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Daily News Blog

22
May

DDT Persistent in Environment 50+ Years After Ban, Found in Deep Ocean Sediment and Biota

Decades later, DDT is found in deep ocean sediment and biota that impacts critical food webs and biodiversity.

(Beyond Pesticides, May 22, 2024) A study in the journal of Environmental Science and Technology Letters, funded by the National Oceanic and Atmospheric Administration, is the first to find halogenated organic compounds (HOCs) in deep ocean sediment and biota off the coast of California. The test area, known as the Southern California Bight (SCB), is home to historic offshore DDT waste dumping, with part of the SCB designated as a U.S. Environmental Protection Agency (EPA) Superfund site. 49 HOCs were detected in the sediment and biota, many of which are DDT-related and not previously screened for. The presence of these “unmonitored compounds can significantly contribute to the contaminant body burden across a range of marine taxa,” the study states, which leads to impacts on critical food webs and biodiversity.

While this study is the first to specifically analyze previously overlooked DDT+ compounds, the results are nothing new. There is a body of science around the bioaccumulation and biomagnification of harmful pollutants that continue to lead to a decline in biodiversity, negative impacts on water and soil, and detrimental human health effects.      

To assess the bioavailability of DDT+ and HOCs in the deep ocean food web, this study focused on areas near a dumpsite in the San Pedro Channel between Long Beach, CA, and Santa Catalina Island, CA. Sampling of the sediment and biota occurred in the Santa Cruz Basin and San Pedro Basin, proximal to the dumpsite. The first goal of the study was to determine the presence of overall HOCs with a specific interest in the number of DDT+ compounds within the sediment. The second goal was to “assess the potential for DDT+ bioaccumulation in the deep ocean food web by determining the chemical profiles in one invertebrate and three fish species collected from throughout the water column.” 

For sediment sampling, sediment cores were taken with a remotely operated vehicle (ROV) from three sites. Two of the sites were near visually identified dumped barrels and a ‘no barrel site’ was 90 m from any observed barrels. For the biota, micronekton and fish species (Leuroglossus stilbius, Cyclothone acclinidens, and Melanostigma pammelas) were collected from the water column above the San Pedro Basin and the Santa Cruz Basin. To represent the lowest level of the food web, zooplankton were also analyzed. After sampling, all analyses were performed at San Diego State University and compounds were classified and named according to their mass spectra and retention times.

As a result, the scientists “detected 49 HOCs across all samples, including 15 DDT+ compounds in the sediment and 10 DDT+ compounds in the biota.” This shows that “high DDT+ body burdens were found in biota… indicating widespread DDT+ contamination in the deep ocean… [and] that deep ocean sediment may be a source of DDT+ to the marine food web.” HOCs are known for bioaccumulation and biomagnification, which explains the presence of more compounds in the biota. DDE is the most abundant form of DDT that was identified in the samples, which occurs when DDT breaks down. While the original DDT that was dumped may now be present in different forms, the persistence of these compounds throughout the environment after decades is apparent.

The fish species from the Santa Cruz Basin show “2 to 6 times higher DDT+ abundance compared to the samples collected ∼100 km distant at the examined dumpsite in the San Pedro Basin. This suggests that DDT+ contamination may be widespread beyond [the dumpsite] and may not be directly correlated to the presence of barrels or proximity to the dumpsite.” With 14 known dumping sites off the coast of California, this is concerning. The spread of pesticide pollution is potentially much larger than ever anticipated. “The majority of the DDT+ compounds detected in the sediment and biota were previously detected in SCB birds and marine mammals,” the study continues. “This discovery is critical and suggests that DDT+ from deep ocean sediment enters the water column and subsequently the marine food web.”

DDT (dichlorodiphenyltrichloroethane) was a widely used insecticide, primarily for mosquitos, that became popular in the 1940’s. It was later banned in the United States in 1972 after its high toxicity to wildlife and humans became publicly accepted after Rachel Caron’s book Silent Spring. At that time, Montrose Chemical Corporation, the largest producer of DDT, had disposed of DDT waste into the previously permitted deep-ocean dump sites in the San Pedro and Santa Monica Basins. While the Palos Verdes Shelf is a Superfund site to acknowledge the contamination, EPA continues to state that the DDT pollution does not pose any risks to humans for being in the water or consuming fish collected from this area. According to this study, “EPA suggested that DDT manufacturing waste may have been bulk-dumped (i.e., not containerized) near the dumpsites rather than disposed in barrels.” In addition, documents indicate that approximately 40,000 pounds per year of DDT and other harmful chemicals could have been disposed of between the 1930’s and 1972 in the SCB.

There is much “uncertainty in past estimates of the total magnitude of DDT pollution in the SCB” and a lack of thorough studies. “Most DDT surveys examine four to eight typical compounds… [but] recent work indicates that marine mammals inhabiting the SCB are exposed to more than 45 DDT-related contaminants,” the scientists say. These contaminants are known as DDT+, which includes DDE, DDD, DDX, and further degradation byproducts. With the lack of studies around the amount of contamination and health risks, despite EPA’s assurance that there are none, there is a need for further investigation.  

Most concerning is the bioaccumulation (concentration over time of individual organisms) and biomagnification (exponential increase in concentrations throughout the levels of the food web) that causes a cascade of issues leading all the way up to humans. Since the SCB “has some of the highest recorded concentrations of DDT in the world due to the discharge of DDT manufacturing waste from 1947 to 1982 by the Montrose Chemical Corporation,” all levels of the food web are at risk of exposure. When zooplankton have levels of contamination, they pass this on to the micronekton that consume them. Pesticide load then travels through the trophic levels into small fish and crustaceans before continuing to larger fish and mammals. HOCs, including DDT, are moving up through the deep ocean food webs into species that are directly consumed by humans.

A recent Daily Breeze article highlights this study and interviewed the authors, who further shared the importance of studying the effects from historic waste dumping and their research discoveries. “‘It’s providing the link that there’s a potential that the source of DDT to the food web could be coming from deep ocean sediments…coming off of the Palos Verdes Shelf,” said Margaret Stack, a research specialist at San Diego State University. The two basins where Stack and her co-authors collected samples from are 60 miles apart, and she addressed the importance of this when saying, “‘this broad distribution of DDT pollution in the Southern California environment [shows] we still maybe don’t know the boundary of where DDT pollution is occurring.”

Additional studies are also concerned about the long-lasting presence of HOCs such as DDT. A study from the University of California states that “substantial amounts of DDT remain in these sediments, which are largely unaltered after more than 70 years.” This made the researchers ask questions: “How much DDT waste was disposed offshore? When and where did the disposal occur? Was the DDT waste containerized as once suggested or bulk dumped as indicated more recently by the EPA? Have these wastes persisted in a manner that can lead to ongoing ecological effects?” While the majority of these questions are still unanswered after their study, the persistence of DDT has been documented and ecosystem and health effects have been observed that “include cancer in sea lions and bioaccumulation in endangered California Condors… [and] generational health effects from maternal DDT exposure.”

While much research still needs to be conducted on the long-term effects in the environment for historic pesticide waste, it brings to the forefront how important it is to eliminate current practices that expose all organisms to toxic materials. Beyond Pesticides’ mission is to bring an end to petrochemical pesticide and synthetic fertilizer use by 2032, which will save future generations from the concerns highlighted in these studies. A transition to organic is the answer, such as with organic agriculture and choosing organic food to protect the health of the environment and all its inhabitants. DDT and equivalent products in use today can instead be replaced with safer mosquito management, and individuals can make The Safer Choice by learning how to avoid hazardous home, garden, community, and food use pesticides.

To get involved, reference the Action of the Week and utilize Beyond Pesticides Resources. Non-toxic Lands and Landscapes and ManageSafe™ are also great references for least-toxic control of pests in the home and garden. Become an advocate today to help make changes in your community and to join in the organic movement. 

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

 

Source:

Stack, M.E. et al. (2024) ‘Identification of DDT+ in deep ocean sediment and biota in the Southern California bight’, Environmental Science & Technology Letters, 11(5), pp. 479–484. Available at: https://pubs.acs.org/doi/full/10.1021/acs.estlett.4c00115.

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