Sediments Rise From Seabed to Haunt the Bay

Tons of DDT and other hazardous wastes believed to have been safely buried at the bottom of Santa Monica Bay could be churned back into the water by ocean currents, new scientific studies suggest.

In papers presented Tuesday at a major international coastal zone conference in Long Beach, researchers said they were surprised to find other, less-toxic sediments, thought to have long been buried, near the surface after apparently being stirred up by currents and underwater waves.

The underwater plumes of fine sediment--residue from sewage and other waste dumped from sewage outfalls into the ocean off the Palos Verdes Peninsula--have stretched as long as 2.8 miles along the coast and were detected 60 feet above the ocean floor.

The findings could have disturbing implications for Santa Monica Bay. Over the years, tons of long-lived pesticides like DDT and other hazardous waste have been dumped into the bay. Much of that dumping has been made illegal, and it has been widely believed that the public health and environmental threat has diminished.

But the prospect of tons of contaminates rising from the ocean floor could cause a reassessment.

“We found unexpected things--the occurrence of sediment resuspension on the bottom. . . . There’s some question of whether this previously buried material will stay buried,” oceanographer Libe Washburn of UC Santa Barbara said in an interview.

What remains to be determined, he said, is whether the sediment less than a foot below the ocean floor is being eroded sufficiently by currents and wave action to uncover pesticides and other hazardous waste.

About 400 million gallons of sewage are pumped into the bay each day from outfalls at White Point, off the Palos Verdes Peninsula. An estimated 200 metric tons of the now-banned pesticide DDT were dumped into Santa Monica Bay over the years. The chemical was blamed for pushing the brown pelican population to the brink of extinction. The bird has since made a dramatic comeback following the ban of DDT.

Washburn said there is no direct evidence that the hazardous waste is going to be exposed, but “it’s certainly out there.”

Sewage treatment plants over the years have moved to reduce the amount of particles that are discharged into the ocean to comply with progressively stricter clean water laws. With less material being added to the ocean floor, Washburn said, DDT and other hazardous materials could be exposed much more quickly, assuming that the bottom sediment continues to erode as the studies have suggested.

Another study by William M. Berelson and Kenneth S. Johnson discovered unexpectedly high levels of dissolved copper in the water near the sewer outfalls.

At high levels, copper can be toxic to fish and humans.

“This type of measurement has never been made before,” said Berelson, a researcher at USC’s Center for Earth Sciences. The measurements were made in March, 1989, and again in February.

He reported that enough dissolved copper is rising from the seabed and entering the water to equal 30% to 40% of all the copper that may flow daily from the sewage outfall.

The twin outfalls at White Point deposit the treated sewage effluent about 2 1/2 miles from shore.

In a related matter, a study commissioned by Exxon of shoreline conditions in Alaska’s Prince William Sound found only “short-term” ecological impacts from the 11-million-gallon crude oil spill from the Exxon Valdez in 1989.

Researcher Edward H. Owens of Woodward-Clyde reported “rapid natural recovery” of the pristine Alaskan shoreline. He said little oil remained by the spring of 1990. He also reported that damage was far less extensive than first believed in the lower half of the intertidal zone, which is rich is marine life.

But Owens’ assessment was challenged by Sylvia Earle, chief scientist with the National Oceanic and Atmospheric Administration.

In an interview, Earle said, “To say there are no long-term impacts was an unfortunate overstatement. The (ecological) system has been nudged. It will never be the same (even though) nature is resilient.”

The Coastal Zone 91 conference, co-sponsored by various federal agencies and private groups, is billed as the world’s largest conference on ocean and coastal management issues. An estimated 1,300 scientists, engineers, policy-makers and others from 50 nations are attending the weeklong conference.