In the 1940s and 1950s, the ocean off the coast of Los Angeles was used as a dumping ground for DDT by the Montrose Chemical Corporation, the largest manufacturer of the pesticide. Despite being legal at the time, the dumping of DDT into the waters near Catalina Island has had lasting effects on the marine environment, as the chemical and its toxic breakdown products continue to contaminate the area more than fifty years later. New research from scientists at UC San Diego’s Scripps Institution of Oceanography and San Diego State University (SDSU) has found that deep-sea fish and sediments near the dump site are still contaminated with DDT-related chemicals, raising concerns about the impact on marine food webs.
The study, published in Environmental Science and Technology Letters and funded by the National Oceanic and Atmospheric Administration, highlights the potential ongoing movement of DDT-related chemicals from the seafloor into marine ecosystems where they may be harming wildlife and posing health risks to humans. The research indicates that the deep-sea organisms near Catalina Island are contaminated with these chemicals, suggesting that they are moving up through deep-ocean food webs and could ultimately affect species consumed by people. The rediscovery of the dump site near Catalina Island in 2011 has prompted scientists to further investigate the extent and severity of the pollution, as well as its current impact on marine life.
The dumping of DDT by Montrose Chemical Corporation continued until at least 1961, with barges pumping manufacturing waste laden with DDT into the Pacific Ocean. While this offshore dumping largely escaped public scrutiny at the time, it has since been linked to contamination and health problems in local wildlife, including sea lions, dolphins, and coastal California condors. The discovery of Dumpsite 2 near Catalina Island has piqued public interest, leading to research efforts to determine if the pollutants are staying put on the seafloor or moving through the marine environment in ways that could endanger marine life and humans.
Researchers have been working to identify a unique chemical fingerprint for the contamination from Dumpsite 2 that could distinguish it from pollutants coming from the Palos Verdes Shelf Superfund Site. By testing for a broader range of DDT-related compounds known as DDT+ in sediment and deep-sea animals near Dumpsite 2, the team hopes to gain a more comprehensive understanding of the contamination levels in the area. Initial findings from the analysis of sediment samples and fish collected near Dumpsite 2 revealed the presence of multiple DDT-related compounds, suggesting that the chemicals are indeed being ingested by marine life in the deep sea.
The study found that deep-sea fish near Dumpsite 2 contained ten DDT-related compounds, with species collected at shallower depths having lower concentrations of contaminants but still exhibiting signs of exposure. The presence of two DDT-related compounds in the deepest fishes suggests that contaminants may be entering the deeper water food webs through resuspension of sediments. While the source of the contamination in the fish is not yet conclusively determined, evidence points to the alarming possibility that pollution from the seafloor is making its way into the marine food web, with potential implications for marine mammals and humans.
Further research is underway to identify the pathways by which DDT-related chemicals are entering the deep-sea food web and to determine if larger, open-ocean fish species consumed by humans are also contaminated. Scientists are analyzing samples from fish targeted by recreational anglers and commercial fisheries to compare the chemicals found in the fish with sediment samples from the Palos Verdes Shelf and Dumpsite 2. The ongoing studies aim to shed light on the long-lasting consequences of the DDT contamination and inform mitigation efforts to address the pollution in the deep-sea environment off the coast of Los Angeles.
