‘Underwater Roombas’ Scan Southern California Coast for DDT Barrels

Hundreds of tons of the toxic chemical have likely littered the ocean floor near Santa Catalina Island for decades

A photo of the coast of Santa Catalina Island on California's southern coast
For decades there were rumors of leaking barrels filled with the pesticide DDT littering the ocean floor off the coast of Santa Catalina Island dumped by the now-defunct, Montrose Chemical Corp, the largest global DDT manufacturer based in Los Angeles Sergei Gussev via Flickr under CC BY 2.0

After Los Angeles Times' environmental reporter Rosanna Xia exposed an old DDT dumping ground in an investigative report in October 2020, scientists and policymakers gathered together to map out the extent of the disaster littering the ocean floor.

Last week, a team of 31 scientists and crew members aboard the oceanographic research vessel Sally Ride, kicked off a two-week expedition to survey 50,000 acres of the ocean floor, reports the LA Times. Prompted by the investigation, the team was assembled in just five months—it usually takes up to two years to plan a deep-sea expedition.

Aiding in their search are two remote-operated robots that use sonar to scan the seafloor, sort of like "underwater Roombas," as project lead Eric Terrill of UC San Diego’s Scripps Institution of Oceanography tells the LA Times' Xia. Instead of scanning a carpet for debris, these robots are seeking out thousands of barrels of DDT to help researchers create a detailed map of where each item is.

"We want to provide a common base map of what's on the seabed at a high enough resolution," Terrill tells the LA Times.

The robots are part of a project to advance the National Oceanic Atmospheric Administration's underwater data-gathering programs and will be tested while conducting the surveys. Each one of these high-tech robots can run for 12 to 16 hours on a single charge. One robot will continue to scan the ocean floor while the other one recharges and unloads collected data. The team plans to make data openly available for interpretation and share it all immediately on a NOAA-run data repository.

But the robots' reconnaissance mission is only the very beginning of the dumpsite's clean-up process.

DDT is a chemical compound used as a pesticide for crops that was later revealed to be detrimental to the natural world. During World War II, it was widely used as a repellent for lice, fleas, and mosquitos. In 1962, biologist and science writer Rachel Carson caused a wave of environmental action withe her book Silent Spring, which explored how pesticides have a domino effect on the environment and potentially cause health problems in humans and animals. In 1972, the U.S. banned DDT use.

For decades, it was rumored that the now-defunct Montrose Chemical Corp, the largest global DDT manufacturer based in Los Angeles, dumped leaky barrels filled with the pesticide into the ocean off the coast of Santa Catalina Island, reports Molly Taft for Gizmodo.

It wouldn’t be the company’s first offense. In 2000, the pesticide manufacturer faced a superfund lawsuit for discharging millions of pounds of DDT into Los Angeles County sewers that poured into the Palos Verdes Shelf between 1947 and 1971. But, the barrels were never mentioned in the lawsuit, reports Gizmodo.

Using a deep-sea robot and a hunch, Valentine and his team first found barrels seeping toxic waste 3,000 feet deep in the sea in 2011 and 2013 by happenstance while working on other research endeavors. Old records and shipping logs revealed that between 1947 and 1961, 767 tons of DDT were potentially tossed into the ocean, according to the LA Times' 2020 investigation.

"There's a real need to look at the extent to which these materials, the DDT in particular, are working their way back into the active biosphere. We're not there yet, because we don't understand the distribution," says geochemistry researcher and project lead David Valentine of UC Santa Barbara to the LA Times.

Once they map the dumping grounds’ distribution, the researchers will need to investigate how marine animal and plant life off the Southern Californian coast was affected.