Researchers find toxic DDT compounds in deep-sea fish off Los Angeles coast

Sharon Udasin
·3 min read

A toxic agricultural insecticide banned four decades ago is still contaminating deep-sea fish and sediments off California’s southern coast, a new study has found.

While the U.S. banned the compound dichlorodiphenyltrichloroethane (DDT) in 1972, the study authors believe the substance is continuing to invade marine food webs.

The contamination remains persistent in an environment about 15 miles off the coast of Catalina Island, which served as a DDT dump site in the 1940s and 1950s, according to research published Monday in Environmental Science & Technology Letters.

“These are deep-sea organisms that don’t spend much time at the surface and they are contaminated with these DDT-related chemicals,” said co-author Lihini Aluwihare, a professor of ocean chemistry at University of California San Diego’s Scripps Institution of Oceanography, in a statement.

From 1948 through at least 1961, barges contracted by DDT-producer Montrose Chemical Corporation pumped industrial waste that contained up to 2 percent pure DDT directly into the Pacific Ocean in this area, the researchers noted.

An estimated 100 tons of DDT — a group of pesticides linked to various toxic health effects — ended up in the sediments of this Palos Verdes region offshore, per the study. Ultimately, the Environmental Protection Agency declared the zone an underwater hazardous waste site in 1996, and four years later, a judge ordered the company to pay $140 million in environmental damages.

Research has since confirmed DDT contamination and resultant health problems in local sea lions, dolphins, bottom-feeding fish and coastal California condors, the authors noted.

What remains unclear, however, is whether these impacts are moving through the undersea ecosystem in ways that could pose dangers to other, more widespread marine life or to humans.

“Establishing the current distribution of DDT contamination in deep-sea food webs lays the groundwork for thinking about whether those contaminants are also moving up through deep-ocean food webs into species that might be consumed by people,” Aluwihare said.

The Scripps scientists, who teamed up with researchers at San Diego State University, decided to collect both sediment samples and deep-sea animals from one of two dump sites in the area to test them for DDT-related compounds.

Upon analyzing the sediments, they found 15 different such chemicals, of which 14 previously had been detected in birds and marine mammals in Southern California.

The researchers also collected 215 fish in three areas near the dump site, determining the animals contained 10 DDT-related compounds, all of which were also present in the sediment samples. Those species found at shallower depths showed lower concentrations of the contaminants and had two fewer DDT-related compounds than deeper-sea fish.

The authors noted, however, that none of these fish are bottom-feeders — meaning there must be another way in which they are gaining exposure to the pollutants. One possibility they are considering is the idea the area sediments are becoming resuspended around the dump site and thereby entering food webs.

“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, an environmental chemist at San Diego State University, in a statement.

“That is cause for concern because it’s not a big leap for it to end up in marine mammals or even humans,” Stack added.

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