High concentrations of DDT found across vast swath of California seafloor

Article written by Dani Anguiano
Originally published by The Guardian (Friday, March 24, 2023)

Barrels of the toxic chemical were dumped along the Pacific coast decades ago. New research shows the material never broke down

For years industrial companies in southern California used the coast as a dumping ground for toxic chemical waste, including DDT. Decades later, scientists have found that the pesticide remains in high concentrations on the ocean floor and has never broken down.

Nearly two years after the discovery of tens of thousands of barrels of waste off the coast of Los Angeles, a scientist working on the issue shared this week that the chemical is still spread across a vast stretch of the seafloor, the Los Angeles Times reported.

“We still see original DDT on the seafloor from 50, 60, 70 years ago, which tells us that it’s not breaking down the way that [we] once thought it should,” David Valentine, a UC Santa Barbara scientist, said. The LA Times reported that the contamination covered an area of seafloor larger than the city of San Francisco. “And what we’re seeing now is that there is DDT that has ended up all over the place, not just within this tight little circle on a map that we referred to as dumpsite two.”

DDT, which was widely used in the US as an agricultural pesticide and sprayed in large quantities at beaches to kill mosquitoes, has been linked to cancer and disease in humans and the mass die-off of animals. In the 1970s, it was banned in the US due to its harmful effects on wildlife and potential risks to humans. Research has shown a link between exposure to the chemical and breast cancer as well as reproductive problems.

Southern California was the center of DDT production in the US. The Montrose Chemical Corporation in Torrance produced massive amounts of the chemical between the end of the second world war through 1982. During that time, before Congress banned such activity, up to 2,000 barrels a month of acid sludge waste containing DDT were dumped off the coast. Workers sometimes poked holes in the barrel so they would sink more quickly.

Image Credit: David Valentine

In late 2020, a report from the LA Times told the story of how LA’s coast became a dumping ground for DDT, revealing that as many as half a million barrels could still be on the sea floor, prompting Senator Dianne Feinstein to ask the EPA to take action.

A two-week survey, conducted in 2021 by a team from the Scripps Institution of Oceanography at University of California, San Diego and the National Oceanic Atmospheric Administration, using seafloor robots, sonar acoustic imagery and data helped reveal the scale of the issue, finding more than 25,000 barrels. Scientists identified more than 100,000 human-made items across the entire survey area.

Scientists’ most recent analysis has found that the most concentrated layer of DDT is roughly 6cm deep in the sediment, the Times reported.

“Trawls, cable lays, could reintroduce this stuff back up to the surface,” Valentine told the newspaper. “And animals feeding – if a whale goes down and burrows on the seafloor, that could kick stuff up.”

DDT has already been linked to continued harmful affects on wildlife. On the central California coast, which also served also a dumping ground for DDT, a 20-year-long study found a link between exposure to contaminants and high rates of cancer and herpes in sea lions.

Congress has allotted millions of dollars toward researching the issue. “The federal funding we secured will be significant for advancing research to understand the scope and scale of DDT pollution off the coast of southern California,” Feinstein said on Twitter. “We must act quickly to clean this up.”

Banner Image Credit: David Valentine


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