The Mystery of the Vanishing DDT in the Ocean Near Los Angeles

A deposit of 110 tons of the banned pesticide has rapidly shrunk on the ocean floor and cast doubt on the need to mount an expensive cleanup

By Marla Cone and Environmental Health News

Going, going, gone?: A deposit of DDT and PCBs is sprawled on the ocean floor two miles off the Palos Verdes Peninsula in Los Angeles County. Image: Flickr/Lin Mei

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.?

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.?

?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.

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.

Source: http://rss.sciam.com/click.phdo?i=c60329af6eb413e19d8a425d6b4f6061

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