Investigating DDT Deposits on the Ocean Floor

A recently released documentary, “Out of Plain Sight,” explores how Marine Science Institute scientist David Valentine, in collaboration with Christopher Reddy and his team at Woods Hole Oceanographic Institution, discovered dichlorodiphenyltrichloroethane (DDT) deposits on the Pacific Ocean floor off the coast of Los Angeles (1). Their findings, which led to reporting from the Los Angeles Times, unveiled new insights into the potential contaminants present in DDT, and its impact human health and the environment (1).

Othmar Zeidler, an Austrian chemist, synthesized DDT in 1874, but its utility as an insecticide wasn’t discovered then (2). It wasn’t until 65 years later in 1939 that it was tested for this purpose. However, further analysis has shown that DDT can be hazardous to the health of humans and animals. DDT is an acute toxin, and it can be an endocrine disruptor and possible carcinogen (2). As a result, DDT is thought to be hazardous to embryos (2).

It was legal to dump DDT into the ocean until 1972. Reddy has primarily studied dump sites that formed in the 1940s through 1960s, he told LCGC International, when industry-scale ocean dumping, whether from a barge or container, was permitted.

“This was a practice that was much more prevalent in the mid last century until the 1970s,” Reddy said.

Valentine, Reddy, and their teams investigated a new DDT deposit on the ocean floor using a combination of comprehensive two-dimensional gas chromatography (GCxGC) and oceanography work in tandem to remove DDT from the dump site and analyze the samples to better learn about the ecological impact.

Pacific Ocean panorama with sun reflection. The vast open sea with a clear sky, ripple wave, and calm sea with beautiful sunlight. | Image Credit: © peangdao - stock.adobe.com

Reddy used GCxGC to investigate the components and contaminants in the DDT dump site. He has had an extensive career studying oil spills, plastic pollution, and developing environmentally friendly materials (4). Reddy received his BS in Chemistry from Rhode Island College and his Ph.D. in Chemical Oceanography from the University of Rhode Island (4). He has investigated some of the most well-known oil spills, including the Deepwater Horizon oil spill (4).

Investigating oil spills and dump sites is not easy work. Because of the equipment needed, and where the dump sites reside, it is common that many dump sites go unnoticed for years, including the deposits Valentine and his team discovered off the Pacific Coast.

“One of the reasons why these dump sites have not been identified previously is that they're at 900 meters from the on the bottom of the sea floor,” Reddy said. “And we're at 3000 feet. You can't certainly scuba dive to look for this dumped waste. So then, you have to rely on underwater vehicles to see if you can find them, or other types of devices.”

Reddy, Valentine, and their teams used autonomous and remotely operated underwater vehicles in their investigation. One of them was called sentry, an autonomous underwater vehicle.

“[Sentry] is completely autonomous,” Reddy explained to LCGC International. “It has no wire or cable. There's nobody on it. It's just a device that you can lower over the side on a research vessel. We sent it on a mission to map the bottom of the sea floor in the area in which we thought we would find this debris.”

The second underwater vehicle used by the team was known as Jason, and it was an unmanned vehicle connected to the research vessel with a power cord.

“[Jason] is also unmanned, but it's connected with a big power cord over the side of the boat, and it can last in the water for a long time,” Reddy said. “But it has video cameras, it has two robotic arms, and it has a whole series of tools and equipment that you can use to go right up to where we saw some dumped waste in open barrels. And we could physically collect, with the robotic arms, samples that we could bring back up to the surface.”

Reddy discussed the operation of these underwater vehicles and more in our upcoming video interview with him. Our video series will comprise three parts, each dedicated to discussing a different aspect to this research endeavor. In this video series, we will show how chromatographic techniques played a vital role in analyzing the samples, and how oceanography is helping to preserve and protect the oceans that humans and animal species rely on for survival.

Part 1 will be released on Monday January 27^th. Parts 2 and 3 will be released on Tuesday January 28^th and Wednesday January 29^th, respectively.

References

1. UC Santa Barbara,Out of Plain Sight: L.A. Times and Sypher Studios to Premiere Environmental Documentary Feature ‘Out of Plain Sight’ at DOC NYC. UCSB.edu. Available at: https://msi.ucsb.edu/news/out-plain-sight (accessed 2025-01-20).
2. American Chemical Society, Dichlorodiphenyltrichloroethane. ACS.org. Available at: https://www.acs.org/molecule-of-the-week/archive/d/dichlorodiphenyltrichloroethane.html (accessed 2024-12-04).
3. Texas A&M University, What is Oceanography? TAMU.edu. Available at: https://artsci.tamu.edu/oceanography/about/what-is-oceanography.html#:~:text=Oceanography%20is%20an%20interdisciplinary%20science,using%20ships%20(Research%20Vessels)(accessed 2024-12-04).
4. Christopher Reddy Personal website. Available at: https://christopherreddy.com/about (accessed 2025-01-07).