Going, going, gone? Vanishing DDT is big surprise at ocean deposit off Los Angeles


Palos Verde coastline.  
Lin Mei/flickr

By Marla Cone
Editor in Chief
Environmental Health News

March 13, 2013

LOS ANGELES – A DDT deposit in the ocean off Los Angeles County has rapidly shrunk, shocking experts and casting doubt on the need to mount a controversial $60-million Superfund cleanup, according to new data.

For decades, government officials and scientists have estimated that 110 tons of the banned pesticide – the world's largest deposit of DDT – have been sprawled on the ocean floor, where it was discharged by a now-defunct Los Angeles company. 

Fishing at San Monica Pier.
Laura Bittner/flickr

But now only about 14 tons remain, according to the latest testing by the U.S. Environmental Protection Agency.

What has happened to the DDT off Palos Verdes Peninsula is, for now, a scientific mystery. Scientists have no explanation for how almost 90 percent might have vanished in a mere five-year period – between tests in 2004 and 2009 – after decades of a slow, gradual decline.

“It’s a dramatic decrease,” said EPA site manager Judy Huang. “It’s a lot smaller. We don’t fully understand why.”

Mark Gold, associate director of the UCLA Institute of the Environment and Sustainability, said he was in “absolute shock.”

“It’s a dramatic decrease. It’s a lot smaller. We don’t fully understand why.” -Judy Huang,  EPA site manager  “There was no foreshadowing of this,” said Gold, who has served on the site’s technical review committee since the 1990s. “There’s an order of magnitude less DDT today than what was there five years ago. It doesn’t make sense to me that this degree of a change would have occurred within the last five years. It’s very difficult to assess where it went.”

One theory is that it's a statistical fluke, that when researchers retrieved the new sediment samples from the ocean floor, they somehow missed all the hot spots of DDT. Another is that something has accelerated the pace at which the pesticide has been dechlorinating – perhaps more microbes are suddenly gobbling more of it up and breaking it down into byproducts containing less chlorine. Another possibility is that it has diffused into the water and spread throughout the ocean, although there is no evidence of that and no known impetus for such a rapid change.

“It may be that something is changing out there,” said Robert Eganhouse, a research chemist with the U.S. Geological Survey who began studying the site in the 1970s. “You’re not having any new DDT added so over time the concentrations are going to go down. The $64,000 question is: What is it that controls it?”

A toxic legacy for fish, birds and people

Between 1947 and 1971, pesticide manufacturer Montrose Chemical Corp. discharged millions of pounds of DDT into Los Angeles County sewers, which empty two miles offshore in an area called the Palos Verdes Shelf. The deposit covers about 17 square miles of the ocean floor.

Off Los Angeles, DDT and PCBs have been seeping into the food web, leaving fish, birds and marine mammals with high levels of contamination. Anglers are warned not to eat bottom-dwelling fish near the deposit, and until recently, bald eagles were unable to produce chicks.DDT was banned in the United States in 1972 because it was accumulating in the environment, causing the near-extinction of bald eagles, pelicans and other birds.

Off Los Angeles, the DDT and other banned substances called polychlorinated biphenyls, or PCBs, have been seeping into the food web, leaving fish, birds and marine mammals with high levels of contamination. Anglers are warned to not eat white croaker and other bottom-dwelling fish caught offshore from Santa Monica to Seal Beach because of the risk of cancer and neurological effects from high PCB levels. And until 2007 bald eagles on Santa Catalina Island, 22 miles off Los Angeles, had been unable to reproduce because DDT thinned their eggs.

Juvenile bald eagle.
Institute for Wildlife Studies

Declaring in 2000 that the site poses “an unacceptable risk to human health and the environment,” the EPA has been planning to cover part of the Palos Verdes Shelf with a thick cap of clean sand at an estimated cost of $60 million.

But now there may be little need to build that controversial cap, which is unprecedented in deep ocean waters. The deposit not only has shrunk in size, but its peak concentrations, or hot spots, of DDT and PCBs have been dramatically reduced, according to the new EPA data and maps. The contaminant levels already are what the EPA had hoped to achieve with the cap.

“We’ve either achieved [our goal] without the cap, or close to it,” Huang said. “We have a lot better understanding now based on the 2009 data,” she said. But, “to me, this whole project is like a giant jigsaw puzzle.”

The 100 samples from 59 spots on the ocean floor were collected back in 2009. But then the EPA hired outside experts to review the unexpected findings, which were then confirmed last fall. The data, obtained by Environmental Health News, have not been made public until today.

There have been no major storms, earthquakes or landslides that could explain such a huge, rapid change.

“We’ve been seeing declines in fish tissues and surface sediments for the past 20 years. But this [new finding] was more than what we expected. It appears that the change has accelerated,” said Joseph Gully, supervising environmental scientist at the Los Angeles County Sanitation Districts, which operates the sewage outfall that discharged Montrose’s DDT into the ocean.

“DDTs don’t break down that quickly. I don’t see this as the bacteria all of a sudden eating up all this stuff. It’s a bit of a mystery,” added Steve Bay, head of toxicology at the Southern California Coastal Water Research Project, a government-funded institute that studies pollution off the coast of Southern California.

"If I were a betting man, I'd say that next time we look we'll see a higher inventory of DDE than we did in 2009. My personal hypothesis is that they just missed the places with the highest contamination." -Christopher Sherwood, USGS  Christopher Sherwood, a USGS geological oceanographer who has studied the site's sediment since 1991, suspects that the new data may be a "statistical fluke" because there is nothing he can think of that would make DDT transform so quickly.

"If I were a betting man, I'd say that next time we look we'll see a higher inventory of DDE than we did in 2009," he said. "My personal hypothesis is that they just missed the places with the highest contamination." He acknowledged that such a huge error – missing 90 percent of the deposit – would be "really bad statistical luck."

Essentially, what really is happening on that deep ocean floor remains a mystery. "We're all just grasping at straws," Sherwood said.

A long, twisted saga

The vanishing act is the latest twist in the convoluted saga of the Palos Verdes Shelf, which is considered the most studied piece of ocean floor on Earth. Every day, hundreds of millions of gallons of the county’s treated sewage are discharged there.

The EPA declared the Palos Verdes Shelf a Superfund site in 1996. Two miles offshore in 200-foot deep ocean waters, it is one of the most unusual and challenging sites on the nation's list of the worst dumpsites.

Montrose Chemical Superfund site.

It was the focal point of one of the largest court cases in U.S. history that has sought natural resource damages. The case, filed by the U.S. Justice Department in 1990, led to an acrimonious trial in federal court in 2000. About $140 million in settlement money was paid by Montrose, several other manufacturers and the county sanitation agency.

Ironically, at the time, Montrose company representatives had argued in court that the deposit would degrade naturally so there was no need for costly cleanup. But their key expert was thrown out by the judge when the government provided evidence that he was not a biodegradation expert and may have manipulated some data.

Montrose “was right in saying it was dechlorinating. There was no dispute,” Eganhouse said. “But their rates were not realistic. Data didn’t exist at that time to make an accurate prediction.”

Eganhouse's previous analysis of one location on the shelf shows that the breakdown product, called DDMU, is now more prevalent out there than the original DDT/DDE. Virtually nothing is known about the toxicity of that substance or whether it has potential effects on wildlife or human health.

“The general idea exists that the fewer chlorines, the less toxic a substance is, but nothing can replace actual toxicological studies,” Eganhouse said.

Two miles offshore in 200-foot deep ocean waters, the Palos Verdes Shelf is one of the most unusual and challenging Superfund sites in the nation. Sherwood analyzed about 30 years of DDT data from many locations on the Palos Verdes Shelf and said the rate of decline in the bulk of the sediment was only 1 to 2 percent per year, far slower than anything that could explain the reported loss of 96 tons in five years.

He is particularly suspicious about the accuracy of the new EPA data because it showed most of the PCBs had vanished too, and PCBs do not break down like DDT does.

There also was nothing in Eganhouse's analysis, albeit at only one location, to suggest that the pace of dechlorination has been accelerating. “An analysis of data between 1992 and 2003 and a 2009 core showed the rates haven’t changed out there,” he said.

The upshot, he said, is that “we cannot presently say for sure if the rates have changed in the past or if they will change in the future.”

Eganhouse is now analyzing more locations on the shelf that could provide key answers within six months about what’s happening out there now.

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