Chemical Dumpsite Offshore Southern California

THE LEGACY OF DDT+ IN SOUTHERN CALIFORNIA

What was the historical use of DDT and how was it disposed of?

Commercial use of the insecticide DDT (dichlorodiphenyltrichloroethane) was banned in the United States in 1972, predominantly due to its high toxicity to wildlife and human health. The largest DDT producer in the United States, Montrose Chemical Corporation, historically disposed of DDT acid waste via wastewater outfalls to the Palos Verdes Shelf, as well as dumped into previously permitted deep-ocean dump sites in the San Pedro and Santa Monica Basins. The U.S. Environmental Protection Agency (EPA) designated the near-shore environment of the Palos Verdes Shelf as a Superfund site, meaning the previously contaminated site receives compensation for cleanup efforts and periodic monitoring to date. At this time, the EPA states that DDT contamination does not pose a significant health risk to those engaging in water contact recreation activities in the Palos Verdes Shelf, or consuming fish collected from this area.

Why study DDT in the deep ocean now?

While the impacts of near-shore DDT on the Palos Verdes Shelf have been well-studied, very little is known about the status of DDT and other chemicals dumped in deep-ocean basin disposal sites and their impacts. The significant depth (up to 900 meters or about 2,953 feet) and lack of designated funds have made extensive exploration of deep-ocean disposal sites challenging, even though their existence has been documented since the 1980s. Montrose’s documents indicate that approximately 40,000 lbs per year of DDT and other chemicals could have been dumped in these basins from the 1930’s until 1972. 

Recent media attention and advances in deep sea technology have sparked interest and urgency in further examining the dump sites. Important research interests include the following:

• There is now greater awareness of DDT breakdown compounds and related byproducts (>40 compounds in all), collectively referred to as “DDT+”, that have historically not been monitored and could have underestimated toxic effects.
• Sediments in the San Pedro Basin were found with DDT+ concentrations exceeding those at the Palos Verdes Superfund site, indicating a need for further risk assessment.
• Surveys revealed that “short-dumping” in transit to the disposal sites was commonplace, suggesting that the geographic scope of DDT+ contamination is likely to span beyond the designated deep ocean dump sites.
• Surveys identified numerous barrels on the seafloor with DDT+ contaminated sediment nearby, however, the highest sediment concentrations of DDT+ were not found near barrels, suggesting that DDT+ was largely bulk-dumped directly into the ocean rather than contained in barrels.
• DDT+ can enter the marine food web through ingestion of contaminated sediment. This raises questions about health risks to marine organisms at the top of the food chain, including humans who consume locally sourced seafood. Therefore, a greater understanding of how these higher and more spread out concentrations of DDT+ are impacting ecosystems and the food web is needed.

For more information on the detailed history of DDT and research to date in Southern California, please refer to Chartrand et al, 2022 and the EPA Region 9’s “Southern California Ocean Disposal Site #2 Investigation” website.

Setting the stage for addressing California’s DDT challenge

• In early 2021, Scripps Institution of Oceanography conducted a preliminary survey that mapped the debris field (more than 36,000 acres of seafloor) between Santa Catalina Island and the Los Angeles coast, in the San Pedro Basin. In August 2021, scientists from Scripps Oceanography explored the DDT dumpsite, collecting sediment and biological samples around six barrels to understand potential ecological effects of the dump site and to determine the levels of DDT present in the ecosystem.
• In July 2022, the University of Southern California Sea Grant Program and the California Sea Grant Program engaged scientists, nonprofits, federal and state agencies, tribal representatives, and other Southern California Bight communities to assess what research is most urgently needed to address regional deep ocean DDT+ contamination. The resulting report, A Deep Ocean DDT+ Research Needs Assessment of the Southern California Bight, provides a comprehensive agenda for critical, deep ocean DDT+ research, thus informing future action to protect marine and human health. Scripps Institution of Oceanography researchers participated throughout the Assessment, and are conducting research that directly addresses the gaps outlined in the report. 
• In September 2022, NOAA awarded $5.6 million in spending, directed by U.S. Senators Dianne Feinstein and Alex Padilla, to Scripps Institution of Oceanography. Working with collaborators from UC Santa Barbara and San Diego State University, this new research aims to fully characterize the extent of the dumpsite, identify the toxin “fingerprint” contained in the sediments, survey the effects of toxins on microbial communities and animals on the seafloor near the site, and assess toxin pathways to the upper ocean, including the potential for human exposure to toxins via fish and fisheries. The project will also explore potential remediation strategies, including the capacity for microbes to neutralize the toxins on the seafloor.
• In September 2023, NOAA awarded $6 million in spending, directed by U.S. Senators Dianne Feinstein and Alex Padilla, to Scripps Institution of Oceanography to fully assess contamination from DDT+ and other pollutants and bioremediation mitigation strategies. The additional research will validate an oceanographic DDT+ exposure risk model, conduct chemical sediment mapping of DDT+ wastes that were short dumped en route to Dumpsite 1, examine trophic transfer of DDT+ through biota in and around Dumpsite 1 and 2, assess the origin and fate of toxicants in the marine food web of the Southern California Bight, with a focus on species that may be vectors of contamination to human consumers, characterize the biological remediation potential of sediment microbes in the San Pedro Basin, and determine whether biodegradation can reduce DDT+ accumulation in wildlife destined for consumption. Additionally, the project integrates a comprehensive coordination, data management, and visualization framework, alongside an educational outreach component aimed at translating and presenting data in accessible formats to diverse audiences.