmental Science and Technology Letters on May 6 and funded by the National Oceanic and Atmospheric Administration, revealed that deep-sea fish and sediments collected from the dump site located 15 miles offshore are contaminated with a variety of DDT-related chemicals.According to the National Oceanic and Atmospheric Administration, it is believed that the chemicals related to DDT that were discharged into the ocean many years ago could still be entering marine food chains.
After the discovery of the underwater dumping ground near Catalina Island, scientists have been working to determine how extensive and serious the issue is today. One pressing concern is whether the chemicals from decades ago, now settled on the ocean floor thousands of feet below the surface, are remaining in place or if they are moving through marine ecosystems, potentially harming wildlife and posing health risks to humans.
“These are deep-sea creatures that do notLihini Aluwihare, a professor of ocean chemistry at Scripps and co-author of the study, stated that the DDT-related chemicals are contaminating the deep-sea food webs. This raises concerns about whether these contaminants are moving up through deep-ocean food webs and potentially entering species that are consumed by humans. Between 1948 and 1961, barges contracted by Montrose Chemical Corporation would transport manufacturing waste containing sulfuric acid and DDT from the Port of Los Angeles out toward Catalina.The company dumped up to 2% pure DDT into the Pacific Ocean, which was legal until 1972. This dumping was not widely known because it was overshadowed by another waste disposal practice where a more diluted acidic slurry containing DDT was pumped through L.A. County sewers and into the ocean off Palos Verdes. Around 100 tons of DDT ended up in the sediment of the Palos Verdes Shelf, leading to the Environmental Protection Agency declaring it an underwater Superfund Site in 1996. In 2000, a judge ordered the company to pay $140 million to address the environmental damages. Studies have connected the DDT pollution on the Palos Verdes with harmful effects.Shelf pollution has led to health issues in local wildlife, such as sea lions, dolphins, bottom-feeding fish, and even coastal California condors (likely caused by consuming dead marine mammals).
In 2011, researcher David Valentine from UC Santa Barbara used a robot underwater to rediscover Montrose’s offshore dumping near Catalina, now called Dumpsite 2. The findings gained attention in 2020 when the Los Angeles Times released the first in a series of articles revealing the area’s toxic history of offshore dumping.
Valentine and Scripps researchers have played a role in addressing the issue.Corresponding to the study, researchers have mapped the scope of the dumping. They have discovered DDT-related chemicals spread across a seafloor area larger than the city of San Francisco. What remains uncertain is whether this pollution is staying in place or if it is moving through the undersea environment in a way that could pose risks to marine life or humans.
In 2021, Aluwihare and study co-author Eunha Hoh of SDSU, along with other collaborators, initiated a series of research projects to address two critical questions: Are the DDT-related chemicals present on the seafloor near Dumpsite 2 being stirred up and consumed by deep-sea marine life? And can they identify a specific chemical signature?Is there a way to identify the specific pollution from Dumpsite 2 and other offshore dump sites that sets it apart from the pollutants coming from the Palos Verdes Shelf?
The team gathered sediment samples and deep-sea animals from the water column in the San Pedro Basin near Dumpsite 2 to check for a wide variety of DDT-related compounds. The National Science Foundation and the Schmidt Ocean Institute funded the research cruises to collect these samples.
When the scientists analyzed the sediments for the presence of DDT+, they did not find any evidence of it.Less than 15 chemicals were found in the fish near Dumpsite 2, with 14 of them already detected in birds and marine mammals in Southern California. The researchers gathered 215 fish from three common species and discovered that the fish contained 10 DDT-related compounds, which were also present in the sediment samples. Two of the fish species were collected at depths between 546 meters and 784 meters, while the third species was collected at a depth of 546 meters.The surface. Fish collected at shallower depths had fewer contaminants and lacked two DDT-related compounds that were found in the deepest fish. “None of these fish species are known to feed in the sediment of the seafloor,” said Anela Choy, 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.” The findings cannot yet be fully explained.Aluwihare stated that the Palos Verdes Superfund Site has been ruled out as a potential source of the fish contamination. However, the study uncovered several lines of evidence indicating the alarming possibility of pollution moving from the seafloor into the marine food web. This includes lower overall concentrations and two missing DDT-related compounds in shallower water fish species, as well as the overlap between contaminants found in the sediment and those found in marine mammals and birds. Margaret Stack, an environmentalist, emphasized that regardless of the source, this serves as evidence that DDT compounds are infiltrating the deep ocean food web.Environmental chemist at SDSU and the study’s lead author expressed concern about the presence of DDT-related chemicals in deep-sea fish. He stated that if these contaminants end up in marine mammals or even humans, it could be a significant problem. Understanding how these chemicals are entering the food web is crucial in order to determine the best course of action for mitigation. It is also important to consider offshore development and its potential to stir up these contaminants and worsen the problem. Further research is needed to identify the source of the DDT contaminants and determine if the same contamination exists in larger, open-ocean fish.disposal of DDT,” said Lihini Aluwihare, a research chemist at Scripps Oceanography and a study coauthor. “This is unique and shows the far-reaching impacts of human activities on the environment. It’s important to continue monitoring and studying these contaminants to understand their persistence and potential effects on marine life and human health.”
The research team is also investigating whether the contamination of fish species is limited to the Palos Verdes Shelf and Dumpsite 2 area or if it is more widespread in the Southern California Bight. The team is working to develop more accurate and efficient methods for monitoring DDT levels in fish and sediments to better understand the extent of the contamination and its potential impact on the ecosystem and public health. This may involve the use of advanced analytical techniques and models to track the movement and distribution of contaminants in the marine environment.
The researchers discovered high levels of DDT in the deep ocean that were likely dumped there without consideration of the long-lasting consequences of pollution. The study was a collaborative effort between scientists from Scripps and SDSU.
