Researchers about Research Vessel Falkor used Remotely Operated Vehicle SuBastian to collect sediment push cores off the coast of Los Angeles during the Biodiverse Borderlands Expedition in July 2021. Credit: Schmidt Ocean Institute
Key points:
- A new study reveals that DDT-related chemicals dumped into the ocean decades ago are still impacting Los Angeles’ coastal waters.
- Researchers tested sediment and deep-sea fish samples for a large suite of DDT-related chemicals and found at least 10 of these harmful chemicals present in their samples.
- The findings suggest that pollution may be moving from the seafloor and into the marine food web.
In the 1940s and 1950s, the largest manufacturer of the pesticide DDT dumped the harmful chemical into the ocean off the coast of Los Angeles. A new study, published in Environmental Science and Technology Letters, reveals that these DDT-related chemicals dumped into the ocean may still be making their way into marine food webs.
Researchers collected sediment samples and deep-sea animals from the water column in the San Pedro Basin near Dumpsite 2. They tested these samples for a large suite of DDT-related chemicals, known as DDT+. With sediment analysis, researchers found no fewer than 15 of these chemicals. Similarly, testing 215 fish species revealed that they contained 10 DDT-related compounds – all of which were present in the sediment samples.
Two of the fish species were collected between 546 meters and 784 meters and a third was collected between 546 meters and the surface. The research team found that the species collected at shallower depths contained a lower concentration of contaminants and were missing a pair of DDT-related compounds that were present in the deepest fishes. As these fish are not known to feed in the sediment, the team expects there is another mechanism underlying contaminant exposure. They hypothesize that pollution may be moving from the seafloor and into the marine food web.
“Regardless of the source, this is evidence that DDT compounds are making their way into the deep ocean food web,” said lead author Margaret Stack of San Diego State University. “That is cause for concern because it’s not a big leap for it to end up in marine mammals or even humans.”
More work is needed to determine the source of DDT contaminants found in deep-sea fish. The team also wants to examine if the same contamination exists in larger, open-ocean fish species that are consumed by people. They have planned many studies to address these questions, including analyzing samples from fish species targeted by recreational anglers and commercial fisheries. By comparing the chemicals and their concentrations found in these fish with sediment samples collected from the Palos Verdes Shelf and Dumpsite 2, the team may be able to determine the source of toxins.