The Environmental Protection Agency has suspended planned cleanup efforts at a Southern California site where industrial waste on the ocean floor appears to be vanishing naturally.
The Los Angeles Times reports scientists are at a loss to explain the rapid decline of toxic chemical levels along the Palos Verdes Shelf.
Samples taken from the sediment suggest more than 100 metric tons of the banned pesticide DDT and industrial compounds known as PCBs have dropped by nearly 90 percent in just five years.
The EPA has ordered a new round of tests over the next year.
Four years ago the agency chose a $35 million plan to clean the site by covering the seafloor with clean sediment.
The area was added to the EPA's list of Superfund sites in 1996.
