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
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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.
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11 Comments
Add CommentPlease don't use blanket wording like "DDT was banned in the United States in 1972", it gives the anti-science nutcases an opportunity to bring up their much beloved "Fifty billion trillion million people have died because environmentalists got DDT banned".
Reply | Report Abuse | Link to thisThe 1972 ban only applied to agricultural use. DDT was still legal to manufacture and sell, and in fact it was made in the USA into the 1980's. It is (and always has been) legal for use in controlling disease.
In 1972 the EPA banned nearly all uses of DDT in the U.S. In 1989, all further uses, including public health, were cancelled. Under the UN's Stockholm Convention, DDT use is allowed in some malaria-prone countries. From the EPA: "There is no U.S. registration for DDT, meaning that it cannot legally be sold or distributed in the United States." Marla Cone, Environmental Health News
Reply | Report Abuse | Link to thisI've been diving from Point Conception to Palos Verdes for many decades. Several partners and I started diving there as teenagers in the early 1970s, although not at White's Point where most of the sewage was dumped, it was avoided.
Reply | Report Abuse | Link to thisThere has been some major changes in wave action, wind, and currents in the last twenty years - surf and wind have increased and so the mixed-layer depth has probably increased. Two hundred feet is not deep either, it's well within the mixed-layer depth for this region.
I think it's very likely that much of the deposit has been disturbed and moved. I think they should look to nearby sites as well to see if it has been redeposited but certainly it has been moved and re-suspended, at least partially.
More testing is called for and that should go on but it may well turn out that this deposit has shrunk because it has been moved.
The point being that the ban still allows for the use of DDT in disease control and that DDT can still be legally manufactured in the USA.
Reply | Report Abuse | Link to thisFrom epa.gov ddt-brief-history-status:
"The Convention includes a limited exemption for the use of DDT to control mosquitoes which are vectors that carry malaria - a disease that still kills millions of people worldwide."
From the general fact sheet linked from the epa.gov site:
"Is DDT still used?
DDT can still legally be manufactured in the
U.S., but it can only be sold to, or used by, foreign countries. In the U.S. the only exceptions for DDT use are for public health emergencies involving vector (insect) diseases and control of body lice."
From the CDC toxicity profile on DDT:
"DDT was last imported into the United States in 1972, when imports amounted to 200 tons. Although the use of DDT was banned in the United States after 1972, it was still manufactured for export. In 1985, there were two producers of DDT in the United States, and in that year, 303,000 kg of DDT were exported (HSDB 1988). Presently, there are no producers of DDT in the United States,..."
Use of DDT in disease control is not allowed. The Stockholm Convention allows use in some malaria-prone countries.
Reply | Report Abuse | Link to thisNot allowed in U.S.
Reply | Report Abuse | Link to thisMaybe someone has been "mining" the DDT for some other purpose? Or maybe the people doing the sampling faked the samples to scam the government? There are possibilities that are not being discussed in the article.
Reply | Report Abuse | Link to thisBacteria can dechlorinate DDT. With such a resource free for the taking, it would be surprising if organisms were *not* selected for increased rates of utilization. Perhaps they'll start on PVC next; plenty of that kicking about in the oceans.
Reply | Report Abuse | Link to thisOnly asking, not my field, if there could be a connection to problems like this:
Reply | Report Abuse | Link to thishttp://www.scientificamerican.com/article.cfm?id=southern-california-coast-sees-sea-lions
or, in general:
Reply | Report Abuse | Link to thishttp://www.scientificamerican.com/article.cfm?id=long-lasting-chemicals-may-harm-sea-turtles
how is sea life health in the area? over the last ten years?
Also the PV landfill power plant has closed. Possibly the condensate from the buried DDT is no longer making it's way into the Carson treatment plant.
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